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Drainage Report
Drainage Study FOR RANDALL' S UNIVERSITY PARK Lots 3R2-A thru 3R2-E College Station Brazos County, Texas December 13, 2010 Revision No. 1- January 6, 2011 Revision No. 2 - February 9, 2011 - r~r rr` ill i ~t i Prepared For: Marcelino Diaz Barrera 1221 University Drive East College Station, TX 77840 Prepared BY: RME Consulting Engineers 7607 Eastmark Drive, Suite 252A <77840> P.O. Box 9253 College Station, TX 77845 Texas Firm Registration No. F-4695 RME No. 220-0419 !to \l4•t1 LIST OF TABLES: PAGE Section 3.0 - Hydrologic Modeling Table # 1: T„ - Overland Sheet Flow 6 Table #2: Ttz - Shallow and/or Concentrated Flow 6 Table #3: Tc Summary 6 Table #4: Drainage Basin Runoff Quantities 7 Section 4.0 - Detention Facility Routing Table #5: Detention Facility Routing 10 Section 5.0 - Storm Drainage System Table #6: Culvert Summary 11 • 0 220-0419 Drainage Report-Rev2 Page - ii ATTACHMENTS: Section 1.0 - General Information Replat Vicinity Map FIRM Panel Map Section 2.0 - Watersheds & Drainage Areas Lick Creek Watershed Area Existing Conditions Drainage Area Map Proposed Conditions Drainage Area Map Section 3.0 - Hydrologic Modeling HydroCAD - Existing Conditions Drainage Calculations HydroCAD - Proposed Conditions Drainage Calculations Randall's University Park - Stormwater Drainage Analysis Section 4.0 - Detention Facility & Routing GP-01: Paving, Grading & Drainage Plan HydroCAD - Proposed Conditions Pond Routing Calculations - Pond 1 Section 5.0 - Storm Drainage System THYSYS - Hydraulic Computations • r1 220-0419 Drainage Report-Rev2 Page - iii 9 Drainage Study - Rev. No. 2 RANDALL'S UNIVERSITY PARK Lots 3R-A thru 3R-E College Station Brazos County, Texas 1.0 GENERAL INFORMATION 1.1 Scope of Report. This report addresses the existing conditions and proposed drainage improvements for the replat of Lots 3R-A thru 3R-E of the Randall's University Park Subdivision. This drainage study's scope will analyze the proposed detention facility design methods and proposed configurations, and the internal storm drainage system improvements designed for the development. All drainage system improvements (i.e. on-site detention facilities, storm sewer, etc...) will be designed to accommodate the anticipated proposed/ultimate development conditions. The proposed development and drainage improvements are designed and analyzed in accordance with the criteria outlined in the "Unified Stormwater Design Guidelines" • (USDG) manual of the City of College Station (CoCS). 1.2 Site and General Location: The replat development of Lot 3R-2 of the Randall's University Park Subdivision consists of 3.37 acres of land consisting of five (5) residential lots with the construction of their associated improvements of paving, drainage, and utilities. The existing and proposed conditions of this development is depicted on the Relat which is provided in the "Attachment - Section 1.0" portion of this report. Lot 3R-2 of the Randall's University Park Subdivision has access to Chimney Hill Drive along its southeast property line. Developments adjacent to these lots, to the west and east, are single-family residential (Beverly Estates and the Cooner Addition), property to the north is the CoCS Billie Madely Park, and to the south is the commercial development that occupies the Albertson's shopping center. A Vicinity Map, for this project site, is provided and is located in the "Attachment - Section 1.0" portion of this manual. This map is being provided as an aid in locating the site. Drawings describing the work and its specific locations are contained in the Construction Drawings prepared by RME Consulting Engineers, College Station, Brazos County, TX. These Construction Drawings are included as part of this Drainage Report by reference. 1.3 Description of Existing Conditions and Drainage Patterns: The 3.37 acres of land, which contains the proposed development, is a well sloping (approximately 7.0%) substantially undeveloped site with natural overland drainage that 220-0419 Drainage Report-ReQ Page -1 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 conveys runoff to a secondary drainage system of Burton Creek. This secondary system consist of a natural drainage channel that collects runoff from the upstream commercial development of the Albertson's Shopping Center and drains to the northeast. Runoff collected to this point is conveyed in a 60" diameter storm sewer pipe, and then is further conveyed through the secondary tributary to Burton Creek. The subject development area is primarily an unimproved area with some thick brush, weeds, and trees along the secondary tributary. Elevations range on the site from approximately 296' Mean Sea Level (MSL) to approximately 326' MSL. The Brazos County soil maps indicate that this area is comprised of Type C and D soils which consist of clays or silty clay/sand mixtures. Both pre-and post-runoff from the subject development will drain in a northeasterly direction through the secondary drainage channel and then through the proposed drainage structures or detention facility. Runoff is then discharged into the unnamed drainage channel. Eventually the unnamed tributary discharges into Burton Creek, thence to Carters Creek, thence to the Navasota River, thence to the Brazos River and ultimately to the Gulf of Mexico. 1.4 FEMA Information: A small portion of the subject development lies within mapped 100-year floodplain as graphically depicted by the Federal Emergency Management Agency (FEMA) - Flood Insurance Rate Map (FIRM) Community/Panel number 480083 0142C, with an effective date of July 2, 1992. A portion of this FIRM Panel Map is located in the "Attachment - Section 1.0" section of the Drainage Report. 2.0 WATERSHEDS & DRAINAGE AREAS 2.1 Detention Facility Watersheds (Existing Conditions): As previously discussed, the subject development area is located within a watershed of an unnamed tributary that drains into the Burton Creek Watershed Area. An exhibit of this watershed is taken from the USDG manual with the subject area identified and is entitled as previously mentioned and has been included in the "Attachment - Section 2.0" appendix of the report. Since this drainage study will include the hydrologic/hydraulic modeling of one (1) detention facility, an appropriate drainage area map called the Existing Conditions Drainage Area Map (which is located in the "Attachment - Section 2.0" portion of the Drainage Report), was developed for considerations of existing runoff patterns and analysis and is described as follows. Drainage Area "X" - This drainage area is approximately 3.62 acres and will consist of the proposed development area and upstream contributing areas, at pre-development or existing conditions. At the downstream limit of this drainage area is the secondary unnamed tributary of Burton Creek. Analysis of this drainage area will provide runoff characteristics for the appropriate portion of the subject development at its current existing conditions. This runoff data will be the "benchmark" data for the respective 220-0419 Drainage Report-Rev2 Page - 2 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 post-development area analysis so that increased runoff can be measured and appropriately detained. 2.2 Detention Facility Watersheds (Proposed Conditions): For post-development conditions three (3) individual drainage basins were considered and analyzed and are as follows. The Proposed Conditions Drainage Area Map illustrates these drainage areas and is located in the "Attachment - Section 2.0" section of the Drainage Study. Drainage Area Map "P" - This drainage area consists of Drainage Area "X" and additional watershed area that will discharge to the unnamed tributary of Burton Creek. The comprised total of this watershed will be 8.96 acres. Proposed runoff conditions from this drainage area will be evaluated at the anticipated development conditions. The hydrologic data generated from this drainage area will be utilized to hydraulically size the proposed culvert structure (in addition to the discharge calculated from the Albertsons detention facility); Drainage Area Map "P1" - This drainage area consists of an area within Drainage Area "X" and comprises 0.96 acres of land. Proposed runoff conditions from this drainage area will be evaluated at the anticipated development conditions. The hydrologic data generated from this drainage area will drain into Pond 1, routed through the detention facility and discharged into the existing unnamed tributary of Burton Creek via this project's storm sewer system. Ultimately, routed flows, combined with flows from undetained flows from Drainage Area "P2", will be compared to the runoff values generated from Drainage Area "X"; Drainage Area Map "P2" - This drainage area consists of an area within Drainage Area "X" and comprises 2.73 acres of land. Proposed runoff conditions from this drainage area will be evaluated at the anticipated development conditions and released from the site undetained; 3.0 HYDROLOGIC MODELING 3.1 Rational Formula and Methodology: The Rational Method (Q=CIA) is one of the more frequently used methods to determine the peak runoff from a watershed and is typically reliable for small watersheds 50 acres). The Rational Method generates hydrologic data based on drainage area geometrics, surface conditions, and rainfall intensities. The Rational Method will be employed to determine the sizes of watershed's runoff values for the sub-drainage areas, detention systems, and for the internal storm drain systems, and it is explained further as: Q = CIA where, Q = peak runoff rate (cubic feet per second); 220-0419 Drainage Report-Rev2 Page - 3 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 C = runoff coefficient - This represents the average runoff characteristics of the land cover within the drainage area and is a dimensionless coefficient. Runoff coefficients are interpolated from either Table C-2 or C-3 of the USDG; I = average rainfall intensity (in/hr); A = area of land that contributes stormwater runoff to the area of study (acres); 3.2 Rainfall Intensity "I': Rainfall intensities (I) are the average rate of rainfall in inches per hour for a given rainfall event. The duration of "I" is assumed to occur at the computed Time-of- Concentration for each respective drainage basin. Rainfall intensities can be determined by use of intensity-duration-frequency (IDF) curves or from intensity equations which are provided in the TxDOT Hydraulic Manual. 3.3 Weighted Runoff Coefficient "C". The runoff coefficient (C) for various sub-drainage basins was estimated from the USDG, Table C-2 and C-3 by comparison of runoff surface types to percentage of land coverage and total drainage area. The pre-construction runoff coefficient "C" for the proposed development area is approximated to be 0.41. This coefficient was determined by calculating the weighted average of the runoff coefficient for the different surfaces types. Calculations for the coefficient are as follows: Drainage Area "X" Runoff Coefficient "CWTD 2.01 Acres - Undeveloped (Pasture Areas) 4 "C" = 0.35; 0.63 Acres - Undeveloped (Woodland Areas) 4 "C" = 0.40; 0.98 Acres - Single-Family Residential 4 "C" = 0.55; Pre-construction runoff coefficient "CWTD" (0.35*2.01)/3.62 + (0.40*0.63)/3.62 + (0.55*0.98)/3.62 4 "CWTD" = 0.41 The post-construction runoff coefficient "C" for the proposed development areas are as illustrated below. These coefficients were determined by calculating the weighted average of the runoff coefficient for the different surfaces types. Calculations for the coefficients are as follows: Drainage Area "P" Runoff Coefficient "CWTD 1.31 Acres - Undeveloped (Pasture Areas) "C" = 0.35; 0.72 Acres - Undeveloped (Woodland Areas) 4 "C" = 0.40; 0.41 Acres - Sodded Yard 4 "C" = 0.42; 1.55 Acres - Single-Family Residential 4 "C" = 0.55; 4.97 Acres - Commercial/Impervious 4 "C" = 0.90; Pre-construction runoff coefficient 4 "CWTD" (0.35*1.31)/8.96 + (0.40*0.72)/8.96 + (0.42*0.41)/8.96 + (0.55*1.55)/8.96 + (0.90*4.97)/8.96 «CWTD" = 0.70 220-0419 Drainage Report-Rev2 Page - 4 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 Drainage Area "P1" Runoff Coefficient "CWTD" 0.26 Acres - Undeveloped (Pasture Areas) 4 "C" = 0.35; 0.36 Acres - Undeveloped (Woodland Areas) 4 "C" = 0.40; 0.21 Acres - Sodded Yard 4 "C" = 0.42; 0.13 Acres - Commercial/Impervious 4 "C" = 0.90; Pre-construction runoff coefficient 4 "CWTD" (0.35*0.26)/0.96 + (0.40*0.36)/0.96 + (0.42*0.21)/0.96 + (0.90*0.13)/0.96 4 "CWTD" = 0.46 Drainage Area "P2" Runoff Coefficient "CWTD": 1.05 Acres - Undeveloped (Pasture Areas) 4 "C" = 0.35; 0.36 Acres - Undeveloped (Woodland Areas) "C" = 0.40; 0.20 Acres - Sodded Yard "C" = 0.42; 0.96 Acres - Single-Family Residential 4 "C" = 0.55; 0.16 Acres - Commercial/Impervious 4 "C" = 0.90; Pre-construction runoff coefficient 4 "CWTD" (0.35*1.05)/2.73 + (0.40*0.36)/2.73 + (0.42*0.20)/2.73 + (0.55*0.96)/2.73+ (0.90*0.16)/2.73 4 "CWTD" = 0.46 3.4 Time of Concentration: The Time-of-Concentration (Tc), for each watershed, is used to determine the intensity of the rainfall event for the corresponding drainage basin. Time-of-Concentration is defined as the time required for the surface runoff to flow from the most hydraulically remote point in a watershed to the point of analysis. The Tc is the summation of the flow time for overland sheet flow plus shallow overland flow and/or concentrated flow to the lower reach of the watershed. Overland sheet flow is a method developed by Overton and Meadows and is typically used for flow distances of 300 feet or less. Concentrated flows are estimated by velocities determined by use of the Manning's Equation. These two types of flow time calculations are further explained as follows. Overland Sheet Flow, Tt = 10.007 (n L)°'g} / {Piles So") where, Tt = travel time (hours); n = Manning's roughness coefficient - This represents the flow-ability of runoff across a particular surface type and is a dimensionless coefficient. These coefficients are obtained from Table C-5 of the USDG; Pi = ith-year recurrence interval for the 24-hour rainfall depth (inches) - Rainfall depths are obtained from Table C-6 of the USDG; S = land slope (feet/foot) Shallow Concentrated Flow, Tt = D/(60V) where, Tt = Travel time (minutes); D = Flow distance (feet); V = Average velocity of runoff (ft/sec) - These values are determined from interpolation velocities recorded in Table C-4 of the USDG; 220-0419 Drainage Report-Rev2 Page - 5 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 Table #1 - "Ttl-Overland Sheet Flow" and Table #2 - "Ttz-Shallow Concentrated Flow" illustrates the flow travel times for each segment of the sub-drainage basin in respect to the condition of the flow. The Tc's for each sub-drainage basin where then computed and are summarized below in Table #3 - "Tc Summary". TABLE N TH - Overland Sheet Flow Overland Average Flow Land Travel Drainage Manning's Distance Pi Slope Time Area I.D. "n" (L (100-year) (S Tc) X 0.24 75 11.0 0.0400 0.077 P 0.24 60 11.0 0.0070 0.130 P2 0.24 75 11.0 0.0400 0.077 is 1) Unpaved Shallow Flow average velocities were estimated using the following equation V = 16.135*S05 where, V=fps S = average slope Assumptions - Manning's N = 0.05 & Hydraulic radius = 0.4 ft 2) Paved Shallow Flow average velocities were estimated using the following equation V = 20.328 *S05 where, V=fps S = average slope Assumptions - Manning's N = 0.025 & Hydraulic radius = 0.2 ft TABLE #3 Tc SUMMARY Combined Drainage Overland Channel Flow Tc Area I.D. Flow Time Time (min) X 0.077 2.74 7.4 P 0.13 7.79 15.6 P2 0.077 2.38 7.0 1) The minimum Tc utilized will be ten (10) minutes; 3.5 Stormwater Runoff Quantities: Stormwater runoff quantities were calculated, using the Rational Method with the assistance of the Hydrologic/Hydraulic stormwater modeling program HydroCAD. 220-0419 Drainage Report-Rev2 Page - 6 TABLE #2 Tt2 - Shallow and/or Concentrated Flow Shallow (Unpaved) Shallow (Paved) Channel Flow Average Flow Average Flow Average Drainage Distance Velocity Distance Velocity Distance Velocity Time Area I.D. D1 (VI) (D1) V1 (132 (V2 (Tc) X 450 3.8 236 5.1 2.74 P 136 2.0 772 2.3 324 5.1 7.79 P2 450 3.8 125 5.1 2.38 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 • Runoff values for the larger watersheds are summarized below in Table #4 - "Drainage Basin Runoff Quantities". HydroCAD-Existing & Proposed Conditions Drainage Calculations and their supporting data are contained the "Attachment - Section 3.0" appendix of this Drainage Report. These calculated runoff quantities were reviewed and considered reasonable for the studied watershed. TABLE #4 DRAINAGE BASIN RUNOFF QUANTITIES an a s Detention & Drainage Drainage Drainage Drainage Upstream Rainfall Area Area Area Area Uncontrolled Event (X) (P) (P1) (P2) (RDUU) (cfs) (cfs) (cfs) (cfs) (cfs 2 9.37 25.39 2.79 7.93 5 11.40 30.87 3.39 9.64 10 12.79 34.65 3.81 10.82 25 14.61 39.58 4.35 12.36 50 16.52 44.74 4.91 13.97 100 17.24 46.71 5.13 14.59 247 The 100-year runoff value of 247 cfs is taken from the Drainage Report prepared by ML Hammons (dated 2/15/91) which includes the metered flow from the Albertson's (Randall's) detention facility plus the uncontrolled flow from upstream drainage areas and is bypassing the detention structures. A copy of this Stormwater Drainage Analysis is located in the "Attachment - Section 3.0" section of the Drainage Report. 4.0 DETENTION FACILITY & ROUTING 4.1 Detention Facility Criteria STORAGE: 1. The storage ability of the detention facility is such that it can adequately detain the receiving stormwater runoff from upstream drainage areas so that runoff from the project site is controlled to pre-development "existing" conditions. The storage requirements are more fully explained in the following section; 2. The maximum storage depths for design and ultimate conditions shall be as follows: Facility Location Design Hydrog_raph Ultimate Hydrograph Parking Areas 0.50 ft 1.5 ft Rooftops 0.50 ft 1.0 ft Landscaped Areas 3.0 ft 4.50 ft 3. All detention facilities located on natural streams or water courses that are designed with a permanent storage component shall meet all criteria, in terms of design and construction, for Dams and Reservoirs as required by the Texas Commission on is Environmental Quality (TCEQ); 220-0419 Drainage Report-Rev2 Page - 7 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 4. Detention facilities shall have an additional 10% in storage to account for sedimentation, except those located in parking areas or rooftops. OUTLET STRUCTURES: The detention facility outlet structures are designed so that the system can be drained by means of gravity. Discharge velocities shall be verified that they are below the minimum velocities receivable by the type and nature of the receiving system or attenuated so that they are below these minimums. PHYSICAL CHARACTERISTICS: 1. Side slopes shall not exceed 4:1 for vegetative cover and 2:1 for non-vegetative cover; 2. Bottom slopes must be 2.00% or steeper to low flow outlet; 3. A low-flow invert shall be provided for all facilities which have a vegetative cover at the facility bottom; EMERGENCY OVERFLOW: 1. The geometry of the emergency overflow shall be that of a rectangular weir; 2. Surface treatment of the overflow weir shall be consistent with the expected velocities at ultimate conditions. Proper treatments shall be provided to accommodate or attenuate the discharge velocities; 3. A minimum of 0.5 feet of freeboard shall be provided around the perimeter of the detention facility as measured between the maximum water surface elevation and the pool elevation and the ultimate conditions. 4.2 Methodology: The purpose of a detention facility is to store the increased runoff created by the impervious and improved areas, and discharge it at a rate so that the immediate downstream structure and/or property experiences decreases or no change as compared to existing conditions. Using the peak runoff rates, generated and illustrated in Section 3.6 of this report, hydrographs for each rainfall event and respective drainage basins were created for existing conditions. These hydrographs were constructed by means of triangular approximation method which is limited to smaller watersheds located within the secondary drainage system of a major watershed. Other assumptions and geometric conditions that are used to build these hydrographs are as listed below. Using this data, and inputting it into HydroCAD, approximate hydrographs were determined for each drainage basin at selected rainfall events. Triangular Approximation: 1. Peak Runoff (Q) occurs at "Tc"; 2. The outflow portion of the triangular hydrograph is Tc x 2; Using this information, the storage volume of the detention facility can be estimated. This storage volume shall be such that the peak discharges of the development • hydrograph, or the routed hydrograph, from the detention facilities will be equal to or less than the "Benchmark" discharges. For this project, at proposed development conditions, 220-0419 Drainage Report-Rev2 Page - 8 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 the discharge values shall be such that the routed flows through Pond 1 (from Drainage Area "P"), are equal to or less than the peak discharge rates of Drainage Area "X". 4.3 Detention Facility Configuration: The detention facility for the subject development will consist of one pond. With the construction of this detention facility, called Pond 1, an outlet structure will be installed to detain/meter increased runoff from Drainage Area "P 1". The proposed GP-01: Paving, Grading & Drainage _Plan for this project more fully depicts these improvements and is contained under the "Attachment - Section 4.0" portion of this report. The detention facility is briefly summarized below: Pond 1: Runoff from Drainage Area "P1" is conveyed by means of overland flow. Pond 1 is "dry" pond with a bottom elevation of 302.30' and a maximum berm or ponding elevation of 304.10'. Sideslopes of the detention pond will be vegetative with 4H:1V sideslopes. Runoff routed through Pond 1 is metered through area grate inlet and then is discharged into the storm drainage system of the proposed development; 4.4 Detention Facility Outlet Structure: The detention facility outlet structure has been designed to accommodate and route collected stormwater runoff, from Drainage Area "P1" so that during analyzed/routed rainfall events the post-development discharge rates are near or less than the "benchmark" discharge values generated from Drainage Area "X" (less the undetained flows from Drainage Area "P2"). These "benchmark" discharge values are illustrated in Table #4 contained in Section 3.5 of this report. The discharge structure of each detention pond will serve as the restricting or metering device, and are summarized below: Pond 1: Pond 1 discharge structure through grate inlet. Analyzed with 25% blockage. The maximum berm height will extend also to an elevation of 304.10' which will provide 0.51' of freeboard above the maximum pool elevation occurring during the 100-year rainfall event. Tailwater considerations for the outlet of Pond 1 were set at a free discharge condition. 4.5 Routing Results and Conclusions: Once the project's detention facility and outlet structure was determined, then the hydrograph for Drainage Basin "P1" could be routed through the detention system. The routing of this hydrograph, for each analyzed rainfall event, was accomplished by means of the Hydrologic/Hydraulic stormwater modeling program HydroCAD. The program mathematically solves for continuity between the detention facilities storage capabilities, in respect to height versus storage and height versus discharge rate, with the inflow hydrograph and inputted tailwater conditions. HydroCAD - Proposed Conditions Pond Calculations - Pond 1 and its supporting data is contained the "Attachment - Section 4.0" section of this Drainage Report. 11 220-0419 Drainage Report-Rev2 Page - 9 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 RME Consulting Engineers February 9, 2011 As shown below in Table #5 - "Detention Facility Routing", the designed detention facility system can accommodate inflow runoff and adequately detain this stormwater so that the facility's discharge rates are below the "benchmark" discharges without overtopping the maximum berm elevation. TABLE #5 DETENTION FACILITY ROUTING Route D.A. "P2" Benchmark Diff. in Rainfall Storage Max. Discharge Discharge Discharge Discharge Max. Berm Event Volume Pool Elev Rate Rate Rate Rate Elev. Freeboard ( ) (cu.ft. (ft) (cfs) cfs) (cfs) (cfs) (ft) (ft) DETENTION POND 1 - PROPOSED CONDITIONS 2 1,900 303.13 0.48 7.93 9.37 -0.96 304.10 0.97 5 2,401 303.25 0.51 9.64 11.40 -1.25 304.10 0.85 10 2,749 303.34 0.53 10.82 12.79 -1.44 304.10 0.76 25 3,205 303.44 0.56 12.36 14.61 -1.69 304.10 0.66 50 3,685 303.55 0.59 13.97 16.52 -1.96 304.10 0.55 100 3,870 303.59 0.60 14.59 17.24 -2.05 304.10 0.51 5.0 STORM DRAINAGE SYSTEM The "system criteria" listed below in the follow sub-sections are only the main highlights of the CoCS - USDG. The proposed development and drainage improvements are designed and analyzed in full accordance with the criteria outlined in this manual. 5.1 Culverts SYSTEM CRITERIA: 1. Drainage culverts shall be designed to convey the 25-year storm and analyzed during the 100-year rainfall event; 2. For the design storm, the discharge velocity shall not exceed 6.0 fps; 3. Roughness coefficients for storm sewer pipes were assigned at 0.012 for smooth-lined High Density Poly-Ethylene (HDPE) pipe and 0.013 for RCP; TAILWATER CONSIDERATIONS: Tailwater for the drainage culvert was determined by calculating the water surface elevation of the open-channel immediately downstream of the structure. This resulted in a tailwater elevation of 297.87'. DISCHARGE & HEADWATER: Runoff values utilized for the hydraulic analysis of the culvert system will be a combination of the following Drainage Areas (see Table #4 and routing in Table #5). As illustrated below the runoff values conveyed through the culvert system actually decreases by 2.05 cfs between Post- and Pre-Development conditions. • 220-0419 Drainage Report-Rev2 Page - 10 Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 0 Total Drainage Areas for Culvert System: 100- Year Pre-Development: Drainage Areas: RDUU + (P - P1 - P2 + X) = 291.23 cfs 100-Year Post-Development: Drainage Areas: RDUU + (P - P 1) + P 1 "routed" = 289.18 cfs RME Consulting Engineers February 9, 2011 Utilizing these flows the existing culvert system and proposed culvert extension system (60" diameter pipe and 36" diameter pipe) were calculated to verify capacity. For the proposed condition an iterative process was utilized to balance headwater in conjunction with the conveyance of each pipe. This balanced headwater was determined to be at 304.30' with a discharge of 195.7 cfs and 93.5 cfs through the 60" and 36" pipes respectively. METHODOLGY & CONCLUSIONS: The hydraulic analysis, for drainage culverts, and corresponding results, were determined by using the THYSYS hydraulic program for stormwater modeling. This TxDOT program's typical use is for modeling gravity drainage culverts. The THYSYS data is summarized, for each culvert, under the THYSYS - Hydraulic Computations (reference "Attachment - Section 5.0" portion of the report). Drainage culverts are summarized below in Table #6 - "Culvert Summary". As illustrated below the existing 60" culvert system is currently under-sized and will not convey the 100-year rainfall event by approximately 146 cfs. The culvert crossing, along with a portion of Chimney Hill Drive, is overtopped by an approximate depth of 0.98'. This existing culver structure was analyzed at as-built conditions. TABLE #6 CULVERT SUMMARY Rainfall Pipe Size Lowest Event Diameter Velocity RunoffQ HW Elev. Pvmt Elev. Freeboard r in s cfs ft ft ft EXISTING CULVERT 100 60 14.11 291.23 305.58 304.60 -0.98 PROPOSED CULVERT 100 36 13.23 93.50 304.30 304.45 0.15 100 60 15.26 195.70 304.30 304.45 0.15 To assist in attenuating the discharge velocity a concrete sidesloped headwall will be constructed at the pipe outlet and appropriate sized rock rip-rap will be concreted in at the discharge. • 220-0419 Drainage Report-Rev2 Page - 11 • Randall's University Park - Replat of Lot 3R-2 Drainage Study - Rev. No. 2 6.0 CERTIFICATION RME Consulting Engineers February 9, 2011 "This report for the drainage design of Randall's University Park Subdivision (Lots 3R2-A thru 3R2-E) was prepared by me (or under my supervision) in accordance with provisions of the Bryan/College Station Unified Drainage Design Guidelines for the owners of the property. All licenses and permits required by any and all state and federal regulatory agencies for the proposed drainage improvements have been issued." 11 Rabon Metcalf, P.E. State of Texas P.E. No. 88583 Texas Firm Registration No. F-4695 • • 220-0419 Drainage Report-Rev2 Page - 12 • Section 1.0 9 GENERAL INFORMATION C, n NWwmo ~ N Q < J~ 2F nWU2; nW n3 i FS og ~znw~„Er Rb sz ~Wb° Ng- F` $ gN ou <rc r~ $ I i 0 _ I - 1 8.~69 RED / 4 P~~l C0`i olst168 .a a' \ $ 52 \ Atn I rr ^ N'cV ~ s 3^ I ~ O~- 21. C ski J>>5F .101 y 1 1 I Y _ 1 Ci -Z F r I I ~ u\ w z .oe sq, ~ i.i NN 1 1 1 ~o Z ~Jf LA- z O ~ wci o N O o g a g>B o g~. J LAJ J < mmmm 8 n ~ ~M v~ a I 3~ 1 1 1 g' ° o s8 I 's~ 1 ' ~ ~ r o w = -12 I I a n (,LYSOL 3ONY1s10 -rm lTld) I„ N a ` E$ s I - I ansUM) ` ,so•sot LC .Qf Is , I \Tn is ~933~E3'~d0-_AAJ l---- , I g ---LI__ NY1ALl8 30 .1110 U3a V3N1 OB'r5t• M f0 ~4.81•N 9~° lSl'S f- 30NY1 ll O a~ 11hd) O M-10-1LCMtl ~ € S (1N3NYddV) b ° 6 I o ~ o ~1S MOM' 9" I oLSl~rlc MEAREO \ N N s s IH o F g ~ x Zf%)N Z6 U v`i _ u `G im 2 -o ra, I ~w W I oz. 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X x a O FLL- 55 ofi U ps o ° u a ' 11 • 0 • • C7 City of Bryan Map Output Page i-,aL}:e I of J d te P ; l a. . A. S;.y f l . 17194-,Y 1 . - h `ate - ry ~ -7 y~" ~ ~7(h ~f fir; ' w -y " a 'S!l ~ .'~.Ti W11J 9''+, ' / J ~y ~ 411 ' ~i y9 To y x 411 402 ~,y t • ~ i v 4- ' ~t die S 41' xv 464 $ as k Qv 1 `t r+N4 ~ AEI M fi y , ~ x: n Al f L~ikF. .1 tU. - ~ r s' y ` i cr aJr~ r 41" C+ T `'t ~ 4 ~;a -•x~ 113 ass f~ Jf~:v q~~ Y 7 i t '1-'1 4?3 418. a16 y 'co . 7. ~ rT ~ pp4I 9'.: i a1p.., _ I' 1 E Rid11 i., 4 7611 n' G _ :Y j' y h . y + n 1. , : 45 .u3 rai 1 1 a~ h 54 - IN 7- 3 i + i r 1 $ vw Oil v u Q`t.~ 1': tFi~ M3~•7 1~1~':., ~ `,11 ay" rt}'~ a ''r ia , ~ r Cri l oi. Bin-X\ I`I~ 1 ..i'•.11[l:.. , . .,;.111 i, a ar,'.1o-_, . tiu u. ; fi , ~ r.,...:n ...1. , t?l _'a.,. .:ni,'r I . :r :tr . , 'i!' isle, IInA; xi r. r n:,,.. L..:,. ;:~1 r ,lvt~til.,,.rr _~?e:a_ la 1._ _ . i • .n .,r;._ r~; ~h .t:.t tii;' , : - i : t11. ~'n.tt... _ 1..: ¢ ; r,: , , ..Ii3~.~it'1' 111 x'1.11'; lr: Iil. 1;}:: 1,, ,.itvrlt 5l.11'.'ly .:It,t II:;. . 1.v.f1+1. !:.;1•it, -.i Illy!::-.'.. v .(1: 1,_, r {..1: 1' _...I.- I. r'! 1::: lint thl: d:it:i Illi •r:l?,tl I: '11':1' " ' v, i... i . ..tl 1.1! !',1~1}1'i=i:t ~!)!)?-~II3;1 L i11'fi i;t"..stt ,r li ti ?.;}I1 .'ii]:1i1,11; ~,c•t'1 ii j;; VM13 13r•. ;:It, f~ }:il~ hnp://ims.bryantx.gov/gis/servlet/com.esri.esrimap.Esnmap?ServiceName=REGIONAL_ 12/12/2010 • • Section 2.0 WATERSHEDS & DRAINAGE AREAS 0 9 • t ~ . N . ' fi y ti p Mlk r, r` . E-23rd' r i 1 ~#ll S# E Wil) Pkw I L :P 6rzrar,,,illF RO fry - t i F 1;, cf" r> ~ ell C6 ?t..: r PI rr r. ~ / j r 1f 4 r.r GSV t# - f~ rly S , cal#\ by ~ ~ r1 /rl,~ 10 ~6 . Try r/rR • Fe et 0 11300 3500 700 Figure B-0: Burton Creek Watershed Area • • s • • • N A ~ ~ OjOD 1 a 1► $ > z I m v uu p. o" UD~: 1 OtjjZ D i D U \ ♦ D if~o D rn ♦ NN,~ ~ 'OW0CA ama" c)cCnD~ a o a o o D g C y z m i 0 _ 0 m c o o r + y r +m~ °Z vm°;ao i / C r - o / 5 0 o y g ou mm g 0 z%> m~ fD \ g y v Z Z " m ° ~Om iN Q$D m ~i~ N 0 j4 E C - c - li / l~ _ o o N p u z E g f+l m ID ' i Div F m rrnr-V I 1 i ♦ - 1 Alr ♦ 00 ' O 3E N t ~ -45j ♦ ~~W> ;rC Z LI 1 00>0 mTFD ~d > \ ~m D C~~-Z1 \ Z ;u 67 Z4 00 MZ Z 0 / ~ >a dk2j~ ycy V tz~ n S6 OSGC py~~ ~ O m op- r> z o W ll~ >~i/`~ ~d JZ o m~ z Nz0m~" c ozzzs.. tz) Nye m tOzN 0 I 71 I 1 ~ D~ / n 09 ~O f z 2 -D Q v u r N Z - D 0 f 0 z > ~ D = HOOT $sf* \r r OP C) rnN1 ~ 2 ONZ~ >M D Q D e i _ (J O U O U N mm Z 0 MZ r N r > > O ~ U m ~ N N a m r w a m nl^ 0 " D ^ 0 N ? * " N n o ~D O O O RCS J m r a C D b V v N c / Fn / D m / r i D A D Ooh ~ / K E Z ) i M, r 1 • Section 3.0 HYDROLOGIC MODELING 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Prepared by {enter your company name here} Page 1 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Time span=0.00-1.00 hrs, dt=0.01 hrs, 101 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment DA-P: Post-Development P Runoff Area=8.960 ac Runoff Depth=0.71" Tc=15.6 min C=0.70 Runoff=25.39 cfs 0.530 of Subcatchment DA-P1: Post-Development P1 Subcatchment DA-P2: Post-Development P2 Subcatchment DA-X: Pre-Development "X" Runoff Area=0.960 ac Runoff Depth=0.73" Tc=10.0 min C=0.46 Runoff=2.79 cfs 0.058 of Runoff Area=2.730 ac Runoff Depth=0.73" Tc=10.0 min C=0.46 Runoff=7.93 cfs 0.165 of Runoff Area=3.620 ac Runoff Depth=0.65" Tc=10.0 min C=0.41 Runoff-9.37 cfs 0.196 of Total Runoff Area = 16.270 ac Runoff Volume = 0.949 of Average Runoff Depth = 0.70" 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Prepared by {enter your company name here} Page 2 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P: Post-Development P [48] Hint: Peak<CiA due to short duration Runoff = 25.39 cfs @ 0.17 hrs, Volume= 0.530 af, Depth= 0.71" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Area (ac) C Description 8.960 0.70 Post Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.6 Direct Entry, Proposed Conditions Subcatchment DA-P: Post-Development P Hydrograph 3 0 M 26 25.39 cfs 24 TX-Brazos County 2-Year 22 Duration=10 min, 20- Inten=6.33 in/hr 18- Runoff Area=8.960 ac 16- Runoff Volume=0.530 of 14 12 Runoff Depth=0.71" 10 Tc=15.6 min 8 C=0.70 0 Time (hours) -Runoff u 0 9 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Prepared by {enter your company name here} Page 3 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P1: Post-Development P1 Runoff = 2.79 cfs @ 0.17 hrs, Volume= 0.058 af, Depth= 0.73" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Area (ac) C Description 0.960 0.46 Post-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P1: Post-Development P1 Hydrograph 2.79 CfS r~ U 0 LL TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Runoff Area=0.960 ac Runoff Volume=0.058 of Runoff Depth=0.73" Tc=10.0 min C=0.46 Time (hours) I- Runoff 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Prepared by {enter your company name here} Page 4 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P2: Post-Development P2 Runoff = 7.93 cfs @ 0.17 hrs, Volume= 0.165 af, Depth= 0.73" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Area (ac) C Description 2.730 0.46 Proposed Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft ) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P2: Post-Development P2 Hydrograph 7.93 cfs TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr 0 U. Runoff Area=2.730 ac Runoff Volume=0.165 of Runoff Depth=0.73" Tc=10.0 min C=0.46 0 Time (hours) Runoff E 0 • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Prepared by {enter your company name here} Page 5 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-X: Pre-Development "X" Runoff = 9.37 cfs @ 0.17 hrs, Volume= 0.196 af, Depth= 0.65" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 2-Year Duration=10 min, Inten=6.33 in/hr Area (ac) C Description 3.620 0.41 Pre-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Existing Conditions Subcatchment DA-X: Pre-Development "X" Hydrograph • 3 0 U. 9.37 cfs 9- TX-Brazos County 2-Year 8- Duration=10 min, 7 Inten=6.33 in/hr Runoff Area=3.620 ac Runoff Volume=0.196 of 5- Runoff Depth=0.65" 4- 1 Tc=10.0 min 3 C=0.41 2- 0 0 Time (hours) Runoff 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations • Chimney Hill-Rational-020911 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Prepared by {enter your company name here} Page 6 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Time span=0.00-1.00 hrs, dt=0.01 hrs, 101 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment DA-P: Post-Development P Runoff Area=8.960 ac Runoff Depth=0.86" Tc=15.6 min C=0.70 Runoff=30.87 cfs 0.644 of Subcatchment DA-P1: Post-Development P1 Subcatchment DA-P2: Post-Development P2 Subcatchment DA-X: Pre-Development "X" Runoff Area=0.960 ac Runoff Depth=0.88" Tc=10.0 min C=0.46 Runoff=3.39 cfs 0.071 of Runoff Area=2.730 ac Runoff Depth=0.88" Tc=10.0 min C=0.46 Runoff=9.64 cfs 0.201 of Runoff Area=3.620 ac Runoff Depth=0.79" Tc=10.0 min C=0.41 Runoff=11.40 cfs 0.238 of Total Runoff Area = 16.270 ac Runoff Volume = 1.154 of Average Runoff Depth = 0.85" s • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Prepared by {enter your company name here} Page 7 HydroCAD®? 10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P: Post-Development P [48] Hint: Peak<CiA due to short duration Runoff = 30.87 cfs @ 0.17 hrs, Volume= 0.644 af, Depth= 0.86" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Area (ac) C Description 8.960 0.70 Post Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.6 Direct Entry, Proposed Conditions Subcatchment DA-P: Post-Development P Hydrograph 9 H 0 LL 32 _ 30.87 CfS 30- TX-Brazos County 5-Year 28- 26 Duration=10 min, 24 Inten=7.69 in/hr 22- 20- Runoff Area=8.960 ac 18 Runoff Volume=0.644 of 14_ Runoff Depth=0.86" 12- Tc=15.6 min 101 / \ C=0.70 6 4 2 0 0 Time (hours) -Runoff 9 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Prepared by {enter your company name here) Page 8 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P1: Post-Development P1 Runoff = 3.39 cfs @ 0.17 hrs, Volume= 0.071 af, Depth= 0.88" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Area (ac) C Description 0.960 0.46 Post-Development Conditions Tc Length Slope Velocity Capacity Description _ (min) (feet) (ft/ft ) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P1: Post-Development P1 Hydrograph TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr i w 3 0 LL Runoff Area=0.960 ac Runoff Volume=0.071 of Runoff Depth=0.88" Tc=10.0 min C=0.46 0 Time (hours) Runoff 9 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Prepared by {enter your company name here} Page 9 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P2: Post-Development P2 Runoff = 9.64 cfs @ 0.17 hrs, Volume= 0.201 af, Depth= 0.88" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Area (ac) C Description 2.730 0.46 Proposed Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P2: Post-Development P2 Hydrograph 0 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Runoff Area=2.730 ac Runoff Volume=0.201 of Runoff Depth=0.88" Tc=10.0 min C=0.46 0 U. 0 Time (hours) -Runoff 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Prepared by {enter your company name here) Page 10 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-X: Pre-Development "X" Runoff = 11.40 cfs @ 0.17 hrs, Volume= 0.238 af, Depth= 0.79" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 5-Yeah Duration=10 min, Inten=7.69 in/hr Area (ac) C Description 3.620 0.41 Pre-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Existing Conditions Subcatchment DA-X: Pre-Development "X" Hydrograph 11.40 cfS w 3 0 LL TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Runoff Area=3.620 ac Runoff Volume=0.238 of Runoff Depth=0.79" Tc=10.0 min C=0.41 Time (hours) Runoff • 0 HydroCAD-Existing 8 Proposed Conditions Drainage Calculations 0 Chimney Hill-Rational-020911 TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Prepared by {enter your company name here} Page 11 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Time span=0.00-1.00 hrs, dt=0.01 hrs, 101 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment DA-P: Post-Development P Runoff Area=8.960 ac Runoff Depth=0.97" Tc=15.6 min C=0.70 Runoff=34.65 cfs 0.723 of Subcatchment DA-P1: Post-Development P1 Subcatchment DA-P2: Post-Development P2 Subcatchment DA-X: Pre-Development "X" Runoff Area=0.960 ac Runoff Depth=0.99" Tc=10.0 min C=0.46 Runoff=3.81 cfs 0.079 of Runoff Area=2.730 ac Runoff Depth=0.99" Tc=10.0 min C=0.46 Runoff=10.82 cfs 0.226 of Runoff Area=3.620 ac Runoff Depth=0.88" Tc=10.0 min C=0.41 Runoff=12.79 cfs 0.267 of Total Runoff Area = 16.270 ac Runoff Volume = 1.295 of Average Runoff Depth = 0.96" 0 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Prepared by {enter your company name here} Page 12 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P: Post-Development P [48] Hint: Peak<CiA due to short duration Runoff = 34.65 cfs @ 0.17 hrs, Volume= 0.723 af, Depth= 0.97' Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Area (ac) C Description 8.960 0.70 Post Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft ) (ft/sec) (cfs) 15.6 Direct Entry, Proposed Conditions Subcatchment DA-P: Post-Development P Hydrograph 1 34.65 cfs I TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr 0 24 22 ,8 Runoff Area=8.960 ac Runoff Volume=0.723 of Runoff Depth=0.97' Tc=15.6 min C=0.70 -Runoff I* 0 , Time (hours) HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Prepared by {enter your company name here} Page 13 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P1: Post-Development P1 Runoff = 3.81 cfs @ 0.17 hrs, Volume= 0.079 af, Depth= 0.99" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Area (ac) C Description 0.960 0.46 Post-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P1: Post-Development P1 Hydrograph • i 3 a U. TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Runoff Area=0.960 ac Runoff Volume=0.079 of Runoff Depth=0.99" Tc=10.0 min C=0.46 0 Time (hours) Runoff HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Prepared by {enter your company name here} Page 14 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P2: Post-Development P2 Runoff = 10.82 cfs @ 0.17 hrs, Volume= 0.226 af, Depth= 0.99" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Area (ac) C Description 2.730 0.46 Proposed Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P2: Post-Development P2 Hydrograph 10.82 Cfs w 0 LL TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Runoff Area=2.730 ac Runoff Volume=0.226 of Runoff Depth=0.99" Tc=10.0 min C=0.46 Time (hours) Runoff • C] • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Prepared by {enter your company name here} Page 15 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-X: Pre-Development "X" Runoff = 12.79 cfs @ 0.17 hrs, Volume= 0.267 af, Depth= 0.88" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Area (ac) C Description 3.620 0.41 Pre-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) _ 10.0 Direct Entry, Existing Conditions Subcatchment DA-X: Pre-Development "X" Hydrograph • z TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr a U. ' Runoff Area=3.620 ac 3 Runoff Volume=0.267 of Runoff Depth=0.88" Tc=10.0 min / \ C=0.41 0 Time (hours) -Runoff 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Prepared by {enter your company name here} Page 16 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Time span=0.00-1.00 hrs, dt=0.01 hrs, 101 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment DA-P: Post-Development P Runoff Area=8.960 ac Runoff Depth=1.11" Tc=15.6 min C=0.70 Runoff=39.58 cfs 0.826 of Subcatchment DA-P1: Post-Development P1 Subcatchment DA-P2: Post-Development P2 Subcatchment DA-X: Pre-Development "X" Runoff Area=0.960 ac Runoff Depth=1.13" Tc=10.0 min C=0.46 Runoff--4.35 cfs 0.091 of Runoff Area=2.730 ac Runoff Depth=1.13" Tc=10.0 min C=0.46 Runoff=12.36 cfs 0.258 of Runoff Area=3.620 ac Runoff Depth=1.01" Tc=10.0 min C=0.41 Runoff=14.61 cfs 0.305 of Total Runoff Area = 16.270 ac Runoff Volume = 1.479 of Average Runoff Depth = 1.09" • • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Prepared by {enter your company name here} Page 17 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P: Post-Development P [48] Hint: Peak<CiA due to short duration Runoff = 39.58 cfs @ 0.17 hrs, Volume= 0.826 af, Depth= 1.11" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Area (ac) C Description 8.960 0.70 Post Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.6 Direct Entry, Proposed Conditions Subcatchment DA-P: Post-Development P Hydrograph i 3 0 LL 44 42- - 40- 39.58 cfs 38 TX-Brazos County 25-Year 36-- 34- Duration=10 min, 30 Inten=9.86 in/hr 26 Runoff Area=8.960 ac 24- - Runoff Volume=0.826 of 22 20- Runoff Depth=1.11" ,a ' 16-- Tc=15.6 min 14- 12 _ C=0.70 10- 8- 6 4 2 0 0 Time (hours) -Runoff HydroCAD-Existing & Proposed Conditions Drainage Calculations 46 Chimney Hill-Rational-020911 TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Prepared by {enter your company name here} Page 18 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P1: Post-Development P1 Runoff = 4.35 cfs @ 0.17 hrs, Volume= 0.091 af, Depth= 1.13" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Area (ac) C Description 0.960 0.46 Post-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P1: Post-Development P1 Hydrograph 4.35 cfs 3 0 LL TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Runoff Area=0.960 ac Runoff Volume=0.091 of Runoff Depth=1.13" Tc=10.0 min C=0.46 Time (hours) Runoff 0 r-I HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Prepared by {enter your company name here} Page 19 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P2: Post-Development P2 Runoff = 12.36 cfs @ 0.17 hrs, Volume= 0.258 af, Depth= 1.13" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Area (ac) C Description 2.730 0.46 Proposed Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P2: Post-Development P2 Hydrograph 12.36 cis 0 a v 0 LL TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Runoff Area=2.730 ac Runoff Volume=0.258 of Runoff Depth=1.13" Tc=10.0 min C=0.46 0 Time (hours) -Runoff • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Prepared by {enter your company name here) Page 20 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-X: Pre-Development "X" Runoff = 14.61 cfs @ 0.17 hrs, Volume= 0.305 af, Depth= 1.01" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Area (ac) C Description 3.620 0.41 Pre-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft ) (ft/sec) (cfs) 10.0 Direct Entry, Existing Conditions Subcatchment DA-X: Pre-Development "X" Hydrograph 1 14.61 cfs I 0 LL 17 TX-Brazos County 25-Year 3 z Duration=10 min, I, Inten=9.86 in/hr ° Runoff Area=3.620 ac 9 8 Runoff Volume=0.305 of / \ Runoff Depth=1.01" 6 Tc=10.0 min 5 : 3 C=0.41 Time (hours) Runoff i • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Prepared by {enter your company name here} Page 21 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Time span=0.00-1.00 hrs, dt=0.01 hrs, 101 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment DA-P: Post-Development P Runoff Area=8.960 ac Runoff Depth=1.25' Tc=15.6 min C=0.70 Runoff=44.74 cfs 0.933 of Subcatchment DA-P1: Post-Development P1 Subcatchment DA-P2: Post-Development P2 Subcatchment DA-X: Pre-Development "X" Runoff Area=0.960 ac Runoff Depth=1.28" Tc=10.0 min C=0.46 Runoff=4.91 cfs 0.103 of Runoff Area=2.730 ac Runoff Depth=1.28" Tc=10.0 min C=0.46 Runoff=13.97 cfs 0.292 of Runoff Area=3.620 ac Runoff Depth=1.14" Tc=10.0 min C=0.41 Runoff=16.52 cfs 0.345 of Total Runoff Area = 16.270 ac Runoff Volume = 1.672 of Average Runoff Depth = 1.23" HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Prepared by {enter your company name here} Page 22 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P: Post-Development P [48] Hint: Peak<CiA due to short duration Runoff = 44.74 cfs @ 0.17 hrs, Volume= 0.933 af, Depth= 1.25" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Area (ac) C Description 8.960 0.70 Post Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.6 Direct Entry, Proposed Conditions Subcatchment DA-P: Post-Development P Hydrograph 44.74 cfs 3 0 TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Runoff Area=8.960 ac Runoff Volume=0.933 of Runoff Depth=1.25" Tc=15.6 min C=0.70 Runoff i Time (hours) • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Prepared by {enter your company name here} Page 23 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P1: Post-Development P1 Runoff = 4.91 cfs @ 0.17 hrs, Volume= 0.103 af, Depth= 1.28" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Area (ac) C Description 0.960 0.46 Post-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P1: Post-Development P1 Hydrograph 4.91 cfs • w 0 LL TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Runoff Area=0.960 ac Runoff Volume=0.103 of Runoff Depth=1.28" Tc=10.0 min C=0.46 0 Time (hours) -Runoff 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Prepared by {enter your company name here} Page 24 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P2: Post-Development P2 Runoff = 13.97 cfs @ 0.17 hrs, Volume= 0.292 af, Depth= 1.28" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Area (ac) C Description 2.730 0.46 Proposed Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P2: Post-Development P2 Hydrograph 13.97 cis w 3 O U. TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Runoff Area=2.730 ac Runoff Volume=0.292 of Runoff Depth=1.28" Tc=10.0 min C=0.46 Time (hours) Runoff • 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Prepared by {enter your company name here} Page 25 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-X: Pre-Development "X" Runoff = 16.52 cfs @ 0.17 hrs, Volume= 0.345 af, Depth= 1.14" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Area (ac) C Description 3.620 0.41 Pre-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Existing Conditions Subcatchment DA-X: Pre-Development "X" Hydrograph • 0 LL 1s 17_ 16.52 cfs 16 TX-Brazos County 50-Year 15- 14 Duration=10 min, 13- Inten=11.15 in/hr 12- 11= Runoff Area=3.620 ac 10- Runoff Volume=0.345 of 9. 6= Runoff Depth=1.14" 7- Tc=10.0 min 6- 5- C=0.41 4- 3- 2- . 1-. 0- u Time (hours) -Runoff 11 HydroCAD-Existing & Proposed Conditions Drainage Calculations • Chimney Hill-Rational-020911 TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Prepared by {enter your company name here} Page 26 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Time span=0.00-1.00 hrs, dt=0.01 hrs, 101 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment DA-P: Post-Development P Runoff Area=8.960 ac Runoff Depth=1.31" Tc=15.6 min C=0.70 Runoff=46.71 cfs 0.975 of Subcatchment DA-P1: Post-Development P1 Subcatchment DA-P2: Post-Development P2 Subcatchment DA-X: Pre-Development "X" Runoff Area=0.960 ac Runoff Depth=1.34" Tc=10.0 min C=0.46 Runoff=5.13 cfs 0.107 of Runoff Area=2.730 ac Runoff Depth=1.34" Tc=10.0 min C=0.46 Runoff=14.59 cfs 0.304 of Runoff Area=3.620 ac Runoff Depth=1.19" Tc=10.0 min C=0.41 Runoff=17.24 cfs 0.360 of Total Runoff Area = 16.270 ac Runoff Volume = 1.746 of Average Runoff Depth = 1.29" • • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Prepared by {enter your company name here} Page 27 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P: Post-Development P [48] Hint: Peak<CiA due to short duration Runoff = 46.71 cfs @ 0.17 hrs, Volume= 0.975 af, Depth= 1.31" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Area (ac) C Description 8.960 0.70 Post Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.6 Direct Entry, Proposed Conditions Subcatchment DA-P: Post-Development P Hydrograph • TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Runoff Area=8.960 ac Runoff Volume=0.975 of Runoff Depth=1.31" Tc=15.6 min C=0.70 3 0 U. Time (hours) -Runoff 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Prepared by {enter your company name here} Page 28 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P1: Post-Development P1 Runoff = 5.13 cfs @ 0.17 hrs, Volume= 0.107 af, Depth= 1.34" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Area (ac) C Description 0.960 0.46 Post-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft ) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P1: Post-Development P1 Hydrograph w 0 U. TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Runoff Area=0.960 ac Runoff Volume=0.107 of Runoff Depth=1.34" Tc=10.0 min C=0.46 Time (hours) Runoff • 0 • HydroCAD-Existing & Proposed Conditions Drainage Calculations Chimney Hill-Rational-020911 TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Prepared by {enter your company name here} Page 29 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-P2: Post-Development P2 Runoff = 14.59 cfs @ 0.17 hrs, Volume= 0.304 af, Depth= 1.34" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Area (ac) C Description 2.730 0.46 Proposed Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Proposed Conditions Subcatchment DA-P2: Post-Development P2 Hydrograph 14.59 cfs E 3 0 LL TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Runoff Area=2.730 ac Runoff Volume=0.304 of Runoff Depth=1.34" Tc=10.0 min C=0.46 Time (hours) -Runoff 0 HydroCAD-Existing & Proposed Conditions Drainage Calculations • Chimney Hill-Rational-020911 TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Prepared by {enter your company name here} Page 30 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Subcatchment DA-X: Pre-Development "X" Runoff = 17.24 cfs @ 0.17 hrs, Volume= 0.360 af, Depth= 1.19" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs TX-Brazos County 100-Year Duration=10 min, Inten=11.64 in/hr Area (ac) C Description 3.620 0.41 Pre-Development Conditions Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft ) (ft/sec) (cfs) 10.0 Direct Entry, Existing Conditions Subcatchment DA-X: Pre-Development "X" Hydrograph 0 LL 51 C=0.41 ~s TX-Brazos County 100-Year 15 Duration=10 min, 4 3 Inten=11.64 in/hr 2 Runoff Area=3.620 ac O Runoff Volume=0.360 of 9 Runoff Depth=1.19" a Tc=10.0 min Time (hours) Runoff • E STORMWATER DRAINAGE ANALYSIS RANDALL'S UNIVERSITY PARK SUBDIVISION j UNIVERSITY & TARROW COLLEGE STATION, TEXAS • I I, M. L. FiANMCNS , as Engineer for site grading' and drainage of this development, by seal and signature, certify that these plans and supporting documents are to the best of my knowledge and intent in ccmpliance with the City of College Station Q:dinance #1728 for St'A171~jj1111j11))))))1)J1J//1J/J///mil water management. E OF tF f 1. H4m.MON, S 7.5308 G/STEP. • i' i Figure XII-1 Application Form Development Permit For Areas Outside-Flood Hazard Areas City of College Station, Texas (re: Ordinance No. ) Site Legal Description: \ Randal. l's University. "Park Subdivision Site Address: University and Tarrow Located in: Burton- Creek Carter Creek Watershed 3663-7-r-Tarpark Owner: RandalZ's Properties, Inc. Address:. Houston, Texas 77042 Telephone No. --767r- -College Station, Texas 77840 Address: 1700 Kyle South #240 Engineer: M . L. HAMMON S , P--E- Telephone No.: 696-1 . 444 Contractor: Not selected Address: Telephone No.: Date Application Filed: Approved: i i. - Application is hereby made for the following development: Site grading and drainage i Attached as part of this application: N/A Application Fee 7- Drainage Plan with supporting documentation: two copies of each Other: _ ACKNOWLEDGEMENTS: I, as owner/developer, hereby acknowledge and affirm that the p~ and supporting docents submitted herewith have been presented me as being in oouplianoe with the city of College station ordinanoe #1728 for stormater management and that site development shall be ly, except as might be amended or modified by due and appz~o~iate authority procedure. Owner /Developer Date II • I TABLE OF CONTENTS i I CEO'IFICATICK ......................................................I II DEVELOPMENT P~ APMIC.ATION FORM ...............................II 1.0 IN MDUC;TIM .......................................................1 2.0 SITE ...............................................................1 2.1 Site Topography 2.2 Easements 2.3 Drainage Basin 2.4 Existing Site Drainage 3.0 PROPOSED DRAIMM PLAN .............................................3 3.1 Run-off Calculation Criteria 3.1.1 Variable A, Drainage Area 3.1.2 Variable C, Run-off Coefficient 3.1.3 Variable I, Rainfall Intensity 3.2 Run-off Calculation 3.3 Run-off Control 3.3.1 Detention Volume Requirements 4.0 671100019L MM DEI'=Cff ......................:...................6 1 4.1 Detention Storage Inflow 4.2 Detention Storage Discharge j Illustration 1.1 Site Location Map .....................................7 Illustration 1.2 Proposed Plat (Randall's University Park) .............8 Illustration 2.1 City of College Station Drainage Basin Map............ 9 i Figure 3.1 Triangular Hydrograph Chart... .....10 Figure 4.1 Detention Storage Input Schematic 11 Figure 4.2 Detention Storage Discharge .12 A Drainage Structure Plans .............................13 III PROPOSAL ■ ■ t 1 I • 0 SUBDIVISION DPWTNAGE 1.0 INt'ROI7(TCTIaq~1 The Randall Is Grocery Coanpany hereby proposes the Develapanent of a 9.28 acre real estate tract located in the Northwest quadrant of the University Drive and Tarrow Drive intersection in the city of College Station. The site fronts on University Drive with property line frontage on Tarrow Drive, Arguello Drive and Chimney Hill Drive as illustrated by the vicinity neap (Illustration 1.1). The site to be developed is lot 1, of the recently proposed Randall's University Park subdivision (Illustration 1.2). By physical necessity and by agreement between owners of lot 1 and lot 2, all of lot 2 drainage will be through lot 1 via surface or underground drainage. With all lots and the small perimeter areas, the total development area for drainage consideration is 11.0 acres. All of lot 2 and 8.65 acres of lot 1 are zoned C-1 commercial and is to be developed accordingly. Me remaining 0.63 acres of lot 1 is zoned R-3 and is included in this development proposal for use as stormwater drainage detention only. Roof coverage of lot 1 is approximately 94,000 square feet, equivalent to 23% of the lot area and 19.6% of the 11.0 acre drainage site. Roof coverage of lot 2 is projected to be 4,000 square feet, equivalent to 7.2% of the lotd area and .8% of the 11.0 acre drainage site. 2.0 SITE The drainage site is presently undeveloped and is vegetated by grass and weeds with a few trees located at the Northwest end of the property. 2.1 Site Topography The existing terrain is open lard on a hillside site with an average slope gradient of approximately 4% - 5*. Surface downslope is in a Northwesterly direction away frown the University Drive, Tarrm Drive intersection toward an existing drainage ravine which collects and discharges all drainage from this site, as well as other upstream areas. Mle maximum elevation of the site is apprnatimately 331' at the intersection of University and Tarrow descending to a low of 298' elevation at the natural drainage discharge point. 1 2.2 Easements All easements and rights-of-way are as indicated by the proposed subdivision plat. Each right-of-way is recognized and honored in the proposed development. All easements will remain intact with no construction encroachment. 2.3 Drainage Basin Illustration 2.1 shaves the site to be in the Carter Creek drainage basin, within the Burton Creek run-off area. Therefore, as described by the City of College Station Drainage Policy and Design Standards (hereinafter "DP & DS"), Section II.D., page 10, excess stormwater detention is required to the one hundred (100) year storm frequency. F.I.R.M. flood maps (Camunity #480083, Panel #1 of 5, July 2, 1981) for the area indicate no one hundred (100) year flood plane within or iminently near the site. 2.4 Existing Site Drainage The existing natural terrain dictates a Northwesterly uniform surface flora of rainfall run-off toward and into a natural drainage wash that traverses the Northwest corner of the site a distance of approximately 540 feet. None of the site run-off drains to any of the adjacent streets and none of the street flaw runs onto the site. Development will not change that flow balance. The wash that traverses the site is the dominant drainage feature of the site and is the route of run-off discharge for the entire 11.0 acres of the drainage site. The wash originates at the West property line of this site about 300 feet from the North R.O.W. line of University Drive and, according to the city tcpo map of the area, is fed by a watershed of apprnarimately 37 acres. Run-off arrival at the origin of the wash is via surface run-off and an underground 48" RCP drain pipe. The existing wash appears to have been created historically by run-off resulting from flow consolidation by natural terrain. Any wash area that might have been upstream from the West property line of this site has abeen eliminated by surface development. There are no springs, seeps or other natural or marmmade streams originating on the site. There are no upstream discharges that result in continual flow of the drainage wash. The calculated 100 year peak flaw from the upstream 37 acre area is 185 CFS based on a run-off coefficient factor (c) of .55 and an intensity factor (I) of 9.1. The intensity factor is from Figure III-1 of the DP & DS manual with application of a 20 minute time of concentration. The C factor, is determined by use of Table III-1 of the DP & DS manual. (Q = .55 * 9.2 * 37) 2 3.0 Proposed Drainacte Plan To achieve stormwater control according to city Ordinance #1728, chapter 13 of the code of ordinances of the City of College station,, the following controls are proposed.. 1. Zhe entire Randall's University Park Subdivision, 11.0 acres, is to be considered as the drainage development site. 2. The site's post-develcpmrent storawater run-off rate is not to exceed the pre-development run-off rate. 3. lie upstream, offsite stormiater inflow is to be managed through the site but without detention or other control that would limit the flaw rate. 4. The site stormwater detention control is to be designed for the one hundred (100) year (1% anmaal probability) storm event frequency. 5. All stormwater will continue to discharge at the intersection of the North property line and the Chimney Hill Drive R.O.W., which is the current discharge point. 3.1 Run-Off Calculation Criteria NorI Stormwater run-off is calculated herein according to methods presented in the City of College Station DP & DS manual. Peak discharges (Pre-Davelopment & Post-Development) are calculated by the Rational Formula (Q - CIA) since: A. The run-off area is less than fifty (50) acres. B. The discharge is not a primary system discharge. C. Me flow being calculated is overland and street flow as required by the DP & DS manual (Section III, Paragragb B.2.d., page 17) for rational formula calculation. 3.1.1 Variable A, the developmaent area, is the 10.54 acres as defined by subdivision plat plus a small perimeter (curb to property line) area. The area used for calculation herein is 11.0 I acres. 3.1.2 Variable C. the run-off coefficient, is determined by use of Table III-1 of the previseuly referenced DP & DS manual. Zhree major slope areas are considered in the determination. A. Me broad area between University Drive and Arguello Drive which is approacimately 8.5 acres at an average existing slope of 2.7%. I 3 B. The steep banks of the drainage creek, approximately .75 acres at a slope of 20%±. C. Me West bank of the creek, approximately 1.75 acres at a slope of 9%+. (8.5 * 2.7) + (.75 * 20.0) + (1.75 * 9)/11 = 4.9 Accordingly, the composite Pre-developmroexrt coefficient (C) is 0.45. rj!he Post-development coefficient (C) Jr. 0.85. 3.1.3 Variable I, the rainfall intensity, is established as shown below. Determination is by Figure III-1 of the DP & DS manual with application of the time of concentration (TC) as indicated. Post-Development I 10 = 8.63 in/hr I 25 = 9.86 in/hr I 100 = 12.5 in/hr Pre-Development I 10 = 8.63 irVhr I 25 = 9.86 in/hr I 100 = 12.5 in/hr TC = 10 minutes TC = 10 minutes (TC is less than 10 minutes, both conditions) 3.2 Run-Off Calculation With the factors determined in Paragraph 3.1 above and by use of the Rational formula, site run-off is calculated to be: Post-Develapanent Q 10 = 80.7 CFS Q 25 = 92.2 CFS Q 100 = 116.9 CFS Pre-Development Q 10 = 42.7 CFS Q 25 = 48.8 CPS Q 100 = 61.9 CPS Mis point of calculated discharge is at the intersection of the North property line and the Chimney Hill Drive cul-de-sac R.O.W. line. 3.3 Run-Off Control In order to achieve a p d degree of run-off control, stormwater storage space and regulated discharged flow must be provided. Storage is provided for this site in the Nort1iwest corner of the development site, North of the existing utilities easement. Regulated discharge flaw is by the outlet structure located near Chimney Hill Drive. See Appendix A. 0 • 4 3.3.1 Detention Volume Paquirenwrt Detention volume for this site is determined by cmparison of hydrographs representing the uncontrolled post-develepwnt flow and the "design" flow as allowed by the Oollege Station DP & DS marmal for the conditions represented at this site. The triangular appiroacimation hydrograph is used. The project "design" hydrograph is the flow to which the discharge orifice is designed and is limited to the maximum flow calculated for the pre-development site conditions. Figure 3.1 presents both the Pre and Post Q100 run-off hydrograph. In addition the "design" hydrograph is shown. Me required detention volume is represented on Figure 3.1 as the graph area exceeding the "design" Q100 run-off flow, but within the Post-developanent, Q100 run-off flaw. Calculation is by conversion of the hydrograph areas to the numerical units represented thereon. 'IYue area of volume calculation is from the time of run-off onset until the time at which the uncontrolled Post-del-m1c went flow rate, during decline, is equal the predetermined allowable discharge flaw rate. By such application the required storage volume is 49,500 cubic feet as calculated thus: Incoming Volume/100 yr. Hydrograph: 105,210 CF* * 30 min x 60 x 116.9 CC'S x .5 = 105,210 Discharged Volume/100 yr. Hydrograph: > 55,710 CF** 30 min x 60 x 61.9 CFS x .5 = 55,710 Net Storage Volume Required 49,500 CF*** 105,210 - 55,710 = 49,500 I i I i I i Volume Provided = > 65,000 cubic feet 5 4.0 SW OMM DETEN'T'ION With the ]roam detention volume requirement and the ]mown area of placement, a detention storage structure has been designed and is presented as appendix A.,l herein. 4.1 Detention Storage Inflow Based on the Rational Method of calculation used throughout this analysis, a Q100 peak discharge flow rate has been calculated for the ecuposite area of this subidivision. Peak flow rate input is as indicated by figure 4.1. It should be noted that run-off introduced to the site by upstream discharge has been managed through the site but is not a part of the flow within the detention system. 4.2 Detention Storage Discharge The Post-development run-off discharge Er , this site is concentrated at the point where the existing natural run-off leaves the property. It is at the north end of the site adjacent to the Chimney Hill Drive cul-de-sac R.O.W. line. Appendix A.,1 details the structures involved and the outfall geometry. The outfall structures are designed to re-introduce the outfall flow to the natural drainage stream with flow characteristics that will • not increase the erosion rates beyond that experienced during the pre-,development flow. The total uk-odmum discharge from the site is the combined "design" discharge and the upstream flow. It is 247 CFS which is the same as the calculated Pre-development flow, and is a combination of the 185 CC'S uncontrolled and the 62 CT'S release from the detention area. Masse volumes are peak flows during the one hundred (100) year frequency storm event. Outflow velocity has been set at 7.0 feet per second as shown by calculations of Figure 4.2 herein. 6 0 i ILLUSTRATIONS ■ ■ 1 1 • 0 0 0 1 i •.f•Y. -.M'. i a T1 Wit Ill J 1 h~H,f!i 1? Fq P S E"• ( I. ~Iti~`{'~ $ d 1 ! Lill 3 pP Y y9 f, 1 L. , 1 ¢ Iff 1 , 9~1s 'ij~t t l z S~ n~ g~ 1 :E a j }~~at O }oto,. 2 j0 r if 1 tl ~ Mfg ,f f 1} O Z ~ O } j,}t r t I~i, t o w 4} o f , fit r if t t t b. f} fi, ' • N E iii►~ i I ~}~,!l I i( 1 ~ U t 3 FF~' ~ R71NDAILS CITY PARK BCJBMISIOT ! IlltaStraticcl 1.2 8 LEGEND BASIN REFERENCE NUMBER El REGULATORY CHANNEL REACHES N-- O PRIMARY DRAINAGE SYSTEM SECONDARY DRAINAGE SYSTEM' BASIN BOUNDARY - SUB-BASIN BOUNDARY - - - - I I i ~ - 1 / W I~ it I~' v r - - I 6a IW ION 1 IJ 10 10 I I c TRIG I ~ ~OVFQ 1 ~ ISITE LD w~~P a I 1 o. I ~ c16r~ I ~ o~~F~E TArio~ I Wt: RN 2134 CARTER' CREEK DRAINAGE BASIN (PARTIAL) • U MVMMM 1 r BASIN MAP Tllustrat M 2.1 1 9 E FIGURES ■ ■ 1 11 4- 12A88 i. _ .1. _ _ . _ . - - - - _ TF I: . a _ i 1 i s :i _ tI - . . . . . l : aa 77. 44 . _ :2A I _ _ _ _ UA: LL. L2 AA - H l ' il : 9'I • .ri t ;tl. _ t '7 • •„1 #i ::1:: : _ ::7; J ~ ,J _ _ ' _ , y ? . _ _ :S :?1 -C. y.7i: :.7 _r .t. :I7' +1 I• `l • ~ ail y f,~ . i. _ - ~ µ 14 :r. t,l • - - _ 1 7.t - ~t ~ Nl.. : i 11 i i= - y f ~ ~ t . - - 1 ~ ''L 1. ' ~t:! ' _ ii: al~ it'!♦ ~1 :Ij: ,:1' _ ' Y•=.' !1 _ 1t~' I: 1 T ' - _ - ~ ` _ _1 _:.1 .M• " -e_ S 1t1 : l tea. ;tj • • i - - - ~i - I, L 1' e .1 - :.SIB . . . : - + 7 ice. J:1, 1~ t '1. + 1~ ~ { ~ i ~ t f t 7~ }1 [ + 11 : . 1J+± : ' J ! C +r1. t a ' SITE HYDROGFt AP H . _ 1 FIG LM 3 .1 • 0 10 Mitlimew" to the Centimeter 10 • I 1 I I N I+ I SITE QRAI1M SC MMMC ' ' I ` : FIMM 4.:t-, 11 Trapezoidal Channel Analysis & Design Open Channel - Uniform flow Worksheet Name: RANDALLS OUTFALL Given Input Data: Bottom Width..... Left Side Slope.. Right Side Slope. Manning's n...... Channel Slope.... Discharge........ Computed Results: Depth............ Velocity......... Flow Area. Flow Top Width... Wetted Perimeter. Critical Depth... Critical Slope... Froude Number.... 12.00 ft 1.00:1 (H:V) 1.00:1 (H:V) 0.030 0.0087 ft/ft 247.00 cfs 2.44 ft 7.00 fps 35.28 sf 16.89 ft 18.91 ft 2.21 ft 0.0122 ft/ft 0.85 (flow is Subcritical) Open Channel Flow Module, Version 3.12 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct D~TII~I'I'I~T 8'i~iAGE F GbfM 4.2 • 12 i I I 1 APPENDIX ANN I 1 I SITE DRAINAGE DRAWINGS: Site drainage drawings are furnished by separate 2' X 3' sheets and are an integral part of this analysis and report. Sheets provided: Site Grading Plan Detention Basin Drainage Structures NO SITE DRAINAGE DRAWINGS Appendix A., 1 • U 0 -13 • Section 4.0 DETENTION FACILITY & ROUTING 0 9 C] 0 l i Xl 'uNnOO sozvae 'NOUVts 393TIOD SLNW43AONdni kiru t 8 30VNFVNO '9NNVd Tr i o) - Z Q 01= E= '~v ~~q e p B : • 3Z -2I£ nj4l dZ-21£ S101 " y < I i r 0 o O i0 o x o $ g ~ i< 99 ~ ; Wl: 11 W 4m 2~bd JU IS2l3AINf1 S,lldaNV2I N - ; a < Z N o Ul) H. a P VyS~~ , ` g 0~ Pg F ~VYrz 4qc ~8 3Nt aoi ppIW~<~ 3 a z q ~ Ww" N t o~..uay Ph S 3 .7 a au - 4 -69 to NVId 30dNivNa * ONiavmO ONIAdd r W ¢ li J f/1 J S 2 p~ > Z ~ U WwU a ` ,3 rr 6W MWDMDWW Z61-0S33~o Gi<0 <c~6w<A mg :013: CD W W a i : IAkYTB!®■9$®t094,®661 I, 1 a;ma Ii! 1 IAW N- \ o z cl^ o a z w rotr 1 k' o o~ d \ \ i~ < it < <UZ 2O J'f`O F tz: `Z <<Z < O o r 1~y~ v N W 2 Z OON N UIX 2Q W=Z 2 E it • \ m~ a rrc I w Z w <w lk~ }o r~y~ ~ ~ ~ o ro ~ ~ O ~Q~ of icy woad vi~ wV\i \ / 00 nT ¢ Oro ~J Z n ~rc¢an \ J O W 7r NQ Ix z O O O S $~SS W ~2 WC W < oW3 O~ O~ O~ <Q[~ y>JJ ~ W On m~~N i7 ~hr ago aoso Cc> "!5 4 a 41 °~Tt to l' d 6 OI W Ww"0. ~ 4-- / O ~3X Z z .s, s w p w r O. S IL m \ of I~ _<U c°5w F< rJ" 'i <U \ r8, . i 11om dim W3~a y qq B>p. \ J CW W171 I yw M SSS_ YKSyO~Y / h 4 ~I~I~O j ZF"NA FU->Lia n O> I ~w ooh \ / N^2 Za 1N o=s I ~ KO 4^x 9~O \ sK~ I ti = O % U O W vO ♦ \ < O4 \ 2 I o \ z W \ 1 pp y~ ♦V \ \ Fl: c N-1 \ 1 1 ~ I 1 ~ f/1 ; r ZT I m r Ipn r \ 0 X5 Gow < < •Y ~9~, ' \ ~ 3 vl rcl' ink <5< ° ILM d Ix U SN n'n r gO ' eeL Wmi; I V O~ F w gl yI " 91f V i °m^ ` r 1 1 I / w < U W ~v0.r mr, ~ I I b~2v ~ 0 ~ V n I ao y o air i~g 1 'Ot~ Ip In ttf rc . ~ 4 / 'ter _ n r .OBYSi - M .110 r1 -7 H< I I roan" AY 30~~3 is • ~a o 0 i0 w HydroCAD - Proposed Conditions Pond Calculations - Pond 1 is Chimney Hill-Rational-020911 TX-Brazos County 50-Year Duration= 10 min, Inten=11.15 in/hr Prepared by {enter your company name here} Page 10 HydroCAD®? 10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 Hydrograph i-1 4.91 CfS Inflow Area=0.960 ac Peak Elev=303.55' Storage=3,685 cf U O U. 1A Inflow Primary 0 Time (hours) Pond P1: Pond 1 Stage-Area-Storage Surface/HorizontaMetted Area (sq-ft) n Ann , nnn 1 6nn 2000 .2.500 3.000 3,500 4,000 4,500 d m c 0 m m w Surface Storage • 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,a00 -J,00u a,auu Storage (cubic-feet) . HydroCAD - Proposed Conditions Pond Calculations - Pond 1 Chimney Hill-Rational-020911 TX-Brazos County 50-Year Duration=10 min, Inten=11.15 in/hr Prepared by {enter your company name here} Page 9 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 Inflow Area = 0.960 ac, Inflow Depth = 1.28" for 50-Year event Inflow = 4.91 cfs @ 0.17 hrs, Volume= 0.103 of Outflow = 0.59 cfs @ 0.46 hrs, Volume= 0.042 af, Atten= 88%, Lag= 17.4 min Primary = 0.59 cfs @ 0.46 hrs, Volume= 0.042 of Routing by Stor-Ind method, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs Peak Elev= 303.55'@ 0.46 hrs Surf.Area= 4,478 sf Storage= 3,685 cf Plug-Flow detention time=25.0 min calculated for 0.042 of (41 % of inflow) Center-of-Mass det. time= 19.3 min ( 32.6 - 13.3 ) Volume Invert Avail.Storage Storage Description #1 302.30' 5,803 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 302.30 0 0 0 303.00 3,928 1,375 1,375 304.00 4,929 4,429 5,803 • Device Routing Invert Outlet Devices #1 Primary 302.30' 0.33' x 0.33' Horiz. Orifice/Grate Limited to weir flow C=0.600 Primary OutFlow Max=0.59 cfs @ 0.46 hrs HW=303.55' (Free Discharge) t-1=Orifice/Grate (Orifice Controls 0.59 cfs @ 5.4 fps) 0 HydroCAD - Proposed Conditions Pond Calculations - Pond 1 10 Chimney Hill-Rational-020911 TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Prepared by {enter your company name here) Page 8 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 Hydrograph Inflow Area=0.960 ac Peak Elev=303.44' Storage=3,205 cf 0 U. 1-1 Time (hours) Pond P1: Pond 1 Stage-Area-Storage Surface/Horizontal/Wetted Area (sq-ft) 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 4, m c 0 .W m w - Inflow Primary 0 Surface Storage 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 Storage (cubic-feet) HydroCAD - Proposed Conditions Pond Calculations - Pond 1 Chimney Hill-Rational-020911 TX-Brazos County 25-Year Duration=10 min, Inten=9.86 in/hr Prepared by {enter your company name here} Page 7 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 • Inflow Area = 0.960 ac, Inflow Depth = 1.13" for 25-Year event Inflow = 4.35 cfs @ 0.17 hrs, Volume= 0.091 of Outflow = 0.56 cfs @ 0.46 hrs, Volume= 0.040 af, Atten= 87%, Lag= 17.2 min Primary = 0.56 cfs @ 0.46 hrs, Volume= 0.040 of Routing by Stor-Ind method, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs Peak Elev= 303.44'@ 0.46 hrs Surf.Area= 4,370 sf Storage= 3,205 cf Plug-Flow detention time= 24.8 min calculated for 0.040 of (44% of inflow) Center-of-Mass det. time= 19.2 min ( 32.5 - 13.3 ) Volume Invert Avail.Storage Storage Description #1 302.30' 5,803 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 302.30 0 0 0 303.00 3,928 1,375 1,375 304.00 4,929 4,429 5,803 Device Routing Invert Outlet Devices #1 Primary 302.30' 0.33'x 0.33' Horiz. Orifice/Grate Limited to weir flow C= 0.600 Primary OutFlow Max=0.56 cfs @ 0.46 hrs HW=303.44' (Free Discharge) t-1=Orifice/Grate (Orifice Controls 0.56 cfs @ 5.1 fps) HydroCAD - Proposed Conditions Pond Calculations - Pond 1 i Chimney Hill-Rational-020911 TX-Brazos County 10-Year Duration=10 min, inten=8.63 in/hr Prepared by {enter your company name here) Page 6 HydroCAD®? 10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 Hydrograph Inflow Area=0.960 ac Peak Elev=303.34' Storage=2,749 cf U. 14 0.53 cfS Inflow Primary • Time (hours) Pond P1: Pond 1 Stage-Area Storage Surface/Horizontal/Wetted Area (sq-ft) 0 500 1.000 1.500 2.000 2,500 3,000 3,500 4,000 4,500 d m c 0 io d w I - Storage • 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 Storage (cubic-feet) HydroCAD - Proposed Conditions Pond Calculations - Pond 1 Chimney Hill-Rational-020911 TX-Brazos County 10-Year Duration=10 min, Inten=8.63 in/hr Prepared by {enter your company name here} Page 5 HydroCAD® 7.10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 n LJ Inflow Area = 0.960 ac, Inflow Depth = 0.99" for 10-Year event Inflow = 3.81 cfs @ 0.17 hrs, Volume= 0.079 of Outflow = 0.53 cfs @ 0.45 hrs, Volume= 0.038 af, Atten= 86%, Lag= 17.0 min Primary = 0.53 cfs @ 0.45 hrs, Volume= 0.038 of Routing by Stor-Ind method, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs Peak Elev= 303.34'@ 0.45 hrs Surf.Area= 4,264 sf Storage= 2,749 cf Plug-Flow detention time=24.4 min calculated for 0.038 of (48% of inflow) Center-of-Mass det. time= 19.1 min ( 32.5 - 13.3 ) Volume Invert Avail.Storage Storage Description #1 302.30' 5,803 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 302.30 0 0 0 303.00 3,928 1,375 1,375 304.00 4,929 4,429 5,803 Device Routing Invert Outlet Devices #1 Primary 302.30' 0.33' x 0.33' Horiz. Orifice/Grate Limited to weir flow C=0.600 PrimaryOutFlow Max=0.53 cfs @ 0.45 hrs HW=303.34' (Free Discharge) L1=Orifice/Grate (Orifice Controls 0.53 cfs @ 4.9 fps) 0 HydroCAD - Proposed Conditions Pond Calculations - Pond 1 Chimney Hill-Rational-020911 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Prepared by {enter your company name here} Page 4 HydroCAD®7 10 s/n 003394 © 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 Hydrograph 3.39 cis F 4 0 U. 31 1A 0.51 cfs 304 D~ Inflow Area=0.960 ac Peak Elev=303.25' Storage=2,401 cf 0 Time (hours) Pond P1: Pond 1 Stage-Area-Storage Y Surface/Horizontal/Wetted Area (sq-ft n snn 1 onn 1.500 2000 .2.500 3,000 3,500 4,000 4,500 = Inflow Primary Surface Storage m m L 0 w d 303 w 0 500 1,000 1,500 z,000 z,SUU 5,000 6,aUU 4,000 4,DUU x,000 U'DUU Storage (cubic-feet) HydroCAD - Proposed Conditions Pond Calculations - Pond 1 Chimney Hill-Rational-020911 TX-Brazos County 5-Year Duration=10 min, Inten=7.69 in/hr Prepared by {enter your company name here} Page 3 HydroCAD® 7.10 s/n 003394 0 2005 HydroCAD Software Solutions LLC 2/8/2011 Pond P1: Pond 1 Inflow Area = 0.960 ac, Inflow Depth = 0.88" for 5-Year event Inflow = 3.39 cfs @ 0.17 hrs, Volume= 0.071 of Outflow = 0.51 cfs @ 0.45 hrs, Volume= 0.037 af, Atten= 85%, Lag= 16.8 min Primary = 0.51 cfs @ 0.45 hrs, Volume= 0.037 of Routing by Stor-Ind method, Time Span= 0.00-1.00 hrs, dt= 0.01 hrs Peak Elev= 303.25'@ 0.45 hrs Surf.Area= 4,181 sf Storage= 2,401 cf Plug-Flow detention time= 23.8 min calculated for 0.036 of (51% of inflow) Center-of-Mass det. time= 19.0 min ( 32.4 - 13.3 ) Volume Invert Avail.Storage Storage Description #1 302.30' 5,803 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 302.30 0 0 0 303.00 3,928 1,375 1,375 304.00 4,929 4,429 5,803 Device Routing Invert Outlet Devices #1 Primary 302.30' 0.33' x 0.33' Horiz. Orifice/Grate Limited to weir flow C=0.600 Primary OutFlow Max=0.51 cfs @ 0.45 hrs HW=303.25' (Free Discharge) L1=Orifice/Grate (Orifice Controls 0.51 cfs @ 4.7 fps) • • Section 5.0 STORM DRAINAGE SYSTEM 0 0 output.lis TEXAS HYDRAULIC SYSTEM, CULVERT (ver. 1.2. Feb/2002) Wed Feb 16 09:29:08 2011 CULVERT HYDRAULIC COMPUTATIONS CULVERT NAME: EX C1 Input units: English PROJECT NAME: Randalls output units: English PROJECT CONTROL: 220-0419 COUNTY: Brazos County DESCRIPTION: Existing 60" Culvert ANALYZE SINGLE OPENING CULVERT MATERIAL: CONCRETE SHAPE: RCP CIRCULAR PIPE. ENTRANCE: PROJECT PROFILE: STRAIGHT CULVERT FREQUENCY: 100 YR DISCHARGE: 291.23 cfs TAILWATER: 297.87 ft n value: 0.0120 CULVERT DIAM. = INLET station: OUTLET station: Road profile (X' X 0.00 Ke value: 0.5000 5.00 ft BARRELS = 1 0.00 elevation: 295.97 ft 64.00 elevation: 294.84 ft Y Coordinates) ft Y X Y X Y 306.00 44.00 304.60 110.00 305.30 CULVERT OUTPUT RUN NO 1 ANALYSIS for discharge frequency of : 100 YR Barls. Qpb Rise Span Length Max.HW Calc.HW HW Control Veloc. Out.depth elev elev cfs ft ft ft ft ft ft ft/s ft 1 145.05 5.00 0.00 64.00 0.00 305.58 9.61 Outlet 14.11 2.59 Inlet control depth = 5.18 ft outlet control depth = 9.61 ft Normal depth = 2.16 ft culvert slope = 0.01766 Critical depth = 3.45 ft critical slope = 0.00391 Road top width 24.00 ft. Road pavement type asphalt computed weir coefficient 3.04. Toal Discharge 291.23 cfs Discharge per barrel 145.05 cfs Discharge over the road 146.18 cfs Average velocity over the road 2.31 ft/sec Page 1 • 0 output.lis RUNING MESSAGES LIST: *Computation: Hydraulic jump occurs at culvert outlet. *Computation: Outlet velocity is based on the outlet water depth. *Computation: Hydraulic jump occurs at culvert outlet. NORMAL TERMINATION OF THYSYS, CULVERT. • Page 2 • • • output.lis TEXAS HYDRAULIC SYSTEM, CULVERT (ver. 1.2. Feb/2002) Mon Feb 14 19:23:57 2011 CULVERT HYDRAULIC COMPUTATIONS CULVERT NAME: C2 Input Units: English PROJECT NAME: Output units: English PROJECT CONTROL: COUNTY: DESCRIPTION: ANALYZE SINGLE OPENING MATERIAL: CONCRETE SHAPE: RCP CIRCULAR PIPE. ENTRANCE: MITER PROFILE: STRAIGHT CULVERT FREQUENCY: 100 yr DISCHARGE CULVERT 93.50 cfs TAILWATER: 297.87 ft n value: 0.0120 Ke value: 0.7000 CULVERT DIAM. = 3.00 ft BARRELS = 1 INLET station: 0.00 elevation: 296.48 ft OUTLET station: 124.00 elevation: 294.84 ft Road profile (XY Coordinates) ft X Y X Y X Y 0.00 308.13 56.00 304.45 87.00 304.75 CULVERT OUTPUT RUN NO 1 ANALYSIS for discharge frequency of : 100 yr Barls. Qpb Rise Span Length Max.HW Calc.HW HW Control Veloc. Out.depth elev elev cfs ft ft ft ft ft ft ft/s ft 1 93.50 3.00 0.00 106.00 0.00 304.30 7.94 Outlet 13.23 3.00 Inlet control depth = 10.53 ft Outlet control depth = 7.94 ft Normal depth = 3.00 ft culvert slope = 0.01323 Critical depth = 2.87 ft critical slope = 0.01454 Road top width 0.00 ft. Road pavement type asphalt computed weir coefficient 3.00. No discharge over the road. RUNING MESSAGES LIST: Page 1 output.lis NORMAL TERMINATION OF THYSYS, CULVERT. • Page 2 0 output.lis TEXAS HYDRAULIC SYSTEM, CULVERT (ver. 1.2. Feb/2002) Mon Feb 14 19:23:00 2011 CULVERT HYDRAULIC COMPUTATIONS CULVERT NAME: C1 Input Units: English PROJECT NAME: Output units: English PROJECT CONTROL: COUNTY: DESCRIPTION: ANALYZE SINGLE OPENING CULVERT MATERIAL: CONCRETE SHAPE: RCP CIRCULAR PIPE. ENTRANCE: MITER PROFILE: BROKEN BACK CULVERT FREQUENCY: 100 yr DISCHARGE: 195.70 cfs TAILWATER: 297.87 ft n value: 0.0120 CULVERT DIAM. = 5 INLET station: OUTLET station: Unit slope 1 0.01000 2 0.01766 Ke value: 0.7000 .00 ft BARRELS = 1 0.00 elevation: 296.48 ft 115.00 elevation: 294.84 ft BROKEN BACK CULVERT CONFIGURATION UPSTREAM DOWNSTREAM Length Sta. Elev. Sta. Elev. 51.00 0.00 296.48 51.00 295.97 64.00 51.00 295.97 115.00 294.84 Road profile (XY Coordinates) ft X Y X Y X Y 0.00 308.13 56.00 304.45 87.00 304.75 CULVERT OUTPUT RUN NO 1 ANALYSIS for discharge frequency of : 100 yr Barls. Qpb Rise Span Length Max.HW Calc.HW HW Control Veloc. Out.depth elev elev cfs ft ft ft ft ft ft ft/s ft 1 195.70 5.00 0.00 85.00 0.00 304.30 8.04 Inlet 15.26 3.11 Inlet control depth = 8.04 ft outlet control depth = 3.06 ft Normal depth = 2.56 ft Culvert slope = 0.01426 Critical depth = 4.00 ft Critical slope = 0.00504 Road top width 0.00 ft. Road pavement type asphalt computed weir coefficient 3.00. No discharge over the road. Page 1 • -------------------------------------output_lis------------------------------- RUNING MESSAGES LIST: *Computation: Hydraulic jump occurs inside of the most downstream unit. NORMAL TERMINATION OF THYSYS, CULVERT. • Page 2 0