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Home My WebLink About11 Development Permit 301 Pebble Creek Ph IIICJoe Orr, Inc . Surveyors & Enginee rs 2167 Post 0Jk Circle College Station, Texas 77845 (409) 690-3378 Supplementary Drainage Report Pebble Creek Phase 3 \)\'\Lt~ 3c., " --:::::::=- Prepared by David R . Mayo, P . E . for Pebble Creek Development Company 4500 Pebble Creek Parkway College Station, Texas 77845 July 30, 1995 .l Veronica Morgan, P .E . Asst. City Engineer City of College Station P .O . Box 9960 College Station, Texas 77842 Joe Orr, Inc. Surveyors & E ng in eers 2167 Post Oak Circle College Station, Texas 77845 (409) 690-3378 1 August 1994 Re : Pebble Creek 3C Street and Drainage Plans Dear Veronica, I am submitting the Drainage Report for Pebble Creek Phase 3C along with Construction Plans for the Streets and Drainage. I do not believe an application for a Development Permit for this project is necessary as it is a part of Pebble Creek phase 3 which has been permitted . Please review these documents and give your approval or comments at your earliest convenience . Thank you, Joe Orr, Inc. S urveyors & E ng in eers 2167 Post Oak Circle College Station, Texas 77845 (409) 690-3378 Supplementary Drainage Report Pebble Creek Phase 3 Prepared by David R. Mayo, P .E . for Pebble Creek Development Company 4500 Pebble Creek Parkway College Station, Texas 77845 July 30, 1995 INTRODUCTION This report is supplementary to the drainage report for Pebble Creek Phase 3 submitted in July 1993. It covers the runoff onto the extension of Spearman Drive between St. Andrews Drive in Pebble Creek Phase 3 and Putter Court in Pebble Creek Phase 5. DRAINAGE AREAS Drainage onto this street extension has been divided into four areas for calculation purposes. These were previously addressed in reports submitted for Pebble Creek phases 3 and 5. A map showing these areas in included on the next page . It was determined in the earlier calculations that drainage from the north onto this portion of Spearman Drive could not totally carried in the north gutter and comply with the requirements of the City of College Station Drainage Policy and Design Standards. We plan to intercept this runoff at a point downstream of Putter Court where a future street intersection will be constructed . This will divide the runoff area into four parts . Area Al lies upstream of the proposed intercept point and is approximately 3. 0 acres of residential lots south of Spearman Drive . Area A2 lies upstream of the proposed intercept point and is approximately 1.6 acres of residential lots north of Spearman Drive . Area BI is approximately 1.9 acres downstream of the intercept point and lies north of Spearman Drive. It is composed of large residential lots. Area B2 is approximately 1.3 acres downstream of the intercept point, lies south of Spearman Drive and is approximately 50% street and 50% grass . DRAINAGE DESIGN CRITERIA Regulations: The City of College Station Drainage Policy and Design Standards have been used as the primary design criteria for this project. Material referenced in the Design Standards such as the "Hydraulic Manual" of the TSDHPT have also been used . Development Criteria Reference and Constraints: This project site has had no previous drainage studies made other than the general area studies for the primary drainage basin . There will be little impact on adjoining tracts since the majority of the outflow will be into the existing natural drainage system . Hydrological Criteria: There is one type of street in this project. Spearman Drive is a collector street and will be designed to carry a 10 year storm with one 12' lane clear . All streets will be designed so that the runoff from a I 00 year storm will be contained within the right-of-way. The curb inlets and storm drains will be designed to carry no less than a I 0 year storm. All of the sub-areas for determination of inlet placement and pipe size are small . None are over 5 acres . Therefore we will use the Rational Formula to determine the runoff from these areas . The formula is expressed as Q=ciA where: Q =discharge in acre-inches per hour which is equivalent to cubic feet per second (cfs) c is a runoff coefficient having no units , i is the rainfall intensity in inches per hour, and A = area in acres of land contributing to the runoff Since the drainage areas are small , we have elected to use a nurumum time of concentration instead of determining a flow path from the most hydraulically remote point in each drainage area . A time of 15 minutes will be used which is generally considered the minimum for residential lots Rainfall intensities will be determined from the formula which was developed to plot rainfall intensity versus duration for each recurrence interval as a straight line on log-log paper. where : I = rainfall intensity in inches per hour, tc = the time of concentration of the watershed in minutes , b = the y-intercept of the straight line , d = a constant used to adjust the relationship to plot as a straight line , and e = the slope of the straight line . Values for b, d, and e have been determined for most locations, and a table from the Bridge Division Hydraul ic Manual of the TSDHPT which includes those for Brazos County is included on the following page . 3 Table of Rainfall Intensities The following is a tabulation of the rainfall intensity equation using constants for 10 , 25 and 100 year storm events for Brazos County. Rainfall Intensities Brazos County, Texas Constants for use in the formula l=b/(Tc+d)"e from SDHPT Manual Storm e b d 2 0 .806 65 8 .00 5 0 .785 76 8 .50 10 0 .763 80 8 .50 25 0.754 89 8.50 50 0 .745 98 8 .50 100 0 .730 96 8.00 Tc(min) Storm Intensity Frequency in/hr 15 10 7 .19 15 25 8 .23 15 100 9.73 There is no detention proposed in this project, as previous studies have shown that the Pebble Creek development will have a faster peak runoff than the runoff from the entire Lick Creek watershed . 4 TABLE 5. RUNOFF COEFFICIENTS FOR RATIONAL FORMULA Type of Drainage Area Runoff Coeff lclent Business : Downtown areas Neighborhood areas Resldentlal: Slngle-faml ly areas Multl-unlts, detached Multl-unlts, attached Suburban Apartment dwell lng areas I ndustr l al: Ll ght areas Heavy areas Parks, cemeterles Playgrounds Ra! I road yard areas Unimproved areas Sand or sandy loam so l I, 0-3% Sand or sandy loam sol I, 3-5% Black or loesslal sol I, 0-3% Black or loesslal sol I, 3-5% Black or loesslal sol I, >5% Deep sand area Steep grassed slopes Lawns: Sandy sol I, Sandy sol I, Sandy sol I, Heavy so l I, Heavy sol I, flat 2% average 2-7% steep, 7% f I at 2% average 2-7% Heavy sol I, steep, 7% Streets: Asp ha I tl c Concrete Brick Drives and walks Roofs from ASCE, 1960 BRIDGE DIVISION HYDRAULIC MANUAL 2 - 1 5 o. 70-0.95 0.50-0.70 0.30-0.50 0.40-0.60 0.60-0.75 0.25-0.40 0.50-0.70 o.50-0.80 0.60-0.90 O. 10-0.25 0.20-0.40 0,20-0.40 0,10-0.30 0.15-0.20 0.20-0,25 0, 18-0,25 0,25-0.3P 0,70-0.80 0.05-0, 15 0.10 0,05-0.10 0,10-0,15 0,15-0.20 0.13-0. 17 0, 18-0,22 0.25-0.35 0,70-0.95 0.80-0-95 0,70-0.85 0,75-0.85 0, 75-0,95 12-85 Hydraulic Criteria: The street capacities in this project will be determined by considering each half of the street as a triangular channel with one vertical side . The Manning Equation, V= (1.486/n)R2/3sll2, will be used to determine the velocities and capacities . The roughness coefficient "n" is assumed to be 0 . 015 for part concrete and part asphalt surface . The inlet equations from the City of College Station Design Standards Q=3 .0 Ly312 will be used to determine the length of opening required for all inlets in a sump or on a slope of 1 % or less with a 5" or greater depression at the entrance where Q =total flow upstream of inlet , L= length of inlet throat (ft) and y= total depth of flow at inlet, and Q=O . 7L(l/y)((a+y)5/2_a512) will be used to determine the length of opening required for inlets on grade with gutter depression where Q=total flow upstream of inlet , L= length (ft) of inlet throat required to capture Q, y= depth of flow upstream of inlet and a= depression at inlet. Capacities of reinforced concrete storm drain will also be calculated using Manning's Equation and an "n" value of 0 .014 for concrete will be assumed . 6 Drainage Facility Design General Concept: The initial phase of the drainage design for this project was to analyze the drainage patterns from the topo and determine curb inlet placement from street capacities and lot layout. Inlets were then sized and storm drain pipe sizes were determined . Specific Details: Each drainage area and storm drain will be outlined in this section . Drainage Area "A" Drainage area "A" lies northwest of this portion of Spearman Drive extending from the centerline of Hook Court to the centerline of a proposed future street. It is approximately 4 .6 acres . Spearman Drive slopes southeast at 1.44%. The following tabulation shows the carrying capacity of this 39 ' wide street at 1.44%. Str eet Grade(%) ................................. . Manning's Roughness Coefficient (n-value) ........ . Street Width (feet) .............................. . Street Crown (in .) ............................... . Street Side Slope (horizontal/Vertical) .......... . Program Results : 1.44 0 .01~0 39 7 32 .6 Depth Flow Rate Velocity Velocity Energy Flow Area Top Width (ft .) (cfs) (fps) Head (ft) Head (ft) (sq ft) 0 .1 0 .3 1.58 0 .039 0.139 0 .2 0 .2 1.6 2 .51 0 .098 0 .298 0 .7 0 .3 4 .8 3 .29 0 .168 0.468 1.5 0.4 10.4 3 .98 0 .246 0 .646 2 .6 0 .5 18 .8 4 .62 0 .332 0 .832 4 .1 Drainage Area "Al" This sub-area is approx imately 3.0 acres and stormwater accumulates on the southwest side of Spearman Drive. The Q10 flow calculates to be 8.6 cfs and the Q100 flow is 11.7 cfs . We can see that this Q10 flow will have a spread of less than 13' on the southwest side of Spearman Drive at this point. 7 (ft) 3 .3 6 .5 9.8 13 .0 16 .3 J~ Drainage area "A2" contributes Q 10=4.6 cfs and Q 100=6.2 cfs at this point. We can see from the preceding street flow calculations that the gutter along the northeast side of Spearman Drive will carry the flow from this area of 1.6 acres with more than one lane clear. The combined Q 100=17.9 cfs will not overflow the curbs. / A curb inlet will be installed on the north side of Spearman Drive at this point to pick up the flow from Area A2 . The inlet will be on a slope greater than I%. A stan~ double inlet with a I 0' throat will be used. From the equation for an inlet on grade, we see that this opening will take 15.6 cfs which is more than the Q100 flow at this point. An 18" RCP will be installed to carry the stormwater under the street at this point and will discharge into a temporary drainage ditch. Using Manning's Equation an a roughness coefficient of 0 .014 for concrete pipe, we determine that, at a grade of 0 .5%, the 18" RCP will carry the Q10 flow of 4 .6 cfs at a ( depth of 0 .90 feet and a velocity of 4 .18 fps . This is 59 .7% full which is within the design tf; criteria for 18" culverts. Q 10o of 6 .2 cfs will flow at 4.42 fps and 1.11 feet deep . The 18" RCP will end at the south right-of-way line and a temporary drainage ditch will be installed south through the undeveloped area along the route of a future street. This will be a grass lined "V" ditch at a slope of approximately 0 .5%. Flow from Drainage j o.v Area Al will be allow to exit through a temporary curb break at this point and enter the / ditch . Manning's equation shows that this ditch will carry the combined Q 10 flow 1.09 feet deep at 2.76 fps and the combined Q100 flow 1.23 feet deep at 2 .97 fps . This should be satisfactory . Drainage area "Bl" is approximately 1.9 acres and drains onto Spearman Drive from the olJ...!k~ residential lots to the north. Q10 from this area is 5.5 cfs and Q 100 is 7.4 cfs . The Q 10 flow ~~\;'} A ,.o, in the north gutter on Spearman Drive will be approximately 4" deep with a spread of I 0 ~\cf "'.,, feet and the Q100 flow will be less than 5" deep with a spread of less than 13 feet. This is ~ro" \t, :1 ~ well within the design cri~ria and will be picked up in an inlet at the intersection of ~ Spearman and St. Andrews Drive . The existing storm sewer at this inlet has been P..'5-t'MP ... __.1 designed for this flow. ~ t'C.. ~ riqi>~ ~~~ Drainage area "B2" is approximately 1.3 acres draining onto Spearman Drive from the ~. ~ south . It is approximately 50% pavement and 50% grass . This yields a weighted "c" of 4lLJo " 0 .5. Q10 from this area is therefore 4 .7 cfs and Q1oois 6 .3 cfs . The QIOO flow in the south gutter of Spearman Drive would flow at a depth of about 4" with a spread of about IO'. ~ The combined Q100 flow from north and south along this portion of Spearman Drive ~ would leave a clear lane of approximately 18'. The inlet and storm sewer at the east end .-::::?" of this area has been designed for this flow . ~l0 -<(:;Z \l'\\e,\-VJO..S ().Q.~ _fl I ~ ~ Ch0 ~\0.\CJ\S 8 ~t)r:f \'>) .\9~ ·,\~ \,Ul>) ~~ "" • l\-.1 ~,s U< \o ~ Qloos<' l.9· ~~<:, I Project Description Project File Worksheet Flow Element Method Solve For Input Data Mannings Coefficient Channel Slope Diameter Dischar~e Results Depth Flow Area Wetted Perimeter Top Width Critical Depth Percent Full Critical Slope Velocity Velocity Head Specific Energy Froude Number Maximum Discharge Full Flow Capaci~ Full Flow Slope Flow is subcritical. Aug 1, 1995 11 :42:29 Spearman Drive Storm Sewer Worksheet for Circular Channel c:\fmw\pblcrk3c.fm2 Spearman Drive Storm Sewer Circular Channel Manning's Formula Channel De~th 0.014 0.005000 ft/ft I 1.50 ft ( 4.60 ffl/s 0.90 ft 1.10 ft2 2.65 ft 1.47 ft 0.82 ft 59.72 % 0.006518 ft/ft 4.18 ft/s 0.27 ft 1.17 ft 0.85 7.42 ffl/s 6.90 ffl/s 0.002224 ft/ft Joe Orr, Inc . Hae stad M ethods, Inc . 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 FlowMaster v4.1 c Page 1 of 1 Project Description Project File Worksheet Flow Element Method Solve For Input Data Mannings Coefficient Channel Slope Diameter Discharge Results Depth Flow Area Wetted Perimeter Top Width Critical Depth Percent Full Critical Slope Velocity Velocity Head Specific Energy Froude Number Maximum Discharge Full Flow Capacity Full Flow Slope Flow is subcritical. Aug 1 , 1995 11 :43:53 Spearman Drive Storm Sewer Q100 Worksheet for Circular Channel c :\fmw\pblcrk3c.fm2 Spearman Drive Storm Sewer Circular Channel Manning's Formula Channel Depth 0.014 0.005000 tuft ft ( 1.50 6.20 1.11 1.40 3.11 1.31 0.96 74.10 fflts I ft J ft2 ft ft ft % 0.007332 tuft 4.42 tus 0.30 ft 1.41 ft 0.75 7.42 ffl/s 6.90 ffl/s 0.004041 tuft Joe Orr. Inc. Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 FlowMaster v4.1 c Pa ge 1 of 1 I Project Description Project Fil e Worksheet Flow Element Method Solve For Input Data Mannings Coefficient Channel Slope Left Side Slope Right Side Slope Discharge Results Depth Flow Area Wetted Peri meter Top Width Critical Depth Critical Slope Velocity Velocity Head Specific Energy Froude Number Flow is subcritical. Aug 1 , 1995 11 :47:53 Spearman Drive Channel Q1 O Worksheet for Triangular Channel c :\fmw\pblcrk3c.fm2 Pebble Creek 3C Triangular Channel Manning's Formula Channel Depth 0.025 0.005000 tuft ( I 4.00 H :V I 4.00 H :V j 13 .20 ffl/s 1.09 ft J 4.79 ft2 9.02 ft 8.75 ft 0.92 ft 0.012263 tuft j 2.76 tus 0.12 1.21 0.66 ft ft Joe Orr, Inc. Haestad Methods; Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 FlowMaster v4.1 c Page 1 of 1 Project Description Project File Worksheet Flow Element Method Solve For Input Data Mannings Coefficient Channel Slope Left Side Slope Right Side Slope Dischar~e Results Depth Flow Area Wetted Perimeter Top Width Critical Depth Critical Slope Velocity Velocity Head Specific Energy Froude Number Flow is subcritical. Aug 1, 1995 11 :48:42 Spearman Drive Channel 0100 Worksheet for Triangular Channel c :\fmw\pblcrk3c .fm2 Pebble Creek 3C Triangular Channel Manning's Formula Channel De~th 0.025 I ; 0.005000 ft/ft 4.00 H:V ~ 4.00 H:V / 17 .90 ft3/s 1.23 ft J 6.02 ft2 10.12 ft 9.81 ft 1.04 ft 0.011775 ft/ft I 2.97 ftls 0.14 ft 1.36 ft 0.67 Joe Orr, Inc. Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 FlowMaster v4.1 c Page 1 of 1 I Conclusions The design of these drainage facilities is in compliance with the City of College Station Drainage Policy and Design Standards . The design provides for adequate control of the stormwater flow through this project from both the 10 year design storm and the 100 year flood . The design is for ultimate development. Offsite routing is through existing drainageways to Lick Creek. If no future downstream development is in the floodplain , there should be no stormwater problems . I hereby certify that this report for the drainag e design of Pebble Creek phase 3C was prepared by me in accordance with the provisions of the City of College Station Drainage Policy and p e · tandards for the owners thereof. ,;/ ~~ rr-:_,·..,,·~ ""1 •11v j~··,-~" ; ... lj-G 9 ~ ' • +• fl''t:v.~w 13 August28, 1995 Mr. David Mayo Joe Orr, Inc. Route 3, Box 413 CITY OF COLLEGE STATION Post Office Box 9 960 1 101 Texas Avenue C ollege S tation, Texas 7784 2-99 6 0 ( 4 0 9) 764-3500 College Station, TX 77845 RE : Approval of Spearman Drive Extension Dear Mr. Mayo, Ale The attached plans for the Spearman Drive extension associated w ith Pebble Creek 3C are approved for construction with the following understandings. If by next summer (May of 1996) the future phase of Pebble Creek south of Spearman is not built or does not have approved construction plans , then Pebble Creek Development Corporation must begin constructing the sidewalk along the south side of Spearman Drive . It is agreed that since the temporary channel is temporary in nature , its construction documents were not required to meet the City's drainage ordinance standards . The City, however, will not accept the responsibility for maintain ing it. We understand that Pebble Creek Development Corporation will maintain silt control, vegetation, and erosion control for the channel. Veronica spoke with Brett concerning the earth channel in the College Station Business Center. According to Brett, the City placed Curlex blankets in the bottom and on the sides of that channel for erosion protection and stabilization. You may wish to consider that technique as an option if you find that you are having difficulty with stabilizat ion . Sincerely, Samantha Smith Engineering Assistant cc: Kathryn Anthony Kent Laza Shirley Volk Home of Texas A&M University Development Permit City of College Station, Texas Site Description : Spearman Drive adjoining south line of Lots 1-11Block10 Pebble Creek Phase 3 . Site Owner: Pebble Creek Development Company Address : 4500 Pebble Creek Parkway Telephone: 690-0990 Engineer: Joe Orr, Inc . Contractor: Young Contractors, Inc. Address: 2167 Post Oak Circle, C.S . Telephone: 690-3378 Address: W . Hwy 21, Bryan, TX Telephone : 779-1112 Date Application Filed __________ Approved: _________ _ Application is hereby made for the following development specific waterway alterations : None 7 Application Fee __ Drainage Plan with supporting documentation : Other: ----------------- ACKNOWLEDGMENTS: We, Pebble Creek Development Company and Young Contractors, Inc., developer and contractor, agree as a condition of approval of this permit application, to construct the improvements proposed in this application according to these documents and the requirements of Chapter 13 of the College Station City Code. pf!!:o iff7h ACCOUNT NO . _________________ _ 377630 CITY OF COLLEGE STATION '19ct) ~-+--I--\-~~~~~==---~ ACCOUNT NO . _________________ _