The URL can be used to link to this page

Home My WebLink About22 Development Permit 588 The Heritage at DartmouthSupplelllent DRAINAGE COMPUTATIONS for Heritage At Dartmouth Apartment Complex Lot 2, Block 1, Dartmouth Addition College Station, Brazos County, Texas Prevared for.· Mr. Emmanuel Glockzin Telephone: ( 409) 846-8878 Bryan, Texas 77802 Prenared bv: * August, 1998* REV\EWED FOR coMPL\ANCE . SEP O 3 1998 COLLcGt: ~ l A 110N ENG\NEER\NG CONSUL TING ENGINEERING & LAND SURVEYING 4444 CARTER CREEK PKWY, SUITE 108 BRYAN, TEXAS 77802 C409J 846-2688 C409J 846-3094 August 31, 1998 Ms. Shirley Volk Department Of Development Services P .O . Box 9960 College Station, Texas RE: Alternate Detention Pond Improvements, The Heritage At Dartmouth, Lot 2, Block 1, Dartmouth Addition, College Station, Texas. Dear Shirley, As per the telephone conversation between yourself and Earl Havel this P.M. regarding the above referenced we offer the following: Detention of the run-off generated by the anticipated ultimate 100-year storm event can be achieved on- site without encroaching into the drainage improvements as proposed by Kling Engineering. The ultimate condition assumes developed conditions on Lots 1-3, Block 1, Dartmouth Addition as well as Lot 1, Block One, Dartmouth Crossing. Detention could occur in two (2) locations (See Attached Grading Plan) within the bounds of Lot 2, Block 1, Dartmouth Addition. The major pond (Designated Pond" A") would be constructed with 3:1 sideslopes with the sideslopes being seeded. The depth of Detention Pond "A" would be eight feet (8') at the deepest location and same pond would supply approximately 30,000 cubic feet of storage. The second detention pond designated as Detention Pond "B" would be from three to four feet (3'-4') deep and would supply approximately 7000 cubic feet of storage capacity. The combined capacities of these to detention ponds would supply more than the estimated required detention volume as determined on page 2 (highlighted in yellow). Outlet control structures for U1e two (2) ponds would consist of circular pipe sized to meet the desired metering capacity. A plus to tJ1e design as propo sed is that U1e two (2) proposed ponds could stay in place after the improvments as proposed by Kling Engineering are completed to allow for added detention capacity or the two (2) ponds could be covered-over and U1e land reclaimed for better usage. In summary detention for Dartmouth Addition can be achieved on-site if the need should arise. Determine Post-development Peak Storm Water Discharge (No Detention) Tributary Area ("A"): 7.89 Acres Run-Off Coefficient ("Cwt"): 0.75 Time Of Concentration ("T/c"): 1 O Minutes (Min) Hourly Intensity Rates ("I"): 2-Year: 6.33 5-Year: 7.69 10-Year: 8.63 25-Year: 9.86 50-Year : 11 .15 100-Year: 11 .64 Peak Discharge Rate ("Q"): 2-Year: 37.44 5-Year: 45.52 10-Year: 51.09 25-Year: 58.36 50-Year: 65 .97 100-Year: 68.87 Comparison Of Predevelopment And Post-develo ment Peak Dischar e Rates Inches I Hour Inches I Hour Inches I Hour Inches I Hour Inches I Hour Inches I Hour Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second Predevelopment Post-Development Increase 2-Year: 14.97 Ft3/sec 37.44 Ft3/sec 22.46 Ft3/sec 5-Year: 18.21 Ft3/sec 45.52 Ft3/sec 27 .31 Ft3/sec 10-Year: 20.44 Ft3/sec 51 .09 Ft3/sec 30.66 Ft3/sec 25-Year: 23 .34 Ft3/sec 58.36 Ft3/sec 35 .01 Ft3/sec 50-Year: 26 .39 Ft3/sec 65.97 Ft3/sec 39 .58 Ft3/sec 100-Year: 27 .55 Ft3/sec 68.87 Ft3/sec 41 .32 Ft3/sec Preliminary Determination Of Detention Pond Volume 2-Year: 22.46 Ft3/sec x (26 .7 Min . x 60 Sec . I 2 ) = 17,992 Cubic 5-Year: 27 .31 Ft3/sec x (26 .7 Min. x 60 Sec . I 2 ) = 21,878 Cubic 10-Year: 30.66 Ft3/sec x (26 .7 Min . x 60 Sec. I 2 ) = 24 ,556 Cubic 25-Year: 35.01 Ft3/sec x (26 .7 Min . x 60 Sec . I 2 ) = 28 ,046 Cubic 50-Year: 39.58 Ft3/sec x (26 .7 Min. x 60 Sec. I 2 ) = 31 ,703 Cubic 100-Year: 41 .32 Ft3/sec x (26.7 Min . x 60 Sec. I 2 ) = 33, 101 Cubic 2 Feet Feet Feet Feet Feet Feet Determine Total Pre-Development Peak Storm Water Discharge Rates Tributary Area ("A"): 7 .89 Acres Pervious Area: 7 .89 Acres Impervious Area : 0.00 Acres Run-Off Coefficient ("Cwt"): 0 .30 Time Of Concentration ("T/c"): Woodlands: Low Elevation: High Elevation : Distance (Feet): Slope (% Grade): Velocity ("Vw"): Time: Pastures: Low Elevation : High Elevation : Distance (Feet): Slope (%Grade): Velocity ("Vp"): Time : Pavements: Low Elevation : High Elevation : Distance (Feet): Slope(% Grade): Velocity ("Vpave "): Time: Total Travel Time : Hourly Intensity Rates ("I "): 2-Year: 6.33 5-Year: 7 .69 10-Year: 8.63 25-Year: 9 .86 50-Year: 11.15 100-Year: 11 .64 Peak Discharge Rate ("Q"): 2-Year: 14.97 5-Year: 18.21 10-Year: 20.44 25-Year: 23.34 50-Year: 26.39 100-Year: 27.55 C= 0.30 C= 0.90 0.00 0.00 0 .00 0 .00 0 .00 Feet I Second 0.00 Minutes 0 .00 0 .00 0.00 0 .00 0 .00 Feet I Second 0 .00 Minutes 0 .00 0.00 0.00 0 .00 0.00 Feet I Second 0.00 Minutes 10.00 Minutes Inches I Hour Inches I Hour Inches I Hour Inches I Hour Inches I Hour Inches I Hour Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second Cubic Feet I Second I SUPPLIMENTARY ' DRAINAGE COMPUTATIONS for Heritage At Dartmouth Apartment Complex Lot 2, Block 1, Dartmouth Addition Coll ege Station , Brazos County, Texas Prepa r ed for.· Mr. Emmanuel Glockzin 4500 Carter Creek Parkway Bryan , Texas 77802 ~ "¥'~~ Preparedb y; ~ 0'\j Garrett Engineering 4444 Carter Creek Parkway -Suite 108 Bryan , Texas 77802 Telephone : (409) 846-2688 REVIEWED FOR COMPLIANCE SEP 0 3 1998 COLLl::lji::. t> I A I IO N ENGINEERING / Supplementary Drainage Computations For Heritage At Dartmouth Apartments Complex Lot 2, Block 1, Dartmouth Addition College Station, Brazos County, Texas The following drainage computations attached herewith determine first the full flow capacity of a four foot (4') wide triangular concrete flume depressed six inches (6") at the center line of the flume , n = 0 .013 and slope 3 :1or33 .33% grade . Subsequent flumes numbered 1, 2, 3, and 4 (see attached grading plan) are presented assuming supplied design flow volumes as follows : Flume No. 1 2 3 4 Supplied 25-Year Run-Off 7.93 c .f.s . 13 .08 c.f.s 5.74 c .f.s . 11.19 c .f.s. Velocity Based On Supplied Run-Off 19 .13 feet per second 21 . 69 feet per second 17 .65 feet per second 20 .86 feet per second As can be seen from the tabulation above , the projected velocities are rather high at the foot of each flume. A concrete apron has be placed at the bottom or foot of each flume five (5') in length and four feet (4') wide . A one foot (l ')tall splash wall and toewall are located at the end of said apron to dissipate the energy possessed by the run-off exiting the flumes and keep the apron from being under-cut by the discharge . Rock rubble rip-rap is also placed upstream and downstream from the aforesaid apron (See details on attached grading plan). We feel that the aprons in their designed configuration will adequately dissipate the energy created at the bottom of each flume and minimize the effects of erosion . Triangular Channel Analysis & Design Open Channel -Uniform flow Worksheet Name: Heritage @ Dartmouth Cormnent: Determine Full Flow Capacity Of Flume Solve For Discharge Given Input Data: Left Side Slope .. Right Side Slope. Manning's n ..... . Channel Slope ... . Depth ........... . Computed Results: Discharge ....... . Velocity ........ . Flow Area ....... . Flow Top Width .. . Wetted Perimeter. Critical Depth .. . Critical Slope .. . Froude Number ... . 4.00:1 (H:V) 4.00:1 (H:V) 0.013 0.3333 ft/ft 0.50 ft 25.67 cfs 25.67 fps 1 .00 sf 4.00 ft 4.12 ft 1.21 ft 0.0030 ft/ft 9.05 (flow is Supercritical) Open Channel Flow Module, Version 3.12 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708 Triangular Channel Analysis & Design Open Channel -Uniform flow Worksheet Name: Heritage ®Dartmouth Comment: Determine Actual Depth Given Design Flow Solve For Depth Given Input Data: 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 ... . 4.00:1 (H:V) 4.00:1 (H:V) 0.013 0.3333 ft/ft 7.93 cfs 0.32 ft 19.13 fps 0.41 sf 2.58 ft 2.65 ft 0.75 ft 0.0036 ft/ft 8.41 (flow is Supercritical) Open Channel Flow Module, Version 3.12 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708 Triangular Channel Analysis & Design Open Channel -Uniform flow Worksheet Name: Heritage @Dartmouth Comment: Determine Actual Depth Given Design Flow Solve For Depth Given Input Data: 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 ... . 4.00:1 (H:V) 4.00:1 {H:V) 0.013 0.3333 ft/ft 13.08 cfs 0.39 ft 21. 69 fps 0.60 sf 3.11 ft 3.20 ft 0.92 ft 0.0033 ft/ft 8.67 (flow is Supercritical) Open Channel Flow Module, Version 3.12 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708 Triangular Channel Analysis & Design Open Channel -Uniform flow Worksheet Name: Heritage @Dartmouth Comment: Determine Actual Depth Given Design Flow Solve For Depth Given Input Data: Left Side Slope .. Right Side Slope. Manning's n ..... . Channel Slope ... . Discharge ....... ~~1 Computed Results: Depth ...... ":'-.... . Velocity ........ . Flow Area ....... . Flow Top Width .. . Wetted Perimeter. Critical Depth .. . Critical Slope .. . Froude Number ... . 4.00:1 (H:V) 4.00:1 (H :V) 0.013 0.3333 ft/ft 5.74 cfs 0.29 ft 17.65 fps 0.33 sf 2.28 ft 2.35 ft 0.66 ft 0 .0037 ft/ft 8.24 (flow is supercritical) Open Channel Flow Module, Version 3.12 (c) 1990 Haestad Methods, Inc . * 37 Brookside Rd * Waterbury , Ct 06708 Triangular Channel Analysis & Design Open Channel -Uniform flow Worksheet Name: Heritage @ Dartmouth Comment: Determine Actual Depth Given Design Flow Solve For Depth Given Input Data: 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 ... . 4.00:1 (H:V) 4.00:1 (H:V) 0.013 0.3333 ft /ft 11.19 cfs 0.37 ft 20.86 fps 0.54 sf 2.93 ft 3.02 ft 0.87 ft 0.0034 ft/ft 8.59 (flow is Supercritical) Open Channel Flow Module, Version 3.12 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury , Ct 06708