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Home My WebLink AboutCT 13-03; ROBERTSON RANCH-RANCHO COSTERA; DRAINAGE REPORT - ROBERTSON RANCH RECREATION CENTER; 2015-07-23Table of Contents 1 Introduction and Purpose . 1 1.1 Background and Project Description ...............................................................1 1.2 Pre-Development Drainage Patterns ..............................................................I 1.3 Post Development Drainage Patterns ............................................................. I 2 Rational Hydrology.................................................................................................2 3 Pipe Hydraulics ......................................................................................................3 4 Conclusions............................................................................................................4 Technical Appendices Appendix A: Rational Method Calculations Appendix B: Proposed Drainage Map Appendix C: Hydraflow Calculations Robertson Ranch Rec Center Drainage Report INTERNATIOL I Introduction and Purpose 1.1 Background and Project Description The existing condition is a rough graded pad, sloping southeast at 1%, per Drawing No. 480-3A. In the proposed condition, the site will be graded to slope toward the proposed Robertson Road. A pool recreation area with three buildings will occupy the eastern half of the site. A 16-stall parking lot with a turnaround will occupy the western half of the site. The parking lot will be constructed with un-grouted, permeable concrete unit payers. 1.2 Pre-Development Drainage Patterns The existing condition is a rough graded pad sloped at 1% to the southwest. 1.3 Post-Development Drainage Patterns On the western half of the site, the main building for the recreation center will be constructed adjacent to the parking lot. Runoff from the roof will drain to the parking lot. The parking lot will be comprised of permeable payers with underdrain piping. The underdrain will pipe runoff to bioretention areas south of the recreation building. Runoff that does not drain through the payers will be collected by a ribbon gutter and conveyed to the same bioretention areas. The runoff from the pool hardscape will be collected in slot drains connected to a network of 6" storm drain pipe. The flow will be piped to adjacent bioretention areas. Inlets and underdrain piping contained in the bioretention areas will convey storm water to the existing 36" storm drain on Robertson Road. Refer to the Proposed Drainage Map in Appendix B. 2 Rational Hydrology The Rational Method hydrology study was completed using methodology described in the San Diego County Hydrology Manual. The design storm for this study is the 100-year events. Using the San Diego County Hydrology Manual Isopluvial Map, the 100-year P6 was found to be 2.8 inches. The soil type was assumed to be type 'D'. A runoff coefficient ("C") value of 0.35 was used for pervious area and 0.90 for impervious areas. The time of concentration (Ta) to each node was found using the procedure described in the San Diego County Hydrology Manual: . Initial time of concentration (Ti) was assumed to be 5 minutes. Robertson Ranch Rec Center Drainage Report INTERNATIONAL Travel time (Tt) was found for concentrated flows traveling in a concrete ribbon gutter or in 6" PVC underdrain pipe. See calculations in Appendix A. The overall time of concentration (Ta) was found by adding together T1 and Tt. The intensity was found using Figure 3-2 (San Diego County Hydrology Manual). The drainage areas and node designations used can be seen in Appendix B. The Flow (Q) at each node was calculated using the Rational Equation Q=CIA, where: Q = Flow (cubic feet per second) C = runoff coefficient I = Intensity (inches per hour) A = Drainage Area (acres) The Rational Method calculations performed to find the runoff Q for each node can be found in Appendix A. 3 Pipe Hydraulics "Hydraflow" software was used to verify the adequacy of the proposed pipe systems. The design software uses flows generated from the post—development site hydrology to calculate hydraulic grade line and flow velocity. The software computes pipe hydraulics using the widely accepted "Standard Step" Method, in which iterative calculations are performed to achieve on overall system energy balance, as described in Bernoulli's Principal. The software makes an assumption at the upstream end about hydraulic grade elevation (HGL), and then checks for an energy balance between the two points after considering head loss due to pipe friction and junctions. The assumption process is repeated until the assumed upstream HGL achieves an energy balance, at which time a calculation is done to determine HGL based upon inlet control and is compared to the previous results from energy balance. The more conservative (higher) of the two elevations is added to a computed junction loss. The sum elevation becomes the control for the next upstream segment and the process is repeated. If an energy balance cannot be achieved the software sets the hydraulic grade line at critical depth, and proceeds to the next line. The proposed pipes are sized to accommodate the 100-year storm event. For this improvement project, the proposed storm drain system connects each of the bioretention discharge points for collection and discharge to the proposed storm drain along Robertson Road. Detailed hydraulic calculations for each proposed pipe segment connecting the bioretention areas during the 100-year event are included in Appendix C. 4 Conclusions Onsite storm drain piping has been sized for the 100-year event. Refer to the attached Appendices for Drainage Map and calculations. Robertson Ranch Rec Center 2 Drainage Report INTERNATIONAL Area= 29,092 sqft= 0.67 ac Impervious area= 5,024 sqft= 0.12 ac C= 0.9 x %Imp + C, (1 - %Imp) C= 0.35 (From Table 3-1, Type 0 Soil, Undisturbed Natural Terrain) C= 0.9 x 17% + 0.35 (1 - 17%) C=0.44 T=T1 + Tt T= 5 mm (Assumed) T= Distance/Velocity Distance= 146' Velocity= 1.7 ft/s (Hydraflow Express) T= 146'/1.7 ft/s T= 1.4 mm T= 5+1.4= 6.4 mm 1= 7.44 x P6 x D 05 100-Year P6= 2.8 in/hr 1= 7.44 x 2.8 x 6•4645 1= 6.3 in/hr Qioo= CIA = 0.44 x 6.3 x 0.67 = 1.87 cfs Area B Area= 4,928 sqft= 0.11 ac lmervious area= 3,800 sqft= 0.09 ac C= 0.77 I= 5 mm (Assumed) T= Distance/Velocity Distance= 123' Velocity= 2.8 ft/s (Hydraflow Express) T=0.7min T=5.7min 1= 7.44 x 2.8 x 57.0.645 1= 6.8 in/hr Qioo= CIA = 0.77 x 6.8 x 0.11= 0.59 cfs Area C Area= 5,980 sqft= 0.14 ac Impervious area= 3,716 sqft= 0.09 ac C=0.69 I= 5 mm (Assumed) 1= Distance/Velocity Distance= 96' Velocity= 2.9 ft/s (Hydraflow Express) It= 0.6 mm Tc= 5.6 mm 1= 7.44 x 2.8 x 56-0645 1= 6.9 in/hr Q.ioo= CIA = 0.69 x 6.9 x 0.14= 0.65 cfs Area D Area= 5,029 sqft= 0.12 ac Impervious area= 3,765 sqft= 0.09 ac C=0.76 Tj= 5 mm (Assumed) I= Distance/Velocity Distance= 82' Velocity= 2.8 ft/s (Hydraflow Express) I= 0.5 mm T=5.5min 1= 7.44 x 2.8 x 5•50.645 1= 6.9 in/hr Qioo= CIA = 0.76 x 6.9 x 0.12= 0.61 cfs Storm Sewer Summary Report Page 1 Line Line ID Flow Line Line Line Invert Invert Line HGL HGL Minor HGL Dns Junction No. rate size shape length EL Dn EL Up slope down up loss Junct line Type (cfs) (in) (ft) (ft) (ft) (%) (ft) (ft) (ft) (ft) No. 1 7 3.76 18 Cir 31.300 115.43 123.79 26.709 116.93 124.53 n/a 124.53j End Grate 2 6 1.85 12 Cit 94.060 123.85 124.82 1.031 124.53 125.40 n/a 125.40j 1 Grate 3 5 1.26 12 Cit 50.730 124.76 125.30 1.064 125.40 125.83 n/a 125.83 2 Grate Project File: SD Network.stm Number of lines: 3 Run Date: 06-19-2015 NOTES: Return period = 100 Yrs. j - Line contains hyd. jump. Hydraflow Storm Sewers Extension v6.068 Storm Sewer Inventory Report Page Line Alignment Flow Data Physical Data Line ID No. Dnstr Line Defi June Known Drng Runoff Inlet Invert Line Invert Line Line N J-Ioss Inlet/ line length angle type Q area coeff time El Dn slope El Up size shape value coeff Rim El No. (ft) (deg) (cfs) (ac) (C) (mm) (ft) (%) (if) (In) (n) (K) (if) End 31.300 -75.572 Grate 1.91 0.00 0.00 0.0 115.43 26.71 123.79 18 Cir 0.010 1.45 127.97 7 2 1 94.060 73.000 Grate 0.59 0.00 0.00 0.0 123.85 1.03 124.82 12 Cir 0.010 0.50 129.33 6 3 2 50.730 0.330 Grate 1.26 0.00 0.00 0.0 124.76 1.06 125.30 12 Cir 0.010 1.00 128.83 5 Project File: SD Network.stm Number of lines: 3 Date: 06-19-2015 Hydraflow Storm Sewers Extension v6.OE