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Home My WebLink AboutHYDROLOGY ANALYSIS - TR 25478_25479 RAMSGATE AREA _B_ HYDROLOGY ANALYSIS For RL MSGATE AREA 66B" VOLUME 2 OF 2 TRACT No. 25478 & 25479 COUNTY OF RIVERSIDE Prepared for. CENTEX HOMES 2280 Wardlow Circle,Suite 150 Corona,CA 91720 Prepared by: M HUNSAKER& ASSOCIATES IRVINE, INC. INLAND EMPIRE REGION 2900 Adams Street,Suite A4 5 Riverside,CA 92504 (909)352-7200 PREPARED UNDER THE SUPERVISION OF: Paul Huddleston JR. R.C.E. 58020 Exp. 6/30/06 W.Q.#0919-25478&0919-25479 HYDROLOGY ANALYSIS - FOR TRACT N®a 25478 & 25479 CITY OF LAKE ELSINORE AREA "B99 PREPARED UNDER THE SUPERVISION OF; Paul Huddleston JR. R.C.E.58020 Exp. 6/30/06 W.O.#0919-25479&0919-25419 TABLE OF CONTENTS SECTION TITLE NUMBER I. INTRODUCTION A., PROJECT LOCATION B. STUDY PURPOSE C. PROJECT STAFF D. VICINITY MAP E, DISCUSSION F. HYDROGRAPH SUIVIIViAI2IES & SUPPORTING CALCULATIONS G,HYDROGRAPH DATA H. INTERIM CRITERIA FOR SIZING BASINS I. RUNOFF INDEX NUMBERS J. IMPERVIOUS COVER FOR DEVELOPED AREAS K.RAINFALL/DURATION FOR 2 & 100 YEAS STORMS L., HYDROLOGIC SOILS GROUP MAP M: SLOPE-INTENSITY DURATION CURVE N. PRECIPITATION FOR 2 & 100 YEAR, 1, 3, 6 & 24 HOUR STORM EVENTS II. OVERALL AREA "B" HYDROGRAPHS --EXISTING, PROPOSED (B1+B2+B3) &ROUTED (BI+B2+B3) 2, 5, 10 & 100 YEAR 1, 3, 6 & 24 HOUR STORM EVENTS III. AREA "B1" HYDROGRAPHS -PROPOSED & ROUTED 2, 5, 10 & 100 YEAR 1, 3, 6 & 24 HOUR STORM EVENTS IV. AREA"B2" HYDROGRAPHS -PROPOSED & ROUTED 2, 5, 10 & 100 YEAR 1, 3, 6 & 24 HOUR STORM EVENTS V. AREA "BY' HYDROGRAPHS --PROPOSED A. 2,5, 10& 100 YEAR,1,3,6 & 24 HOUR STORM EVENTS B. HYDROGRAPH MAPS I. INTRODUCTION - A. PROJECT LOCATION Tract No. 25478 and 25479(subject site)are located within the Riverside County Limits. The subject site is generally bounded by Route 74 on the west,Wasson Creek on the south,undeveloped land on the north and easterly; (See Vicinity Map included) B. STUDY PURPOSE The purpose of this study is to analyze the generated run-off for the existing and proposed conditions of the-subject site. C. PROJECT STAFF Hunsaker&Associates, Inc. engineering staff involved in this study include: Paul R.I3uddleston,,Jr;,R:C.E. Matthew Busch,Project Manager,P.L.S. Don Cambell, Project Manager,P.L.S. E. DISCUSSION The subject site is divided into onsite drainage areas "A", "B", "C", "D", and "E". This volume of the report deals with the runoff for Area "B"., consisting of sub-areas "Bl", "B2,9 &"B397 Area "B" is tributary to the Lake Elsinore Overflow Channel; which eventually drains to the Santa Ana River. Existing Area "B" consists of 341.4 acres and produces a runoff of 661.7 cfs in a 100-year storm. Proposed Area`B" consists of 345.22 acres and produces a runoff of 690.6 cfs in a 1007year storm. The proposed area is slightly larger than the existing area due to a temporary diversion of 5.6 acres from Area "D"; that will be re- directed back to Area "D" upon completion of Tract 31792; by others, to the south. A combination water quality/natural detention basin is proposed for Sub-area "B 1" under Ramsgate Drive, and a combination water quality/detention basin is proposed for the Park-site and Multi-Family development in Sub-Area "132"; both to mitigate onsite flow and water quality for in tract flows. Sub-area "BY mostly contains runoff from natural and landscaped slopes, so no mitigation is to be done for this area. The proposed basins for Area "B" successfully mitigated the flow for all storms, except the 2 and 5 year, 24 hour storm events. There was an increase in flow of 12.4 cfs and 9.0 cfs; respectively, for these two storms. A summary of the rational method hydrology results and areas follows this discussion. The basins were sized to detain a 2 year storm event and completely drain within 40 hours per the Conditions of Approval using the "Urban Runoff Quality Management" handbook. The sizing analysis follows: Basin B1 Area Draining to Basin("B I") =299.4 acres Percent Impervious(i) =21.0% Storage Time =40 hours Mean Storm Precipitation(P6) =0.57 inches (froni FIG. 5.3) 40 Hour Drain Time of Capture Volume(a4o)= 1.463 (by interpolation of Table 5.4) Calculate Watershed Runoff Coefficient "C" using Equation 5.1 of "Urban Runoff Quality Management"handbook: C=0.858(i)3—0.78(i)2+0.774(i)+0.04 C=0.858(0.21)3—0.78(0.21)Z+ 0.774(0.21) + 0.04 C=0.1760 Calculate Maximized Detention Volume "Po" using equation 5.2 of "Urban Runoff Quality Management"handbook: Po=1140 X C X P6= 1.463 X 0.1760 x 0.57=0.147 inches Basin 11B1"Water Quality Capture Volume=(MA acres)(0.147 inches)(1112) 3.668 acre-feet x 1.20(20% for sedimentation)=4.401 Acre-Feet Basin 11B1"total volume including detention=9.057>4.401 Acre-Feet required Basin B2 Area Draining to Basin("B2") =29.8 acres Percent Impervious(i) = 16.0% Storage Time =40 hours Mean Storm Precipitation(P6) =0.57 inches(from FIG. 5.3) 40 Hour Drain Time of Capture Volume(a40)=1.463 (by interpolation of Table 5.4) Calculate Watershed Runoff Coefficient "C" using Equation 5.1 of "Urban Runoff Quality Management"handbook: C=0.858(i)3—0.78(i)z+0.774(i)+0.04 C=0.858(0.16)'--0.78(0.16)2+0.774(0.16)+0.04 C=0.1473 Calculate Maximized Detention Volume "Po" using equation 5.2 of "Urban Runoff Quality Management"handbook: Po=a40 X C X P6= 1.463 X 0.1473 x 0.57=0.123 inches Basin 11B2"Water Quality Capture Volume=(29.8 acres)(0.123 inches)(1112) =0.306 acre-feet x 1.20(200/o for sedimentation)=0.367 Acre-Feet Basin 11B2"total volume including detention=1.666>0.367 Acre-Feet required UNIT AREA HYDROGRAPH SUMMARY - MITIGATION OF PROPOSED STORM FLOW- AREA "131"" AREA 81 PROPOSED STORAGE ROUTED "Q" STORM EVENT CONDITION*(CFS) VOLUME(AC.FT) (CFS) 2 YEAR -1 HOUR 176.5 1.563 145.9 2 YEAR-3 HOUR 119.5 1.252 104.6 2 YEAR-6 HOUR 102.6 1.124 89.7 2 YEAR-24 HOUR 22,7 0.438 22.2 5 YEAR-1 HOUR 269.2 2.221 221.1 5 YEAR-3 HOUR 196.1 1.773 178.6 5 YEAR-6 HOUR 170.9 1.616 156.5 5 YEAR-24 HOUR 35.2 0.585 33.2 10 YEAR-I HOUR 386.6 3.460 298.2 10 YEAR-3 HOUR 302.0 2.819 259.3 10 YEAR-6 HOUR 271.1 2.520 241:2 10 YEAR-24 HOUR 99.4 1.178 97.5 100 YEAR- 1 HOUR 624.4 6.259 472.7 100 YEAR-3 HOUR 502.9 5.438 421.8 100 YEAR-6 HOUR 455.2 5.063 399.2 100 YEAR-24 HOUR 181.4 1.765 179.2 "PROPOSED CONDITION FOR 2, 5,'10 & 100 YEAR STORMS BASED ON ULTIMATE DEVELOPMENT MSHCP MITIGATION AREA ENCOMPASSES ENTIRETY OF OFFSITE TRIBUTARY AREA WHERE TENTATIVE TRACTS ARE NOT SHOWN HydrographSummaryB1.xls - H •� --�i l.�Y i14y1� � g U...� c tY� aal"d• hr'" .yy�'.h�y �a'. � 11j y ,y, � �\y ', c� 1'Y �, �.. + � "?t�.�' .0 ,y�,��. it + .� �� :�k�' _•- ` �,`'�.- , r _ o ,r j �10 s "r =1 O (5 G16, 14g Lmj ' . ��' a15 xZ 4 cn �o� to