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Home My WebLink AboutCUP 01-19; ARCO AM/PM AT TAMARACK; CONCEPTUAL HYDROLOGY REPORT; 2002-04-08CONCEPTUAL HYDROLOGY REPORT ARCO PRODUCTS Co. 810 Tamarack Avenue Carlsbad, CA Date: 4/08/02 CUP # 01-19 Tait Job # AR1219-D Prepared By: Tail & Associates, Inc. 701 North Parkcenter Drive Santa Ana, CA 92705 (714)-560-8200 CHRISTOPHER HAHN RCE 58971 Date TABLE OF CONTENTS DISCUSSION VICINITY MAP HYDROLOGY MAPS HYDROLOGY CALCULATIONS PRECIPITATION MAPS SUSMP CALCULATIONS Page 1 I I DISCUSSION PURPOSE: The purpose of the following conceptual hydrology report is to comply with the requirements of the City of Carlsbad Planning Department, CUP 01-19, to determine the 10-year storm event runoff at the proposed gasoline station and compare it with the existing runoff generated. DESCRIPTION: The existing site consists of a gas station with a 1,750 sf building surrounded by hardscape and landscaping. The existing site drains via sheet flow across the sidewalks and driveways to two separate locations. One area drains northwesterly to the cross- gutter at the intersection of the Jefferson Street and Carol Place. The other area drains southwesterly toward the intersection of Tamarack Avenue and Jefferson Street. All drainage in the surrounding public streets is conveyed via surface flow. The proposed site consists of a 2,900 sf convenience store with a car wash, fueling area and parking. Based on the Conceptual Grading plan prepared, the proposed site will eliminate drainage across the sidewalk and out the driveways. Onsite drainage is collected in a series of gutters which drain into a three separate catch basins. One catch I basin will be discharge to Jefferson Street, another will discharge to Carol Place, and the other will drain to Tamarack via a parkway culverts. I METHODOLOGY: The Rational Method was used to determine runoff produced by a 10-year storm event as I described in the County of San Diego Hydrology Manual (1985 with 1993 update). Maps, tables and standards pertinent to the project site as provided in the Appendix of this report for reference. The following formula was used in calculating the total I generated flow: Q=C*I*A I Q = flow (cfs) C = runoff coefficient I I = precipitation intensity (in of rain/hr) A = area (acres) Nodal analysis was used in determining peak flows in both developed and pre-developed conditions. Advanced Engineering Software (AES) Rational Method Hydrology Program, Version 1.5A, was used in this study. The project site is located within soil area "D". For the existing sub-areas, the study utilized runoff coefficients of C=0.95 on the south half and C=0.70 on the north half to I I I I I I I I allow for the differing hardscape areas. The proposed site used "C" values of 0.95 for Al I and A3 and value of 0.85 for A2 because there was a portion of landscaping found. Using the ABS Rational Method Hydrology Program, a nodal analysis was performed on the existing and proposed systems. The ABS Rational Method Hydrology Program was I used to determine the time of concentration (Tc) and associated rainfall intensities (I), see appendix. I As shown in the accompanying existing and proposed hydrology maps, two common nodes were analyzed to compare the total site post- and pre-construction runoff. The * existing site drains via sheet flow in two sub areas. The north half flows to the right-of- way of Jefferson Street and Carol Place where it is collected by curb and gutter. These join at a common node at the intersection cross gutter specified as node 300. The southern half similarly sheet flows to the right of way of Tamarack Avenue and Jefferson I Street, joining at the common node 103 at the intersection cross gutter. The proposed hydrology map alters the contributory areas to each node slightly. The north sub-area, A3, flows to an on-site catch basin and discharges via an underdrain pipe to the public I right-of-way and node 400. An additional sub-area, Al, collects drainage near the storefront area. This runoff discharges via a catch basin and underdrain pipe to the public right-of-way. Sub-area A2 is south of Al. Runoff drains southwesterly to a catch basin I and transferred out to the public right-of-way through an underdrain pipe. Areas A2 and A3 were analyzed at the same node 102 to accurately compare the total site existing versus proposed runoff at the same point. SUMMARY: I In summary, the pre-developed runoff is 2.81 cfs and the post-developed runoff is 2.96 cfs. The sub-areas' associated piping and catch basins will need to be sized to their respective runoff totals in the final Hydrology Report. Included in the Appendix are I preliminary calculations for flow based sizing of post construction BMP's based on San Diego County's SUSMP requirements (excerpt included in appendix.) "Fossil Filter" catch basins are proposed for areas Al, A2, and A3. These will need to treat a maximum I flow rate of 35 gpm based on a 0.2 in/hr intensity. Per "Fossil Filter's" Hydraulic Capacity Chart, one linear foot will treat 12 gpm; therefore, 3.91 linear feet of filter will be necessary. A 24"x24" catch basin will treat 96 gpm. L I I I I I I I I I I SECTION II: VICINITY MAP I I I I Li I I Li I I I I I I H H I H I H I H I H H I I I I I I I I NO SCALE VICINITY MAP I SECTION III: HYDROLOGY MAPS I LEGEND . - PROPOSED ON—SITE CATCH BASIN W/ FOSSIL FILTER C A F? 0 L P L A C E FLOW ARROW I I (SANDRA PLACE) I I 200 NODE o a' o l/2 H.P. 1 1/2 P INITIAL SUBAREA FLOW PATH c - —C- - __' ______________________ C DRAINAGE AREA .E • LI') s8FEP( . • 6Fl~' AcP —w k --- w ILSGR 1/ —.-- c • k90T1f 42 WT • to /SB -O 1.56B LLJ R/W ____ _ _ i T rl 0 to 1 11 4P °r1 __ A3=0.12 AC. . .04 A 00 __ I I 01 I A WASH 7 Q(A3)=0.45CFs a' 0 I Z ,BBT IN FEET) A1=0.41 AC. I I I 00 L= 260 LF S=1.2%EL a 4.641 T4 IMF Q(A1) 1.55 CFS - L- 2O FT 1.3%Lu A2=0.31 AC. 244 :2LF > co I -.-- — — — Q(A2)= 1.05 CES Ld 00 I .___t — — — — — — 4.90T B4.3a 2% 20CF- . Ld (OD Eo L ,?ft) MEA-£"Ll . CL DATE :3-28-02 60-71 24 DATE:3-28-02 48T I.521 220 77 I I I I . REVISION NO: I JOB I T A M A F? A C K A V E. oanmB6ntjwbØ AR12 CUP SUBMITTAL master release dot. 03/07/01 2_ N R1 20 20' E 't - I. 'by NO. DATE REVISIONS BY PROJECT RELEASE 12/18/0t BL F4C08525 05dm, U - PERMIT - faclllly/Proj.ot BID - 06525 - CONST. sheet To 01 1S—BUILT TOPOGRAPHIC AND BOUNDARY INFORMATION SHOWN HEREON IS BASED ON THE ALTA DATED MAY 25. 2001 BY KENORICKS AND ASSOCIATES, INC APN# 204-292-24-00 - pr—hyd.dwg 4-1-02 7:06:32 pm EST X2= 0.31 AC L= 165 LF S= 2.1 % Qx2= 0.77 CFS X1= 0.54 AC L= 230 LF S=1.8% Qx1= 2.04 CFS LEGEND - FLOW ARROW 200 NODE —> - INITIAL SUBAREA FLOW PATH DRAINAGE AREA TOPOGRAPHIC AND BOUNDARY INFORMATION SHOWN HEREON IS BASED OR THE ALTA DATED MAY 25, 2001 BY KENORICI<S AND ASSOCIATES. INC APN# 204-292-24-00 CAROL PLACE I (SANDRA PLACE) L 3 ,100..-- -_--__ t, I 6j.04 - 0. AC PAVE. 1 *2=0 .31 AC I \ \ 7 I I IN-2O IT IN FEET I IIS%1 =.7c PA. X1=0.54 AC \ . 0 C=..95 L ri •: UO TII< AREA BLDG Li._ IL 01 • . Lij __-- \ 2 FUEUNOA (' I ø cs PAVE. 9 ) I' : 1031 4% A M A [A C K V - > 02 — 0 c•.l o -, a- L4J LL. < UJ af C.) E >o 0, <Ls_ W—.ji 0_ :3JO- '-5-- -5-•O Z 0 0 < E L.X <ED E — cI oc o2 <CD >< Z C.) P) wcu DRAWN: EAJ DATE: 3-28-02 0<0: GEH DATE:3-28-02 7Ai TNT C AflTtS TIC. RETsISION NO OATS: JOB NOARI2IBA ae' date drawn by PROJECT RELEASE 12/18/01 8L PERMIT FIIena,ne 05.dno - FaaIIIty/PraJ.at BID - 06525 CONST. - cheat AS-BUILT - 01 - ex-hyd.thtg 4-1-02 70917 On EST -ii I I I SECTION IV: HYDROLOGY CALCULATIONS I I I I I I I I I I I I I 1219x1 . res ** ** * *** * * RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2001 Advanced Engineering Software (ae s) Ver. 1.5A Release Date: 01/01/2001 License ID 1334 Analysis prepared by: TAIT & ASSOCIATES, INC. 701 N. PARKCENTER DRIVE SANTA ANA, CA 92705 PH: 714-560-8200 ************************** DESCRIPTION OF STUDY ***************** ********* * 10 YEAR- EXISTING ANALYSIS- Xl * * * * * ********* FILE NAME: C:\aes200l\hydrOsft\ratscX\1219X1.dat TIME/DATE OF STUDY: 1614 12/17/2001 ------------------------------------------------------------------ USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ------------------------------------------------------------------ 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 10.00 6-HOUR DURATION PRECIPITATION (INCHES) = 1.700 SPECIFIED MINIMUM PIPE SIZE(INCH) = 6.00 Page 1 I 1219x1. res I I SPECIFIED PERCENT OF GRADIENTS (DECIMAL) TO USE FOR FRICTION SLOP E = 0.95 SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD I NOTE: CONSIDER ALL CONFLUENCE STREAM COMBINATIONS FOR ALL DOWNSTREAM ANALYSES ********** I FLOW PROCESS FROM NODE 100.00 TO NODE 103.00 IS CODE = 21 I >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< I USER-SPECIFIED RUNOFF COEFFICIENT = .9500 S.C.S. CURVE NUMBER (AMC II) = 92 INITIAL SUBAREA FLOW-LENGTH 230.00 UPSTREAM ELEVATION = 64.84 DOWNSTREAM ELEVATION = 60.65 ELEVATION DIFFERENCE = 4.19 I URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) = 3.353 TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 10 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.982 I SUBAREA RUNOFF(CFS) = 2.04 TOTAL AREA(ACRES) = 0.54 TOTAL RUNOFF(CFS) END OF STUDY SUMMARY: TOTAL AREA(ACRES) = 0.54 TC(MIN.) = 6.00 1 PEAK FLOW RATE (CFS) = 2.04 END OF RATIONAL METHOD ANALYSIS I Page 2 1219x2 .res ***************************************************************** * ** ** * * * * * * RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2001 Advanced Engineering Software (ae s) Ver. 1.5A Release Date: 01/01/2001 License ID 1334 Analysis prepared by: TAIT. & ASSOCIATES, INC. 701 N. PARKCENTER DRIVE SANTA ANA, CA 92705 PH: 714-560-8200 ************************** DESCRIPTION OF STUDY ** ** * * ** * * 10 YEAR EXISTING SITE ANALYSIS- X2 * * * * * ******** ******** ************************************************* ********* FILE NAME: C:\aes200l\hydrosft\ratscx\1219x2.dat TIME/DATE OF STUDY: 10:27 12/17/2001 ------------------------------------------------------------------ USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ------------------------------------------------------------------ 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 10.00 6-HOUR DURATION PRECIPITATION (INCHES) = 1.700 SPECIFIED MINIMUM PIPE SIZE(INCH) = 6.00 Page 1 Li 1219x2 .res I I SPECIFIED PERCENT OF GRADIENTS (DECIMAL) TO USE FOR FRICTION SLOP E = 0.95 SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD I NOTE: CONSIDER ALL CONFLUENCE STREAM COMBINATIONS FOR ALL DOWNSTREAM ANALYSES ****************************************************************** ** *** * * * ** I FLOW PROCESS FROM NODE 100.00 TO NODE 300.00 IS CODE = 21 ---------- I >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< I USER-SPECIFIED DEVELOPMENT RUNOFF COEFFICIENT = .7000 SOIL CLASSIFICATION IS "D" S.C.S. CURVE NUMBER (AMC II) = 90 ' INITIAL SUBAREA FLOW-LENGTH = 165.00 UPSTREAM ELEVATION = 64.84 DOWNSTREAM ELEVATION = 61.30 I ELEVATION DIFFERENCE = 3.54 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) = 7.171 10 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.550 I SUBAREA RUNOFF(CFS) = 0.77 TOTAL AREA(ACRES) = 0.31 TOTAL RUNO FF(CFS) = 0.77 END OF STUDY SUMMARY: TOTAL AREA(ACRES) = 0.31 TC(MIN.) = 7.17 I PEAK FLOW RATE (CFS) = 0.77. END OF RATIONAL METHOD ANALYSIS I I I I I Page 2 [11 I ***************************************************************** I *********** INTEGRATED RATIONAL METHOD/UH METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE I Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2001 Advanced Engineering Software I (aes) Ver. 1.5A Release Date: 01/01/2001 License ID 1334 I Analysis prepared by: Tait & Associates, Inc. I 701 N. Parkcenter Drive Santa Ana, CA 92705 714-560-8200 fax: 714-560-8211 I ************************** DESCRIPTION OF STUDY ************************** * 10 YEAR PROPOSED SITE ANALYSIS - AREA 1 & 2 I * * * * I * I ***************************************************************** FILE NAME: C:\aes200l\hydrosft\ratscX\1219PR10.dat__________ I TIME/DATE OF STUDY: 20:41 04/01/2002 I USER ------------ SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: I 1985 ------------ SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 10.00 6-HOUR DURATION PRECIPITATION (INCHES) = 1.700 I SPECIFIED MINIMUM PIPE SIZE(INCH) = 6.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.95 I SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD NOTE: CONSIDER ALL CONFLUENCE STREAM COMBINATIONS FOR ALL DOWNSTREAM ANALYSES I *USERDEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL* I I HALF- CROWN TO STREET-CROSSFALL: CURB GUTTER- GEOMETRIES: MANNING WIDTH CROSSFALL IN- / OUT-/PARK- HEIGHT WIDTH LIP HIKE FACTOR NO. (FT) (FT) SIDE / SIDE/ WAY (FT) (FT) (FT) I (FT) I i 24.0 12.0 0.020/0.020/ --- 0.50 1.50 0.0313 0.167 0.0150 I GLOBAL STREET FLOW-DEPTH CONSTRAINTS: 1. Relative Flow-Depth = 0.00 FEET as (Maximum Allowable Street Flow Depth) - (Top-of-Curb) I 2. (Depth)*(Velocity) Constraint = 6.0 (FT*FT/S) *SIZE PIPE WITH A FLOW CAPACITY GREATER THAN OR EQUAL TO THE UPSTREAM TRIBUTARY PIPE.* UNIT-HYDROGRAPH MODEL SELECTIONS/PARAMETERS: WATERSHED LAG = 0.80 * Tc S.C.S. S-GRAPH USED. SAN DIEGO COUNTY DEPTH-AREA FACTORS USED (See Page II-B-4.) TYPE B: 6-HOUR DESIGN STORM USED. UNADJUSTED 6-HOUR RAINFALL DEPTH (INCHES) = 1.70 *ANTECEDENT MOISTURE CONDITION (AMC) II ASSUMED FOR UNIT HYDROGRAPH METHOD* ***************************************************************** *********** FLOW PROCESS FROM NODE 100.00 TO NODE 101.00 IS CODE = 21 >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< USER-SPECIFIED RUNOFF COEFFICIENT = .9500 S.C.S. CURVE NUMBER (AMC II) = 92 INITIAL SUBAREA. FLOW-LENGTH = 260.00 UPSTREAM ELEVATION = 64.65 DOWNSTREAM ELEVATION = 61.57 ELEVATION DIFFERENCE = 3.08 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) = 4.115 TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 10 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.982 SUBAREA RUNOFF(CFS) = 1.55 TOTAL AREA(ACRES) = 0.41 TOTAL RUNOFF(CFS) = 1.55 I I I ***************************************************************** FLOW PROCESS FROM NODE 101.00 TO NODE 102.00 IS CODE = I 61 ------------ >>>>>COMPUTE STREET FLOW TRAVEL TIME THRU SUBAREA<<<<< I >>>>>(STANDARD CURB SECTION USED)<<<<< UPSTREAM ELEVATION(FEET) = 61.57 DOWNSTREAM ELEVATION(FEET) = 60.65 I STREET LENGTH(FEET) = 120.00 CURB HEIGHT(INCHES) = 6.0 STREET HALFWIDTH(FEET) = 24.00 DISTANCE FROM CROWN TO CROSSFALL GRADEBREAK(FEET) = 12.00 I INSIDE STREET CROSSFALL(DECIMAL) = 0.020 OUTSIDE STREET CROSSFALL(DECIMAL) = 0.020 1 SPECIFIED NUMBER OF HALFSTREETS CARRYING RUNOFF = 2 Manning's FRICTION FACTOR for Streetfiow Section(curb-to-curb) = 0.0150 I **TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 1.57 STREETFLOW MODEL RESULTS USING ESTIMATED FLOW: I STREET FLOW DEPTH(FEET) = 0.25 HALFSTREET FLOOD WIDTH(FEET) = 6.20 AVERAGE FLOW VELOCITY(FEET/SEC.) = 1.56 I PRODUCT OF DEPTH&VELOCITY(FT*FT!SEC.) = 0.39 STREET FLOW TRAVEL TIME(MIN.) = 1.28 Tc(MIN.) = 7.28 10 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.514 I USER-SPECIFIED RUNOFF COEFFICIENT = .9500 S.C.S. CURVE NUMBER (AMC II) = 92 SUBAREA AREA(ACRES) = 0.00 SUBAREA RUNOFF(CFS) = 0.00 I TOTAL AREA(ACRES) = 0.42 PEAK FLOW RATE(CFS) = 1.58 END OF SUBAREA. STREET FLOW HYDRAULICS: DEPTH(FEET) = 0.25 HALFSTREET FLOOD WIDTH(FEET) = 6.20 I FLOW VELOCITY(FEET/SEC.) = 1.58 DEPTH*VELOCITY(FT*FT/SEC.) = 0.39 LONGEST FLOWPATH FROM NODE 100.00 TO NODE 102.00 = I 380 .00 FEET. I I I I Li ***************************************************************** *********** FLOW PROCESS FROM NODE 102.00 TO NODE 102.00 IS CODE = 1 ---------------------------------------------------------------- ------------ >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<< < TOTAL NUMBER OF STREAMS = 2 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE: TIME OF CONCENTRATION(MIN.) = 7.28 RAINFALL INTENSITY(INCH/HR) = 3.51 TOTAL STREAM AREA(ACRES) = 0.42 PEAK FLOW RATE(CFS) AT CONFLUENCE = 1.58 ***************************************************************** *********** FLOW PROCESS FROM NODE 200.00 TO NODE 102.00 IS CODE = 21 ------------ >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< I = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = USER-SPECIFIED RUNOFF COEFFICIENT = .8500 S.C.S. CURVE NUMBER (AMC II) = 92 INITIAL SUBAREA FLOW-LENGTH = 244.00 UPSTREAM ELEVATION = 64.84 DOWNSTREAM ELEVATION = 60.65 ELEVATION DIFFERENCE = 4.19 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) = 5.870 TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 10 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.982 SUBAREA RUNOFF (CFS) = 1 . 05 TOTAL AREA(ACRES) = 0.31 TOTAL RUNOFF(CFS) = 1.05 ***************************************************************** ** ** * * * **** FLOW PROCESS FROM NODE 102.00 TO NODE 102.00 IS CODE = 1 ---------------------------------------------------------------- ------------ >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< >>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< TOTAL NUMBER OF STREAMS = 2 El n I Li H Li I I I I I I I I I Li I CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE: TIME OF CONCENTRATION(MIN.) = 6.00 RAINFALL INTENSITY(INCH/HR) = 3.98 TOTAL STREAM AREA(ACRES) = 0.31 PEAK FLOW RATE(CFS) AT CONFLUENCE = 1.05 ** CONFLUENCE DATA ** STREAM RUNOFF Tc INTENSITY AREA NUMBER (CFS) (MIN.) (INCH/HOUR) (ACRE) 1 1.58 7.28 3.514 0.42 2 1.05 6.00 3.982 0.31 RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO CONFLUENCE FORMULA USED FOR 2 STREAMS. ** PEAK FLOW RATE TABLE ** STREAM RUNOFF Tc INTENSITY NUMBER (CFS) (MIN.) (INCH/HOUR) 1 2.45 6.00 3.982 2 2.51 7.28 3.514 COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS: PEAK FLOW RATE(CFS) = 2.51 Tc(MIN.) = 7.28 TOTAL AREA(ACRES) = 0.73 LONGEST FLOWPATH FROM NODE 100.00 TO NODE 102.00 = 380.00 FEET. END OF STUDY SUMMARY: TOTAL AREA(ACRES) = 0.73 TC(MIN.) = 7.28 PEAK FLOW RATE(CFS) = 2.51 PEAK FLOW RATE TABLE *** Q(CFS) Tc(MIN.) 1 2.45 6.00 2 2.51 7.28 END OF RATIONAL METHOD ANALYSIS I I I I I I I I I I I I I I I I I I I H I ***************************************************************** *********** INTEGRATED RATIONAL METHOD/UH METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2001 Advanced Engineering Software (aes) Ver. 1.5A Release Date: 01/01/2001 License ID 1334 Analysis prepared by: Tait & Associates, Inc. 701 N. Parkcenter Drive Santa Ana, CA 92705 714-560-8200 fax: 714-560-8211 I ************************** DESCRIPTION OF STUDY ***** ** *** ** *** ** * * * *** * * * * 10 YEAR PROPOSED SITE ANALYSIS - AREA 3 I * * * * I * I ***************************************************************** FILE NAME: C:\ae52001\hydrosft\ratScX\1219PR13.dat__________ TIME/DATE OF STUDY: 18:51 04/01/2002 I USER ------------ SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: 1 ------------ 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 10.00 6-HOUR DURATION PRECIPITATION (INCHES) = 1.700 I SPECIFIED MINIMUM PIPE SIZE(INCH) = 6.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION I SLOPE = 0.95 SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD NOTE: CONSIDER ALL CONFLUENCE STREAM COMBINATIONS FOR ALL DOWNSTREAM ANALYSES I *USERDEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL* I I I I I I I I ***************************************************************** I *********** FLOW PROCESS FROM NODE 300.00 TO NODE 400.00 IS CODE = 21 ---------------------------------------------------------------- ------------ >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< I = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = USER-SPECIFIED RUNOFF COEFFICIENT = .9500 I S.C.S. CURVE NUMBER (AMC II) = 92 INITIAL SUBAREA FLOW-LENGTH = 149.00 UPSTREAM ELEVATION = 65.35 I DOWNSTREAM ELEVATION = 61.30 ELEVATION DIFFERENCE = 4.05 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) = 2.362 I *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 10 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.982 I SUBAREA RUNOFF(CFS) = 0.45 TOTAL AREA(ACRES) = 0.12 TOTAL RUNOFF(CFS) = 0.45 I = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = END OF STUDY SUMMARY: I TOTAL AREA(ACRES) = 0.12 TC(MIN.) = 6.00 PEAK FLOW RATE (CFS) = END OF RATIONAL METHOD ANALYSIS LI I I I 1 ITI] SECTION V: PRECIPITATION MAPS I I I — - COUNTY OF SAN DIEGo 1 . . FLOOD CONTROL DEPARTMENT OF SANITATION & 10-YEAR 2448th '20--/ ISOPLUVIALS 3F PflEC1Tit I 10YEJR 24-HOUR 451 PR ECIPITATION RI tETUS OF A ICII 4 Z U so 45 INA 30' 4 ç \ SAN CL MENI,t j' S. 15 1 60 1 1 I 20 I ) \\ \ 39 33 c~ jo. 7 J1 40 - 25 ro 451 _______ r • •%4 10. m t( VdLJ, a - —td Prfp.Iedby S ( U.S. DEPARTjI TOFCOMMERCE \\ . L 0 /) NATfONAL OCEANIC AND AT .IOSP,t,C ADMINISTRATION PEdAL STUDIES DRACII OFJ'ICE OF I DROLOGY NATIONAL WEATHER SERVICE IiIfLf U 5 . 30' . 118° 451 30' 15' 117° . 451 301 I1° COUNTY OF SAN DIEGO DEPARTMENT OF SANITATION 10-YEAR 6-nounPRECIPITATION FLOOD CONTROL -- I '-is----ISCAUVI US Of 10-YE1W G-iJ PUECIpIT!TI( In 1E1TUS OF AN ICU j \•,. i ii 30' 15' 330 , X, 451 Prepfre U.S. DEPARThTET NATIONAL OCEANIC AND SPECIAL STUDIES ORANCI! OFFICE OF ItYD 30' ime I 18° 45' 30' 15' 1170 45' 30' 15' 1451 — — — — == — — - — — — — — INTENSITY-DUMTI ISIGO, CHART Directions for Application: From precipitation riaps determine 6 hr. and 24 hr. amounts for the selected frequency. These maps are printed in the County. Hydrology Manual (10, 50 And 100 yr. maps included in th Design and Procedure Manual). Adjust 6 hr. precipitation (if necessary) so that it is within the range of 45% to 65% of the 24 hr. precipitation. (Not Applicable to Desert) Plot 6 hr. precipitation on the right side of the chart. HI( . Draw a line through the point parallel to the . plotted lines. This line is the intensity-duration curve for the location being analyzed. 50 Application Form: 0) Selected Frequency tO "2.5 1) p6 = L In., p24 , P6_ 5S %* P 24 I.Ill2•0: 2) Adjusted *p5 1.7 in. 3 t = mm. -. -C - 4) I _In/hr. 1.0 *Not Applicable to Desert Region 10 15 20. 30 40 50 1 2 3 4 5 6 Minutes ...-.,-.- Hours APPENDIX XI IV-A-14 Revised 1/85 1 Li 1 11 I I SECTION VI: SUSMP CALCULATIONS 1 I I I - - - - - - - - - - - Tait & Associates, Inc. Si) j s) 4 s)$J j :) 19, @ Z521 LIJ11Eiøi FILTRATION CAPACITY Charts shown below reflect the effectively filtered hydraulic flow capacity of both rectangular grated inlets and curb inlets of various sizes. The data shown on the charts is based on the hydraulic testing performed by Sandine & Associates (see attached letters). Testing has shown that a flow rate of 12 GPM per linear foot of Fossil Filteirhh'* is effectively filtered by the installed Fossil RocId1s filter media. HYDRAULIC CAPACITY CHART Rectangular Grated Inlet Application 180 160 140 120 G P 100 M 80 40 20 24"x24' 24"00" 24"06" 30"00" 24"x48' 36"x36' 36'x48" INLET DIMENSION HYDRAULIC CAPACITY CHART Curb Inlet Application 250.............................................................. ... .. .......................................................... 200 48"x48" 36"48" 60" 72" 84" 96" 108" 120" 0 KriStar Enterprises 4/9/96 CURB JJ'J' SIZE I Order No. 2001-01 Page 15 of 52 February 21, 2001 S:1STORM\SD PERM IT\SdPerm99-01\Permit\SDMUniPermit 3.doc (9) Post-development runoff from a site shall not contain pollutant loads which cause or I contribute to an exceedance of receiving water quality objectives or which have not been reduced to the maximum extent practicable. I F.1.b. Modify Development Project Approval Processes Prior to project approval and issuance of local permits, Copermittees shall require each proposed project to implement measures to ensure that pollutants and runoff from the development will be I reduced to the maximum extent practicable and will not cause or contribute to an exceedance of receiving water quality objectives. Each Copermittee shall further ensure that all development will be in compliance with Copermittee storm water ordinances, local permits, all other applicable I ordinances and requirements, and this Order. (1) Development Project Requirements I Each Copermittee shall include development project requirements in local permits to ensure that pollutant discharges and runoff flows from development are reduced to the maximum extent practicable and that receiving water quality objectives are not violated throughout the I life of the project. Such requirements shall, at a minimum: Require project proponent to implement source control BMPs for all applicable development projects. I Require project proponent to implement site design/landscape characteristics where feasible which maximize infiltration, provide retention, slow runoff, and minimize impervious land coverage for all development projects. Require project proponent to implement buffer zones for natural water bodies, where I feasible. Where buffer zone implementation is infeasible, require project proponent to implement other buffers such as trees, lighting restrictions, access restrictions, etc. Require industrial applicants subject to California's statewide General NPDES Permit for I Storm Water Discharges Associated with Industrial Activities (Except Construction), (hereinafter General Industrial Permit), to provide evidence of coverage under the General Industrial Permit. Require project proponent to ensure its grading or other construction activities meet I the provisions specified in Section F.2. of this Order. Require project proponent to provide proof of a mechanism which will ensure ongoing long-term maintenance of all structural post-construction BMPs. I (2) Standard Urban Storm Water Mitigation Plans (SUSMPs) Within 365 days of adoption of this Order, the Copermittees shall collectively develop a I model Standard Urban Storm Water Mitigation Plan (SUSMP) to reduce pollutants and runoff flows from all new development and significant redevelopment projects falling under the priority project categories or locations listed in section 17.1.b.(2)(a) below. Within 180 days of approval of the model SUSMP in the public process by the SDRWQCB, each I Copermittee shall adopt its own local SUSMP, and amended ordinances consistent with the approved model SUSMP, and shall submit both (local SUSMP and amended ordinances) to the SDRWQCB. I Immediately following adoption of its local SUSMP, each Copermittee shall ensure that all new development and significant redevelopment projects falling under the priority project categories or locations listed in F.1.b.(2)(a) below meet SUSMP requirements. The SUSMP I requirements shall apply to all priority projects or phases of priority projects which have not yet begun grading or construction activities. If a Copermittee determines that lawful prior approval of a project exists, whereby application of SUSMP requirements to the project is I infeasible, SUSMP requirements need not apply to the project. Where feasible, the Copermittees shall utilize the 18 month SUSMP implementation period to ensure that I Order No. 2001-01 Page 16 of 52 February 21, 2001 I S:\STORM\SDPERMIT\SdPerm99-01 Permit\SDMuniPermit 3.doc projects undergoing approval processes include application of SUSMP requirements in their 1 plans. (a) Priority Development Project Categories - SUSMP requirements shall apply to all new I development and significant redevelopment projects falling under the priority project categories or locations listed below. Significant redevelopment is defined as the creation or addition of at least 5,000 square feet of impervious surfaces on an already developed site. Significant redevelopment includes, but is not limited to: the expansion I of a building footprint or addition or replacement of a structure; structural development including an increase in gross floor area and/or exterior construction or remodeling; replacement of impervious surface that is not part of a routine maintenance activity; and I land disturbing activities related with structural or impervious surfaces. Where significant redevelopment results in an increase of less than fifty percent of the impervious surfaces of a previously existing development, and the existing development was not subject to SUSMP requirements, the numeric sizing criteria discussed in I section F.1.b.(2)(c) applies only to the addition, and not to the entire development. I. Home subdivisions of 100 housing units or more. This category includes single- family homes, multi-family homes, condominiums, and apartments. ii. Home subdivisions of 10-99 housing units. This category includes single-family homes, multi-family homes, condominiums, and apartments. I iii. Commercial developments greater than 100,000 square feet. This category is defined as any development on private land that is not for heavy industrial or I residential uses where the land area for development is greater than 100,000 square feet. The category includes, but is not limited to: hospitals; laboratories and other medical facilities; educational institutions; recreational facilities; commercial nurseries; multi-apartment buildings; car wash facilities; mini-malls I and other business complexes; shopping malls; hotels; office buildings; public warehouses; automotive dealerships; commercial airfields; and other light industrial facilities. I iv. Automotive repair shops. This category is defined as a facility that is categorized in any one of the following Standard Industrial Classification (SIC) codes: 5013, 5014, 5541, 7532-7534, or 7536-7539. I V. Restaurants. This category is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling prepared foods and drinks for immediate consumption (SIC code I 5812), where the land area for development is greater than 5,000 square feet. All hillside development greater than 5,000 square feet. This category is I defined as any development which creates 5,000 square feet of impervious surface which is located in an area with known erosive soil conditions, where the development will grade on any natural slope that is twenty-five percent or I greater. Environmentally Sensitive Areas: All development and redevelopment located within or directly adjacent to or discharging directly to an environmentally I sensitive area (where discharges from the development or redevelopment will enter receiving waters within the environmentally sensitive area), which either creates 2,500 square feet of impervious surface on a proposed project site or I increases the area of imperviousness of a proposed project site to 10% or more of its naturally occurring condition. Environmentally sensitive areas include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; I I I Order No. 2001-01 Page 17 of 52 February 21, 2001 S:\STORM\SDPERMIT\Sdperm99-01\Permit\SDMUfliPermit 3.doc areas designated as Areas of Special Biological Significance by the State I Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and amendments); water bodies designated with the RARE beneficial use by the State Water Resources Control Board (Water Quality I Control Plan for the San Diego Basin (1994) and amendments); areas designated as preserves or their equivalent under the Multi Species Conservation Program within the Cities and County of San Diego; and any I other equivalent environmentally sensitive areas which have been identified by the Copermittees. "Directly adjacent" means situated within 200 feet of the environmentally sensitive area. "Discharging directly to" means outflow from a drainage conveyance system that is composed entirely of flows from the I subject development or redevelopment site, and not commingled with flows from adjacent lands. I viii. Parking lots 5,000 square feet or more or with 15 or more parking spaces and potentially exposed to urban runoff. Parking lot is defined as a land area or facility for the temporary parking or storage of motor vehicles used personally, for business, or for commerce. 1 ix. Street, roads, highways, and freeways. This category includes any paved surface which is 5,000 square feet or greater used for the transportation of I automobiles, trucks, motorcycles, and other vehicles. X. Retail Gasoline Outlets. Retail Gasoline Outlet is defined as any facility engaged in selling gasoline. I(b) BMP Requirements - The SUSMP shall include a list of recommended source control and structural treatment BMPs. The SUSMP shall require all new development and I significant redevelopment projects falling under the above priority project categories or locations to implement a combination of BMPs selected from the recommended BMP list, including at a minimum (1) source control BMPs and (2) structural treatment BMPs. The BMPs shall, at a minimum: I i. Control the post-development peak storm water runoff discharge rates and velocities to maintain or reduce pre-development downstream erosion, and to protect stream habitat; I ii. Conserve natural areas where feasible; iii. Minimize storm water pollutants of concern in urban runoff from the new development or significant redevelopment (through implementation of source I control BMPs). Identification of pollutants of concern should include at a minimum consideration of any pollutants for which water bodies receiving the development's runoff are listed as impaired under Clean Water Act section 303(d), any pollutant associated with the land use type of the development, and I any pollutant commonly associated with urban runoff; iv. Remove pollutants of concern from urban runoff (through implementation of structural treatment BMPs); I v. Minimize directly connected impervious areas where feasible; Protect slopes and channels from eroding; Include storm drain stenciling and signage; Include properly designed outdoor material storage areas; I ix. Include properly designed trash storage areas; X. Include proof of a mechanism, to be provided by the project proponent or Copermittee, which will ensure ongoing long-term structural BMP maintenance; I A. Include additional water quality provisions applicable to individual priority project categories; I Order No. 2001-01 Page 18 of 52 S:\STORM\SDPERMIT\SdPerm99-01lPermitlSDMUfliPermit 3.doc February 21, 2001 Be correctly designed so as to remove pollutants to the maximum extent practicable; Be implemented close to pollutant sources, when feasible, and prior to discharging into receiving waters supporting beneficial uses; and Ensure that post-development runoff does not contain pollutant loads which cause or contribute to an exceedance of water quality objectives or which have not been reduced to the maximum extent practicable. (c) Numeric Sizing Criteria - The SUSMP shall require structural treatment BMPs to be implemented for all priority development projects. All structural treatment BMPs shall be located so as to infiltrate, filter, or treat the required runoff volume or flow prior to its discharge to any receiving waterbody supporting beneficial uses. Structural treatment BMPs may be shared by multiple new development projects as long as construction of any shared structural treatment BMPs is completed prior to the use of any new development project from which the structural treatment BMP will receive runoff. In addition to meeting the BMP requirements listed in item F.1.b.(2)(b) above, all structural treatment BMPs for a single priority development project shall collectively be sized to comply with the following numeric sizing criteria: Volume Volume-based BMPs shall be designed to mitigate (infiltrate, filter, or treat) either: The volume of runoff produced from a 24-hour 85th percentile storm event, as determined from the local historical rainfall record (0.6 inch approximate average for the San Diego County area);3 or The volume of runoff produced by the 85th percentile 24-hour rainfall event, determined as the maximized capture storm water volume for the area, from the formula recommended in Urban Runoff Quality Management, WEF Manual of Practice No. 23/ASCE Manual of Practice No. 87, (1998); or The volume of annual runoff based on unit basin storage volume, to achieve 90% or more volume treatment by the method recommended in California Stormwater Best Manaaement Practices Handbook - Industrial/Commercial, (1993); or The volume of runoff, as determined from the local historical rainfall record, that achieves approximately the same reduction in pollutant loads and flows as achieved by mitigation of the 85th percentile 24-hour runoff event;4 MW 1 3 This volume is not a single volume to be applied to all of San Diego County. The size of the 85th percentile storm event is different for various parts of the County. The Copermittees are encouraged to calculate the 85th percentile storm event for each of their jurisdictions using local rain data pertinent to their particular jurisdiction (the 0.6 inch standard is a rough average for the County and should only be used where appropriate rain data is not available). In addition, isopluvial maps contained in the County I of San Diego Hydrology Manual may be used to extrapolate rainfall data to areas where insufficient data exists in order to determine the volume of the local 85th percentile storm event in such areas. Where the Copermittees will use isopluvial maps to determine the 85th percentile storm event in areas lacking rain data, the Copermittees shall describe their method for using isopluvial maps in the model and local SUSMPs. I Under this volume criteria, hourly rainfall data may be used to calculate the 85th percentile storm event, where each storm event is identified by its separation from other storm events by at least six hours of no rain. Where the Copermittees may use hourly rainfall data to calculate the 85th percentile storm event, the Copermittees shall describe their method for using hourly rainfall data to calculate the 85thpercentile storm event in the model and local SUSMPs. I Order No. 2001-01 Page 19 of 52 February 21, 2001 S:\STORMSDPERMIT\Sdperm99-01PermitSDMuniPermit 3.doc Flow Flow-based BMPs shall be designed to mitigate (infiltrate, filter, or treat) either: i. The maximum flow rate of runoff produced from a rainfall intensity of 0.2 inch of rainfall per hour; or The maximum flow rate of runoff produced by the 85th percentile hourly rainfall intensity, as determined from the local historical rainfall record, multiplied by a factor of two; or iii. The maximum flow rate of runoff, as determined from the local historical rainfall record, that achieves approximately the same reduction in pollutant loads and flows as achieved by mitigation of the 85th percentile hourly rainfall intensity multiplied by a factor of two. Equivalent Numeric Sizing Criteria - The Copermittees may develop, as part of the model SUSMP, any equivalent method for calculating the volume or flow which must be mitigated (i.e., any equivalent method for calculating numeric sizing criteria) by post- construction structural treatment BMPs. Such equivalent sizing criteria may be authorized by the SDRWQCB for use in place of the above criteria. In the absence of development and subsequent authorization of such equivalent numeric sizing criteria, the above numeric sizing criteria requirement shall be implemented. Pollutants or Conditions of Concern - As part of the model SUSMP, the Copermittees shall develop a procedure for pollutants or conditions of concern to be identified for each new development or significant redevelopment project. The procedure shall include, at a minimum, consideration of (1) receiving water quality (including pollutants for which receiving waters are listed as impaired under Clean Water Act section 303(d)); (2) land use type of the development project and pollutants associated with that land use type; (3) pollutants expected to be present on site; (4) changes in storm water discharge flow rates, velocities, durations, and volumes resulting from the development project; and (5) sensitivity of receiving waters to changes in storm water discharge flow rates, velocities, durations, and volumes. Implementation Process -As part of the model SUSMP, the Copermittees shall develop a process by which SUSMP requirements will be implemented. The process shall identify at what point in the planning process development projects will be required to meet SUSMP requirements. The process shall also include identification of the roles and responsibilities of various municipal departments in implementing the SUSMP requirements, as well as any other measures necessary for the implementation of SUSMP requirements. Restaurants Less than 5,000 Square Feet - New development and significant redevelopment restaurant projects where the land area development is less than 5,000 square feet shall meet all SUSMP requirements except for structural treatment BMP and numeric sizing criteria requirement F.1.b.(2)(c) and peak flow rate requirement F.1.b(2)(b)(i). A restaurant is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling prepared foods and drinks for immediate consumption (SIC Code 5812). Waiver Provision - A Copermiftee may provide for a project to be waived from the requirement of implementing structural treatment BMPs (F.1.b.(2)(c)) if infeasibility can be established. A waiver of infeasibility shall only be granted by a Copermittee when all available structural treatment BMPs have been considered and rejected as infeasible. Copermittees shall notify the SDRWQCB within 5 days of each waiver issued and shall include the name of the person granting each waiver. I ri I I I I I U I I I I I I I I I I I I I Order No. 2001-01 Page 20 of 52 February 21, 2001 S:STORM\SDPERMlT\Sdperm99-01\Permit\SDMuniPermit 3.doc As part of the model SUSMP, the Copermittees may develop a program to require I project proponents who have received waivers to transfer the savings in cost, as determined by the Copermittee(s), to a storm water mitigation fund. This program may be implemented by all Copermittees which choose to provide waivers. Funds may be I used on projects to improve urban runoff quality within the watershed of the waived project. The waiver program may identify: I i. The entity or entities that will manage the storm water mitigation fund (i.e., assume full responsibility for) ii. The range and types of acceptable projects for which mitigation funds may be expended; I iii. The entity or entities that will assume full responsibility for each mitigation project including its successful completion iv. How the dollar amount of fund contributions will be determined. I (i) Infiltration and Groundwater Protection - To protect groundwater quality, each Copermiffee shall apply restrictions to the use of structural treatment BMPs which are designed to primarily function as infiltration devices (such as infiltration trenches and I infiltration basins). Such restrictions shall ensure that the use of such infiltration structural treatment BMPs shall not cause or contribute to an exceedance of groundwater quality objectives. At a minimum, use of structural treatment BMPs which are designed to primarily function as infiltration devices shall meet the following I conditions:5 L Urban runoff shall undergo pretreatment such as sedimentation or filtration prior I to infiltration. All dry weather flows shall be diverted from infiltration devices. Pollution prevention and source control BMPs shall be implemented at a level appropriate to protect groundwater quality at sites where infiltration structural I treatment BMPs are to be used. Infiltration structural treatment BMPs shall be adequately maintained so that they remove pollutants to the maximum extent practicable. I v. The vertical distance from the base of any infiltration structural treatment BMP to the seasonal high groundwater mark shall be at least 10 feet. Where groundwater basins do not support beneficial uses, this vertical distance criteria may be reduced, provided groundwater quality is maintained. I vi. The soil through which infiltration is to occur shall have physical and chemical characteristics (such as appropriate cation exchange capacity, organic content, clay content, and infiltration rate) which are adequate for proper infiltration I durations and treatment of urban runoff for the protection of groundwater beneficial uses. Infiltration structural treatment BMPs shall not be used for areas of industrial or light industrial activity; areas subject to high vehicular traffic (25,000 or greater I average daily traffic on main roadway or 15,000 or more average daily traffic on any intersecting roadway); automotive repair shops; car washes; fleet storage areas (bus, truck, etc.); nurseries; and other high threat to water quality land I uses and activities as designated by each Copermittee. Infiltration structural BMPs shall be located a minimum of 100 feet horizontally from any water supply wells. I As part of the model and local SUSMPs, the Copermittees may develop alternative restrictions on the use of structural treatment BMPs which are designed to primarily function as infiltration devices. These conditions do not apply to structural treatment BMPs which allow incidental infiltration and are not designed to primarily function as infiltration devices (such as grassy swales, detention basins, vegetated buffer strips, constructed wetlands, etc.) I