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HomeMy WebLinkAboutPOUDRE SCHOOL DISTRICT 1999 ELEMENTARY - SITE PLAN ADVISORY REVIEW - 19-97 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT3.2.4 Detention Pond Analysis Detention of developed flows from the Elementary School site is provided in an existing detention/retention pond on the Preston Jr. High School site. The "Regional Drainage Evaluation for the 1999 Elementary School' (Lidstone and Anderson, Inc., August, 1997) was prepared to address existing problems with the pond as well as the impacts from the proposed elementary school. The report indicates that some additional berming and the addition of orifice plates on the pond outlet structure will solve the current problem as well as mitigate the impacts from the proposed elementary school 3.3 Erosion Control Most of the area from this site contributing runoff will be trapped at inlet filters, pipe filters, in perimeter silt fence, or by straw bale check dams located in the channels. Long term erosion protection will include reseeding of all disturbed areas, and pipe outlet riprap. The onsite measures and the offsite detention/retention should ensure no detrimental effects to water quality. 12 TABLE 4. SUMMARY OF RIPRAP DESIGN it lit, "itGIIAIVNEL VELOCITY BAS IN:::� ESCRIPTh . ......SLOPE 0-1 ''.1 A STORM SEWER ST- I OUTLET 14.63 6.07 0.40 1.82 CLASS TST, INC. CONSULTING ENGINEERS 8/4/97 000—hydl TABLE 3. SUMMARY OF INLET ANALYSIS AND DESIGN 01 YV i Ptti Pt l,1. ip ill Ni SI rN:: it Ill HASIN' POINT -P. MIF A 4 TYPE "R" SUMP 0.50 1.10 14.63 13.30 Is TST, INC CONSULTING ENGINEERS 811/97 000_hydi in j j3.2.2 Inlet Analysis The proposed inlet will be a CDOT Type "R" curb inlet. The 15-foot inlet will be in sump condition and will intercept the 100-yr runoff from Subbasin A5. The results of the Inlet analysis and design can be found in Table 3 with supporting calculations presented in Appendix C. 79 3.2.3. Channel and Rinran Desitrn Proposed channels were designed to prevent erosion caused by storm runoff and were evaluated with a program which utilizes Manning's Equation to determine flow depth and velocity based on input design flows, bed slopes, channel cross section, and roughness coefficients. 100-year flow velocities were determined to be non -erosive, but a concrete trickle pan was needed to adequately convey low flows. Riprap was not required for bed stabilization in the channels, but is needed at the outlet of storm line ST-1. A summary of the riprap requirements for this site can be found in Table 4. Our A analysis of the channels and spillways is presented in Appendix D. 9 TABLE 2. SUMMARY OF STORM SEWER DESIGN a iRDESIGN " PIPS TO FLOW DIAMETERFROM LINE (DOWN STREAM) ..m.;:4up ST-1 24" ADS F.E.S. M.H. LIST-1 14.63 24 ADS M.H. FIST-1 INLET ST-1 14.63 24 ADS TST, INC CONSULTING ENGINEERS 8/1/97 000—hyd I m 3.2.1 Storm Sewer Design Line ST-1 represents our design of the storm sewer for the 1999 Elementary school. This system will allow for the interception of the 100-year runoff to be directed to a retention/detention facility south of Preston Jr. High School just to the southeast of our site. Line ST-1 was analyzed with UDSEWER. The water surface at the downstream end of Line ST- 1 was determined to be equal to 1.3 ft above the invert of the pipe by the channel flow depth. This was based on an estimated capacity of the pipe using Manning's Equation, which should be conservatively high. The results of the Storm Sewer Analysis and Design can be found in Table 2 with supporting calculations and model outputs presented in Appendix B. , 7 Lr L..r- L-r L.-.t "I- � -L..� L.� L...� L.m L.-M I L-A L--.A �� L-J, L.l L- TABLE 1. HYDROLOGIC CALCULATIONS WORKSHEET N M M MAW- El;*.TlCUTTER R IbvklkLAND "UPA. SUB X"N'. NGTW. BASIN IDASIN:: "POINT• -yr R In in) Al 1 1.67 0.29 1.00 1.25 150 1.00 19.55 16.89 550 A2 2 1.46 0.54 1.00 1.25 150 1 10.00 1 6.00 4.55 650 A A3 1 1 2.67 0.37 1.00 1.25 300 1.50 1 20.68- 18.06 510 - 4 ----M i 3 2.06 0.25 1.00 1.23 330 2.00 23." 21.92 620 A 5 4 2.26 0.74 1.00 1.23 200 3.00 6.63 3.22 300 T !;'AVERAGEi;: 1Xli!,GUTT9R TlmkI OF CONCENT..IiON gGE..q lil J�j;v PiHPT;;j g ... ... .. ... . q (jr, )j 111:111 P'l 001-yr j.1 :' I 10. 1 SUB, MOW.. KiiM I .:. . �llC BASIN: :BASIN": "g ji :PII : N!cfs Al 1 0.60 1.27 7.22 25.77 24.11 1.60 4.50 0.77 2.72 A2 2 .2.00 2.32 4.67 10.67 9.23 2.40 7.00 1.89 6.90 A A3 1- 1.50 2.01 4.23 24.92 .22.30 1.60 4.60 1.59 5.68 A4 J 2.00 2.32 4.46 29.11 26.38 1.50 4.30 0.77 2.77 Al +4 ---lL 2.59 -3.22 9.84 6.44 2.60 7.00 4.35 14.63 0[:: TST, INC. CONSULTING 811/97 ENGINEERS 000-hydl I where L is the length of overland flow in feet (limited to a maximum of 500 feet), S is the average basin slope in percent, C is the composite runoff coefficient, and Cf is the storm frequency coefficient. The formula limits the product of CCf to 1.0 and when the product exceeds this value 1.0 is used in its place. Gutter (or channel) travel times were determined by calculating the flow velocity within the conveyance element assuming a flow depth equivalent to a minor storm. The travel time was then determined by dividing the gutter flow length by the velocity. This procedure for computing time of concentration allows for overland flow as well as travel time for runoff collected in streets, gutters, channels, or ditches. The time of concentration for the design point was taken as the greatest time of all the contributing subbasins. 3.2 Drainage Plan Development The proposed drainage plan consists of a combination of overland flow and gutter flow. The runoff will sheet flow across the parking lot into gutters on the upstream side of landscaped medians, then concentrate at a proposed low point with a 15' Type `R' Inlet. From there, the runoff is carried by storm sewer pipe to a grass -lined swale with a 2' concrete pan. Runoff is then directed into a larger existing swale and routed to a retention/detention pond south of Preston Jr. High School. Runoff on the extreme west side of our site is swaled with a 2' concrete pan and directed to the existing swale on the south side of the project. Gutter flow in the street and parking area will be collected at a low point with a curb inlet and then conveyed to the pond via storm sewer pipes and swales discussed above. Subbasins were delineated based on proposed grading. Final grading and basin delineation are shown on the Final Grading, Drainage and Erosion Control Plan sheets which can be found in the back of this report. Basin delineation was grouped under one basin with 5 subbasins. The school building itself is the major separation points between the subbasins. All flow is routed around this building and eventually ends up in an existing swale at the downstream end of the site and then carried to a retention/detention pond. Subbasins Al and A2 represent runoff areas on the west and south sides of the site. Subbasin A5 represents the parking lot and north side of the school. Subbasins A3 and A4 are for the east and north side of the project. Design points are placed at the downstream ends of each subbasin for runoff calculations. The results of the Rational Method Hydrologic Analysis can be found in Table 1 with the methodology of calculations shown in Appendix A. C F �` 5 , K j 3.0 Developed Conditions Plan 3.1 Design Criteria The drainage system presented in this report has been developed in accordance with the criteria established by the City of Fort Collins Storm 'Drainage Design Criteria and Construction Standards Manual (SDDC) dated May 1984 and revised in January 1991. Where applicable, design guidelines and information were also obtained from the Denver Regional Council of Government Urban Storm Drainage Criteria Manual (USDCM). l Developed condition hydrology was evaluated based on the 10-year and 100-year storm ,e1 frequencies as dictated by Table 3-1 of the SDDC manual. Detention of developed flow is provided offsite in an existing retention/detention pond located on the Preston Jr. High School lsite. A discussion of the detention pond is provided later in this report. Because of the limited size of the subbasins on the site, the Rational Method was selected to calculate runoff. The Rational Method utilizes the SDDC manual equation: Q = CCfIA where Q is the flow in cfs, C is the runoff coefficient, Cf is the storm frequency coefficient, I is the rainfall intensity in inches per hour, and A is the total area of the basin in acres. The runoff coefficient, C, was calculated from Table 3-3 of the SDDC manual based on the proposed developed condition land use. A composite runoff coefficient was calculated for each sub -basin based on the percentage of impervious surface (C = 0.95) and pervious surface (C = 0.20). Cf was taken from Table 3-4 of the SDDC manual and was determined to be 1.0 for the 10-year storm and 1.25 for the 100-year storm. The appropriate rainfall intensity was taken from the rainfall intensity duration curve in Figure 3-1 of the SDDC manual. To obtain the rainfall intensity, the time of concentration had to be determined. The following equation was utilized to determine the time of concentration: tc = tj + tt where tc is the time of concentration in minutes, t; is the initial or overland flow time in minutes, and tt is the travel time in the gutter in minutes. The initial or overland flow time was calculated with the SDDC manual equation: t; = [1.87(1.1 - CCf)L"']/(S)0.33 4 F J zo Historic Conditions Runoff from the northern end of the site sheet flows at flat to moderate slopes to an existing swale at the south end of the site. The runoff is collected in a channel and conveyed east to a retention/detention pond south of Preston Jr. High School. Vegetation is sparse consisting mostly of dryland grasses and volunteer alfalfa. An existing 4' concrete irrigation lateral flows west to east along the northern side of the property. This ditch is to be removed during construction of this project. A second 4' concrete irrigation lateral flows north to south along the western side of property. This ditch is still in use l by others and will remain in use after this development is completed. It E 3 I I Figure 1 - Vicinity Map zf AKMON�I/."Ay y'l,� '/'! 9 �COLLINDA F O z¢ t,nr.n...2 C"T \ c •z= F C7r� / ,S 4j,O WDUSMJA ¢ m�-U� ��pCHE#R�OWPFR-p R<O %F.9: \ D C7 6 FAR9Qey_C3 9 I # PARK w�' y ZDPA CT STONE CT"�L =Sc '901 DR'- st f, I2 TICONDEROpGA Dfl 1 . '- a any � WAPITI RDA O I W 1 6Sr WARREN p'+ ;, 3 6RRT NY C7R. • _ . ¢s I YOT� L p�0 NTELOP S w ¢ O D20 i Fpq�3,_ PARK±�� " 4SDORCHESTERCT, WO UMq'� O �O' S! �- zI ACT rc� N�BOtlTM.R 7S �'r 6 DEV V7VE 3; •': PL�y 0~ pK ¢ApPLEICo� ty`,t g" ' O' A LA COLL/NOALE++ �'p[��nl y,IGr+���� 2 W SNEPARDS +r' GOLF:�i»Yd I' �{r`C lNDALE ,\4.��wC !N� 'Y SCHOOLCOURSEx }' V' .r �- BUS/NESS , �s�.`Q =0 t�, `�`OA AD Z CTI m x, ¢I I- ` zzU xr� 1 PA 3'p� r O� rr0 x RLIE LA Y3 5j,2 R R EtlHURR5 RD >.000 URST DR. D $�INg���a,0a 1 NOt�` p- ,x �="' r �'_ r..j ¢O. _ •c'.,,. wx:STON ATzw UNTON O w¢OW � SCHOOL R T T' P+Y N Q• SU Rom:'- :: V-H' RRINf3. CA P 301 L S �N CT i 20 �� I SUNGGHT CT Oj=yF IR TCHKIg �+�'?' W~ ,,,,� l 0' 2 TpLICHSTONE CT p = B © SUMMERS p�1'' 9 -`.3 BRIDGESTONE CT °mac c ° �Z 49 QU) N T �r Cl a. �` [ N pr ' CF�f.O� S�cM•OO 1 STONE CRST .. �. ` �I STONEC7 PR JE T E'. O I], Sc I RMONY wr W w 4 WA ¢ �mMn-Zo-!KRusE JaeO�Gtlu prz. �= W Co O�D er 2QCSCHDCL t O W2 lop LO ATI N m� s w A 4,p„J T.INIBERL11 LA q CA M R RD MOUNTAIN m OAKR/DGE::..> BEHAV O/ RAL 9 P ON ` .. BUS/NESS ? HEAL7N P sC OL .. pK 1-CARESYSTEMS ��p TIMBERIY fl,Q�1 INDI11 G CIR N T I �lR�''- 2JAMISON z� K PORT CT i. INDIGOiCT tUL R SILK CT�S _, 6T DR 3M ER CT V K LNE OAK :GZ O TERAAC R7 D. T S PALM O RIDG _ '+ NIN ARK D OB� P na.. SS L o AVENACT :T RAEV T�Bi_. j '�O )•P pKRy ANTERp �W �x'flg R? 1�RDR p ,�. C7IFJDTG�CIR S W�I{kx �7 FpRp-�rCT f CTO Cp JT� C2 I+ OAI�GT T,Ty/1l CTOgft kRjt CT IclOp. T OT,q 4 Sy`z� C t SNOW E$A CT 1� 2 TIMBER CREEEK CT SP ISH 7 � n,, I$TERIA•CT yDRI ZANOM , S NII EBACTK CT _ A O'nm0 i EF T K7f 5 STILLS N R K ERFlYI,r^¢~ _ 191E' S 6' ¢pyg 6 MIS N CREEK DR SERE W .: �: ¢ D9PT ANG Oj 9r awz� !{FEK Clj'E9� 4- T wc1 OP QCai- �Wfw C O F OAw :... c> MACKENZIFS,h3 �^�ec ¢ m R c2 WS CATKIN T W f ~O O LC a Aloz UTOR W 1�p F /m QywPN��In .CTA TAL DO ALPL.� v- vtDAc.�.F1 OWU Om iccR RSL� �` � � 'Z• QW�ggI Q� =y 9m 3¢ _ f 1 coo0CMD We D/R _QL S I SOUTHBQIOGP1.1`� -'•% GOLFCOU � VICINITY MAP SCALE 1" = 2000' I 2 J 1.0 Introduction J1.1 Scone and Purpose This report presents the results of a final drainage evaluation of the 1999 Elementary School for the Poudre School District. A hydrologic analysis of the proposed development plan was completed to determine the location and magnitude of the storm runoff. The hydrologic data was then used to evaluate conveyance and detention facilities based on City criteria. 1.2 Proiect Location and Description The 1999 Elementary School is a proposed school site located in the Southeast '/4 of the Northwest '/4 of Section 5, T6N, R68W of the 6°i Principal Meridian. The project is south of Harmony Road between Timberline Road and County Road 11, just south of Timberwood Drive. The school will be located west of Preston Jr. High School. The site is bounded on the north by Timberwood Drive, on the east by Preston Jr. High School, and on the south and west by unplatted vacant land. A vicinity map illustrating the project location is provided in Figure 1. -� The 1999 Elementary School Site consists of approximately 10.1 acres. The development will consist of I building pad for the school building with a parking lot for 100 vehicles. There will be designated playground areas and landscaped areas. All of the street and parking areas within the —� site will be private and will be maintained privately. 7 TABLE OF CONTENTS 1.0 Introduction Page 1.1 Scope and Purpose...............................................................................................1 1.2 Project Location and Description.........................................................................1 2.0 Historic Conditions......................................................................................................... 3 3.0 Developed Conditions Plan............................................................................................4 3.1 Design Criteria.....................................................................................................4 3.2 Drainage Plan Development................................................................................. 5 3.2.1 Storm Sewer Design................................................................................. 7 3.2.2 Inlet Analysis ................. :.......................................................................... 9 3.2.3 Channel and Riprap Design.,,-- .... ... *---, .... — .... - ... — ... ---9 3.2.4 Detention Pond Analysis.............................................................4........... 12 3.3 Erosion Control.................................................................................................12 Figures Figure1 - Vicinity Map ....................................... :........................................................................ 2 Tables Table 1 - Hydrologic Calculations Worksheet..............................................................................6 Table 2 - Summary of Storm Sewer Design................................................................................. 8 J Table 3 - Summary of Inlet Analysis and Design........................................................................10 Table 4 - Summary of Riprap Design.........................................................................................11 Technical Appendices Appendix A - Rational Method Analysis Appendix B - Storm Sewer Design Appendix C - Inlet Analysis and Design Appendix D - Channel and Riprap Design Appendix E - Erosion Control Calculations Sheets Grading, Drainage & Erosion Control Regional Drainage Evaluation August 7, 1997 Mr. Glen Schlueter City of Fort Collins Stormwater Department P.O. Box 580 Fort Collins, CO 80522 RE. 1999 Elementary School Project No. 10-883-000 Dear Mr. Schlueter: We are pleased to submit this Final Drainage Report of the 1999 Elementary School for the Poudre School District. The report includes our evaluation of the proposed storm runoff interception and conveyance facilities, detention analysis, and erosion control plan. Please be advised that this report is for your information only. City of Fort Collins criteria was used in our analysis and design of drainage issues. Any comments or concerns you may have will be noted and considered. If you should have any questions please feel free to contact us. Sincerely, TST, INC. CONSULTING ENGINEERS Arlene A Xadowen, P.E. SAS/KDA/jts TST, INC. Consulting Engineers 748 Whalers Way — Building I: Fort Collins, CO 80525 (970) 226-0557 Metro Denver (303) 595-9103 Fax (970) 226-0204 /9-- Kevin D. Ash 102 Inverness Terrace East Suite 105 Englewood, CO 80112 (303) 792-0557 Fax (303) 792-9489 FINAL DRAINAGE REPORT FOR 1999 ELEMENTARY SCHOOL 'OR THE POUDRE SCHOOL DISTRICT Submitted to: CITY OF FORT COLLINS August 7, 1997