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Home My WebLink AboutRIVERSIDE-J.L. WEST - MINOR SUBDIVISION - 58-94 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTDETENTION POND BASIN A-1 HIGH .WATER LINE VOL. = 1/3 (AREA ABOVE) (DIFFERENCE IN COUNTOUR ELEV.) 2. FOR THE REMAIMDER OF THE VOLUMES BETWEEN CONTOURS (SECTION 9.2) VOL. = DEPTH/6 (A + 4AB mean + B) 3. HWL=(VOL.REQ.—VOL.LOW CUML)*6/(AREA LOW+4*AVG.AREA+AREA HIGH) 56 95'= HWLPOND; ORIFICE SIZING ORIGINAL DESIGN DATA 0.90 = Allowable Des. Release Rate cfs 54.80 = Flowline Orifice Elevation ft 0.65 = Orifice Coefficient Cd 2.15 = Avaliable Driving Head ft NOTE: 1. HORZ. PLATES WILL BE PLACED 6' BELOW GRATE 2. VERT. PLATES WILL BE PLACED AT PIPE FLOWLINE VERT. CIRCULAR PLATE 11 IF VERT. SQUARE PLATE II No Text ***** COMPUTATION OF POND SIZE ---------------------------------------------------- RAINFALL RAINFALL INFLOW OUTFLOW REQUIRED DURATION INTENSITY VOLUME VOLUME STORAGE MINUTE INCH/HR ACRE -FT ACRE -FT ACRE -FT ---------------------------------------------------- 0.00 0.00 0.00 0.00 0.00 5.00 9.00 0.04 0.01 0.04 10.00 7.50 0.07 0.01 0.06 15.00 6.35 0.09 0.02 0.07 20.00 5.20 0.10 0.02 0.07 25.00 4.70 0.11 0.03 0.08 30.00 4.20 0.12 0.04 0.08 35.00 3.85 0.13 0.04 0.08 40.00 3.50 0.13 0.05 0.08 45.00 3.25 0.14 0.05, 0.08 50.00 3.00 0.14 0.06 0.08 55.00 2.80 0.14 0.06 0.08 60.00 2.60 0.15 0.07 0.08 65.00 2.47 0.15 0.08 0.07 ----------------------------------------------------- THE REQUIRED POND SIZE = .0847646 ACRE -FT THE RAINFALL DURATION FOR THE ABOVE POND STORAGE= 35 MINUTES 3, 7OZ cv,. fit. ----------------------------------- ----------------------------------- DETENTION POND SIZING BY FAA METHOD Developed by Dr. James Guo, Civil Eng. Dept., U. of Colorado Supported by Denver Metro Cities/Counties Pool Fund Study Denver Urban Drainage and Flood Control District, Colorado ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ USER=Stewart and Associates -Ft Collins Colorado...... ......................... EXECUTED ON 12-09-1994 AT TIME 14:28:31 PROJECT TITLE: J.L. West @ Lemay & Riverside **** DRAINAGE BASIN DESCRIPTION BASIN ID NUMBER = 1.00 BASIN AREA (acre)= 0.84 RUNOFF COEF = 0.80 ***** DESIGN RAINFALL STATISTICS DESIGN RETURN PERIOD (YEARS) = 100.00 INTENSITY(IN/HR)-DURATION(MIN) TABLE IS GIVEN DURATION 5 10 20 30 40 50 60 80 100 120 150 180 INTENSITY 9.0 7.5 5.2 4.2 3.5 3.0 2.6 2.1 1.7 1.5 1.2 1.0 ***** POND OUTFLOW CHARACTERISTICS: MAXIMUM ALLOWABLE RELEASE RATE _ .9 CFS OUTFLOW ADJUSTMENT FACTOR = .945 AVERAGE RELEASE RATE _ .8505 CFS AVERAGE RELEASE RATE = MAXIMUM RELEASE RATE * ADJUSTMENT FACTOR. DETENTION SIZING FOR J.L. WEST PROPERTY NW 1/49 S.E. CORNER LEMAY & RIVERSIDE DRAINAGE CRITL ,A MANUAL RUNOFF 50 30 F_ 2 0 z w U a 10 z w a OJ 5 w cc 3 O U 2 cc w t- a F� 1 �„'■■ A„'I• r . I ��r�I■�I�■■ilk I��■■■■� :' WD :1�C�:C■■■�� .2 .3 .5 1 'S 2 3 5 10 20 VELOCITY IN FEET PER SECOND FIGURE 3-2. ESTIMATE OF _AVERAGE FLOW VELOCITY FOR "i USE WITH THE RATIONAL FORMULA. *MOST FREQUENTLY OCCURRING "UNDEVELOPED." LAND SURFACES IN THE DENVER REGION. REFERENCE: "Urban Hydrology For Small Watersheds" Technical Release No. 55, USDA, SCS Jan. 1975. 5 -1-84 URBAN DRAINAGE & FLOOD CONTROL DISTRICT No Text Standard Form SF-9 Calc'ed.By: AVE Date: 12-94 Checked By: FDB J.L. West, Tract in the NW 1/4 Section, 18-7-68 Storm Drainage System Design (Rational Method Procedure) Job N o. 542 Project: J.L. West Design Storm:2/ 10 / 100 Year J.L. West is on the Southeast comer of Lemav and Riverside NOTE: TOC computations include overland, channel • • r,- L-A December 1994 Time Of Concentration/ Intensity Calculations For: Developed Area for J.L. West By: Stewart and Associates T() = 1.87(l.1 -C*CQD ^ 1.2 (S - 1/3) T(c) = Length / (Velocity 60) Yard slopes are assumed to be 2% unless otherwise indicated. 0.58 = Runoff (C) for Basin Sub -Basin Type Flow Length Slope Time (Ti) Channel Time (Tt) Total Time Comments M sit ... ........ Y. ....... ...... ....... .......... (feet) percen (min) Vel. (fps) (min) TOC,:(mih)j t) Historic Overland 185.0 0.51 16.7 2-yearTOC .1952 Grass Channel 0.0 0.01 0.0 0.0 3 42 0 ... . ....... . . Concrete Channel 170.01 1.01 2.0 1.4 0.20 = Runoff (C) for Basin NOTES: Intensities are based on information from the City SDDCCKA Fin R-P 1 Developed A Overland 20.01 1.01 7.51 ... 10 ...... K �ras Channel 1 0.01 1.01 1 0.01 0.1 92.1 10-yearTOC 1 �14.55:L:��:: :10.-.,... 0 cri C C oncrete Channe� 195.01 1.01 1 2.01 161.:::. ... H-I 47 16],: 10110 . .... .. 10 Future Total Developed A 00 yr Developed B 0.61 = Runoff (C) for Basin Overland 45:0 1.0 6.11 .::2,75*,--. Z, Grass Channel 1 0.01 0.01 0.01 0.01 -ZO] 10-year TOC 11 4 75 104. c I Concrete Channel 225.01 1.01 1 2.01 1.91 0.64 = Runoff (C for Basin Overland 45.01 1.01 5.81 Grass Channel 0.01 0.01 1 0.01 0.0 1 10 yearTOC 434 10. I Concrete Channel 225.01 1.01 1 2.01 1.9 .4 Future Total ..yr.. ....... 0.25 = Runoff (C for Basin Overland 20:0�- 1.0 1 7.11 8 7 Grass Channel 0.01 0.01 1 0.01 0.0 4 63 10 r Concrete Channe 195.01 1.01 1 2.01 1.6 100 -year TOC 7.23 1W 0.76 = Runoff (C) for Basin Overland 45:0:T- 1.0 4.21 rT7777M Grass Channel 1 0.01 0.01 0.01 0.0 6.1 I I Concrete Channel 225.01 1.01 1 2.01 1.91 100-year TOC 7.66 100- 0.80 = Runoff (C) for Basin Overland 45.�O 1.0 3.81 1 77777771 Grass Channel 1 0.01 0.01 0.01 0 0.d I Concrete Channel 225.01 1.01 2.0 1.9 100-year TOC SITE HYDROLOGY FOR J.L. WEST PROPERTY NW 1/49 S.E. CORNER LEMAY & RIVERSIDE December 1994 COMPOSITE RUNOFF CALCULATIONS FOR J.L. West By : Stewart and Associates b:\compositwk3 Area "C"I Area 0.95 SUMMARY OF BASINS NnTF- N 3,200.0 640.0 0.20 111 Develo ed A ::i:<BASIN 36,514.0 22,238.3 - 0.61 --:�BASIN 39.714.0 25.510.8 0.64 Future 0.0 0.0 N/A = Total Construction Area N/A = Composite Site Runoff Coefficient NOTE : — All composites are based on the equation in 3.1.6 SDDCCS Manual BASIN CONSTITUENTS FOR J.L. WEST PROPERTY NW 1/49 S.E. CORNER LEMAY & RIVERSIDE PAGE 26 0.40 0.35 0.30 0 0.25 0.20 O.Z 0.10 0. ff, ESTABLISHED GRASS AND C-FACTORS FORT COLUNS, COLORADO .............. ............. ............. ............. ............. .............. ............. ............ ....... .... ............. ............. I ............. ............. .... ............. .. ......... ............... .................... ............. ............. ............. . . ...... ............. ............. ....... ............. . ... ............. ............. ............. .... ... ............. -- ------ ............ ............. ............ .......... *' ............. . . .... . ...... ............. ............. ............. .......... ............. ............. .............. ............. ...... ............. ............. ......... ...... .... .... . ..... .. 0 20 30 40 50 60 70 80 90 100 ESTABUSHED CRASS GROUND- COVER (7) FIGURE 5.1 PAGE 24 Table 5.2 C-Factors and P-Factors for Evaluating EFF Values. Treatment C-Factor P-Factor BARE SOIL Packed and smooth . . . . . . . . . . . . 1.00 1.00 Freshly disked . . . . . . . . . . . . . . 1.00 0.90 Rough irregular surface . . . . . . . . . 1.00 0.90 SEDIMENT BASIN/TRAP. . . . . . . . . . . . . . 1.00 0.50(1) STRAW BALE BARRIER, GRAVEL FILTER, SAND BAG. 1.00 0.80 SILT FENCE BARRIER . . . . . . . . . . . . . . 1.00 0.50 ASPHALT/CONCRETE PAVEMENT. . . . . . 0 0.1 1.00 ESTABLISHED DRY LAND (NATIVE) GRASS. . . See Figure' 1.00 SOD GRASS. . . . . . . . . . . . . . . . . . 0.01 1.00 TEMPORARY VEGETATION/COVER CROPS . . . . . . . 0.45(2) 1.00 HYDRAULIC MULCH @ 2 TONS/ACRE. . . . . . . 0.10(3) 1.00 SOIL SEALANT . . . . . . . . . . . . . . . 0.01-0.60(4) 1.00 EROSION CONTROL MATS/BLANKETS. . . . . . . . . 0.10 1.00 HAY OR STRAW.DRY MULCH 103- A O After planting grass seed, apply mulch at a rate of Z tons acre minimum) and adequately anchor, tack or crimp material into the soil. Maximum Slope Length (q) (feet) 1 to 5 400 . . . . . . . ... 0.06 1.00 6 to 10 200 . . . . . . . . . 0.06 1.00 11 to 15 150 . . . . . . . . . 0.07 1.00 16 to 20 100 . . . . . . . . . 0.11 1.00 21 to 25 75 . . . . . . 0.14 1.00 25 to 33 50 . . . . . . . . . 0.17 1.00 > 33 35 0.20 1.00 NOTE: Use of other C-Factor or P-Factor values reported in this table must be substantiated by documentation. (1) Must be constructed as the first step in overlot grading. (2) Assumes planting by dates identified in Table 7.4 thus dry or hydraulic mulches are not required. (3) Hydraulic mulches shall be used only between March 15 and May 15 unless irrigated. (4) Value used must be substantiated by documentation. Effectiveness Calculation Project: LS Standard Form B By: Stewart & Associates Completed: ' P,141 103 S. Meldrum Fort Collins, Colorado 80521 Date: It Erosion Control Method C— Factor Value Y — Factor Value Conunenis: GMZ; i- koo D-'?O SLUT rtQ 1 •o0 0.5� �r �yE�aNe Gauss0. o No�� rKi. 1�SNQQ,Ftn� ��2ia:. 1�a�uc� �oc Ciao ._,ic 30 ooaS� - vNDMe 1000 S¢. �-'Ooq HDI/SF—B:1989 STEWART$,�S..JCIATE$ PH. 482 933D1RFAX 482 938OLLINS, CO 80521 Consulting Engineers and Surveyors By: AU Q Date: 11- 3 - Client: 7 A- W e`T Sheet No. of Project: 2 nF Ce�"C:, i �I S Subject: SE7e�<z: I. I I III I, I I E i I I I I• i I I I I I i _' lTE_ PrI, lht L?It1v/i+22_+_�F_�i1�E FLor�w2q Au(L'W��. � j,YR��i �D. ...;le-•.�5'is7�cTloi� .`Wig i �(;E �A �a� e2 I I� f C Cr�siwc�lo U- t U' c IILSS TH A i I I l,L i Y'�-Z I 1�I i_-117�.P'�'51 I I I I, A is( t�. 1ta- o.>i4 1 S0.» 4i C)es .Slag or-; sip I _O;c_i_r3�0C�- j�vNO�nno.i i S..1.1�1h�Q Tr�i �P iL (° i ODD; .mot Ll. ...CjZ.ao�cc... �� SINCCu(Z,`ialCM' i�izS C(�itc D+��s�ll Fo' �- I I � , L i4Z INl, t'(� `� i zr i Ft) (-Lw I i ili�!I, II!!i it Ill.l� I I �I I I.. I I I ,I I I I I I i I I I lil I I l I I ( I !I,I �Illil I i Vo FLOW LENGTH (FT) �100 200 300 400 500 . 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2500 3000 3500 4000 4500 5000 PERFORMANCE STANDARDS FOR FORT COLLINS, COLORADO -- - --- ----------------------- ---------------------------------------------------------- SLOPE (%) - 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 6.0 7.0 8.0 9.0 10.0 20.0 30.0 40.0 50.0 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -------------------- 70.9 74.6 76.8 78.4 79.5 80.3 81.1 81.6 82.1 82.5 83.0 83.4 83.6 83.8 8 72..0 76.3 78.2 79.5 80.5 81.2 82.1 82.5 82.8 83.2 83.6 83.9 84.0 84.2 8 72.4 77.0 78:8 80.0 80.9 81.6 82.5 82.8 83.1 83.5 83.8 84.1 84.2 84.3 8 72.6 77.4 79.1 80.3 81.2 81.8 82.7 83.0 83.3 83.7 84.0 84.2 84.3 84.4 8 72.7 77.7 79.4 80.5 81.3 81.9 82.8 83.1 83.4 83.8 84.1 84.3 84.4 84.5 8 72.8 77.9 79.5 80.6 81.4 82.0 83.0 83.2 83.5 83.9 84.1 84.3 84.4 84.5 8 72.8 78.0 79.-7 80.8 81.5 82.1 83.0 83.3 83.5 84.0 84.2 84.4 84.5 84.5 8 72.7 78.1 79.7 80.& 81.6 82.2 83.1 83.4 83.6 84.0 84.2 84.4 84.5 84.6 8 72.7 78.2 79.8 80.9 81.7 82.2 83.2 83.4 83.6 84.1 84.3 84.4 84.5 84.6 8 72.7 78.3 79.9 81.0 81.7 82.3 83.2 83.5 83.7 84.1 84.3 84.4 84.5 84.6 8 72.6 78.3 79.9 81.0 81.7 82.3 83.3 83.5 83.7 84.1 84.3 84.5 84.6 84.6 8 72.6 78.4 80.0 81.0 81.8 82.3 83.3 83.5 83.7 84.2 84.3 84.5 84.6 84.6 8 72.6 78.4 80'.0 81.1 81.8 82.4 83.3 83.6 83.8 84.2 84.4 84.5 84.6 84.6 8 72.5 78.5 80.1 81.1 81.8 82.4 83.4 83.6 83.8 84.2 84.4 84.5 84.6 84.7 8 72.4 78.5 80.1 81.1 81.9 82.4 83.4 83.6 83.8 84.2 84.4 84.5 84.6 84.7 8 72.4 78.5 80.1 81.1 81.9 82.4 83.4 83.6 83.8 84.2 84.4 84.5 84.6 84.7 8 72.3 78.5 80.1 81.2 81.9 82.4 83.4 83.6 83.8 84.3 84.4 84.5 84.6 84.7 8 72.3 78.6 80.1 81.2 81.9 82.4 83.4 83.7 83.8 84.3 84.4 84.5 84.6 84.7 8 72.2 78.6 80.2 81.2 81.9 82.5 83.5 83.7 83.9 84.3 84.4 84.5 84.6 84.7 8 72.2 78.6 80.2 81.2 81.9 82.5 83.5 83.7 83.9 84.3 84.4 84.6 84.6 84.7 8 71.9 78.6 80.2 81.3 82.0 82.5 83.5 83.7 83.9 84.3 84.5 84.6 84.7 84.7 8 71.6 78.7 80.3 81.3 82.0 82.5 83.6 83.8 84.0 84.4 84.5 84.6 84.7 84.7 8 71.4 78.7 80.3 81.3 82.0 82.6 83.6 83.8 84.0 84.4 84.5 84.6 84.7 84.7 8 71.1 78.6 80.3 81.3 82.0 82.6 83.6 83.8 84.0 84.4.84.5 84.6 84.7 84.8 8 70.9 78:6 80.3 81.3 82.0 82.6 83.7 83.9 84.0 84.4 84.6 84.6 84.7 84.8 8 70.6 78.6 80.3 81.3 82.0 82.6 83.7.83.9 84.0 84.4 84.6 84.7 84.7 84.8 8 ------------------------ 4.0 84.7 84.8 84.9 84.9 4.3 84.8 84.9 84.9 84.9 4.4 84.8 84.9 84.9 85.0 4.5 84.8 84.9 84.9 85.0 4.6 84.9 84.9 85.0 85.0 4.6 84.9 84.9 85.0 4.6 84.9 84.9 85.0 4.6 84.9 84.9 85.0 4.7,84.9 84.9 85.0 4.7 84.9 84.9 85.0 4.7 84.9 84.9 4.7 84.9 84.9 4..7 84.9 85.0 4.7 84.9 85.0 4.7 84.9 85.0 4.7- 84.9 4.7 84.9 4.7 84.9 4.7 84.9 4.7 84.9 4.8 4.8 4.8 4.8 4.8 4.8 Rainfall Performance Standard Evaluation J.L. Wat 7 Project: S. �. CIM ,a (F } 21 �q, bE Standard Form A By: Stewart & Associates Completed: N—C 103 S. Meldrum Fort Collins, Colorado 80521 Date: I l / 3 / l Developed Subbasin Erodibility Zone Asb acres Lsb feet Ssb % Lb feet Sb % PS % �t t-10DC-ZIk-%F Q ALL. U.i.1 1� C�,� -71 ,0 HDI/SF—A:1989 STEWART&,S.,JC(ATES 10 S. ME 3DiFFAXFORT gOLLINS, CO80521 Consulting Engineers and Surveyors By: Date: Client: 5•L• LJP-S i Sheet No. I of f Project: ILa7i- N-NzVb Jr of p., Subject: �•_�,.IAC.C43$�l�S4�. } I I I I, II,I I�. I il�lll I I Sig ; ' I i ( I III: II I ; II- !� I I it j�lilillil';�, I ' ; i I , , I I I I j •• CONSTRUCTION SEQUENCE PROJECT: • STANDARD FURI.1 C SEQUENCE. FOR 19 iS ONLY COMPLETED BY: DATE: 11 - Z-14 i.._icate by use of a bar line or symbols when erosion control measures will be installed. Major modifications to an approved schedule may require submitting a new schedule for approval by the City Engineer. YEAR I 5S MONTH�_�?__ OVERLOT GRADING � � ! ;. I - i ---{ WIND EROSION CONTROL Soil Roughing f Perimeter Barrier Additional Barriers { Vegetative Methods Soil Sealant Other RAINFALL EROSION CONTROL STRUCTURAL: Sediment Trap/Basin Inlet Filters Straw Barriers Silt Fence Barriers Sand Bags Bare Soil Preparation Contour Furrows Terracing Asphalt/Concrete Paving Other VEGETATIVE: Pennanent Seed Planting Mulching/Sealant Temporary Seed Planting -Sod Installation Nettings/Mats/Blankets Other I --------------------------------- �i I I � TRUCTURES: INSTALLED .BY 6 .0 . MAINTAINED BY EGETATION/MULCHING CONTRACTOR �� Pt ATE SUBMITTED \\ -14 APPROVED BY CITY OF FORT COLLINS ON 01 •-C:1989 i 'I it �I EROSION CONTROL CALCULATION FOR J.L. WEST PROPERTY NW 1/4, S.E. CORNER LEMAY & RIVERSIDE EROSION CONTROL REPORT The 0.91 acre site will not require any special means to control potential for wind and rainfall erosion. Moderate wind and moderate rainfall erodibility characterize the project area. The site is surrounded by existing developed property that will need to be protected during construction activity. This protection will take the form of structural method identified in the SDDCCM. Highest exposure to erosion during the construction will be at the point of rough grading for the parking area. Before any construction begins, a silt fence will be installed around the perimeter of the project with a gravel inlet filter placed at the Lemay Street curb inlet. These factors alone will suffice in providing the performance standard, 71.0 percent, calculated for the site. The effectiveness of these measures will be 94.8 percent, well above what is required. With the accelerated construction generally incorporated for this type of project no concern has arisen because of erosion concerns. Please reference the erosion calculations included as part of this total report submission package. Page 5 Final Storm Drainage Report J.L. West CONCLUSIONS This use -by -right project does not present any concerns to the adjacent land owners or land use. Detention is being provided onsite with the undetained areas being subtracted at the 100-yr rate from the 2-yr allowable historic release rate. No records are available regarding the pipe network on the East side of Lemay. This methodology will provide a level, of confidence that the existing pipe network will not be overwhelmed in either the 2-yr or 100-yr events. Should questions arise during your review for approval of this storm drainage design please feel free to contact Alex Evonitz or myself so we may help in your understanding. Respectfully, Richard A. Rutherford, P.E. & L.S. # 5028 qF R • cs 5028 _ Page 4 Final Storm Drainage Report J.L. West DETENTION A detention pond is being included,in the design of the J.L. West property. The pond is being sized to account for future development which has been conceptually shown by the architect. Using the FAA method to establish the pond size, and the 2-yr historic rate minus the 100-yr undetained runoff led to a volume of 3,702 cu.ft. being required. Under future condition the runoff coefficient increased from the current developed value. This increase went from a weighted value of 0.61 to a future value of 0.64. Weighting of these values is following the methods outlined in the SDDCCM. Inlet control is being used to regulate the outlet flow rate. The 0.9 cfs was the result of the calculation 1.03 cfs(2-yr site historic) minus the undetained (100-yr) 0.13 cfs equaling the 0.9 cfs rate. The pond release will be directed into the existing curb inlet as mentioned, with a 12-in ADS pipe conveying the flow. No information is available regarding the actual pipe network going to the Poudre River, but this design method is sufficiently conservative to assure no complications. Page 3 Final Storm Drainage Report J.L. West There is a 12-inch outlet pipe exiting this inlet, that releases into the Poudre River. The river is ± 500-ft north of the project area and crosses Lemay. This inlet will be the point of release for the newly constructed detention pond on this project. A new 12-in ADS pipe will be connected to this inlet that will be installed as the outlet to the detention pond. The following table is a summary of the site hydrology: HYDROLOGY SUMMARY TABLE J.L. WEST BASIN C Q10 (cfs) TOC(min) Q100(cfs) TOC(min) COMMENTS HISTORIC 0.58 * 1.0 18.1 N/A N/A * 2-YR (Q) DEV."A" 0.25 0.06 9.2 0.13 8.7 UNDETAINED DEV."B" 0.76 2.43 8.0 4.89 6.1 DETAINED "UT Z; rur.ure aevelopmenti nets peen 111u.LUUeU ror ueLenLlon sizing, and the release rate has been adjusted down for the 100-yr undetained. HYDRAULICS No specific hydraulic design will be a part of this report. The only hydraulic element that will be considered is the orifice sizing on the outlet from the new pond. The orifice size will be 2.38-in radius for a round opening with the available driving head at the pond HWL of 4956.95-ft. Because of the historic condition of the site and the inability to identify specifics associated with the piping to the Poudre River the approach taken is within the criteria of the SDDCCM. Page 2 Final Storm Drainage Report J.L. West HYDROLOGY Historic hydrologic conditions on the site have been established using the roofing company as existing. Years before the improvements were made at the Riverside, and N. Lemay intersection that land use, building and outdoor storage, existed. Using information from topography collected in. 1980, the building was 6734-sq. ft. and the gravel covered the entire site. This led to a historic runoff coefficient of 0.58 and a time of concentration (TOC) for historic conditions of 18.1 minutes. Using "heavy soils" with slopes of less than 2 percent, the Rational Method yielded 2-year direct runoff of ± 1.0 cubic feet per second (cfs). This runoff was released as sheet flow into the flowlines of Riverside and Lemay. Detention will now be provided for this site allowing nothing greater than the 2-year historic mentioned. Following construction of the current proposal and anticipating the future development, the Rational Method showed flows of 2.4 cfs and 4.9 cfs for the 10 and 100 year events respectively. Important to note is that these runoff rates are based on the additional parking and a second small structure suggested on the architectural plan. Detention will be provided with releases directed into the existing storm drainage collection system along Lemay. At a location approximately 100-feet South of the Lemay & Riverside intersection, on the East side of Lemay, is a 3-foot combination inlet. FINAL STORM DRAINAGE REPORT FOR NW 1/4 SECTION 18-7-68 Southeast corner of Lemay and Riverside GENERAL SITE The project proposed for this site is a drive thru restaurant on the 0.91 acres parcel. This parcel is zoned C. commercial, and the restaurant use proposed is consistent with current land use planning. Land use is considered a "use -by -right," by the City of Fort Collins Planning Department. Historically indoor storage for B&M Roofing was housed in a metal building onsite, including a gravel parking lot. In approximately 1991 the steel building was dismantled and only a gravel parking along with some concrete pads remain. Adjacent land uses include the Fort Collins Firestone Tire Store on the South off Lemay Avenue (Lemay) and Autobahn West car repair shop on the East addressed off Riverside Avenue (Riverside). Both existing businesses have been graded and built so that no runoff from offsite will be directed onto this project. Following the dismantling of the B&M Roofing facilities the site was left with a rough irregular surface that has become overgrown with dryland grasses and weeds. I r. • • -11 _ ss �- bp PROJECT , 9 SITE -OUT 4*1 • � tip` i - RH _ T •. J • 1 � :I I'll �_� 1 .k(. �{ IG iCCU N V, 1 Final.Storm'Drainage Report for J.L. WEST, A TRACT OF LAND IN THE' NW 1/4;, SECTION 18-7-68 Q U a November 1994 ^}Id �r•$b a3M� f�`�`Z1. yr.�.,..�r11.�,.......:. •'I': fN � ,,,. ' I I PuiiP�J�{ Wj'/Ill'1.'�� 1'II 141•..rl�llli 11 �� .t ii x Stewart & Associates Consulting Engineers and Surveyors 103 South Meldrum Street Fort Collins,. Colorado 80521 (303) 482-9331