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HomeMy WebLinkAboutDrainage Reports - 04/25/1996F1nal'l�-�r. �JC FINAL DRAINAGE STUDY AND EROSION CONTROL REPORT FOR FOOTHILLS UNITARIAN CHURCH EXPANSION "low Lnndmiirh "1 FINAL DRAINAGE STUDY AND EROSION CONTROL REPORT FOR FOOTHILLS UNITARIAN CHURCH EXPANSION Prepared For: The Architect's Studio 117 E. Mountain Avenue, Suite 200 Fort Collins, CO 80524 ?, Revised April 3, 1996 Project No. ARST-5I8A-01-215 u CONSULTING ENGINEER Landmark Engineering Ltd. ' 3521 West Eisenhower Boulevard 4, Loveland, Colorado 80537 CERTIFICATION I hereby certify that this Drainage Study for Foothills Unitarian Church was prepared by me or under my direct supervision in accordance with the provisions of the City of Fort Collins Storm Drainage Criteria for the Owners thereof. Colo. P.E. 19195 TABLE OF CONTENTS SECTION 1 - EXECUTIVE SUMMARY DRAINAGE STUDY Introduction ........................................... 1-1 Findings, Conclusions and Recommendations .................... 1-3 1) Offsite Drainage & Existing Drainage Patterns 2) Proposed Storm Drainage System 3) Detention Facilities SECTION 2 - PROJECT DESCRIPTION Location and Project Description ............................: 2 - 1 Exhibit No. A, Existing Drainage Condition ..................... 2-3 SECTION 3 - EROSION AND SEDIMENT CONTROL APPENDIX ONSITE AND OFFSITE DRAINAGE CALCULATIONS DETENTION VOLUME CALCULATION EROSION CONTROL EVALUATION DESIGN AIDS EXHIBIT A - Drainage Plan EXHIBIT B - Grading and Erosion Control Plan SECTION 1 EXECUTIVE SUMMARY . DRAINAGE STUDY This section explains the purpose of the Drainage Study and presents a summary of the major ' findings and recommendations. The development of the recommendations is presented in the following sections of this report. Introduction The Foothills Unitarian Church is located in Tract A of the Lexington Green Second Filing, situated in the South 1/2 of the Southwest 1/4 of Section 22, Township 7 North, Range 69 West of the 6th Principal Meridian in Larimer County. The site contains 3.0335. acres. The proposed improvements for this site consist of the following: building additions, grading and paving of a 46 vehicle parking lot and miscellaneous site and landscape improvements. The purpose of this drainage study is to provide comprehensive . drainage planning for the proposed improvements. This includes identifying and defining solutions to drainage problems which may occur onsite and offsite as.a result of the improvements and identifying drainage structures and other drainage features which should be included in the improvement plans to provide a safe and economical drainage system design. This Drainage Study evaluates the existing drainage patterns for the development based on the Comprehensive Drainage Plan for this site. This includes evaluating historic runoff, investigating ' routing for design storms through the site, determining what improvements and structures are necessary along with required design capacity and evaluating offsite drainage which may be affected by the site improvements. The policy and guidelines in the 1984 City of Fort Collins Storm Drainage Criteria and Construction Standards Manual have been utilized for planning drainage facilities. A major storm drainage system and a minor storm drainage system have been planned and designed as shown on the Drainage Exhibit. The major storm drainage system is designed to convey water from a 1-1 ' 100-Year Storm through the site in a. manner which minimizes health and life hazards, damage to structures and interruption to traffic and services. The minor storm drainage system is ' designed to convey water from a 2-Year storm and/or nuisance flows through the development with a minimum disruption to the site and traffic flow. ' The Spring Creek Master Drainageway Plan completed for the City of Ft. Collins by Engineering ' Professionals, Inc. was utilized as a reference for this Drainage Study. ,. Findings, Conclusions and Recommendations ' The principal findings, conclusions and recommendations which arise out of this Drainage Study are presented as follows. These findings are supported by the detailed material presented in the body of the report. ' 1) Offsite Drainage and Existing Drainage Patterns The site lies in the Spring Creek Drainage basin in the reach East of Taft Hill Road as identified by the Spring Creek Drainageway Planning Study. Spring Creek crosses Drake Road approximately 300 feet East of the property site. The 100-Year flood plain elevation at the Drake Road crossing is approximately 5057. The lowest elevation of the site at the Southeast comer is 5060. There is no offsite drainage which is routed through the site. The drainage boundaries adjacent to the site are shown on the Existing Drainage Condition Exhibit. This site is situated in the portion of the Spring Creek Basin that drains South to Drake Road and East to Spring Creek. Offsite drainage flows from the North are intercepted by Yorktown Avenue and Drake Road, and then conveyed East to Spring Creek. The area which drains to the Southwest corner of the ' site at the intersection of Yorktown Avenue and Drake Road is comprised of approximately 20.7 acres of urban residential land. Attached to this report is a draft of the "Final Drainage Report for Drake Road Improvements Between Dunbar Avenue and Taft Hill Road," dated January 10, 1996, by Lidstone & Anderson, Inc. This draft report indicated a 36" diameter storm sewer will be installed in Drake Road adjacent to this site. The storm sewer and street system will have sufficient capacity to convey 1-2 [1 the existing 2-Year, 10-Year and 100-Year frequency storm runoff from this site. Therefore, the detention pond release rate will be restricted to the existing peak runoff rates. 2) Onsite Storm Drainage System ' The onsite drainage system consists of overland sheet flow from the existing parking area and a portion of the existing structures to Yorktown Avenue. The portion of the site that drains to Yorktown Avenue is approximately 0.68 acres or 22% of the site area. The remainder of the site, approximately 2.35 acres, consisting of the buildings, proposed parking lot and landscape areas ' drain by sheet flow to the North gutter on Drake Road. ' 3) Detention Facilities ' According to the Spring Creek Master Drainageway Plan on site detention is not required. However, according to the City of Fort Collins Drainage Design Criteria, detention facilities are ' required if the increased flow form the developed conditions exceed the specified conveyance capacity of the street receiving the drainage flow. As the attached draft, Final Drainage Report for Drake Road Improvements illustrates; the conveyance. capacity of the street is adequate for current conditions for the 2-Year initial storm and the 100-Year major storm. Therefore, detention ponding will be provided in the West parking lot to detain the difference between the current 100-Year runoff and the developed 100-Year runoff. As shown on the attached calculations, the required volume of detention is 2927 cubic feet and approximately 3015 cubic feet of detention will be provided. The detention pond 100-Year outflow will be restricted by a 6" diameter pipe which will limit the runoff. The historic 100-Year runoff rate for Area A4 is 1.41 cfs and the undetained 100-Year developed runoff rate associated with the proposed construction is 0.50 cfs. Therefore, the pond's 100-Year release rate will be the difference between historic and undetained developed runoff. The 100-Year release rate will be 0.91 cfs. The Two -Year pond outflow will be restricted by a 3" diameter pipe to limit the runoff to the difference between the historic and the undetained developed runoff. The 100-Year ponding depth is limited to 1.0 feet. Any storm in excess of the 100-Year storm will overtop the berm and sheet flow into Drake Road. 1.- 3 4) Drake Road Improvements The City of. Fort Collins is planning construction of major improvements to Drake Road during the summer of 1996. The proposed improvements include roadway widening, adding bike paths and raising the grade at the Spring Creek crossing with the construction of a new bridge. The proposed construction may increase the conveyance capacity of Drake Road to the extent that the increased flows from this project may not exceed the capacity of Drake Road.. Increasing the conveyance capacity of Drake Road may eliminate the need for detention storage for this site. When the construction plans for Drake Road are complete the conveyance capacity should be recomputed to determine.if the parking lot detention can be eliminated. If any modifications to the drainage facilities are made after the plan approval, a plan revision must be submitted to and approved by the City of Fort Collins Stormwater Utility. r . 1-4 k [1' 1 H L� I I SECTION 2 PROJECT DESCRIPTION This project description defines the limits and general topography of the.study area and provides a description of the proposed construction improvements. Location and Project Description The study area for drainage evaluation is the area within the platted boundary of Tract A of the Lexington Green Second Filing, and the offshe evaluation of the tributary drainage area North of Drake Road. The study area is located in the. South 1/2 of the Southwest .1/4 of Section 22, Township 7 North, Range 69 West of the 6th P.M. and is within the city limits of Ft. Collins, Colorado. The site is bounded on the North by Yorktown Avenue, on the West by Yorktown Drive, on the South by Drake Road. Access to the site is from Yorktown Avenue. The existing 3.0335 acre site is comprised of a 7,810 square foot building and a 25,212 square foot asphalt paved parking area. The proposed improvements consist of an approximately 3,550 square foot building addition on the North side of the existing building, a 1,980 square foot building addition on the South side of the existing building, an 17,711 square foot asphalt parking area on the West property boundary and 2,620 square feet of sidewalk. The existing and proposed impervious lot coverage for areas draining to Yorktown Avenue and Drake Road is as follows: 1) Yorktown Avenue Drainage Basin Feature Building Walks Parking Total Impervious Turf & Landscape Total Existing Area Net Proposed Total So. Ft. Area (Sa. Ft.) Developed (Sa. Ft.) Acre 0 1644 1644 0.04 801 0 801 0.02 14,327 0 14,327 0.33 15,128 1,644. 16,772 0.59 14,324 <1644> 12,680 (�29 29,452 0 29,45.2 0.68 Ac. 2-1 % Impervious Existing = 15,128/29,452 = 51A % Impervious Proposed = 16,772/29,452 = 56.9 2) Drake Road Drainage Basin Existing Area Net Proposed Total Feature So. Ft. Area Mi. Ft.) Developed (So. Ft.) (Acre) Main Building 7,810 4,017 11,827 0.27 Out Building 0 338 338 0.01 Walk 2,977 2,621 5,598 0.13 Parking 10,885 17,711 28.596 0_66 Total Impervious 21,672 24,687 46359 1.07 Turf & Landscape 80,853 <24.687> 56,166 1_28 Total 102,525 0 102,525 2.35 % Impervious Existing = 21,6721102,525 = 21.1 % Impervious Proposed = 46,359/102,525 = 452 The current and proposed zoning for the site is residential RL. For that portion of the site where the proposed construction is planned, the topography slopes to the South at an approximate 3% slope. The grades of the perimeter streets are respectively: Yorktown Drive at 2.8% Yorktown Avenue East and South at 2% Drake Road East at 1.5 to 1.0% 2-2 SECTION 3 EROSION AND SEDIMENT CONTROL This report describes methods which are recommended to control wind erosion, water erosion and sediment during and after the construction of drainage structures and site grading. DISCUSSION The clearing and stripping of land for site grading, overlot grading, or for the construction of drainage structures, and swales, may cause high localized erosion rates with subsequent deposition and damage to offsite properties. Uncontrolled, such erosion could destroy the aesthetic and practical values of individual sites, and cause damage to downstream property. In general, erosion and sediment control measures may consist of minimizing soil exposure, controlled runoff across exposed areas, and sediment control at drainage structures. Each of these measures is described below and should be utilized by the developer and/or the contractor during any construction activity which occurs at this site. GENERAL EROSION AND SEDIMENT CONTROL MEASURES Minimizing Soil ExVosure: Where practical, the construction area and duration of soil exposure should be kept to a minimum. All other areas should have a good cover of vegetation or mulch. Grading should be completed as soon as possible after commencement. A temporary cover. crop, 1 a permanent vegetative cover crop, or other landscaping should be established in the disturbed areas. Revegetation may consist of native grasses, lawn..grasses, or various winter wheat. Decorative rock, flower gardens,.or shrubs may also be utilized in the final landscaping to cover the soil. Reseeded areas should be mulched with straw or hay to protect exposed soil until vegetation is established: i . 3-1 Controlled Runoff Across Exposed Areas: Where practical, construction may include constructing temporary swales to intercept and direct storm water around exposed areas. Swales can be constructed to control surface water which collects on exposed areas and prevent gross erosion in the form of gullies. Riprap, or other temporary erosion control devices may be installed to control storm water velocities across exposed areas. Sediment Control: Temporary and/or permanent sediment control devices may be installed at the ' major drainage structures and flow concentration points. Such structures can be used to intercept and trap sediment once produced and prevented from migrating offsite onto downstream property.. EROSION CONTROL PLAN The proposed erosion control measures are presented on the Grading and Erosion Control Plan of the Utility Drawings for this project. The evaluation of the Performance Standard and Net Effectiveness are presented in the Appendix. In summary, the erosion control measures consist of: 1. Installation of silt fences along Yorktown Drive, Drake Road and a portion of the East 1 site boundary. In addition, a silt fence will be installed along the perimeter of the disturbed area for the North building. additions. 2. Installation of a straw bale dike upon commencing the parking/overlot grading at the low point of the proposed parking. The straw bale dike will be removed upon completion of the drain pipe and sidewalk culvert necessary for the parking lot detention. Thereafter, a gravel inlet filter will be installed in front of the parking lot drain pipe. 3. Drill seed irrigated drought tolerant turf seed mix (hydro mulched) or turf sodded. Drill seeding or sodding will be placed during or immediately following parking lot/overlot grading. 4. Landscaping in parking islands, walkways and other disturbed areas. 3-2 i i 1 1 1 1 1 1 1 1 1 1 The cost estimates for the erosion control measures are as follows: Erosion Control Cost Estimate No. Item Qty., Unit Unit Cost Total Comments 1. Drill seed with irrigated drought tolerant turf 0.93 Ac. $1,300.00 $ 1,209.00 $0.0298/s.f. 2. Inlet gravel filter 1 Ea. 300.00 300.00 3. Straw bale dike 1 Ea. 300.00 300.00 4. Silt fence 1005 L.F. 3.00 3,015.00 Construction Cost $ 4,824.00 50% of Construction Cost 2,412.60 . Total Security $ 7436.00 1. Reseeding Construction Cost 50% of Construction Cost Total Security Total Disturbed Area Citv Reseeding Cost *2.17 Ac. 650.00 $1,411.00 $0.0149/s.f, 1,411.00 706.00 $ 29117.00 3-3 1 1 1 1 I 1 f 1 1 r 1 1 CERTIFICATION I hereby certify that this Erosion Control Report for The Foothills Unitarian Church was prepared by me or under my direct supervision in accordance with the provisions of the City of Fort Collins Storm Drainage Design Criteria and Construction Standards for the Owners thereof. Patrick M. Mesta Colorado P.E. 13 3-7 r A DRAINAGE CALCULATIONS [- I H i' H ld- 1- 2/S coo or ev r N •F� I 1 1 1 1 1 1 .- Pro�Oose� l--o -'7S (S( 1b6) Pro/Cb sed C. _ Al 2 s ze .. 13 Zy G TG' ?Or xe7.=/37.rryiv - --- .--_ :. __,(,./oo�.ycrr___=_.�o,Z_Ff.�it._l/fir•-- -�-.-_..� _...---.�_.._ ....._. ..- ----- :.. .:. _.. .-..__ _--- Q..2.Yecr;___=_0�_Ho��2.:�3)�.2,3_S) _ �ZA9 .cfS ._-_:-_-__.__- - ••------�----_._,__ _ _ Q /9- ye or = 0,-oC3,)$) ('•Z.35)_ 3:.s3. c Fs__...... - - _. 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'_Dis/!2s_e.__w-/._6 r__C. �.cZ✓r_ _ T'TaZ wor /.i87_C-/•/_..CCG).a"`/ 3 /`t. B i�a,�/... , • ..., - � " .�. _ � .:-.__Tc.a. =l�8�</,/-<o_zs.1l/.zs•))'l_�P.o)�(_3� §_= /3,7_r_�%�./.-- -__ - �O,WB.)-- _ - ;- Q/op-yeor Comorife t/owrs..�o,n..oreq ivifh-i�p...�%/en�io� �toT-i /1fFWt.+>l�cv,�04s_.s�, A3_'._ .. r-e/cose.no/e wpm Por-vey_Lof.!_-_._`. .' . Qa= 0,3q-O,IG� O.Z3cJr Qi4 .D.67 Ql O,G l2,1S)(0,719) _ 03 0 0 /0 =_0,4;;�` 4F,7_S)(0,7/_P),=-f,�O_'c Oroject. Foothills Unitarian Church Project. No. ARST 518AO1 ' Dentention Volume Required. Inflow Data: Design Storrrr 2 yr Drainage Area (Ac): 0.718 Runoff C x Cf: 0.67 Outflow Data: C x A: 0.48106 Design Storm: 2 yr ' Discharge Rate (cfs): 0.23 Total ' Time i Q-In Volume in Q-out Volume out Volume Win. C x A in/hr cfs CU FT cfs CU FT CU FT .10.00 0.48 2.52 1.21 727 0.23 138 589 0.48 2.12 1.02 918 0.23 207 711 '15.00 20.00 0.48 1.85 0.89 1068 0.23 276 792 25.00 0.48 1.62 0.78 1169 0.23 345 824 0.48 1.48 0.71 1282 0.23 414 068 '30.00 35.00 0.48 1.32 0.63 1333 0.23 483 850 40.00 0.48 1.22 0.59 1409 0.23 552 857 45.00 0.48 1.12 0.54 1455 0.23 621 834 ' 50.00 0.48 1.04 0.50 1501 0.23 690 811 -- 55.00 0.48 0.98 0.47 1556 0.23 759 797 0.48 0.92 0.44 1593 0.23 828 765 '60.00 90.00 0.48 0.68 0.33 1766 0.23 1242 524 120.00 0.48 0.52 0.25 1801 0.23 1656 145 150.00 0.48 0.43 0.21 1862 0.23 2070 -208 180.00 1 0.48 0.39 0.19 2026 0.23 2484 -458 I ' Project: Foothills Unitarian Church Project No. ARST 518AO1 Dentention Volume Required Inflow Data: Design Storm: 10 yr ' Drainage Area (Ac): 0.718 Runoff C x Cf: 0.67 C x A: 0.48106 Outflow Data: Design Storm: 10 yr Discharge Rate (cfs): 0.38 Time i Q-in ' Min. C x A in/hr cfs 10.00 0.48 4.40 2.12 15.00 0.48 3.75 1.80 ' 20.00 0.48 3.25 1.56 25.00 0.48 2.86 1.38 30.00 0.48 2.60 1.25 ' 35.00 0.48 2.38 '• 1.14 40.00 0.48 2.20 1.06 45.00 0.48 2.02 0.97 50.06 0.48 1.86 0.89 55.00 0.48 1.72 0.83 60.00 0.48 1.62 0.78 90.00 0.48 1.20 0.58 120.00 .0.48 0.92 0.44 150.00 0.48 0.75 0.36 ' 180.00 0.48 0.65 0.31 Total Volume In 0-out Volume out Volume CU FT cfs CU FT CU FT 1270 0.38 228 1042 1624 0.38 342 1282 1876 0.38 456 1420 2064 0.38 570 .1494 2251 0.38 " 684 1567 2404 0.38 798 1606 2540 0.38 912 1628 .2624 0.38 1026 1598 2684 0.38 1140 1544 2730 0.38 1254 1476 2806 0.38 1368 1438 -3117 0.38 2052 1065 3187 0.38 2736 451 3247 0.38 3420 -173 3377 0.38 4104 -727 7 Project: Foothills Unitarian Church Project No. ARST 518A01 Dentention Volume Required Inflow Data Design Storm: 100 yr Drainage Area (Ac): 0.718 Runoff C x Cf: 0.84 C x A: 0.60312 ' Outflow Data: Design Storm: 100 yr ' Discharge Rate (cfs): 0.91 Time i Q-In Volume In Q-out Volume out Total Volume ' Min. C x A in/hr cfs CU FT cfs CU FT CU FT 10.00. 0.60 7.20 4.34 2605 0.91 546 2059 15.00 0.60 6.00 3.62 3257 0.91 819 2438 '20.00 0.60 5.20 3.14 3763 0.91 1092 2671 25.00 0.60 4.60 2.77 4162 0.91 1365 2797 30.00 0.60 4.15 2.50 4505 0.91 1638 2867 '35.00 0.60 3.82 2.30 4838 0.91 1911 2927. 40.00 0.60 3.50 2.11 5066 0.91 2184 2882 45.00 0.60 3.24 1.95 5276 0.91 2457 2819 '50.00 55.00 0.60 3.00 0.60 2.78 1.81 5428 0.91 2730 2698 . 1.68 5533 0.91 3003 2530 60.00 0.60 2.60 1.57 5645 0.91 3276 2369 '90.00 120.00 0.60 1.85 0.60 1.43 1.12 0.86 6025 6210 0.91 4914 1111 0.91 6552 -342 150.00 0.60 1.18 0.71 6405 0.91 8190 -1785 .180.00 0.60 1.05 0.63 6839 0.91 9828 -2989 I / /�✓i .-V�IV r�.J V/V ,/ �JTI /V G—/7'CIiC(/ G/ �ETZ"/�/TiON L�oG4ME.'�.Q!>�//OE.Ds OET�,erni.VE " ✓a uJ-oE 1-3E77�4=Xl /6�C 6B. 3 GT A e"r=w fTz 7s (o`J,O '176.6 /l079 /Zz0 69. 3 7 ZGG S89f' 3o/s > t.&c h'Ecr� wow Coo ''" (4 Forme Z Y.� SToe✓--7 s Q Z _ ev a Z yR 51ati� = O.5 J`�GT ' �nr G?= c��N oe G1/cam �i� � = O•z 3�<o.65i z lsa. z�la,yes') = D, oYy s a ter= �.33 s4 /.,� y e SJv.��7 : Qio = o. 38 Cis VoLu/yJo-- o Z8 /=Or-3 f�BFTJY Jim .�oti-,o @ Lo riP Siai�i�i=0,77,=T ' /938�Co,6S) .z .3a, z Jla.6y�7 =O.o 907 S4 1--.7-= /3.0 6 sa /1/6�O �O/A PIPE - =o,o �'73 SOFT DEPns+ o� PA.o 99, - 009 = 6-7 c-o/6,5 y=,Y?. z /9 = 0,91//(o.6s) . 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Qioo �wA E_ = 3�c czf, - ., i 13 APPENDIX EROSION CONTROL EVALUATION W W W 0 w 0 000 Y+or aaa 'rrr 1 1 1 1 CdaT�ic.c.s it✓/T,4R/� .. f�UlzG�-^EIZOSI�. CDe(�Tf�dL - a9lklO /Da % . 4t fop z7; 2. GUlY E,V T Go�✓i� it/0 /J S 7 00 s� $i Op00 rr' PlllCll/Nfr^. ` 't _ .2$T.�o s JJ i j,011fJ:e4peo 7 /gor z 95 /76 SW . _. ......., ;3 _PO{aoo$E�a,�77EtJ�GdP,NEtilT _.._PROPOSED _ Da✓/(1E� = 'ECC106 AJ 77AL RL...: . •NEGv _f3LbL� ,�•nz��rla�ls�_�'�boo snJ R 5 r AWA LU9 ETA = ' 2(o ZO JT :.. ..:...._ �EG�4ti/pSc4�� (Etilff�llG�sbs �_izEs�E,d, yrs�55 r�iscr✓'r�,E . , L4AIDSCRP�r� 1c45s�ss. _- ... . _ -� . /Z,E56EDC_V / &h 7W �p<ipsC.APE c Pius ,oET4/4S . e4lT/G/9Y DrU5. -/_//E _ Reoecm � EQ h2ASS SPEGaFI�o.,._77E�EG�c/, Tf/� e v4j -RA-Groh wtl-L ee rE65b -TD Y-zov/ok- ,¢ J0, uy- .. Tb'T,4C 29¢Sz s� t O2505. 131977 s� -Z'r . ls. I M rer" is e o r;W-.4T r#5- 6&f/I O/A/Er Aab/Tio c/s 4,4N.GbMgfUGE P/Z/o'R 7-0 ©VERGbr C�Rsfa/�clH a r�fE _...�/T'E, Dl�E!?l,Or E.�/rgb/N�7� �S'PEGiA•[.c.�! �2.. �� . P.4�t/f/�14.. - eor: /S Ivor IleceSSAley Po a Tif/S sire Uldr/LL 77'A6 fi(_/ 0/,ClC-7_ ihbJ7/Tl'041S' VCAfel&L7 GDMP4E770A% ,0pB'v GdIY1P�E7-/oA/ bF E oVE1?4.077 61e4z0/NC7 �4r ICWFK/N4 tor � {�R�c✓IANeAj-r 2E LgAJC7.7G�4PlN� � RESEEa/1/4 ._....:L�jz,4SS ..Gl��t/ .GD�t�I�/l.ENG�� ..._ . ....._.. .• 1 1 1 1 1 1 1 RAINFALL PERFORMANCE STANDARD EVALUATION PROJECT: o Tii�1G.6 S .117XR1.4 Al CVaReM STANDARD FORM A. COMPLETED BY: �i(/% XAFXTA.S DATE: DEVELOPED ERODIBILITY Asb Lsb Ssb Lb Sb PS SUBBA$IN ZONE (ac) (ft) M (feet) Av5 s8*!! l� ll'li� 3. Z �ClT7l��Lrf7! . 52 8 /, 65/ . 3, 3 ,eon-o se o 730 SSA, I (3,33�f 3d(. 9.i 7 a 730 %Aa/ 3,b3 &5(�,� j f /, (z.35� /,gel 3;b3 MARCH 1991 8-14 DESIGN CRITERIA EFFECTIVENESS CALCULATIONS' PROJECT: Fo1hi/ls STANDARD FORM B COMPLETED BY: PNI ti1e5><n5 DATE: /o ?/ y5 Erosion Control C-Factor P-Factor Method Value Value Comment NYD/Id-MU�4fl:. :� ./0 /lo � ZTbuS��RE 57-1z,4W ItA:Le ho D,8 &g4verc. F& mk S71L;r A0A.4r9 .A0,41LCIj!FR 60 bit7 MAJOR PS SUB AREA BASIN BASIN (Ac) CALCULATIONS 7-0rc Bp6Z/ rMrreo r./ Go%s- s17F A.ve Ir �. I /�`� l-�/rT•GE dF ESTR-BL/SffEb TfJ1�'F SB wlc sC >7Ls7���n �L.4�-JpSGAPEo FtnE<F A-5 �STa�LISI�£4 ci�ass- Z A-,SPN-4�'l'/Gd,uG -C�/5T PKh LOr�{/IdLk) p—j4t�o Ga/�s.-�-- l� Z�/6 77 FE,tIGE_ MARCH 1991 8-15 DESIGN CRITERIA 11 EFFECTIVENESS CALCULATIONS PROJECT: r�T-1-,-1LLG Z1X117-, R1,o4A./ STANDARD FORM B COMPLETED BY: DATE: /° ✓/ �� Erosion Control C-Factor P-Factor Method Value Value Comment MAJOR PS SUB AREA BASIN BASIN (Ac) CALCULATIONS %OT L 6to, Z ORA0, 2,3yr G _ 1C GALGS. �8 I. UNi�/STurzoEt� lUttF A= fG,35 Ac D, re, 2G 23� 2 't)ISrvrzzc-p TUtt F ' jqjq"pSG4pec> fZESEEvEp C�Jz�55 m/eTc��E / OR3 3 EI(/S7', ,t).SP/-hA-LT�GONG WALK,>`BGD(�r: 4 /I�EW .ASfffFL-T�G6�/G w,oLK (� P�KI�� (or� �R2E fa'no TiGc- PvEa �: 6¢7�G, C'F% �i� DZ8 f� FG*4cz. MA-> p >r� G. 1. PE2/METE/� S/Lr'>=E,c✓GE(SEE Z. S>,Q,¢uW B/LE t�rf;E o.l7�luh �17ob.l�CRKrJ�co. Gu1zli' / NGEi �/G.� EI�,rLI�EL R-�PL�7L 45 1 .T-Nti MARCH 1991 DESIGN CRITERIA 1 1 1 1 1 EFFECTIVENESS CALCULATIONS" PROJECT: f=po7 µ��S �//TA2/.F� �fY/�Gh� STANDARD FORM B COMPLETED BY: Pi<VIle 4164--r 4 DATE: t/ 95 Erosion Control C-Factor P-Factor Method Value Value Comment MAJOR PS SUB AREA BASIN BASIN (Ac) CALCULATIONS TaTAL MARCH .1 W t 8-15 DESIGN CRITERIA CONSTRUCTION SEQUENCE - ' PROJECT: STANDARD FORM C SEQUENCE FOR 19 ONLY COMPLETED BY: Mer11/5 DATE: ' Indicate 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 MONTH J F M M J J I A OVERLOT GRADING (3l-06r GONS>"2UG7/D�t/ WIND EROSION CONTROL' (S!-n Wo L8Ul K DIN RKl �D bG 61 STTZ Soil Roughening 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: Permanent Seed Planting Mulching/Sealant Temporary Seed Planting Sod Installation Nettings/Mats/Blankets Other ' STRUCTURES: INSTALLED'BY i VEGETATION/MULCHING CONTRACTOR ' DATE SUBMITTED MARCH 1991 MAINTAINED BY APPROVED BY CITY OF FORT COLLINS ON 8-16 . DESIGN CRITERIA 'Tiohl) 1 1 P O O O 1 1 1 1 1 1 1 1 1 1 1 �1 u.a) 0.34 0.25 0 0.20 N w 0.10 0.05 0.00 MARCH 1991 Figure 8-A ESTABLISHED GRASS AND C-FACTORS FORT COIIJNS;,COIARADO 0 20 40 60 ESTABUSHED GRASS GROUND COVER W g_g 80 l0o DESIGN CRITERIA 1 1 ' O A a 0 U E z H a 0 U a a* a W z H ra 0 rn0,000 o valnlnln In o 0 o CID. 00 o MMMMOOOOOO o d VvvinlntnMMU) -W 000000c0000 o Dornolrno,o+olrno+rnrnrn000 o vvvvd vd vvvvd Inlnln M 00000COCO00000000 O n0000101010101010101010101010101C10% O v v v V v v v v v v v v v v v v v v v v N COoo0000o00000COoo00o00oCDOO O OMvtn1010101Drrrrrrrrrrrrt000C000C000 . . . . . . . . . . . . . . . . . . . . . . ... . . O v v v v v v -0 lot v v v v v v v v v v v v v -We v v v H'I o CO CO 00 CO o 0 o CD o 0 0 00 CO o CO o CO 00 CO o o CO o CO CO 0 oNMvInIn�n101010w0 0rrrrrrrrrroc0o . .dsv v dv......v..s.d...d..l.'d.d.d.d.a. al M v 00.0000oODo00000000W00000000000 O 10 O N M It v In In In In 10 10 10 10 10 10 10 10 10 10 r n r r r r .. . . . . . . . . . . . . . . . . . . . . • • . . CO Mvd'vvvvWTowvvved. v'd'vvvvvvv"WvV,d. o,0000000000000000ODo00o0000000000o00 O v0 W-4NMM V d'vvU)InLntnin nIntnIn W%D%OtO%On . . . . . . . . . . . . • . . . . . . . . . . . n M M v v v v v v v v v v v v V v V V V v v V V v v v CD CO o CD CO 00 CO CO o 00 CO CO CO o CD CO CD 00 CO 00 CD 00 00 o CO o O owwot-I'-INNMMmmoTvvvvvvvinln.lnlnt0%0 10 N) M M v v v v v v v v v v v v v V v v v v v v v v v o CO CO o OD o CO CO o CO o CO o 0 0 00 CO CD [0 o CO CO o 0 o CO t. `-'IC1 NMMMmMvvvvv V vvvvvvvvvvvvvv 0 0 00 CD 00 o 00 00 0 0 00 00 M M o CD CD CD CD .CO 00. CO CO o 00 OD p�l[1 r M0 4Mvlf)Lf)W Onnr00000DCOCDCDCT010100000 O. . . . . . . . . . . . . . . . . • . . . . . . av NNCMMMMMMMMMC'1MMM'MMMMMMv V v V v Vi o CO CO o 0 o CO o CO CD o 0 0 00 o CD CO o CD CD o CD 00 0 0 0 O 10 In co o.-i NM *sr In In In 1O 101010 W r n In r CO C0 CO 0101 v 14 NNMMM CI m M M M rn In M M M M M M M M M M M c4 c4 o CO OO CO CO CO 00 CO CO OD OD OD CO OD CO CO CO OO CO 00 OD CO CO CO CO CO Ic1 H"Ir♦Lc) no00r-INNMMMvvv V -it InInIn101010rr M N N N N. M M M C9 r1 M M M M M M f1 M M cM M cM c. M M M CO CO 00 C0 CO 00 0 o CO o CO 00 CO 00 00 CO CO o 0 o CO o o CO o CO O MN10000! cH cN M M M V V V V V V IntCllntnl0101010 M 0 H .-I Hi Hi N N N N N N N N N N N N N N N N N N N N N CO CO CO o [0 o CO CO o CO o CO CO o CO CO o CO CO o 0 0 0 o CO CO In 0m01NM V InlOnrr-ww O01(3)01010101000000' N 01OOHiHi4ri44444HiHiHHiHiHiHiHiNNNNNN nco0ocooco0ococOcoaococoDODococotDtOcocoDocDooaDOo O v0• 0m000O0000HH. .-1H• N• NN. c • 1Mr! N co0000OO.004riHir•riH•HHHHHiHHMH. H• H. 'M-.I n r o o O CO CO o CD CD o o CO CO CO CO CD CO CO o 0 o CO CO CO o In 00NCDHV InnrODON0100H -iriHi-INNNMMMMM Hi 10oc001010101010101010.000000008O8808 nrnrrnnnrrr00CID CDCO0DooCOo0DGO00CD00-o O 10 M O v r 01 O H N M M v V 0 0 In to 10 10 10 10 n r 10 10 10 ri V 10rnnrcDcOci 000OCDCDOOCOCOODCOCOcDOCOCDwmw rnrrrrrrrrrrrrnnnnrrrrrnrr In01.0v10ncoODnnn10to%01nITvMMNNM%0vriON 0 O ON NNNNNNNNNNNNNNN-NNNriHiri.-100 nrnrrrrnl�nrrrnrrrnnnrrnrrr 3EE-4- 00000000000000000000000000 0cp OOOOOOOOOO00000000000OOOaO 4 Z, T4 .-I NM V M%Dt WOO HiNMvin10r000100OMOM0 r4�W— HirIHririr•IH Hr-IHiNNMMvvm MARCH 1991 8-4 DESIGN CRITERIA 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1 DESIGN AIDS wwmww aa�dd wwr�t �a 1 :�7 A�q F 1 1 I L 0 7� // /h%A YBS� 2 YR -o/�e/�t. ri1�cnS r%��/rrj /b J7,r7 Al SsTfensi �in��ir� ioa Y/V s ro eM n e s, 7,ZO / 2</2<75 61od s, Zo 30 1,46 3, is 4 -/5; 45 /i 22 2¢ . 3 00 55 O, 99 i o, qo ZO O, 52 p, 9z /r 43 /So G, ¢3 6175 No Text 1 1 1 1 1 ' MAY 1984 .7 rL Cr o .6 H U L.L s:0.4% F=0.5 z 5 0 U � I uj .4 .3 BELOW MINIMUM ALLOWABLE I STREET GRADE .2 .I .0 0 2 4 6 8 10 12 14 SLOPE OF GUTTER (%) Figure 4-2 REDUCTION FACTOR FOR ALLOWABLE GUTTER CAPACITY Apply reduction factor for applicable slope to the theoretical gutter capacity to obtain allowable gutter capacity. (From: U.S. Dept. of Commerce, Bureau of Public Roads, 1965) 4-4 DESIGN CRITERIA DRAINAGE CRITERIA MANUAL RUNOFF .5 0' WE F- 20 z w U tr W 10 z w a. 0 5 C w cc 3 0 U 2 w F- 1 �■ ■■■l �I 11// moll oil Ell �IJI•�►I III ■/■�/�����■■■■� II NCI ■I,MA mm ■■■mv� MEAN 5 -- 1:—-...2.---3-----5........ _-..._1 _. ?....-....3.._. 5 101 20 VELOCITY IN FEET PER SECOND FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR USE WITH THE RATIONAL FORMULA. -1 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 -1784 URBAN DRAINAGE & FLOOD CONTROL DISTRICT I LOVELAND STORM DRAINAGE CRITERIA MANUAL TABLE 704 1 1 1 i 1 i 1 1 1 1 i 1 1 WEIR FLOW COEFFICIENTS SHAPE COEFFICIENT COMMENTS Sharp Crested— _ Projection Ratio (H/P = 0.4) 3.4 H 21.0 Projection Ratio (H/P =. 2,0) 4.0. H 21.0 Broad Crested _ w/Sharp U/S Corner 2.6 Minimum Value w/Rounded U/S Corner 3.1 Critical Depth Triangular Section _ A) Vertical U/S Slope _ 1:1 D/S Slope 3.8 H >0.7 4:1 D/S Slope 3.2 H >0:7 10:1 D/S Slope 2.9 H 20.7 B) 1:1 U/S Slope _ 1:1 D/S Slope 3.8 H >1.0 3:1 D/S Slope 3.5 Trapezoidal Section 1:1 U/S Slope, 2:1 D/S Slope 3.4 H >1.0 2:1 U/S Slope, 2:1 D/S Slope 3.4 H >1.0 Road Crossings Gravel 3.0 H >1.0 Paved 3.1 H >1.0 ..� ., .., M .. .. a .. awa a sue.[•c[.c[ w ADJUSTMENT FOR TAILWATER WRC ENG. REFERENCE: King Brater, Handbook of Hydraulics, McGraw Hill Book Company, 1963 =739- No Text JDAMS Spillways 41-7 .above A sub= )fMitions Is This Id for i es to appe circular i are f :se data tucted r tion- 3 285. Iles for f286 ition of .1 ower f H. r the farther ,will , pp farther ace, 0.5. Mrest nular flaw w, ilor weir. 4. 3.6 3.4 MEN COOMMEN MOMENNNEMNE��� IMM_` IMEME MEMEM ON����� IMENNEM —MENNE NOMENNEMEN IMIMMMW-MMNIMINEMEM������� IMIMMEMEMMOMIN ON �MEEM ME ME - NE WMENE NE M: NEMEN b" MEE MIM IMIMMoEMIME M MEN ___. EEM MNEENEENNEENEEN_� �am�ie_�__ �M�� i ��� �����- NEIMIMM�: C =���G AMEN IMMIMMIMo�������G��ME U., o a H 1.2 0 RS 1.6 1 Figure 283. Relationship of circular crest coefficient C. to R' for different approach depths (aerated npppe). 288—D-2441. The profiles become increasingly suppressed for larger R' values. Below the high point of the profile the traces cross and the shapes for the higher heads fall inside those for the lower heads. Thus, if the crest profile is designed for heads where H" exceeds about 0.25 to 0.3, it appears that subatmospheric pressure will occur along some portion of the profile when heads are less than the designed maximum. If subatmospheric pressures are to be avoided along the crest profile, the crest shape should be selected so that it will give support to the 2.0 overflow nappe for the smaller He ratios. Fig-. R. ure 288 shows the approximate increase in radius required to minimize subatmospheric pressures on the crest. The crest shape for the enlarged crest radius is then based on a HI. ratio of 0.3. (d) Transition Design. —The diameter of a jet issuing from a horizontal orifice can be determined for any point below the water sur- face if it is assumed that the continuity equation, Q—av, is valid and if friction and other losses are neglected. 1 1 DRAFT FINAL DRAINAGE REPORT FOR DRAKE ROAD IMPROVEMENTS ' BETWEEN DUNBAR AVENUE AND TAFT HILL ROAD PREPARED FOR: City of Fort Collins Stormwater Utility 235 Mathews Street Fort Collins, CO 80525 ' PREPARED BY: Lidstone & Anderson, Inc. 736 Whalers Way, F-200 Fort Collins, CO 80525 (LA Project No. COAEG01) 1 ' January 10, 1996 LIDSTONE & ANDERSON, INC. Water Resources and Environmental Consultants January 10, 1996 ' Mr. Link Mueller City of Fort Collins Stormwater Utility ' 235 Mathews Street Fort Collins, CO 80524 73.6 Whalers Way, Suite F-200 Fort Collins, Colorado 80525 (970) 226-0120 Re: Draft Final Drainage Report for Drake Road Improvements between Dunbar Avenue and Taft Hill Road. (LA Project No. COAEG01) ' Dear Link, Lidstone & Anderson, Inc. (LA) is pleased to submit this draft of the Final Drainage Report for 1 the improvements to Drake Road between Taft Hill Road and Dunbar Avenue. The hydraulic and hydrologic evaluation of the site, documented herein, was performed in accordance with the specifications set forth in the City of Fort Collins Storm Drainage Design Criteria Manual. For this draft report, the storm sewer design has been completed at a preliminary level. The final hydraulic analysis of the storm sewer system will be completed after the vertical and horizontal alignments have verified by the street design engineer. At the time this report was completed, we had not been given information concerning the relocation of the storm sewers and/or curb inlets due to existing utility conflicts. It is anticipated that this report will be finalized upon our receipt of final design information (to be supplied by the street design engineer) and completion of our hydraulic pipe analyses. ' If you have any questions regarding the procedures and results given in this report, please do not hesitate to call us. Sincerely, LIDSTONE & ANDERSON, INC. Christo her L. Doherty, E.I.T. ' Project Engineer 4Gr o J och, P.E. Senior ngineer ' CLD/GMtlt ' Attachment Branch Office: Box 27, Savery, Wyoming 82332 TABLE OF CONTENTS I. INTRODUCTION ......................................... 1 1.1 General......... 1 1.2 Purpose of the Study ................................ 1 1.3 Study Area and Scope of Study ........................... 3 1.4 Previous Studies ..................................... 4 H. HYDROLOGIC ANALYSIS ................................. 5 2.1 Description of General Drainage Pattern ...................... 5 2.2 MODSWMM Model Parameters and Subbasin Description ........... 5 2.3 - Results of the Hydrologic Analysis ......................... 9 III. HYDRAULIC ANALYSIS AND DESIGN ........................ 12 3.1 Allowable Street Capacities ............................. 12 3.1.1 Design Criteria and Methodology .................... 12 3.1.2 Results of the Street Capacity Analysis ................. 13 3.2 Curb Inlet Design .................................. 15 3.2.1 Design Criteria and Methodology ................... 15 3.2.2 Results of the Curb Inlet Desien ..................... 15 3.3 Storm Sewer Design ................................. 16 3.3.1 Design Criteria and Methodology .... .............. .16 3.3.2 Results of Storm Sewer Desien ...................... 18 3.4 Riprap Design .................................... 18 FIGURES/TABLES/APPENDICES/SHEETS FIGURES Figure 1.1. Vicinity Map for the Drake Road Improvements . ................ 2 TABLES Table 2.1. Summary of Design Flows on Drake Road ..................... 10 i ' TABLE OF CONTENTS (CONTINUED) Table 3.1. Summary of the Street Capacity Analyses for the Proposed Drake Road Configuration. .................... 14 Table 3.2. Summary of Inlet Design Parameters. ...................... 17 APPENDICES Appendix A: MODSWMM Subbasin Parameters ' Appendix B: Hydrologic Analysis of Drake Crossing Detention Facilities Appendix C: .Hydrologic Analysis of Existing Detention Ponds Appendix D: Modification of Cimmaron West Northwest Detention Pond Appendix E:- Modification of Kensington South Detention Pond Appendix F: MODSWMM Input and Output Files Appendix G: Appendix H: Street Capacity Calculations Curb Inlet Calculations Appendix I: Storm Sewer Calculations SHEETS, Sheet 1: SWMM Subbasin Delineation and Schematic Diagram and Location of Proposed Drainage Improvements Between the Pleasant Valley & Lake Canal and Taft Hill Road Sheet 2: SWMM Subbasin Delineation and Schematic Diagram and Location of Proposed Drainage Improvements Between Taft Hill Road and Hanover Drive Sheet 3: SWMM Subbasin Delineation and Schematic Diagram and Location of Proposed Drainage Improvements ' Between Hanover Drive and Raintree Drive I ' Drake Road is a major east -west arterial running. through the central portion of Fort Collins. Major street improvements are planned for a 3,500 foot reach bounded by Dunbar Avenue on the east and Taft Hill Road on the west. The planned improvements include widening of the street to accommodate four traffic lanes, two bike lanes and a raised median, along with construction of curb, gutter and sidewalk, and installation of all required drainage ' appurtenances. The 1,000 foot reach of Drake Road east of Dunbar Avenue to Canterbury Drive was recently widened in conjunction with the construction of the infrastructure for the 11 Preserve P.0 D. A vicinity map is included in Figure 1.1. In addition, major improvements are proposed for Spring Creek in conjunction with the improvements to Drake Road. The preliminary design of Spring Creek improvements indicate a split conveyance configuration which includes a 42-inch RCP to convey low flows and a 41- foot wide skewed bridge section to convey the 100-year flood flows under Drake Road. It is anticipated that the final configuration of the Spring Creek improvements will route the entire 100-year discharge through a 44-foot wide bridge section; the low flow pipe would not be included in the final design. In order to accommodate the proposed bridge section, a local high point will be created at the bridge. For the proposed condition, low points will be located west of Taft Hill Road, near Constitution Drive, and at the location of the existing low point near the Kensington South detention pond, which is located approximately 200 feet east of Dunbar ' Avenue. ' 1.2 Purpose of the Study ' The primary purpose of this study is to quantify the runoff reaching Drake Road within the project improvement reach, as well as the reach between Dunbar Avenue and Canterbury Drive, identify locations where facilities are needed to provide adequate street drainage, and hydraulically design these facilities in conjunction with the preparation of the final design plans for the Drake Road improvements. In this context, providing adequate drainage implies that ' facilities are furnished such that City criteria for street runoff encroachment, for both initial and major storms, are,not violated. These criteria are identified in the City of Fort Collins Storm ' Drainage Design Criteria and Construction Standards (SDDC Manual). 1 J ='-' J Rr � �I W + "•,A � E E• Cl I • rO^ SAwt u _ Cy = �n O.are Or o �l a'enrs•' WLate •000 Dr ' •e` or. .e4T•S r.nre h. J • •00A 04 • is y 1r E W N F `0• • u O ,' , Gl •`• •.. 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Brook � J a V � � Figure 1.r 1 Vicinity Map for the Drake Road Improvements. 2 01 . 1.3 Study Area and Scope of Study The study area for this drainage evaluation and design extends beyond the limits of the street improvement project (concentrated west of Dunbar Drive), due to the interconnectedness of the surface and subsurface drainage facilities east of Dunbar Avenue. The Kensington South Pond, located just east of Dunbar Avenue, receives runoff from the proposed street improvement ' area and, hence, required evaluation by this study. The Cimmaron West Detention Pond, which is located at the southeast comer of Constitution Drive and Drake Road, directs storm sewer flows to the Kensington South Pond. In addition, that portion of the surface runoff from the. ' Kensington South development which is directed north to Drake Road (along Canterbury Drive) is carried west on Drake Road to the low point associated with the Kensington South Pond. Consequently, drainage analyses of a relatively large area east of Dunbar Avenue were required to evaluate drainage conditions at the Kensington South Pond. ' As stated previously, street improvements east of Dunbar Avenue are not scheduled as part of this project. However, this study identified inadequacies in the street drainage system east of Dunbar Avenue. Where inadequacies exist within the drainage study area (i.e., criteria is not being met), drainage improvements have been hydraulically designed as identified in this report. However, those which fall outside of the street improvements area may not be constructed as part of this project. The information included herein is intended to be adequate for completing final design of the necessary drainage facilities either as part of the current street ' improvement project or as a.separate project to be completed in the future. The scope of the analysis and design portions of this study included: (a) data collection and field reconnaissance; (b) hydrologic analysis for the proposed condition using the modified ' version of the Urban Drainage Storm Water Management Model (MODSWMM); (c) evaluation of the street capacity for Drake Road in the proposed condition; and (d) hydraulic sizing of curb ' inlets and storm sewer pipes. Additional analyses have been performed to assess the hydrologic and hydraulic performance of the two major local. storm sewer crossings of Drake Road associated with the Drake Crossing P.U.D. and the Kensington South Detention Pond. In general, the hydrologic analyses have been performed for existing basin conditions. Specific cases where future runoff characteristics have been assumed are outlined in Section 2.2. It is noted that only two parcels within the drainage basin have not been fully developed at the time of this study. It was assumed that any additional development which occurs within the ' basin tributary to Drake Road within the study area will provide detention storage to limit, at a minimum, the developed condition 100-year discharge to the 100-year existing condition runoff rate. All hydraulic, analyses have been performed based on proposed road grades and street sections. 3 ' 1.4 Previous Studies. ' The Spring Creek Master Drainageway Plan [EPI, 1988] defined general drainage patterns and presented preliminary designs for certain major drainage facilities within the Spring ' Creek Basin. The hydrologic analysis for the Master Plan was performed using the original Urban Drainage Storm Water Management Model UDSWM-2PC. In addition, the Master Plan ' delineated the 100-year floodplain and floodway for Spring Creek. In the vicinity of Drake Road, the floodplain is shown to spread across a 1,250 foot section of Drake Road. The Master Plan UDSWM-2PC model was modified in conjunction with the Spring Creek and Drake Road project and was documented in the report "Hydrologic Model Update for the Spring Creek Master Drainage Plan" [LA, 1995]. That report provided updated discharges, defined using MODSWMM, along four reaches near the Drake Road crossing. The hydraulic evaluation of Spring Creek has been addressed in the "Preliminary Design Report for Spring ' Creek Channel Improvements near Drake Road" [LA, 1995]. The hydraulic analysis will be revised in conjunction with the final design of the channel improvements and will be documented ' in the final design report. In drainage addition, reports and utility plans have been prepared and approved for several other developments within the current study area. These reports and plans document ' drainage basin boundaries and provide design information for detention ponds and conveyance facilities within individual developments. Report and/or plan sets utilized in the current study ' include: (a) Browns Farm P.U.D., 3rd Filing [Hogan & Olhausen, P.C., 1975] ' (b) Childrens World at Drake Landing P.U.D. [Columbine, 1984] (c) Cimmaron West P.U.D. [Parsons & Associates, 1985) (d) (e) Drake Crossing P.U.D. [TST, 1982] Faith Evangelical Free Church [Stewart & Associates, 1990] (f) Hampshire Court Subdivision [Stewart & Associates, 1992] (g) Hampshire Square P.U.D. [McRae & Short, 1986] ' (h) Kensington South P.U.D. [James H. Stewart & Associates, 1977] (i) The Preserve P.U.D. [TST, 1993] ' (j) The Shops at Drake Crossing P.U.D. [TST, 1985]. 4 ' II. HYDROLOGIC ANALYSIS 2.1 Description of General Drainage Pattern ' In general, the drainage area which is tributary to Drake Road within the study reach is concentrated in a narrow band along the street. However, there are two locations where flow crosses Drake Road in a storm sewer or as crown overtopping. At these locations, the drainage basin boundaries are located up to a half -mile from Drake Road. These locations are associated with the Drake Crossing Shopping Center, located at the northwest corner of the intersection of ' Drake and Taft Hill Roads, and the Kensington South Detention Pond located south of Drake Road approximately 200 feet east of Dunbar Avenue. For the proposed condition, the Drake Road drainage basin between Canterbury Drive and Taft Hill Road is generally separated into six areas. These six areas are separated by two ' east -west divides located at Taft Hill Road and at the proposed high point over the Spring Creek bridge. In addition, the proposed Drake Road street crown/raised median would serve as a north -south drainage divide for local runoff along the entire reach. ' 2.2 MODSWMM Model Parameters and Subbasin Description ' MODSWMM was used to model the basin response for the 2-, 10-, and 100-year rainfall events. The rainfall hyetographs, surface runoff resistance factors, surface storage values and infiltration parameters were taken from the Spring Creek Master Drainage Plan. The remaining ' subbasin parameters (area, width, slope, and percentage of imperviousness) and conveyance parameters (street geometry, length and slope) were taken from aerial topography generated in 1 conjunction with this study. Additional information was required for the areas tributary to the Drake Crossing outfall pipe and the Kensington South Detention Pond. For these two areas, ' drainage basin boundaries and subbasin parameters were developed for these areas using grading and utility plans and City of Fort Collins aerial topographic mapping. Reference is made to Sheets 1, 2 and 3 which show all subbasins within the current study area. It is noted that the subbasin numbering scheme intentionally resulted in a non-consecutive enumeration pattern. The percentage of impervious area was calculated for each subbasin assuming the following values: (a) 100 percent for all streets; (b) 90 percent for all commercial/retail developments; (c) 70 percent for developed church properties; (d) 45 percent for all single family residential developments; and (e) 10 percent for all undeveloped and/or grassed areas. A description of the drainage patterns for each of the subbasins tributary to the Drake Road drainage system is provided in the following paragraphs. 5 11 1 1 1 Subbasins 2 and.3 are tributary to the northwest corner of the Drake Road and Taft Hill Road intersection. Subbasin 2 represents runoff directly tributary to the north side of Drake Road from the Pleasant Valley and Lake Canal to Taft Hill Road.._ Under existing conditions, the tributary area actually extends from the PV&L Canal west approximately 2,400 feet to Yorkshire Drive. This area is located within the Canal Importation Basin and is intended to be collected by the future PV&L Parallel Channel. As a result, the area west of the PV&L Canal was assumed not to be tributary to Subbasin 2 in the fully developed condition. Subbasin 3 represents runoff directly tributary to the west side of Taft Hill Road north of Drake Road. The combined flow from Subbasins 2 and 3 is collected by an existing double 4-foot City of Fort Collins standard inlet and conveyed to the outlet for the Drake Crossing development by a 12- inch RCP. It is noted that the capacity of the 12-inch RCP is limited to 9.5 cfs. For the 10- and 100-year events, a portion of the discharge would overtop the crowns of Drake Road and Taft Hill Road and continue overland to the east and south on those roads, respectively. Subbasins 10 through 19 and 138 consist of the areas tributary to the 36-inch RCP. outfall for the Drake Crossing development. A detailed hydrologic and hydraulic analysis of the outfall system and tributary area was performed in conjunction with this study in order to evaluate the operation of the eight detention ponds tributary to the 36-inch RCP outfall pipe. The revised Spring Creek Master Plan analysis (LA, 1995] represented a simplified version of the drainage system which evaluated the Drake Crossing area with two subbasins and modeled only the Manchester Detention Pond. (The seven other detention ponds tributary to the Drake Crossing outfall pipe are small, on -site ponds that. serve drainage basins which are of a size that is smaller than is typically included in a Master Plan model.) The Master Plan model indicated a discharge which would exceed the capacity of the 36-inch RCP for both the 10- and 100-year events. Due to the simplifying assumptions inherent in the Master Plan model, it was decided that a more detailed analysis of the Drake Crossing area was necessary to better define the operation of the drainage system. The results of the detailed analysis for the Drake Crossing outfall are summarized in Section 2.3. A detailed description of the analysis and results of the Drake Crossing outfall system is provided as Appendix B. Subbasin 21 consists of the area which is tributary to the south side of Drake Road west of Taft Hill Road. All runoff would be conveyed to Spring Creek as gutter flow on the west side of Taft Hill Road south of Drake Road. The subbasin delineation and schematic diagram for the Drake Road drainage system west of Taft Hill Road is provided on Sheet 1. Subbasins 31 through 39 consist of the area tributary to the low point on the north side of Drake Road east of Constitution Avenue. Subbasin 31 consists of the area directly tributary to the east side of Taft Hill Road north of Drake Road, and the north side of Drake Road between Taft Hill Road and the Fellowship Bible Church site outflow point located 300 feet east of Taft Hill Road. All runoff collected within Subbasin 31 is conveyed as gutter flow south on Taft Hill Road and then east on Drake Road. C� ' Subbasin 32 consists of the area within the Fellowship Bible Church site located northeast of the Drake and Taft Hill Road intersection. The site is currently half developed, ' runoff is directed'south to the north side of Drake Road approximately 300 feet east of Taft Hill Road. Due to limitations associated with the proposed downstream drainage facilities, it was ' determined that specific release requirements would be necessary for Subbasin 32. In order to ensure that the proposed facilities will operate as designed, releases from Subbasin 32 will need to be limited to, at a maximum, 2.5 and 7.6 cfs for the 10- and 100-year events, respectively. This requirement is specified for both the currently undeveloped and developed halves of the subbasin. It is noted that these release rates are less restrictive than would normally be required by a development. The 2-year historical peak runoff from the subbasin was estimated to be 0.8 cfs; the typical requirement would necessitate detaining the runoff from the 100-year developed condition event to this 2-year historical rate. Subbasin 33 consists of the area directly tributary to the north side of brake Road ' between the church outflow and Yorktown Drive. Runoff from Subbasins 31 through 33 is conveyed as gutter flow on the north side of Drake Road to the northwest corner of the ' intersection with Yorktown Drive. Subbasin 34 consists of the area tributary to the west half of Yorktown Drive at the intersection with Drake Road. The area tributary to the east half of Yorktown Drive at Drake ' Road is defined by Subbasin 35. Subbasin 36 consists of the area directly tributary to the north side of Drake Road between Yorktown Drive and Constitution Avenue. Runoff from Subbasins 31 through 36 is conveyed as gutter flow along the north side of Drake. Road to the northwest corner of the ' intersection with Constitution Avenue. Subbasins 37 and 38 consist of the areas tributary to the west and east halves of Constitution Avenue, respectively, at the intersection with Drake Road. Subbasin 39 is defined ' as the area tributary to the north side of Drake Road east of the low point near Constitution Avenue. The entire 100-year runoff generated within Subbasins 31 through 39 would be collected by a series of curb inlets along the north side of Drake Road and conveyed in storm sewer pipes directly to the existing Spring Creek side channel north of Drake Road. Subbasins 41 and 42 consist of the area tributary to the south side of Drake Road between Taft Hill Road and the local high point at the proposed Spring Creek bridge. Runoff generated within Subbasin 41, which is located west of the low point near Constitution Avenue, would be conveyed to the low point as gutter flow. Runoff from Subbasin 42. would be generated east of the low point and conveyed as gutter flow. The total runoff from Subbasins ' 41 and 42 would be collected by an curb inlet located at the low point and conveyed to the proposed curb inlet at the northeast corner of Constitution Avenue and Drake Road. 7 ' Subbasin 61 consists of the small area tributary to the local low point on Hanover Street immediately south of Drake Road. All runoff generated would be collected by curb inlets on both sides of Hanover Street and conveyed directly to the proposed Spring Creek main channel in a storm sewer. The subbasin delineation and schematic diagram for the Drake Road drainage system between Taft Hill Road and Hanover Street is provided on Sheet 2. Subbasins 51 and 52 consist of the area tributary to the south side of Drake Road ' between the local high point at the proposed Spring Creek bridge and the high point located near Canterbury Drive. Runoff generated within Subbasin 51, which is located west of the low point associated with the Kensington South Detention Pond, would be conveyed to the low point as ' gutter flow. Runoff from Subbasin 52 would be generated east of the low point and conveyed as gutter flow. The total runoff from Subbasins 51 and 52 would be collected by a curb inlet located at the low point and conveyed to the Spring Creek overbank north of Drake Road in a short storm sewer pipe. ' Subbasin 70 consists of the area tributary to a local grated inlet located near the northwestern corner of the Faith Free Evangelical Church.. Runoff collected by the inlet is conveyed north under Drake Road to Spring Creek in an 18-inch RCP, which has a pipe full ' capacity of 15.2 cfs. For the 100-year event, the capacity of the pipe would be exceeded, the incremental runoff above the capacity of the pipe would discharge directly to the south side of Drake Road approximately 150 feet east of Hanover Street. Subbasin 71. consists of the area directly tributary to the south side of Drake Road between Hanover Street and Dunbar Avenue. The majority of the runoff is generated within the Faith Free Evangelical Church site and is routed through the site to Drake Road. The discharge ' is then routed to Dunbar Avenue as gutter flow. Subbasin 72 consists of the area tributary to the west half of Dunbar Avenue at the intersection with Drake Road. It is noted that for the 100-year event, the carrying capacity of the west half of Dunbar Avenue would be exceeded. A normal depth analysis of the Dunbar Avenue street section showed the capacity of the west side of the street to be 35.8 cfs. The incremental discharge above the street carrying capacity was assumed to overtop the crown to the east side of Dunbar Avenue. The area tributary to the east half of Dunbar Avenue at Drake Road is defined by Subbasin 73. Subbasins 77 and 74 consist of the areas tributary to the east and west halves of Canterbury Drive, respectively, at the intersection with Drake Road. Subbasin 75 is defined as of the area tributary to the south side of Drake Road between Canterbury Drive and the Kensington South Pond. Subbasin 76 consists of the area which is tributary to the Kensington South Detention Pond through local storm drainage facilities constructed in conjunction with the Kensington ' South development. 8 Subbasin 78 consists of the area tributary to the detention pond located at the northwest comer of the Cimmaron West P.U.D. The discharge from the pond is controlled by an orifice ' plate. Initial SWMM results indicated that the pond would not have sufficient capacity to contain the entire 100-year runoff volume. Consequently, the orifice plate was redesigned as ' part of this study to allow sufficient volume out of the pond so that the 100-year volume can be contained within the pond. Discharge from the pond is conveyed to the Kensington South ' Detention Pond in an existing 15-inch RCP. The results of the analysis of the existing and proposed pond configurations are summarized in Section 2.3. Calculations for the analysis of the existing Cimmaron West Detention Pond are provided in Appendix C. Calculations for the ' modification of the pond outlet are provided in Appendix D. Runoff from Subbasins 71 through 77 as well as the overflow from Subbasin 70 and the ' outflow from the Cimmaron West Detention Pond (Subbasin 78) is tributary to the Kensington South Detention Pond located south of Drake Road, approximately 200 feet east of Dunbar ' Avenue. An analysis of the Kensington South Detention Pond was performed in conjunction with the revised Spring Creek Master Plan SWMM model. The results of that analysis indicated that a significant portion of the outflow from the pond would overtop the crown of Drake Road ' for both the 10- and 100-year events for the existing condition. Consequently, the pond outlet was redesigned in conjunction with this study. Calculations for the analysis of the existing ' Kensington South Detention Pond are provided in Appendix C. Calculations for the modification of the pond outlet are provided in Appendix E. The results of the redesign of the Kensington South Detention Pond outlet and the remainder of the Drake Road hydrologic analyses are summarized in Section 2.3. 2.3 Results of the Hydrologic Analysis The results of the hydrologic analysis for flows along Drake Road for the 2-, 10, and 100-year rainfall events are presented in Table 2.1. The discharges cited in this summary are representative of the total discharge in both the proposed street section and storm sewer system. The calculation of the actual flow in the street section, in relation to street conveyance capacities, is addressed in the following chapter. The input and output of the MODSWMM model is provided in Appendix F. ' The procedures for the analysis of the eight detention ponds and the outfall storm sewer associated with the Drake Crossing development are summarized in Appendix B. The results of the analysis indicate that the capacity of the 36-inch outfall pipe would not be exceeded for the 100-year event. In general, sufficient storage has been provided for each of the ponds to ' adequately detain the 100-year runoff without overtopping. As documented in the "Hydrologic ' 9 I 1 11 n I Table 2.1 Summary of Design Flows on Drake Road. SWIvIM ID ' Locatlon Peak Discharge (cfs) 2 year IO-year 100 ear;; Drake Road :North Side 102 West of Taft Hill Road 3.9 9.0 16.8 503 Northwest Corner of Taft Hill Road Intersection 4.5 10.2 19.3 631 Taft Hill Road Crown Overtopping to Drake Road 0.0 0.5 7.3 621 Drake Road Crown Overtopping to Taft Hill Road 0.0 0.2 2.5 131 Between Taft Hill Road and Church Outflow 2.1 4.4 12.4 332 At Church Outflow 5.9 12.9 30.4 133 Between Church Outflow and Yorktown Drive 8.1 19.1 41.6 334 Northwest Comer of Yorktown Drive Intersection 12.2 28.5 59.4 335 Northeast Comer of Yorktown Drive Intersection 16.1 37.2 78.4 136 Between Yorktown Drive and Constitution Avenue 21.0 49.8 98.4 337 Northwest Comer of Constitution Avenue Intersection 25.5 61.4 120.8 338 Northeast Comer of Constitution Avenue Intersection 26.5 63.8 124.7 139 East of Low Point near Constitution Avenue 0.8 1.6 2.9 339 At Low Point near Constitution Avenue 26.9 64.6 125.8 151 West of Low Point near Kensington South Pond. 2.4 5.0 8.9 152 East of Low Point near Kensington South Pond 3.1 6.9 13.1 352 At Low Point near Kensington South Pond. 5.5 11.9 22.1 Drake Road, South Slde 321 West of Taft Hill Road 2.7 5.5 10.9 141 West of Low Point near Constitution Avenue 4.1 8.6 15.8 142 East of Low Point near Constitution Avenue 0.6 1.1 1.9 342 At Low Point near Constitution Avenue 4.7 9.7 17.7 171 West of Dunbar Avenue 4.8 10.2 21.3 372 Southwest Comer of Dunbar Avenue Intersection 19.9 40.7 82.7 173 Between Dunbar Avenue and Kensington South Pond 20.3 44.7 91.7 177 Southeast Comer of Canterbury Drive Intersection 1.5 4.3 9.0 374 Southwest Comer of Canterbury Drive Intersection 7.7 18.9 39.3 175 Between Canterbury Drive and Kensington South Pond 8.2 20.1 40.9 11 10 Model Update for the Spring Creek Master Drainage Plan"` [LA, 1995], a significant portion of ' the discharge from the Manchester Detention Pond overflows the crown of Taft Hill Road toward Manchester Drive. The capacity of the 24-inch outlet pipe for the Manchester Detention Pond, which is tributary to the Drake Crossing outfall pipe, was found to be 17 cfs. The ' discharge in the Drake Crossing outfall pipe was determined to be 54 and 69 cfs for the 10- and 100-year events, respectively. The hydrologic analysis for the Master Plan update did not ' specifically model the on -site detention ponds tributary to the Drake Crossing outfall. Consequently, the results of the current analysis show a decrease in discharge of 90 cfs and 197 ' cfs compared to the revised Master Plan analysis for the 10- and 100-year events, respectively. The results of the existing condition analysis for the Cimmaron West Detention Pond show that the 100-year discharge through the outlet pipe is 2.7 cfs. However, an additional 7.9 cfs would overtop the pond embankment for the 100-year event. Consequently, the pond orifice plate was redesigned in conjunction with this analysis in order to increase the pipe discharge and eliminate the overtopping discharge. The results of the analysis indicate that the existing 0.55- foot diameter orifice opening should be enlarged to a diameter of 0.85 feet. With the proposed ' orifice configuration, the pond discharge would be increased to 6.2 cfs for the 100-year event. The existing condition analysis of the Kensington South Detention Pond shows an overtopping discharge which violates street criteria for both the 10- and 100-year events. The ' 10-year discharge from the pond is 14.4 cfs which corresponds to an overtopping depth of 0.14 feet over the crown of Drake Road. The 100-year discharge from the pond is 140 cfs which ' corresponds to an overtopping depth of 0.64 feet. Consequently, the pond outlet was redesigned in order to eliminate .street overtopping for the 10-year event and to reduce the 100-year overtopping to a depth less than the 6 inches allowed by criteria. For the proposed condition, the outlet for the Kensington South Detention Pond would be lowered by 1.5 feet in order to accommodate the proposed storm sewer which would serve the south side of Drake Road west of the pond. The existing pond outlet pipe, a 12-inch CMP., would need to be replaced with a 36-inch RCP in order to meet the street overtopping criteria. ' For the 10-year event, the pond discharge would be 55 cfs which would be conveyed entirely through the 36-inch RCP and corresponds to a depth of 4.5 feet in the pond. The 100-year pond ' discharge would be 93 cfs, of which 74 cfs would be conveyed under Drake Road in the 36-inch . RCP. The remaining 19 cfs would overtop the crown of Drake Road at a depth of 0.3 feet. With the proposed pond outlet configuration, the street overtopping criteria would be met for ' both the 10- and 100-year events. 1 ' M. HYDRAULIC ANALYSIS AND DESIGN 1 1 H 11 1 1 11 The hydraulic analysis and final design for this study involved: (a) . determination of allowable street capacities along Drake Road; (b) the location and sizing of curb inlets to divert runoff from the streets; and (c) sizing of storm sewers to convey runoff collected by the curb inlets. In addition, design calculations were performed to modify the outlets for: (1) the Kensington South Detention Pond, in order to meet the allowable street overtopping criteria at that location; and (2) the Cimmaron West Detention Pond, to avoid overtopping during the 100- year event. The methodologies and results of these design procedures are given in the following sections. 3.1 Allowable Street Capacities 3.1.1 Design Criteria and Methodology The hydraulic capacity of each section of Drake Road were determined assuming normal flow conditions. Normal depths were computed for each distinct road section using a separate single cross section in the HEC-2 model [U.S. Army Corps of Engineers, 1991]. Individual reaches were identified along Drake Road between locations of major inflows. Street capacities were calculated for each reach along Drake Road based on the minimum gutter slope in that reach. It is noted that reduction factors were not applied to the computed discharges. The street capacity reduction factors are meant to reflect possible flow blockage by parked vehicles and road surface overlays. However, the potential for blockage will be minimal since Drake Road is a major arterial on which parking will not be allowed and a concrete road surface is proposed. Therefore, a variance is requested allowing street capacities to be determined without applying reduction factors. Allowable street capacities for both the initial and major storms are defined in the SDDC Manual. For a major arterial, the initial storm criterion allows for up to one-half of the roadway width to be inundated in each direction, provided the flow depth does not exceed the curb height. The major storm criterion requires that the depth of water not exceed 6-inches over the crown, or 18 inches over the gutter flowline, whichever is more restrictive. The intent of the proposed drainage system design is to limit the major storm flow to a depth below the crown of the roadway or the roadway elevation at the base of the raised median, whichever is more restrictive. Therefore, street capacity calculations for the major storm are reflective of the crown elevation as opposed to the less restrictive SDDC. In accordance with SDDC Manual 1 12 I H 1 1 11 1 guidelines for major arterials, the initial and major storms were defined for the purposes of this. study as those rainfall events which are associated with 10- the 100-year return periods, respectively. The one exception to this definition is at the northwest corner of Drake and Taft Hill Roads; reference is made to Section 3.1.2 where the drainage condition at that location is discussed in detail. 3.1.2 Results of the Street Capacity Analysis The initial analysis of allowable street capacities was utilized in the location and sizing of on -grade and local sump curb inlets. Inlets were located and sized as described in the following section as dictated by allowable street capacities. Following the final inlet design, the actual street flow was compared to the allowable street capacity. The results of the analysis indicate that the capacity would be violated at two locations along Drake Road. A comparison of allowable street capacities and actual street flows is provided in Table 3.1. The street capacity calculations are given in Appendix G. For the minor storm, the discharge on the north side of Drake Road west of Taft Hill Road would exceed the allowable capacity. This is due to the existing inlet and storm sewer system which serves the area northwest of the intersection having a limited capacity. The capacity of the existing 12-inch RCP which conveys runoff from the northwest corner of the intersection has a capacity of 9.5 cfs, which is less than the 10-year discharge of 10.2 cfs. However, the existing system can effectively collect and convey the 2-year discharge of 4.5 cfs. Consequently, a variance is requested to allow the 2-year event to serve as the minor storm event for the northwest corner of the Drake and Taft Hill Roads intersection. The other location where the street capacity is violated corresponds to a local inflows along Drake Road. The Faith Evangelical Free Church property located south of Drake Road between Hanover Street and Dunbar Avenue contributes runoff to the south side of Drake Road near Station 95+00. Runoff from the property results in a localized violation of street capacity; an on -grade inlet is proposed downstream of the inflow point to reduce the gutter flow to allowable levels. Under current development conditions, street capacity would be violated at one other location. The Fellowship Bible Church property located northeast of the Drake and Taft Hill Roads intersection (Subbasin 32) has a downstream outflow point along the north side of Drake Road at approximately Station 95+00. As indicated in the MODSWMM analyses, the 10- year existing condition discharge from the site would exceed the local street capacity by 1.1 cfs at the location of the inflow and by 7.6 cfs halfway between the church outflow and Yorktown .. Drive. Since roughly half of the site is currently undeveloped and these runoff values exceed r 13 I I I I I I I I I I I 11 I I I I I I Table 3.1 Summary of the Street Capacity Analyses for the Proposed Drake Road Configuration 11,06 Allowable Street Actual Street.Tlow.- (Statton, flow Slope;' Slope Width Flow c s with Inlets. WsV:!:�.�:� 1recuonY::�::.:,::., . .. .... 10- :IC�year* Drake ..Road,........ o id N 68+10, E 0.8 2.0 31 5.8 35. 4.51, 19.3 72+50, E 2.1 2.0 41 11.8 122 6.2 b 20.01 75+709 E 2.7 2.0 29 9.6 55 9.6 26.6 78+90, E 2.0 2.0 29 8.7 49 7.3 21.6. 80+00, E 1.1 2.0 29 6.4 36 1.7 11.9 84+200 E 1.2 2.0 29 6.7 38 3.4, 11.4 86+37, E 1.2 3.9 29 10.0 110 9.5 19.4 87+82) W 0.4 3.4 29 6.4 51 1.6 2.9 98+80, E 0.4 2.0 35 6.2 37 5.0 8.9 98+95, W 1.0 2.0 1 35 9.3 56 6.9 13.1 ........... . .. .... . .. .......... ....... . ...... .. ... ­DrAe7RbAdi'S6utli+Si .... .. 'd& . . .... ........... .. . ... .... . .. .. ...... ............ 68, + 10, E 0.8 2.0 53 13.9 147 5.5 10.9 86+80, E 1.2 2.0 41 9.0 93 8.6 15.8 87+85, E 1.2 3.4 29 11.0 88 8.6 15.8 88+00, W 0.4 3.4 29 6.4 51 1.1 1.9 95 + 00, E 0.4 2.0 29 3.9 22 10.2 21.3 95+40, E 0.4 2.0 29 3.9 22 3.3 7.2 98+00, E 0.4 2.0 35 6.2 37 3.1 36.6 9 8+95, W 1.0 2.0 35 9.3 56 7.3 27.9 110+00, W L 0.4 I 2.0 I 35 IL .2 �_ I 37 L .0 26.3 The value represents the 2-year discharge at this location. A variance has been requested to allow the 2-year event to serve as the minor storm event on the northwest comer of Drake Road and Taft Hill Road (refer to Section 3.1.2). Discharge assumes future on -site detention for Subbasin 32 (see Section 3.1.2). Local street capacity violation due to point inflow to Drake Road; an inlet has been designed directly downstream of the inflow location to reduce flows to allowable levels. I 14 the typical allowable release rates for developing areas in Fort Collins. (usually the 2-year historical runoff), this study has specified allowable release rates for the site. As defined in Section 2.2, the 10- and 100-year release rates for Subbasin 32 are 2.5 and 7.6 cfs, respectively. By specifying these rates, allowable street capacities will not be exceeded in the area east of the ' church site. However, until the property develops, the allowable 10-year street capacity of 8.7 cfs would be .exceeded by 7.6 cfs between the church outflow and Yorktown Drive. ' 3.2 Curb Inlet Design 3.2.1 Design Criteria and Methodology . As indicated in the previous section, it was determined that a series of on -grade and local ' sump inlets are required to meet street capacities at several locations along Drake Road. On - grade inlets were located and sized in order to collect runoff to meetthe allowable street capacities in the reach downstream of the inlet. At each cross -street along the study reach, ' Yorktown Drive, Constitution Avenue and Dunbar Avenue, a local sump was created in order to remove existing crosspans and to more efficiently collect runoff. In addition, a local sump ' was designed immediately east of Constitution Avenue and a local sump currently exists approximately 200 feet east of Dunbar Avenue. ' The theoretical capacity of each inlet was calculated using inlet nomography from the Fort Collins SDDC Manual. Reduction factors were then applied to determine the design capacity of each inlet according to values given in the SDDC Manual. For a 5-foot inlet, the reduction factor is 0.80; for a 10-foot inlet, the reduction factor is 0.85; for a 15-foot inlet, the reduction factor is 0.90. For inlets larger that 15 feet, a reduction factor of 0.90 was utilized. ' The discharge at each inlet was calculated by first determining the total discharge at that location from the SWMM model. The gutter discharge was then determined by subtracting out ' all upstream inlet diversions. Results of the curb inlet design process are summarized in the following section. 3.2.2 Results of the Curb Inlet Design On -grade inlets were designed at six locations to reduce the street runoff to allowable levels determined in the street capacity analysis. The theoretical capacity of the on -grade inlets were calculated using the inlet nomograph which utilizes the gutter slope, cross slope, roughness coefficient, flow depth and flow top width parameters. The geometric parameters were obtained 1 15 0 ' from the utility plans for the proposed Drake Road improvements. The flow depth and top width were calculated for actual flow conditions using a HEC-2 normal depth. analysis. A summary of on -grade inlet design parameters is given in Table 3.2. All calculations are provided in Appendix H. ' Inlets were designed at three local sumps formed by the crown of the side streets at Yorktown Drive, and Constitution and Dunbar Avenues. For the minor storm, the depth of ponding at each of the inlets was limited to 0.5 feet. In addition, the flow depth was not allowed to spread beyond half of the width of Drake Road and was not allowed to overtop the crown of the local cross street. For the major storm, the depth of crown overtopping of the ' cross street was not allowed to exceed 6 inches; furthermore, the Drake Road crown was not . allowed to overtop. Design parameters for all sump inlets is also provided in Table 3.2. ' At the sump located east of Constitution Avenue (which is formed by the proposed bridge), the inlets on the north and south sides of the street were both designed to collect the 100-year street flows at a depth of 0.6 feet which corresponds to the depth at which the flow would overtop the minimum flowline elevation at the bridge and continue to the east. The minor storm ponding depth was limited to a depth of 0.5 feet at each of the inlets. ' At the sump located east of Dunbar Avenue a significant portion of the 100-year outflow from the Kensington South Detention Pond would overtop the crown of Drake Road and flow ' overland in a northerly direction to the Spring Creek floodplain. Consequently, the inlets located on both sides of the street at this location were designed to convey only the 10-year flow ' at those points. Incremental discharges above the 10-year event would commingle with the overtopping flows from the detention pond. Two additional inlets have been designed on both sides of Hanover Street immediately ' east of Drake Road. The eastern inlet was designed to collect the 100-year discharge at an ponding depth of 0.13 feet which corresponds with the overtopping elevation formed by the IDrake Road curb return. For the western inlet, the allowable ponding depth was limited to 0.5 feet which corresponds to the curb height. 1 3.3 Storm Sewer Design 3.3.1 Design Criteria and Methodology In general, the storm sewer pipes were designed to convey the 100-year discharge ' collected by all upstream inlets. Typically, each of the on -grade inlets were designed to limit street flows for the minor storm event. However, the storm sewers have been designed to ' convey the 100-year discharge collected by the inlets. In addition, the storm sewers have been ' 16 1 1 1 1 Table 3.2. Summary of Inlet Design Parameters. Gutter Discharge Inlet Diversion Gutter Discharge Inlef: Curb Inlet Upstream of Inlet (cfs) Downstream of Inlet; Location Length /Type Location (cfs) Location (cfs). (Station) 10 year 100 year :10 year 100;year 10 year f00 year >: Drake Road...... Side 68+ 10 Double 4-ft City Standard, 10.2 19.3 9.5 9.5 0.72 9.81 Local Sump 75+70 15-ft Type-R, On -Grade 9.6. 26.6 5.1 9.6 4.5 17.0 78+66 25-ft Type-R, Local Sump 16.7 39.4 16.7 31.5 0.0 7.9 79+80 20-ft Type-R, On -Grade 8.8 27.0 6.1 15.1. 1.7 11.9 84+00 20-ft Type-R, On -Grade 9.1 23.8 5.7 12.4 3.4 11.4 86+37 20-ft Type-R, Local Sump 11.7 20.0 21.1` 41.8` 0.0' 8.51 86+82" 10-ft Type-R, Local Sump 9.4 13.3 87+67 15-ft Type-R, Sump 10.0 18.0 . 10.0 18.0 0.0 0.0 98+80 15-ft Type-R, Sump 11.9 22.1 11.9 11.90 0.0 10.2 Drake Road,South Side 87+85 15-ft Type-R, Sump 9.7 17.7 9.7 17.7 0.0 0.0 95+20 15-ft Type-R, On -Grade 10.2 21.3 6.9 14.1 . 3.3 7.2 96+ 17 35-ft Type-R, Local Sump 33.8 43.0 33.8 41.0 0.0 2.0 98+80 15-ft Type-R, Sump 10.4 64.5 10.4 10.46 0.0 54.11 109+80 20-ft Type-R, On -Grade 18.9 39.3 12.8 13.00 6.1 26.3 Hanover:' Street West Side 5-ft Type-R, Local Sump 0.3 0.6 0.3 0.6 0.0 0.0 East Side 5-ft Type-R, Local Sump 0.3 0.6 0.3 0.6 0.0 0.0 ' Based on Table 2.1, 0.5 cfs overtops Drake Road to the east and 0.2 cfs overtops Taft Hill Road to the south. '" Based on Table 2.1, 7.3 cfs is conveyed east and 2.5 cfs is carried to the south. Total inflow to the Station 86+37 and 86+82 sump inlet system. Total outflow from the Station 86+37 and 86+82 sump inlet system. ` Due to curb overtopping flows at the low point associated with the Kensington South Pond during the 100-year event, the inlet and downstream storm sewer was designed to convey only the' 10-year runoff (refer to Section 3.3.1).. ' 'Overland flow to Spring Creek. ' 17 1 tdesigned to convey the 100-year discharge collected by local sump inlets. Due to the overtopping of Drake Road at the low point associated with the Kensington South Detention Pond, the storm sewer pipes leaving the inlets on both sides of the street have been designed to convey the 10-year discharge. The storm sewer which would convey flows from the Cimmaron tWest Detention Pond and the proposed inlet located near Canterbury Drive to the Kensington South Detention Pond was designed to convey the 100-year discharge from the Cimmaron West ' Pond and the 10-year discharge collected by the inlet. The initial design of all storm sewer pipes was accomplished using Manning's equation and assuming pipe full flow conditions. All storm sewers were designed as -reinforced concrete ' pipes (RCPs). Design slopes for all pipes range from 0.4 to 3.0. percent. ' 3.3.2 Results of Storm Sewer Design ' A preliminary, plan of the horizontal location and vertical alignment of all storm sewers has been prepared. However, at the time of this analysis, the location of existing utilities and ' other potential conflicts had not been completed. Consequently, the final horizontal and vertical location of the storm sewer has not been determined at this time. The assumed location and size ' of each of the storm sewers associated with the Drake Road improvements is shown on Sheets 1, 2 and 3. A detailed hydraulic analysis of the proposed storm sewer will be submitted in ' conjunction with the final version of this design report. The detailed hydraulic analysis and hydraulic gradeline determination of the final pipe design will be performed using the pipe hydraulic analysis model Urban Drainage and Flood Control District's (UDSewer). The ' maximum tailwater at the downstream end of each storm sewer will be considered for the hydraulic analysis. The tailwater elevations will be obtained from the analysis of the Kensington South Detention Pond and the proposed Spring Creek channel. 3.4 Riprap Design tAt all storm sewer outlets, riprap outlet protection will be provided to minimize the potential for erosion. Riprap protection for the two storm sewers which outlet directly to Spring ' Creek near the proposed bridge will be designed in conjunction with the final design of the Spring Creek improvements. The riprap protection for the two pipes which outlet into the ' Kensington South Detention Pond and the two pipes which discharge into the Spring Creek floodplain north of the Kensington South Detention Pond will be designed following the final ' hydraulic analysis of the storm sewer pipes. 1 18 No Text No Text U Z ` I1,7 f�• �V r �t4 i, oe Z z WA- MI rp i L UL=-s i .n• '" _ — _ -- `� Imo',• �,t=` .�®���I�►�`��_ — ��iS� sue.=`.- .p '^+�1�•.' , - n..' •n aI/i ,, 's{y�. Ip � �� • �.—�1 ��Y'� ,r '___" 'Y1Y[Y�®--1f ` ' • q_�•'11� I ��J• : I� . ,1 •® I� . ' • Pali f�l - -. 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