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HomeMy WebLinkAboutDrainage Reports - 05/12/1995a Fnal An ..roved Repor OVERALL DRAINAGE STUDY OAK/COTTONWOOD FARM - MAIL CREEK AND FOSSIL CREEK BASINS FORT COLLINS, COLORADO I 1 I I I n 1 1 OVERALL DRAINAGE STUDY OAK/COTTONWOOD FARM - MAIL CREEK AND FOSSIL CREEK BASINS FORT COLLINS, COLORADO May 4, 1992 Revised January 16, 1995 Prepared for: Miramont Associates 309 West Harmony Road Fort Collins, CO .80526 Prepared by: RBD, Inc. Engineering Consultants 209 South Meldrum Fort Collins, Colorado 80521 (303) 482-5922 RBD Job No. 504-001 RMINC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 ' FAX: 303/482-6368 ' January 16, 1995 Mr. Basil Hamdan ' City of Fort Collins Utility Services Stormwater ' 235 Mathews Fort Collins, Colorado 80522 RE: Overall Drainage Study for Oak/Cottonwood Farm - Mail Creek and Fossil .Creek Basins ' Dear Basil: We are pleased to submit to you, for your review and approval, this Revised Overall ' Drainage Study for Oak/Cottonwood Farm, those portions located within the Mail and Fossil Creek Master Drainage Basins. That portion of Oak/Cottonwood Farms located within the McClellands Master Drainage Basin is examined by a separate study. All ' computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria ' We appreciate your time.and consideration in reviewing this submittal. Please call if you have any questions. ' Respectfully, RED Inc. Engineering Consultants \\\\\\%,lllllllllll/�/ i Pp0 REG�1/iif pLDEN GlFSFU Roger A. Curtiss, P.E. =� 27362 Project Engineer ' Denver3031458-5526 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE BASINS A. MAJOR BASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA A. REGULATIONS 2 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 2 C. HYDROLOGICAL CRITERIA 3 D. HYDRAULIC CRITERIA 3 E. VARIANCES FROM CRITERIA 3 IV. DRAINAGE FACILITY DESIGN -OVERALL DRAINAGE STUDY A. GENERAL CONCEPT 4 B. SPECIFIC DETAILS 4 V. EROSION CONTROL A. GENERAL CONCEPT 10 VI. CONCLUSIONS A. COMPLIANCE WITH STANDARDS 11 B. DRAINAGE CONCEPT 11 REFERENCES 11 APPENDIX A VICINITY MAP 1 SITE HYDROLOGY 2 EXCERPTS FROM THE SWMM MODEL FOR MAIL CREEK 15 EXCERPTS FROM THE FOSSIL CREEK MASTER DRAINAGE STUDY 19 TABLES AND FIGURES 29 11 1 OVERALL DRAINAGE STUDY OAK/COTTONWOOD FARM - MAIL CREEK AND FOSSIL CREEK BASINS FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION A. Location The Oak/Cottonwood Farm development is located in the southeast part of Fort Collins, immediately south of Harmony Road and west of Lemay Avenue. The Oak/Cottonwood Farm development consists of approximately 271.7 acres occupying the east half of Section 1, Township 6 North, Range 69 West, of the 6th Principal Meridian. See the Overall Drainage Plan in the back pocket of this report..This study will deal with the area within the Mail Creek and Fossil Creek Basins, essentially the area south of the Mail Creek Irrigation Ditch, bounded on the east by Lemay Avenue and on the west by Mail Creek Lane. The area north of the Irrigation Ditch is addressed under a separate study for the McClellands Master Basin portion of the Oak/Cottonwood Farm. B. Description of Property This site contains and existing elementary school and one approved development; Castleridge P.U.D., currently under development. The remainder of the existing site, prior to the start of construction of the single family developments, consisted of cultivated farmland and natural grasses. The Mail Creek Irrigation Canal runs across the northerly boundary of the site from northwest to southeast. Topography south of the Mail Creek Irrigation Ditch is generally sloping from north to south at approximately 5.7%. Mail Creek and Fossil Creek is located in the southern part of the development, .generally running from west to east. A small portion of the site, planned for residential development, is located south of Mail Creek. Castleridge and Werner Elementary School are the only existing developments presently located within this study area. Werner I ' Elementary School is located south of the Castleridge Development. A ' preliminary drainage and erosion control study has been submitted on the remainder of the area in this study area. A Final Drainage and Erosion Control Study has been submitted to the City for review for Miramont ' 3rd Filing, or approximately the northerly 1 /3 of this study area. With the exception of developed flows from Castleridge, Werner Elementary School, and the area south of Mail Creek, the hydrology included within ' the Overall Study is the same as what was submitted for Miramont Phase 3 Preliminary Drainage Study. Reference should be made to each individual Drainage reports for more specific detail associated with each ' project. ' II. DRAINAGE BASINS A. Major Basin Description ' The Oak/Cottonwood Farm site lies within the Mail Creek Basin, and the Fossil Creek Basin per the vicinity map in the appendix. The major basin delineations are also shown on the Overall Drainage Plan. DRAINAGE DESIGN CRITERIA A. Regulations ' The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. ' B. Development Criteria Reference and Constraints The portion of the Oak/Cottonwood Farm site within the Mail Creek Basin historically drains to Mail Creek. From the Mail Creek Major Drainage Plan, this portion of the Oak/Cottonwood Farm site lies within the ' SWMM Basin 51 and drains undetained directly into Mail Creek. Mail Creek outfalls into Fossil Creek immediately southeast of Basin 51. No ' detention requirements are being required for this site by the Mail Creek Basin Master Plan. Since this report was originally submitted, a report entitled "Preliminary Design Report for Mail Creek Stability Study", dated January 28, 1993, prepared by Lidstone and Anderson, Inc, has been ' prepared and submitted to the City of Fort Collins Stormwater Utility. All, recommendations put forth in this report wi►I also be required to be complied with for development within this site located in the Mail Creek ' Basin. Specifically, buffer limits have been established in that study, 2 I ' requiring development to be setback from Mail Creek. These buffer limits ' have been taken into account in the Preliminary Site plan submitted to the City for the Third Phase of Miramont. The study also recommends improvements to Mail Creek when a point of stormwater discharge is directed to the Creek. The study goes on to discuss what improvements will ultimately be installed to prevent stream migration and further erosion of Mail Creek. Bank armoring will need to be addressed at time ' of final plans by the developer. One point of discharge already exists, namely the point of discharge from the westerly half of Castleridge and Werner Elementary School. No additional improvements will be made to this discharge point. Two additional point of discharge will be ' incorporated into the Miramont 3rd Filing design. Temporary siltation ponds and additional bank armoring will be designed with that ' development. The portion of the Oak/Cottonwood Farm site within the Fossil Creek Basin historically drains to Fossil Creek. For the Fossil Creek Basin, the Oak/Cottonwood Farm site drains undetained directly into Fossil Creek. Fossil Creek lies south of the Oak/Cottonwood Farm site. Again, no ' detention requirements are imposed on this site by the Fossil Creek Basin Master Plan. The same treatments for bank erosion that are recommended for Mail Creek will be used in final design of those areas draining to Fossil Creek. A small portion of this study area (Basin 302) will be routed ultimately south to Fossil Creek. ' C. Hydrological Criteria The rational method was used for master planning purposes in the Mail ' Creek and Fossil Creek Basins to give a general overview of the anticipated drainage runoff flows which could occur with the proposed development. A SWMM model exists for the Mail Creek Basin, but was ' not utilized at this time. The rational method was also used to determine runoff for the Preliminary design of The Upper Meadow at Miramont First ' Filing. The 2 and 100 year rainfall criteria, which was obtained from the City of Fort Collins, is the criteria which was utilized for the rational calculations. This criteria is included in the appendix. ' D. Hydraulic Criteria ' All calculations with this report have.been prepared in accordance with the City of Fort Collins Storm Drainage Criteria. E. Variances from Criteria 1 3 1 ' No variances are being sought for the Oak/Cottonwood Farm site. ' IV. DRAINAGE FACILITY DESIGN - OVERALL DRAINAGE STUDY FOR OAK/COTTONWOOD FARM ' A. _ General Concept As development continues to occurs within the Oak/Cottonwood Farm ' site, the drainage concepts shown on the Overall Drainage Plan in the back pocket of this report should be followed. No detention requirements exist in the Mail Creek Basin and the Fossil Creek Basins, ' allowing for undetained storm water runoff directly to -Mail Creek and to Fossil Creek. The Overall plan shows a water quality pond to be located prior to the final release into Mail and Fossil Creeks. ' B. Specific Details ' MAIL CREEK BASIN From the Overall Drainage Plan, the southwestern portion of the ' Oak/Cottonwood Farm site lies within the Mail Creek Basin. Per the City of Fort Collins Stormwater Utility, no on -site detention requirements exist for this portion of the Mail Creek Basin. Thus developed runoff from the ' site may be routed directly to Mail Creek. A report entitled "Preliminary Drainage and Erosion Control Study for Miramont 3rd Phase P.U.D., dated February 4, 1994, by RBD inc. was prepared and submitted to the City of Fort Collins Stormwater Utility for ' review. In that report, anticipated outfall point to Mail Creek were identified. No water quality/permanent water features were identified for future development within that portion of the site located within the Mail Creek Basin. As final site layouts and plans are developed for that portion of the site adjacent to mail Creek, the prescribed buffer limits and outfall protection requirements will need to be addressed. A copy of the ' hydrology contained in that preliminary study has been included as Appendix B of this report, and a copy of the Preliminary Drainage and Grading plan has been included in the back pocket of this report. Within the Mail Creek Basin, as mentioned above, a bank stability study has been prepared and submitted to the City of Fort Collins Stormwater ' Utility. Requirements as specified in that report will need to be complied with as development occurs within this basin. Specifically, there are a 1 4 ' number of improvements that the report suggests. to help minimize ' erosion within Mail Creek. Development within this basin and adjacent to the Mail Creek Ditch will need to be located outside of a prescribed buffer defined in the report. Detention was not suggested as a stabilization measure, however all outfall points into Mail Creek will need to be provided with measures to stabilize the bank adjacent to the outfall. ' It is our understanding that the Mail Creek Irrigation Ditch leaked in the past. Seepage from the ditch had caused problems in the adjacent ' Oakridge development. In 1993,. Miramont Associates, in coordination with the Mail .Creek Irrigation Co. relined that portion of the Mail •Creek Irrigation ditch within the limits of this site.. ' This overall drainage plan utilized the rational method to determine a single runoff calculation for this basin. In the preliminary design of Miramont Phase 3, a more detailed approach to thisbasin was taken, ' with an updated street and lot configuration. During final design of the remainder of this basin, each outlet point to mail Creek can be evaluated and appropriate protection measures incorporated. FOSSIL CREEK BASIN From the Overall Drainage Plan, the southeastern portion of the Oak/Cottonwood Farm site lies within the Fossil Creek Basin. Excerpts ' from the Executive summary and the report entitled "Fossil Creek Drainage Basin Master Drainageway Planning Study" by Simons, Li & Associates dated August 1982 have been included in the appendix of ' this report. Per the City of Fort Collins Stormwater Utility and the above referenced study, no on -site detention requirements exist for this portion of the Fossil Creek Basin. Thus developed runoff from the site may be ' routed directly to Fossil Creek. The Fossil Creek Master Drainage plan recommends improvements to be made to the Fossil Creek Drainage Basin, and these regional improvements will be made by the City. ' Anticipated storm sewer locations have been shown, with the upstream ' extent of the storm sewer systems dependent on the available street capacities to transport storm water runoff to Fossil Creek. When this portion of the site proceeds into final design, the extent of the storm ' sewer systems will be better defined. The extent of these water features and their use will be determined as the development progresses. Outlet points into Fossil Creek will need to address bank stabilization protection ' similar to the requirements prescribed by the Mail Creek Bank Stabilization Study, Master Plan. and the Fossil Creek ' 5 ' The Mail Creek Irrigation Ditch crosses the Oak/Cottonwood Farm property immediately north of Basins 1 (from Castleridge) and basins 101 A & 101 B. The entire ditch adjacent to that portion of the site within the Fossi► Creek Basin has been lined in coordination with the Mail Creek ' Irrigation Co (The Ditch Co. has signed the Final Approved Utility plans for Miramont First, Second, and Third Filings, and Castleridge). At the time of final design of this area, these points of discharge will be further ' examine to determine the level of protection required to prevent damage. ' V. EROSION CONTROL ' A. General Concept t The Oak/Cottonwood Farm site lies within the Moderate and High Rainfall Erodibility Zone and within the Low to Moderate Wind Erodibi►ity Zone per the City of Fort Collins zone maps. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, at the time of final design of the site, the erosion control performance standard will need to be calculated and appropriate measures taken to control erosion ' from the site. ' VI. CONCLUSIONS A. Compliance with Standards ' All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. ' B. Drainage Concept ' The proposed drainage concepts adequately provide for the transmission of developed on -site runoff to the downstream conveyance facilities. ' The street systems will need to convey storm water runoff to the downstream outlets without exceeding the capacities of the street conveyance systems. If the street capacities are exceed, storm sewer ' systems may be required to transport storm water runoff to the downstream outlets. Per the City criteria, only the initial storm event is required to be transported to the downstream outlets by' storm sewer systems once the street systems become overloaded. City requirements for the transportation of the 100 year developed flows must also be M I ' observed and complied with. The City of Fort Collins will maintain the storm sewer systems located within dedicated right-of-ways. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. ' 3. Master Drainage Study for the Oakridge Business Park in Fort Collins, Colorado, by RBD Inc., September 1990. ' 4. Final Drainage and Erosion Control Study for The Upper Meadow at Miramont ' First Filing, Fort Collins, Colorado, by RBD, Inc., November 10, 1992. 5. Final Drainage and Erosion Control Study for The Upper Meadow at Miramont Second Filing, Fort Collins, Colorado, by RBD, Inc. 6. Final Drainage and Erosion Control Study for Castleridge at Miramont First ' Filing, Fort Collins, Colorado, by RBD, Inc., October 7, 1993. 7. Preliminary Design Report for Mail Creek Stability Study, by Lidstone and ' Anderson & TST, Inc., January 28, 1994. 8. Preliminary Drainage and Erosion Control Study for Miramont 3rd Phase P.U.D., Fort Collins, Colorado, by RBD, Inc., February 4, 1994. 9. Final Drainage and Erosion Control Study for Miramont P.U.D. Third Filing, Fort ' Collins, Colorado, by RBD, Inc., April 4, 1994. 10. Preliminary Drainage and Erosion Control Plan for the Oak Hill Apartments, Fort ' Collins, Colorado, by RBD, Inc., February 4, 1994 1 11 7 I I APPENDIX I tJ 1 1 I i I CLIENT JOB NO PROJECT CALCULATIONS FOR MADE BY DATE CHECKED BY DATE - SHEET I OF RMINC ' Engineering Consultants 1 L 1 I I I 1 I Z/ SITE HYDROLOGY 1 1 1 1 1rI �1 N .nn 8 r'l F-' U N � N � + 1 �AA u' V 1 N L. to O a a f' < 1 cc Zrn o i cc LL ui U 1 0 DC Q Z U 0 Z LL 1 w m _ O W c m J U 1 0 v) < 1 N 0 1 n 0 2 ' ^^Q U � 3/ r 0 r o r Qo r } pp T J w to u a a z 0 d ¢� a >4 W U 0 "Q 0 19 w F= w °: am — N N w� w 0O 0 r- co � Z to c W J +. p s^ to Q 0 I o-- w co N N N N N <m x F- F- z ^ w (� J — � U Z Q O O ol d O o 0 0 0 Q O O o cn m w 4 d fa u N N N ma 0� m NI �; 0 0 N N n N , Loin N N ��U `/ I' �V1 U Z Z cc W W z z .J r 57 r U r J C I /.1 fp UN N 1 \0 r 4/ jr `'' V Vy O w U U Z O N W4 F F aN cn O O '4o U U TLOO w cn I w� >'� W oo co ►— N N T CI N� ZI.I to N f(} a Lo ctj N Q- a' mcr- r r o� oe 0 0 0 to 0 f 0 i Ul Ui U% VJ U1 u/ U7 40 Q N ma-FQ, < m o N N-d N N N c — _ �► LO o V c S/ Ty- � � � N 8� o N 8N 8N 8 LL.21 �o — G m - � � - — V 0 � I to U ow J �\ ar a 0 a0 Vn ao u d v U �- N r f- t d r m 1 j N N I w a. m N •9 N l� In w.� Q w a o^ CO (i1 Q .9 N j lNfl In Lr o ti to — 0 OJ Q I`� Q Q Q l ' o N N N N N N ` N Jw a� _ 0 Q O Lo u z O o 0 0 0 d 0 aD O o 0 0 �0 mQ aN —— r�— c c w�- — — — — — a 1 1 1 1 1 1 1 i 1 1 V) Z N O d LL (� N Q a OC 0 O w LL U �' c 0 Q Z. 0 � LL Z 0 LU r W m F- .o w° J O a)U � J 1 rn a U n rrn� V! U VI CLI 6 xtio1 fJ �► N N Ll � � �► � N c� � �► o N � N o N B 1 V �M/ W I O w to U z 0 E-+ E- f-I a to ao ¢o U U ., s w J w �- aa.w 1� b 0 0 00 09 0 $ � ° `" 0f �d m N0 a z���00 b0 w V j r0 m N oil �._ ID cr- UJ,LO a 0 0 0 Q 0 0 rJ 0w z .. w U. �- � qq 0 0 L/ 0 uJ U/ U) v In U1 U' 1 z O o O p o 6 0 O o 4 616 a N °° Q w v LON of N N ' mod a N cv — O o = Ifs E N w v r c0 p _ i N N N f v Z c7 z FX w w z 0 z lal u Ir t= Y of �l a N 0 Ni to y O p w jui U Z O w ,� F F a cn :Do UU w W (L I Q 7J r 9 F- '`` >" w a $ � N o 00 9 .D cn '" • N I m N 0 0 z�: .$ R w Z N Q` r N �► _ M_ �•c Q0 r N N -' Ci �^ a Q 0 0 0 0 >,. � o °to co° �w Z LLI to v z a 0 0 �J n /J p p 0 0LD 0 0 f co w a Q Q U1 In co aN c� O a _ N f o v N N N N — 5, 1 tj Q o1 Y N N oI T r w a =Nj1; r co V V 1 O z " oW F H rr a o ell vo ., .= s w w CL a� m >�� w,y aa.,00 W LD a z 8 Z •0: i to Cd r N N cra. W ^ 0 i *. \e 9 ow amNJ _ Q Q o U, r z 0 0 (J 0 0 0 0 0 0 i (33 W (3\ C� oil Q Q v m M m" co d �� mo —=m �� O O N N c w U z z a W W Z T.. LLi U cr zy 1 I 9/ 1 1 11 F 11 I �I 11 u HYDROLOGY 1 1 1 1 c 1 a 1 e 1 F 1 �a 1 _u U 1 1 1 2�'�, tC) 4 M���(1o1,}r �oUr�} o� l�lln�l��P�'� to - o0 7C)s�-��.,� \' F�Y �10>✓r,ss -�,.T i:lusvi Z2,.1994 STORM DRAINAGE SYSTEM PRELIMINARY DESIGN DATA Flow Time Street Pipe Street Pipe Location 0 C -- y c 0 E o w m ,� ,. o w o w Remarks of C •_ p 0 0 ,��, yG C C O U O d O E O C O d G O C U U •U '^ Design Point 9 C« o+ .,,, v C C o d C cg E o .0 _ o U 5: m a O C C y L 7 .� E C 7 O d O\ O. y O .- a O - N •- C d w O •►• y y m .� O an d 0.. �.. o d Z `f t�a� Co E rn E a E 1- c> E c� _. c_ a= o o U N o c� u cn o > w 1 2 3 4 5 1 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22 23 123 IZ3 - - IZ.3 O, 2.30 2.58 Z.97 Z.97 O.S 3.99 2.�7 Z.I Fux.� To _.... 3.35D. Z. ZS 3.1-7 3.5 357 0.5 S-99 3.5-7 1 . 11-7 13 1 O.SO 2,20 1.89 2.0S 2.08 Z•O 9.at Z. Z-g - I= 1 I•S Is. I d•So 2-10 5.� 5.31 5.31 Z-O 9.81 r✓•31 Z.S T.�iM6 �si,.l 114To D•P. 11� 1.g Ig .7 O,So Z-C>5 )-75 1 -19 I.79 O.S 3,9fl 1=19 1-6 ) IS Z0,6 0.50 1-80 3.-is 1 3.38 3.3a .O.S 3.901 115 113 U Zn.b O,SD ,80 S-So 4.95 4.95 Ilio - 13.4 0.5D 2.2.5 2.59 Z.9► 291 -7.d S-S T"rlrnE r->.P.IIS T5 A.P- t146 Ilb 113 i�5 116 O.9 Z1.5 0,-SD 1-'75 S.o9 •OS 7.08 7,0 8.5 _ 7.08 S•Z %.O 0.50 3.cx> 0,53 D.So 0.8o Z.o 9.81 7- "T,nn- o.P. TD D.P. I I a 0.8 113I n 0,8 ZZ.3 D•SO 1.70 1&68 11.63 II.63 114 , 11l Ito I I . a o. so 2.3o 1. 2+3 1,41 3. 8 .4-1 3. _ (o" v sex-- c v 113115 11(014.1 Z4.1 O,So 1.(�S )6.S1 13.6Z 1316Z 3.8 15.8 15.62 3.8 T.Tnne >=eoM D.P.ltt3Ta ID 2a-= IZO I17.11 12b 1?_Q I (�. l O.So 3.oc7 0.4Z 0.63 0.63 3.8 is•S 0.63 3.8 T.T nnE 1=eorn D,P. 12o to D.P.IZ6= 113 115 O ICY ZS .0 O. SO 1. 60 I g. 39 14.-71 14. 71 P-t-t v T-O 2L�,, 'C 1.) I'` Le-r it It Z I 14 I •I - ID. 7S Z.4S I.4b Z.68 Z 68 b:CQ. 8•05 Z.c� 1•C-� . 19 II•rJ D.SOr�2, 1.4s? 1,75 I.15 3.3 15.5 T, t-IMETa D.R IZS = O.9 nni.1 125 - 8.6. O.so O.4S 0.6Z 0,6Z 3.8 l5 •� 0.6Z 3.a 129 lo,6 o'iS 1,4S Z.66 Z.6t6 0,6 6-05 z-� I .. GDMP�Cy = 4 o.Sc + 1.45 o1S IZS 119,1E ,IZ9 0,9 12.4 !]-l01 3.39 4-.7(v 4 �6 ' 13o ISO 13.2 0.50 . 1.31 1.47 47 _ �� I IQ 4' 13Z - IZ•8 C�•30 Z.z5 1.99 [•S1- I 1=uxu TO S1DE-u1ALr-dL�Lrce� I Z7 z O. "70 2. Zo 7.94 12.23 12.23 ' (pMPC, _ '7.94 O"7o + I.99 O••3� 9.93 IZ7 132,I7-7.130 3 7.1 O.(�Z Z.c)o 11,Z4 13.94 13, 13 7. 1 0:75 2.S5 Z•OSI4.39 S.o 14.a I I - 8.3 IS.4 0.15 2,10 3.61 S.S3 �S•S3 O•b 8.05 S-S3 •� 17• 17.66 (� p'C' = 3•s O• /S I(=.93 0.� 44 1Z(o 113 115 116 114. 25.0 �. Pl.-OW TD ZO' CJJe 1♦.11.,6T- in 11s 12A 1 a ¢� rl 1# �8D Jaa___►.�l�.at.-- S�4-.-oog - Remarks ���iii�ii�� -- - - •iiiiiiiii • = iiii -iiiiiii - - - • iiiil ���®�i®- iiii�i = =• i�iii = =• �� l�iiii®�iiii - -• i =- iiiii i •• • • . iiii�� - - ii = - iiiiiiiii • • • . • •- •iiiiii ► - �i - - - iiiiiiii • • •• • •: �!'�®��®• .. i • - • i _- iii • - •iii •.�ii�/Jiiii�i iiiiiii i • • •i _ i'ii� :.. ii. _ - = iii®i i - - • • •. •I iiiiiiiii ®iiiiR!�iiiii _iiiiiiiii • iiiiiii®i i©ii • •' i!'iii • • ��C�3- 7 iiiiiii®i - _ - s • . • . _ IG�I�iiiiiiiii iiiiiii i i iiii�®iii®_ iiiiiii i • ice.!-�i�i©iiC�_ i - • i _• • i®iiiii i R•Z�iii �i� - ®i - - ®®iiiii i i •:• IGlii® • • i®i®®iiiiii i .,. •• ii®i • 1��-- ®iiiiiiiii i • I ■11�iiii®�ii�7iir��3-7iG�7iiiii i ®iiiiii =• • • ®®iiiiiiii - - iiiiiiii E.T1 Ss, O'AINAGE SYSTEM PRELIMINARY DESIGN DATA Location . Design Point Nil .:Pipe ���� �� • • �®moo - = ������ � �i3D ..ion ►.�.o..- �--- "� .. �_ o J ' EXERPTS FROM THE SWMM MODEL FOR MAIL CREEK LEGEND J�3= SWMM ,SUB -CATCHMENT . 34 -- CONVEYANCE ELEMENT A- DETENTION ELEMENT 319 -NODE - POND 5/ ut d FU1UPX-- DEVELChiEN-j 3.69 95. 2.1 0 42. 367 57. 1.4 0 44. ' 366 320 102. 61. 1.8 .1 3.6 0 1 42. 10. 372 66. .8 0 38. 244 256. (DIRECT FLOW) 0 40. 373 123. 3.4 0 40. 371 166. 1.9 0 40. 254 72. 1.0 0 36. 19 61. 1.5 1 12. 28 45. 1.7 0 36. ' 287 40 113, 63. 2.5 ,8 0 0 38. 42. 362 98. 1.0 0 36. 104 17. .1 12.1 2 12. 243 289. (DIRECT FLOW) 0 40. 36 116. 1.1 0 36. ' 107 78,- .1 1.5 1 6. 32 165. 1.2 0 38. 29 109. 2.5 0 38. 27 163, 2,9 0 42. ' 375 43. 3.6 0 52. 374 84. 1.1 0 40. 38 201. 2.6 0 36. 43 31. .1 19.3 6 40. 321 78. .1 1.3 0 48. ' 318 82. 1.7 1 0. 105 20. .1 7.3 1 38. 30 232. 3.4 0 40. 18 199.- 3.2 0 42. 300 96. (DIRECT FLOW) 0 6. ' 245 298. (DIRECT FLOW) 0 38. 42 75. 2.6 0 36. 35 249: 1.2 0 36. 319 95 .� (DIRECT FLOW) 1 34. ' 17 415: 4.3 0 44. 301 96. (DIRECT FLOW) 0 6. 103 221. .1 6.6 0 50. 102 80. .1 16.0 1 40. ' 16, 596. 4.1 0 48. 290 69. 5.0 7.0 1 12. 262 36. 3.0 16.3 1 28. 33 170. .1 12.0 2 20. 15 543. A 1.9 0 54. ' 271 186. (DIRECT FLOW) 0 6. 270 69. 4.4 3 0. 261 59. 3.5 .8 0 50. ' 14 272 715. 224. 3.9 7.7 0 3 54. 0. 13 774. 4.8 0 54. 12 987. 7.0 0 56. 210 1015. (DIRECT FLOW) 0 54. 101 1009. .5 4.6 0 56. 211 1056. (DIRECT FLOW) 0 54. 100 1000. .5 24.1 1 6. 11 10 1017. 1055. 5.4 4.9 1 1 10. 14. �tJ�/HYA.►JG t=l >=A/1f=�� d C FLOW) 1 I n�lhJ cJ STc>r?.�p- 1' ENDPROGRAM PROGRAM CALLED ��lf 1=LOt� M E.I.bT 11 I/ 11 Ig� 27. 21. 0. 16. 42. 49. 4. 2. '.0( 6 32. ) 374. .4(S) 370. O(S) 358. 8.7(S) 202. 15.3(S) 166. 20.5(S) 27. 3.7(S) 28. M ) 1. 0. 21. 3.1( ) 3.3( ) 4.3( ) 1.8( ) 1.4( ) O(S) .9( ) .3( ) .2( ) .9( ) 21. 0. 138. 0. 0. 0. 16. 31. 31. 0. .0( ) 1( ) 4.3(S) .0( ) .1( ) :0( ) .8( ) 2.2( ) 19.2(S) .0( ) 36. 36. 1. 369. 358. 34. 16. 5. 21. 21. 2.1( ) 3.2(0) .3( ) 13.6(S) 3.0(S) 15.3(S) 5.2(S) 5.5(S) 1(S) 1.3( ) ' 21. 0. 0. 0. 0. 0. 0. 0. 0. 0. 23.7(S) 1( ) .0( ) -I( ) .0( ) .2( ) .1( ) .1( ) .0( ) -I( ) 0. 0. 0. 0. 2. 2. 1. 0. 0. 0. ' .0( ) .1( ) .0( ) -I(,) .2( ) .2( ). .3( ) .0( ) .O( ) .0( ) 0. 1. 156. 64. 64. 0. 353. 42. 357. 21. .0( ) .3( ) 6.5( ) 80.0(I) .0( ) .0( ) .0( ) .0( ) .0( ) .9( ) ' 27. 21. 0. 16. 42. 48. 4. 2. .0( ) .4(S) O(S) 8.5(S) 15.4(S) 19.9(S) 3.7(S) .3( ) ' 1 MAIL CREEK BASIN, DEV. CONDITIONS 1987 100-YEAR STORM/W UPDATED POND 8105 INCLUDES MOUNTAINRIDGE 10/93-ALTERNATIVE NOA-C RID FILE 10.02011802.DAT 11/94) ' ***.PEAK FLOWS, STAGES AND STORAGES OF GUTTERS AND DETENSION DAMS CONVEYANCE PEAK STAGE STORAGE TIME ELEMENT (CFS) (FT) (AC -FT) (HR/MIN) 206 60. 1.8 0 36. 203 56. 1.8 0 36. ' 205 17. .1 1.6 1 10. 207 15. .1 1.4 1 10. 204 82. 2.2 0 38. 201 107. 3.1 0 40. 202 15. 1.2 1 22. 200 192. (DIRECT FLOW) 0 40. 49 327. 3.7 0 46. 48 342. 3.3 0 48. 44 66. 2.0 0 42. ' 50 404. 5.2 0 48. 280 59. 2.1 0 38. 25 157. 2.9 0 40: 24 51. 3.2 0 44- 23 318. 3.9 0 40. 47 404. 3.6 0 48. 279 17. .1 1.5 1 B. 222 524- (DIRECT FLOW) 0 40, 185 59. 1.7 0. 36. 51 405. 4.3 0 48. 46 67. 2.0 0 36. 22 22. .1 29.5 2 28. 364 107. 1.0 0 38. ' 278 56. .1 31.2 2 44. 45 103. 2.4 0 38. 221 160. 2.5 0 38. 21 2. 1.3 2 . 399 5. .1 4.9 2 22. 22 ' 365 97. 1.0 0 38. 247 42. .1 15.4 6 40. 20 169. (DIRECT FLOW) 0 38. 368 56. .8 0 36. ' 370 '121. 3.1 0 36. 1 iEXCERPTS FROM THE FOSSIL CREEK DRAINAGE BASIN 1 , 1 MASTER DRAINAGEWAY PLANNING STUDY EXECUTIVE SUMMARY The results of a master drainageway planning study, for the Fossil Creek Basin upstream of Fossil Creek Reservoir are detailed in this report. The report was prepared for the City of Fort Collins, Larimer County and the i Colorado Water Conservation Board. The report defines the basic data used in the hydrologic, hydraulic, sedimentation, erosion and economic analyses and presents alternative improvement plans to solve the potential flooding and erosion problems. One improvement plan is selected, based primarily on the economic analysis, as the recommended improvement plan. For this plan, preli- minary design data and a detailed discussion of the plan implementation are presented. Basin Characteristics The tributary area for the Fossil Creek Basin upstream of Fossil Creek Reservoir is approximately 20.9 square miles. Tributaries analyzed as a part of this study are Stanton Creek, 2.5 square miles; Lang Gulch, 6.7 square miles; Smith Creek, 2.4 square miles; and Burns Tributary, 2.1 square miles. The basins are composed of grass covered, rolling hills mostly used for grazing. Some urbanization exists or is proposed in the lower portion of the basins. Hydrologic Analysis A hydrologic analysis was performed to determine peak flow rates and flood hydrograph volumes at design points for the 2-, 5-, 10-, 50-, 100- and 500-year flood frequencies. The hydrologic analysis was performed for both existing and developed basin conditions. Developed basin conditions assumed land uses according to zoning within the Urban Growth Area. Rainfall depths for the 2-, 5-, 10-, 50-, 100- and 500-year storm fre- quencies were from NOAA and assumed to define hydrographs of the corresponding flood frequency. The Stormwater Management Model (SW4M) was used for the ana- lysis. The input data were based on subcatchment and channel unit delineation and watershed parameters estimated from a previous U.S. Army Corps of Engineers (COE) study. Hydraulic Analysis Hydraulic analyses of Fossil Creek, Stanton Creek, Lang Gulch, Smith Creek and. Burns Tributary were made to determine water -surface elevations for the 2-, 5-, 10-, 50-, 100- and 500-year floods for existing and developed con- ditions. The Water Surface Profile Model, HEC-2, was used to determine. water - surface elevations at cross section locations. Cross sections that were digi- tized from 1977 mapping were obtained from the COE. Cross sections for Stanton Creek were obtained from City of Fort Collins topographic mapping. The topographic maps used in the report are at a scale of 1"=2001, with two - foot contour intervals. The results of the hydraulic analysis defined a relatively narrow flood plain confined to a valley channel except where floodwater ponds behind railroad and roadway embankments. Generally the ponded area is a few hundred feet wide except upstream of the Union Pacific Railroad at Fossil Creek which ponds water over approximately 85 acres during the 100-year flood. Of 19 major channel crossings along Fossil Creek and the four tributaries, nine would be overtopped by one foot or more of water during the 100-year flood. Improvement Plans Improvement plans were developed to alleviate flooding. Alternate impro- vement plans were developed considering (1) leave the system "as is," (2) eli- minate storage behind embankments and.channelize for the 10-, 50- and 100-year flood flows, (3) enlarge culverts as necessary to prevent embankments from overtopping and allow three feet of freeboard for the 100-year flood, and (4) raise embankments as necessary to prevent embankments from overtopping and allow three feet of freeboard for the 100-year flood without culvert enlarge- ment. Improvement plans considered improvements along Fossil Creek and the four tributaries. The economic analysis and preliminary design is for Fossil Creek only. Economic Analysis The economic analysis involved estimating flood damages, costs for the alternate improvement plans, and the corresponding flood damage reduction in dollars as a result of the improvements along Fossil Creek. No dwellings are inundated by flooding. Flood damages were associated with replacement costs of roads that were overtopped and assumed to fail. The analysis was performed on a reach -by -reach basis. The results are presented as benefit -cost ratios and net benefits for each reach for each improvement plan. The range of the benefit -cost ratio was from 0.04 to 0.85. All ratios are less than one since there is little existing damage potential ' to economically justify the cost of improvements. The average benefit -cost ratio for Alternative 2 was 0.10 as compared to 0.45 for Alternative 3 and 0.38 for Alternative 4. These ratios differ from the range of ratios because all benefits and costs are considered to affect the entire basin whereas on a reach -by -reach basis only cost and benefits for each reach are considered. Total costs for Alternatives 2, 3 and 4 are $21,117,900, $3,355,300, and $3,814,300 for the 100-year design flow. Total annual cost is $1,632,200 for Alternative 2, $276,900 for Alternative 3, and $3161100 for Alternative 4. ' The annual costs are based on a 50-year life and a discount rate of 7-3/8 per- cent. The discount rate is from federal guidelines. Alternative 3 was the selected improvement plan based on the highest benefit cost ratio. Stability Analysis of channel Banks ' A stability analysis was performed to evaluate bank stability and deter- mine equilibrium slopes for existing and developed hydrology and hydrology corresponding to the selected improvement plan. Bank stability along Fossil Creek and the tributaries ranged from extremely stable to extremely. unstable. Unstable banks were generally on the outside of meander bends. Major bank instability problems are produced by general degradation of the streambed. The equilibrium slope analysis determined aggradation and/or degradation potential of reaches along the channel system for three flow regimes. Recommended improvements to limit degradation and stabilize banks in these reaches were based on the flow regime corresponding to Alternative 3. ' Plan Formulation The selected improvement plan was based on enlarging culverts and main- taining three feet of freeboard behind embankments which pond water. The suggested improvements are guidelines for the local communities. The improve- ments are based on the 100-year flood frequency for developed conditions. 7- V The plan calls for a vegetated channel from Fossil Creek Reservoir to the Union Pacific Railroad. The crossing at Timberline Road (County Road 11) should be enlarged. A headwall should be.placed at the upstream end of the Union Pacific Railroad. The road at Trilby Road (County Road 34) should be raised and the culvert enlarged. The channel crossing at Lemay Avenue (Co ... ... unty Road 13) should be enlarged. The reach between Mail Creek and the Colorado & Southern Railroad requires riprap along the south bank near Portner Reservoir in order to stabilize the bank. The upstream wingwall on the south side of the C&S Railroad should be stabilized. It appears to be failing due to embankment sloughing. The downstream embankment at Fossil Creek Drive should be adequately protected to handle one foot of overtopping. Currently there is downstream protection and the stability during a 100-year storm should be checked. The channel crossing at Shields Street should be enlarged to prevent overtopping. The channel at the downstream side of all culverts and channel crossings should be riprapped. Also, based on the proposed improvements, the equilibrium slope analysis determined locations for erosion control structures along Fossil Creek. Five - feet of degradation should be allowed for downstream of Lemay Avenue (County Road 13). The reach upstream of Lemay Avenue will degrade slightly but will stabilize due to the aggradation occurring in the reach upstream of the Mail Creek confluence. Between Highway 287 and the C&S Railroad about 8.7 feet of degradation is expected due to high velocities. Two erosion control struc- tures located at the railroad crossing and the center of this channel length are recommended. Another Fossil Creek channel reach that will tend to degrade is between the Burns Tributary Confluence and Shields Street.. Here, an ero- sion control structure that allows for three feet of degradation should be placed at the center portion of the reach and another 3.3 feet of degradation should be allowed at Shields Street. Slight aggradation is expected along Smith Creek and Burns Tributary to achieve an equilibrium slope and no improvements are recommended. Both Stanton Creek and Lang Gulch require improvement to limit degradation. I I Z4� Reach 5: Shields Street to upstream embankment of Taft Hill Road Stanton Creek - Reach 6: Confluence with Fossil Creek to County Road 32 Lang Gulch - Reach 7: Confluence with Fossil Creek to 1/2 mile upstream of Shields Street Smith Creek - Reach 8: Confluence with Lang Gulch to 1/2 mile upstream of Shields Street Burns Tributary -Reach 9: Confluence with Fossil Creek to upstream embankment of Taft Hill Road. The reaches are located in Figure 2 and described individually below. 2.2.1 Fossil Creek, Reach 1 The land along Reach 1 is grassland and fairly flat. The channel reach is generally swampy, especially downstream of Timberline Road (County Road 11). The channel is perched and sized for low flows. Storm water flows northeast from the channel along a wide swale and ponds. The water creates a wide, shallow flooded area upstream and downstream of Timberline Road before it'flows into Fossil Creek Reservoir. x 2.2.2 Fossil Creek, Reach 2 The land along Reach 2 is grassland with slightly rolling hills. Currently, the area east of County Road 13 (Lemay Avenue) is platted for homes and a golf course. The area west of Lemay Avenue and bordering Portner c' Reservoir has been purchased by the City for a park. Other development is proposed at the park border. The channel along this reach is meandering, with steep banks and bank sloughing occurring. The flood plain is narrow except where the water ponds behind the Union Pacific which backs water up 1/2 mile above County Road 34 (Trilby Road). Also, water ponds above County Road 13 (Lemay Avenue). The confluence of Fossil Creek and Stanton Creek and the confluence of Fossil Creek and Mail Creek are located near the downstream and upstream boundaries, respectively, of this reach. 2.2.3 Fossil Creek, Reach 3 The land use along this reach is low=density residential and open grassland. Part of the flood plain is confined by a natural embankment to the recurrence intervals on semilogarithmic paper. Resource Consultants Inc. of ' Fort Collins, Colorado, provided a two-year, one -hour rainfall depth that was obtained from a frequency analysis of 30 years of precipitation records at ' Fort Collins. This is 0.13 inch higher than the value given by the two-year rainfall intensity duration curve. The Colorado Urban Hydrograph Procedure ' was used as a guide in distributing the incremental rainfall values. The one -hour distribution is shown in Table 1. The point rainfall depths ' for each recurrence interval along with an 85 percent areal reduction are shown in Table.2. Table 3 contains the rainfall.hyetographs used for the dif- ferent recurrence interval storms for the Fossil Creek basin. 3.3 Drainage Basin Parameters ' The parameters required to determine runoff peaks and volumes from SWMM are subcatchment area, width, percent of impervious area, infiltration rate, depression and detention storage, overland roughness coefficient and storage discharge curves for ponded areas. The percent of impervious area was deter- mined for existing and developed conditions. For existing conditions, the percent of impervious area was determined by the COE (ref. 9) and checked with U.S. Geological Survey topographic maps (ref. 20). The percent of impervious area for developed conditions.was_based on land use as defined by the Zoning Map for the Urban Growth Area in Figure 4 (ref. 6). Percent of impervious ' area by land use is in Table 4. The hydrologic analysis for the 2-, 5-, 10-, 50-,,100- and 500-year ' recurrence intervals was performed for two cases in the Fossil Creek watershed. Existing and developed conditions with all storage behind existing ' roadways were two cases. A third case was for developed conditions without existing storage behind roadways to evaluate the effectiveness of detention ' storage behind roadways. This was for the 10-, 50- and 100-year floods. Infiltration rates for pervious areas are based on soil types obtained from the "Larimer County Soil Survey," (ref. 23). Table 5 shows the range of ' infiltration rates used for each soil type. The Heldt-Renohill-Kim asso- ciation was predominant. Depression and detention storage used was 0.3 inch ' for pervious areas and 0.2 inch for impervious areas. Subcatchment roughness characteristics were consistently 0.013 for impervious areas and 0.12 for per- vious areas. Channel units, lengths, slopes and geometries were defined from field surveys, 1" = 200 feet topographic maps (ref. 1, 7) or USGS 1" = 2000 ' 8. z6/ 1 1 1 1 1 1 1 1 1 1 Table 7. Fossil Creek Basin, Discharge in cfs for Existing Conditions. Location (SWMM Channel Unit) FOSSIL CREEK Taft HI II Road (56) above (310) below Shields Street (48) above (305) below Burns Tributary (204) above (205+204) below Lang Gulch (47) above (47+200) below Colorado 3 Southern (206) above Railroad (307) below Highway 287 (47) above (312) below Mall Creek (38) above (2 9+38) below Lemay Avenue (211) above (County Road 13) (313) below Stanton Creek (22) above (22+23) below lnlon Pacific (22+23) above lallroad (300) below rimberl ine Road (202) above (County Road 11) (314) below itudy Limit (15) above 0 5+19) below STANTON CREEK Lemay Avenue (24) above (County Road 13) (15+19) below ' County Road 32 (331) above (331) below ' Confluence with Fossil Creek (23) LANG GULCH Distance Drainage Recurrence Interval (Years) from Area Mouth (sq. mi.) 2 5 10 50 100 500 (mi) 0.7 .110 190 270 480 620 910 80 130 160 200 220 240 1.2 90 200 290 520 640 910 90 160 200 480 640 910 1.3 100 170 200 510 670 980 3.4 190 340 430 850 1040 1420 3.6 190 340 430 790 980 1390 10.3 290 660 920 1490 1780 2350 10.4 290 660 920 1490 1780 2390 290 660 920 1490 1780 2350 10.5 290 660 920 1490 1780 2350 290 660 920 1490 17BO 2350 11.5 290 670 960 1620 1970 2690 14.1 330 760 1100 2030 2520 3500 14.2 330 760 1100 2030 2520 3500 310 740 1100 2030 2520 3500 16.0* 310 740 1130 2170 2720 3910 18.5* 340 830 1330 2560 3360 5180 18.5* 340 830 1330 2560 3360 5180 300 450 700 1310 1380 1490 19.7* 300 450 700 1340 1410 1540 270 410 540 1200 1350 1490 2 0.0* 270 410 540 1200 1350 1490 21.1* 270 410 550 1210 1360 1500 1.6 50 170 300 730 970 1500 50 130 170 270 470 1010 1.8 60 130 170 300 530 .1140 60 130 170 300 530 1140 2.5 80.150. 220 450 670 1380 ' Study Limit (79) 1.7 Shields Street (76+200) above 2.8 (301) below ' Colorado E Southern (201) above Ra ) (road 14 (302) below 50 90 140 280 350 510 70 200 350 800 1040 1570 70 160 200 300 470 1030 70 160 200 300 470 1030 70 160 200 300 470 1000 12.59 11.27 11.12 10.45 10.17 9.70 7.70 7.34 5.66 5.60 4.71 3.98 1.43 1.31 0.00 3.31 2.63 2.47 Z7/ Table 24. Detention Data for Embankments, 100-Year Flood - Developed Conditions: Location FOSS I L CREEK County Road 11 Union Pacific RR 3 Tr I Iby Road (Cty. Road 34) Lemay Avenue (Cty. Road 13) Colo. d Southern RR Fossil Creek Dr. Shields Street Taft HI 11 Road STANTON CREEK County Road 32 Lemay Avenue (Cty. Road 13) LANG GULCH Colo. d Southern RR 12 Tr I iby Road (Cty. Road 34) and Colo. E Southern RR 13 Colo. d Southern RR 14 Shields Street SMITH CREEK Shields Street Taft Hi I I Road BURNS TRIBUTARY Shields Street Taft Hi II Road Maximum Maximum Depth of Detention Water Flcw Over Embankment Volume Depth Road Height (ac-ft) Ift) (ft) Ift) 210 11 2 9 570 25 - 52 - 18 3 15 37 15 2 13 19 12 - 33 - 8 2 6 12 15 1 14 19 10 - 22 18 14 2 12 54- 13 1 12 5 5 - 18 9 9 2 17 2 11 12 7 - i1 56 13 2 i1 40 6 - 11 53 16 32 14 - 28 47 17 Comments Enlarge channel cross I ng. Perform stability ana- lysis Dervelop adequate detec- tion Enlarge channel crossing Unstable wing wall at U/S face of crossing Increase culvert and weir capacity Enlarge channel crossing En 1 arge channel crossing Check stability of embankments Check stability of embankments 1 Z3% 8.2.2 Alternative 2 ' Channelization and enlarged road crossings were considered under Alternative 2 as shown in Figure 30. Vegetated, trapezoidal channels with concrete trickle channels were designed to carry the 10-, 50- or 100-year developed flows. Alternatives 2a, 2b and 2c refer to the 10-, 50- and ' 100-year channel design frequencies,. respectively. Manning's equation, assuming uniform flow, was used to size the channels. ' Design flow depths were limited to four feet, channel velocities were limited to 7.5 ft/sec, side slopes ranged from 4h:1v to 5h:1v, and Manning's roughness ' coefficient was equal to 0.035, For the design channel, one foot of freeboard was allowed and a 10 foot access road for maintenance was included in the top width Right -of -Way (ROW) requirement. ' Table 27 presents a summary of the channel design data for Alternatives 2a (10-year), 2b (50-year) and 2c (100-year) along Fossil Creek. Enlarged crossings are required at nine locations along Fossil Creek. The dimensions of the box culverts and spans are listed in Table 28 for ' Alternatives 2a (10-year), 2b (50-year) and 2c (100-year). Velocities along the channels downstream of Highway 287 were less than ' five ft/sec, which will limit erosion along the channel. Velocities along the channels upstream of Highway.287 were between 6 and 7.5 ft/sec. Enlarged openings at channel crossings along the -tributaries were assumed ' when computing design flows for Fossil Creek. ' 8.2.3 Alternative 3 Alternative 3 utilized the natural storage behind road embankments, ' Figure 31.' Where necessary to prevent overtopping the road during the 100-year, recurrence interval flood for developed conditions, the culverts at ' the channel crossing were enlarged. Development would not be allowed in the flood plain. A vegetated trapezoidal channel between Fossil Creek Reservoir and Union Pacific Railroad is recommended because of the limited storage ' upstream of County Road 11. Enlarged channel crossings along Fossil Creek are required at County Road 11, Trilby Road (County Road 34), Lemay Avenue (County ' Road 13) and Shields Street. Improvements along the tributaries were sized for Stanton Creek at County Road 32 and Lemay Avenue (County Road 13) and Lang ' Gulch at Trilby Road (County Road 34) and Shields Street. These improvements were not considered in the economic analysis. '6 II II ICI CHARTS, GRAPHS, TABLES U i L d t Z4/ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 �i 1MORENO DRAINAGE CRITERIA MANUAL 50 30 1- 20 Z W U Cr W a .10 Z w a O 5 In W 3 O cU 2 OC W 1- 3 1 RUNOFF -Mmmm 11._ mmoll�111C , 1 NINE 11-- FAME IA■ NoNo NONE %NN■N= •, . 1, I' mom■■O �W" I■ Ir■NIl �I110111 FAI•►/NI./ MENEM s .0 .l 2 3 5 10 20 VELOCITY IN FEET PER SECOND FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR 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, SCSJan. 1975. 5 -1-84 URBAN DRAINAGE & FLOOD CONTROL DISTRICT DRCOG 30/ No Text