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Home My WebLink AboutWATERFIELD PUD - PRELIMINARY - 7-95B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT� w .w A� 1� �* � � � � al � it mw =1 m+ WWI �t ', xueu a v,si es By wrt Landstar K urveying, nc. Project No: A9485 cfienc: mtt a,a, .,.1.,.....�..�......,.w,3, 'K�1.7_3M �,,,,_n„ �. �...�� LAND EXIHIBIT ro a ..u.om. m� � smom vrtr rnrcmcs 1 1 / ' now, IWIlt 111111W 1 LARR.(R C01INTY CITY OF FORT COLLINb COLORADO COOPER SLOUGH RECOMMENDED IMPROVEMENTS SHEET 6 wastr talx,a get M „ iddi O :FEET.:.: •M � 1 , 8QP it 1 I 1 • �o acl 11 33 1-uaaaza ¢z I • • J� r~ lv r;a- .• •o 'IC e�aa+pae a Soo 5013 x a \ • • %_ `\� " — .. / a 499 f99O1 T 8 N "ON -^I as I T 7 N 4495 N .10 S ♦ I .----•--- fl. 1 — .................._,...... �11 1 \ :. •---- ---- -- (j`--••--- " BAR/ER 94 .4 °a ' '•....•: *�lJ ems' ♦�Ll.l.�..�1 I T y a � . c ul:� b Black ow n ru o»i Nortn var I h; •IUnC n 1nd 'Ile Q •r. I ) Tra •';� �=a _�_. as ra i WNTO FORT CO �Ss9f/----------gySinn N93 ,I�. A RPAR -e�.a a a1 •: aas�`_ — , 19 J ■ • ■ i-., ♦ 'I lawn �� ♦. Ce .I 35' a 1� i r ' II 1 -it Trak \\ railer\ q F G==91- Park _ .� �. ,..... „�, -v-- II � 9°•s ;quo • g � � �'' �,. E, "k. `y/� II '•�•• 'I . ' I' ; as Q Zo.�'•7yET L ' ♦,,♦♦ • `\ A 'J4 • • • hl 116 air `S �\ MIAa �a'If 'iU. 4r f • Ijp � a i N 1^ti 1491 i I' r •• ' Il IIIFF• 1x �..+.9 • I �� CG (I n•1' A E k O r dio V � �F• .. '�, cam.,... o-.n. _.. i . 1. �. ) r. .. �.. � ! .. - � i i i i i J I I I I i N VICINITY MAP 1 "=2000' I APPENDIX 1 2. 3. REFERENCES Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. Cooper Slough Master Drainage Study, by Simons, Li Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. preliminary grading and drainage plans adequately provide for the conveyance and detention of developed runoff from the proposed development. If groundwater is encountered during construction, and dewatering is used to install utilities, a State of Colorado Construction Dewatering Wastewater Discharge Permit will be required. Because water quality is important to this developer, water quality mechanism will be incorporated into all aspects of final design of drainage systems. The proposed water quality measures proposed in this study will require regular maintenance to remove deposits as they accumulate. The storm water quality outlet works will release the first flush of storm water runoff over a period of time in order for pollutants to settle out of the runoff. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, at the time of Final Design, the erosion- control performance standard will need to be calculated and appropriate measures taken to control rain and wind erosion from the site. required detention volume of 7.08 cfs, for a total of 8.64 ac.ft. Total volume required. Based on the preliminary grading plan, the pond as shown provides approximately 8.87 ac.ft. of storage. This is based on a maximum water surface elevation of 4944.0. There are two irrigation laterals that feed from the Larimer and Weld Canal. The south lateral was installed to service this farm. The northerly shorter lateral is still in use by two separate users. This lateral will be replaced with a pipe which will convey flows to the headgate which provides flows to the user east of this site. The remaining flows to the user.to the south will be maintained in a piped system (installed previously by the user). This development will not have a negative impact on either of these two irrigation users. Improvements will be coordinated with these users. Drainage in the southeast corner of this site historically drains to a sump area located adjacent to the Plummer School. Developed runoff from this site will be intercepted in an open channel prior to entering the Plummer School site, and routed around to Pond W37. Developed flow from improvements to Summit View will also be picked up in a proposed curb inlet, and also routed to Pond W37 N, EROSION CONTROL General Concept Waterfield PUD lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. At the time of final design, Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, the erosion control performance standard will need to be calculated, and appropriate measures designed to control rain and wind erosion during and after construction. All construction activities must also comply with the State of Colorado permitting process for Stormwater Discharges associated with construction activities. A Colorado Department of Health NPDES discharge permit will be required before any construction grading can begin. y, CONCLUSIONS Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. Drainage Concept The proposed drainage concepts presented in this study and shown on the The vast majority of the developed runoff from this site will be routed either by curb and gutter, open channels, or storm sewers to either the existing wetlands or the proposed detention pond located at the southwest corner of the site. With the exception of the 100 cfs future release from the regional pond north of this site, no other offsite flows enter the site. All conveyance elements within the site will be sized to accommodate the proposed 100 cfs release rate from upstream. These flows will be routed through the wetland area and the proposed onsite detention pond. It is unknown when these future improvements, including the siphon under Larimer and Weld canal will be installed. Detention for the site has been based on the difference between the 2 yr historic and the 100 year developed flows. Only those areas that historically drain to lake canal have been used to calculate the allowable release rate from the site. The historic contributory area to Lake canal is approximately 121.5 acres. The maximum allowable release rate into Lake Canal has been calculated to be approximately 25.51 cfs. Small portions of the site (Developed basins 38 and 39) will be released undetained. Basin 38 (a portion of Vine Drive lower than elevation 4944) is that area of Vine Drive unable to be physically routed into the onsite detention pond. Developed runoff from this basin will be released directly into Lake canal via a proposed curb inlet located adjacent to the canal. This undetained flow was accounted for in calculating the total allowable release from the site, and in sizing the proposed detention ponds. Basin 39 (a small portion of the developed site in the northeast comer of the site) will be released into Larimer and Weld canal undetained. Approximately 77.12 acres of this development will be routed through the existing wetlands. Peak 100 year flows to the wetlands were calculated to be approximately 344 cfs, including 100 cfs from upstream contribution. This will provide water to the wetland area, as well as provide a water quality mechanism for developed runoff. Detention storage was calculated from elevation 4950 to elevation 4952 only. A release structure will be incorporated into the wetlands which would maintain a permanent water surface elevation at 4950. An overflow weir would be installed at elevation 4952 which would prevent water from ponding beyond that elevation. Preliminary calculations show that this 2 foot interval would provide approximately 16.58 ac.ft. Of storage. Utilizing the FAA method for sizing small detention ponds, and using a release rate of 12.75 cfs, the required volume needed would be 7.62 ac.ft. Total downstream release from the pond would be 12.75 cfs from onsite plus 100 cfs from upstream contributions (112.75 cfs total). The site detention pond (Pond W37) will have approximately 65.01 acres of contributory area. 100 year peak inflow into the pond was calculated to be approximately 316.1 cfs (including 100 cfs from upstream plus 12.75 cfs release from the wetlands). Water quality storage volume for 65.01 acres is approximately 1.3 ac.ft plus an additional 0.26 ac.ft. volume for sediment. Based on a release rate of 14.61 cfs (25.51 cfs allowable minus 10.9 released from Basin 38), the FAA method gave a To calculate the historic flows, used to determine the allowable historic release from the site to Lake Canal, Basins H-1 through H-4 were used. Developed flows located in historic basin H-5 will be routed to Lake Canal. A small portion of the northeast corner of the site will also release into the Larimer and Weld Canal. As mentioned above there is an existing wetlands located on this site. A report entitled "Jurisdictional Wetlands Delineation Survey for the Country Club Farms LLC, Larimer County, Colorado" by Riverside Technology was prepared for this wetland, and submitted to the City under separate cover. A copy of the wetland delineation map has been included in the appendix of this report. FrININE . • ..:__ Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual. and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been used for this Preliminary Drainage Study. The Rational Method was used to estimate peak stormwater runoff from the proposed site. The 2 year storm event and the 100 year storm event was used to evaluate the proposed drainage system. Rainfall intensity data for the Rational method was taken from the City of Fort Collins Stormwater Utility Intensity curves (Figure 3-1). City of Fort Collins Storm Drainage Criteria has been used for all hydraulic calculations. In addition, the detention volumes required for this development have been sized using the FAA method for detention ponds developed by the UDFCD was used. Per the Master plan for the Cooper Slough, the developed runoff from this site is to be routed to the Lake Canal (See the attached sketch from the Master plan in the appendix of this report). This Master plan also shows the installation of a regional detention facility northeast of this site, adjacent to the Larimer and Weld Canal and Summit View Drive. Per the Master plan, this pond would provide approximately 36 ac.ft. of detention storage volume, with a maximum release rate of 100 cfs. These guidelines, established by that Master plan have served as basis of this preliminary design. Preliminary Drainage Report for Waterfield PUD The Waterfield PUD development is located at the northwest corner of East Vine Drive (County Road 48) and Summit View (County Road 9E) . The site is also bounded on the north by the Larimer and Weld County Canal. The existing Plummer School is located to the southeast of this site. The site can also be described as a portion of the southwest quarter of Section 5, Township 7 North, Range 68 West of the 6th PM, City of Fort Collins, Larimer County, Colorado. A vicinity map of the site is included in the appendix of this report. This site includes approximately 140 acres. The site is presently undeveloped, has most recently been used for agricultural purposes. The site generally slopes from the west to the east at slopes between 1 % and 5%. There is an existing wetlands located on site, which occupies approximately 11.50 acres. Plans for this site include the development of single-family units, multi -family units, patio homes, an elementary school, a city park, and a small commercial pad site. This site is located within the Cooper Slough Master Drainage Basin. A copy of an excerpt from the Cooper Slough Master plan pertinent to this site has been included in the appendix of this report. Historically, the vast majority of the site drains to the existing Lake Canal, located at the southwest comer of the site. A copy of the existing site, with the historic drainage basins has been included in the appendix of this report. Basins H-1 and H-2 drain south to existing irrigation laterals and on south to Lake Canal. Basin H-3 drains to the existing wetland area, and then on to Lake Canal. Basin H-4 drains directly to Lake Canal. Basin H-5, located at the southeast corner of the site, drains to an existing low point located around the old Plummer School. Drainage from this basin would eventually overtop Summit View, and drain to the east. Basin H-6, located in the extreme northeast corner of the site, drains to the existing Larimer and Weld Canal. Virtually no offsite drainage enters the site. January 20, 1997 Mr. Glen Schleuter City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: Waterfield PUD Fort Collins, Colorado Project Number: 9652.00 Dear Glen: Northern Engineering is pleased to submit this Preliminary Drainage Report for the Waterfield P.U.D. for your review. It represents a study of existing and proposed stormwater characteristics of the project site. This report was prepared in compliance with technical criteria set forth in the, City of Fort Collins, Storm Drainage Design Criteria and Construction Standards manual. If you should have any questions or comments as you review this report, please feel free to contact me at your convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Fl Roger A. Curtiss, P.E. a �� 27362 cc: Jim McCory - Colorado 420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159 Preliminary Drainage Report, for Waterfield PUD Fort Collins, Colorado Jn January 21, 1997 r Prepared For: Colorado Land Source 8101 East Prentice Avenue, Suite M180 Englewood, Colorado 80111 Prepared By: Northern Engineering Services, Inc. 420 South Howes, Suite 202 Fort Collins, Colorado 80521 (970)221-4158 i Fax (970)221-4159 Project Number: 9652.00 C Initial Submittal 11 _ i II Preliminary Drainage Report for Waterfield PUD Fort Collins, Colorado i l J<? January 21, 1997 N O R T H E R N ENGINEERING S E R V I C E S I N C