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Home My WebLink AboutWATERFIELD PUD, FIRST FILING - FINAL - 7-95C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI DI i 1 1 gVICINITY MAP � „=2000' ww / rla oh n wrz R 3 ar Surveying, RC. Proj.<t No: A9485 Client , C..r..11 . A..,_n/. I >e/ ,_ ,, m. �.�, �� LAND EXIHIBI P o.an.:w M. s fui[r,.o 3UIW1 rl[a PPOPIR1IIa 1 a¢,s sx¢n . I _ —1- BUpUNGTON � • le . , ,,� ... �. •:<.y _. '.T�•. \ Cis^' 1 I 1 •°y. • 33 ...... 4496 I,IW <r w• I � �I r• m Ip T 8 N 99 i9901 T7N ' 4495 �• ` �Itia.ra'siratatilk—. -•---• •----• r �N P D t a•, �4 w9 BW6 OW R r unc nIF PaM r ¢ N. . ; N I •a �e e 4 • , WNTO "I s9s M a — • FORT C0 S_ ��_ '-rr� L _-----------1 1 PAR - •w •r f9 A R� ■ L- •• '• I rails\ w ' -17 V�_r We-m-I I, •\ n \'ice .rt ••• �• .. .: .1 s:. Af-Ti yi' + F f.. w ,� � �, ♦ • � �� V�/ ' INLET v,T � ��' kr�.�,w,.�+dt}' •- ... _ a saa4� L.._ !' '_ 3 !�� '..Lr�rr� '-:.; }"Y'R Cam: 1 • . r 1' '� ' �`1L••R,-�'1. a ��e.. - �' y%, •y '� �i�R. l�. M��R },d7i ,� yam'. •... i -^, 1: 4 YP^ ;•*rl R -�.in y �, � Tt�H: r ... t �yrft� � :,, ^`a�s' Mr. Mike Ludwig Page 2 ' June 20, 1997 In addition, a chemical analysis of the irrigation canal water, ground water, and wetland pond water will be conducted. This analysis will help in determining the source of water for the wetlands. An analysis of the major ionic species (Ca, Mg, Na, K, Cl, HCO,, and SO,) for the three waterbodies would provide sufficient information to determine water types. A trilinear diagram plot will graphically display the differing water compositions. Please do not hesitate to contact me if you have any questions concerning this letter or the future work planned for the Waterfield P.U.D. Site. Sincerely, Riverside Technology Terry Geiselman Registered Geologist cc: Rob Wilkinson, City of Fort Collins Basil Hamdan, City of Fort Collins Jim McCory, Colorado Land Source Bud Curtiss, Northern Engineering Patrick Plumley, RTi Richard Spotts, RTi gmcmUlud.,gl.dnc 06,20197 PRiverside Technology, inc. Water Resources Engineering and Consulting June 20, 1997 Mr. Mike Ludwig Project Planner Fort Collins Planning Department 281 N. College Ave. Fort Collins, CO 80526 Dear Mr. Ludwig: This letter is in response to the Waterfield P.U.D. Fist Filing scheduled for June 18, 1997. It is Riverside Technology, inc.'s (RTi s) understanding that the Waterfield P.U.D. First Filing will consist of the apartment complexes and single family dwellings located on the property's east side. We also understand that the City wishes to avoid any impacts to the wetland area if possible. There is some concern because a subdrain system will have to be installed to allow for the construction of basements in the single family dwellings. The current plan is to route the water collected in the subdrain system to a detention area located to the southwest of the property. If the diverted water is currently supplementing the wetland hydrology, the reduction in ground water flow may impact the wetlands. RTi conducted an initial study of the ground water system at the Waterfield Site during April, 1997. The results of this study were summarized in a report entitled Preliminary Evaluation of the Ground Water System at the Waterfield P.U.D. Site dated April, 1997. As part of this report, a potentionietric surface map was constructed from existing ground water elevation information. The map indicates that the basic direction of ground water flow in the area of the First Filing is to the south and not towards the wetlands area. If this is the case, diverting the collected ground water from the subdrain system to the detention area should not impact the wetlands. RTi is proposing to conduct additional ground water work at the Waterfield site during July and August, 1997. This work will consist of installing additional peizometers and modeling the ground water system using a model called "MODFLOW." The model will provide information on how the ground water system will be effected by the First Filing construction activities as well as future development that is planned for the site. If the model indicates that ground water flows-, from the First Filing area are supplementing the wetlands hydrology, the subdrain system will be rdesigned and the collected ground water will be directed into the wetlands. Mr. Basil Hamdan with the City of Fort Collins Storm Water Division is familiar with the applications of MODFLOW and will be contacted to review and comment on the results of the modeling program. R., emOudma2.ea anavi r2290 E. Prospect Road, Suite 1 Fort Collins, Colorado 80525 (970) 484-7573 FAX: (970) 484-7593 i 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. V. 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 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. Stormwater Quality Because water quality is important to this developer, water quality mechanisms 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. Erosion Control Concepts The developer of this project understands that the wetlands adjacent to this project, must be protected during the construction process. Therefore, all erosion control measures, specified within these plans must be maintained and protected until all disturbed areas have been stabilized with vegetative methods. developed flows from this project will be allowed to enter either the Plummer School outparcel, or the 5 acre outparcel (designated as Basins OFF2 and OFF3. The conveyance system for this development is being sized to account for flows coming from the 5 acre outparcel. The detention pond contains approximately 11.92 ac.ft. Of storage volume up to an elevation of 4948.0. Required detention based on the FAA method of determining detention volume was calculated to be approximately 9.96 ac.ft. of storage. This.is based on a release rate from the pond of 2.75 cfs. The difference between the allowable release rate of 7.55 cfs and the proposed 2.75 cfs is from the adjacent roadway sections which cannot drain to the pond area. Water quality capture volume needed for.the site was calculated to be approximately 0.82 ac.ft., for a total pond required of 10.78 ac.ft. This is accomplished with a 100 year water surface elevation of approximately 4947.57. An emergency overflow weir will be constructed at the southwest comer of the site, which would direct flows towards the Lake Canal if the proposed outlet system was to plug. The offsite channel sections, storm sewer pipes, and the proposed detention pond will be constructed in dedicated easements to the City of Fort Collins. The same owner of the area contained within the First Filing also owns all of the areas necessary for these easements. IV. 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 was calculated and copies included in the appendix of this report. . In general, all disturbed areas not in a roadway section or a building pad area will be treated with a temporary seed and mulch, if not stabilized within 90 days of overlot grading, or sooner if any problems occur. In addition, straw bale check dams will be installed at 250' minimum intervals in all open channels, gravel filters will be installed and maintained on all curb inlets. Silt fence will be installed on the west side of disturbed areas, as shown on these plans, to protect the existing wetlands area. Also, silt fence will be installed around all disturbed areas in proximity to either the Plummer school outparcel, or the 5 acre outparcel on the south end of the project. 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. U r I J '1 II 11 at the southwest comer of the Waterfield PUD. With the exception of the 31.3 cfs of overtopping of the Larimer and Weld Canal north of this site, and the 5 acre outparcel located along Merganser and Vine Drive, no other offsite flows enter the site. All conveyance elements within the site have been sized to accommodate these offsite historic flows. No developed flows from this Filing will be routed through the wetland area, only to the proposed onsite detention pond. 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 37.77 acres (basin H-4). The maximum allowable release rate into Lake Canal has been calculated to be approximately 7.55 cfs. A small portion of the site, adjacent to the Larimer and Weld Canal, and not within any of the development, will continue to release directly into the Larimer and Weld Canal. An overflow weir will be constructed along the southerly portion of the Canal adjacent to the Northwest corner of the site. In the remote possibility of a 100 year storm occurring simultaneously with the Irrigation Canal running full, this weir would direct undeveloped flows from Basin OFF-1 through this site. A small interception Swale (Section B-B) will be installed to route these flows around the single family lots, through a small Tract and on to Merganser, and eventually to Lake Canal. As mentioned above, all developed flows from this site will be routed to the detention pond located offsite at the corner of Future County Road 11 and Vine Drive. An interception swale (Section D-D) will be installed to intercept flows and direct them south. This swale will also be used to convey flows from a subdrain system which is proposed for the single family lots. As future filings are designed, some, if not all of these flows, as well as the subdrain, may be routed to the Wetlands instead. It is the intent of the future filings to utilize the wetlands area for detention. For only the development connected with the First Filing, the offsite pond as shown has more than adequate capacity to accommodate this project. There are two irrigation laterals that feed from the Larimer and Weld Canal. The south lateral was installed to service this farm, which will obviously be eliminated with this development. 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 the Detention Pond. Developed flow from improvements to Summit View will also be picked up in a roadside ditch, and also routed to Pond W37. In any case, no I t 1 7 II tM To calculate the historic flows, used to determine the allowable historic release from the site to Lake Canal, per City criteria, only Basin H-4 is considered historic to Lake Canal. Developed flows located in historic basin H-5 will be detained and released into Lake Canal. A small undeveloped portion of the northeast comer of the site will also release into the Larimer and Weld Canal. As mentioned above there is an existing wetland 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 with the Preliminary PUD submittal under separate cover. A copy of the wetland delineation map has been included in the appendix of this report. Included in the appendix of this report is a letter from Riverside Technology, who are in the process of developing a groundwater hydrological model of this site. III. DEVELOPED DRAINAGE Design Criteria and References 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 Final Drainage Study. Hydrologic Criteria 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 were 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). A SWMM model will be provided for the entire Waterfield PUD with the second filing, when both the wetlands area and the detention pond proposed for this site are utilized for detention storage. Hydraulic Criteria 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. Drainage Concepts The vast majority of the developed runoff from this site will be routed by either curb and gutter, open channels, or storm sewers to the proposed detention pond located 0 Final Drainage Report for Waterfield PUD, First Filing L GENERAL LOCATION AND SITE DESCRIPTION The Waterfield PUD development is located at the northwest comer 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. The Waterfield PUD 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 wetland located on site, which occupies approximately 11.50 acres. The First Filing of Waterfield includes the Bull Run Apartment project, located in the southeast corner of the site, as well as approximately 42 single family lots located in the northeast comer of the site. The parcel which is intended to contain the future Senior Cottages of America project is included as a Tract in this Filing, but is not intended to be developed as part of this project. At this time it is anticipated that the remainder of the site will be filed as a final by Fall 1997. IL HISTORIC DRAINAGE 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 the existing wetlands area. Basin H-3 drains directly to the existing wetland area. This existing wetlands appears to overtop at approximately elevation 4952, and flows south to Lake Canal. This assumption is based on the existing topography which clearly delineates historic drainage in this direction. Basin H-4 drains directly to Lake Canal. Basin H-5, located at the southeast comer 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 comer of the site, drains to the existing Larimer and Weld Canal. Virtually no offsite drainage enters the site. June 20, 1997 Mr. Glen Schleuter City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: Waterfield PUD, First Filing Fort Collins, Colorado Project Number: 9652.00 Dear Glen: Northern Engineering is pleased to submit this Final Drainage Report for the Waterfield P.U.D, First Filing. 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. Roger A. Curtiss, P.E. cc: Jim McCory - Colorado Land 420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159 Final Drainage Report for Waterfield PUD, First Filing Fort Collins, Colorado June 20, 1997 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 Fax (970)221-4159 Project Number: 9733.00 Initial Submittal j Final Drainage Report for . Waterfield PUD, First Filing Fort Collins, Colorado June 20, 1997 e NORTHERN ENGINEERING