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HomeMy WebLinkAboutWATERGLEN PUD PDP - 71 93A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT (3)Cw+ �• Mr. Steve Olt April 4, 1994 Page 3 Please feel free to contact us if you have any questions or require additional information regarding this submittal. Sincerely, LOVE & ASSOCIATES, INC. -M Attachment: Preliminary Drainage Report �y Mr. Steve Olt April 4, 1994 Page 2 The check list items for Preliminary Drainage Report follows this transmittal letter. 0 WETLAND ISSUES: Several important new facts have been learned about the groundwater flow regime related to the Cooper Slough. The Slough is not a warm water spring but instead a natural drainage feature that is fed by groundwater including groundwater which is conveyed to the Slough via the tiles which traverse under to the Larimer Weld Canal. The tiles collect groundwater and seepage from the canal system throughout the calendar year. Please refer to the enclosed report from Groundwater Specialists for additional information. • Water Quality The existing farm use of the site is perhaps one of the most detrimintal land uses that occur to impact the water quality in the Cooper Slough. The site is deep plowed on an annual basis which exposes soil to wind and water erosion which adds extreme amounts of sediment to the Cooper Slough on an annual basis. Recently, the land has been planted with corn and is typically fertilized with nitrogen and phosphorous. The fertilizer adds non -point source pollutants to the Slough. The proposed development will decrease the amount of sediment load to the Cooper Slough with the detention ponds improving surface water quality tributary to the Slough. Proposed buffer areas between the Slough and the development will trap much of the pollutants in the surface runoff before they reach the Slough which is use of a Best Management Practice (BMP). • Water Quantity. The proposed development will not appreciably change base flows in the Cooper Slough due to the lean clay type subsurface soils. Likewise, the 100-year developed runoff will be detained to a 2-year historic release rate thereby decreasing peak flow rates to lower than historic rates. Water Temperature. The proposed development will not affect existing water temperature of the Slough. Temperature readings were taken on April 1, 1994, the temperature of the Slough water is 9 degrees C or 48 degrees F and is the same as the temperature of the goundwater measured in the irrigation well located at the north edge of the property along the Larimer and Weld Irrigation Canal and will not be affected by the proposed development. Ii dy rologL. The proposed development will not increase flow rates into the Cooper Slough. However, the duration of the detained releases into the Cooper Slough will be longer than under historic conditions. It is our opinion that there will be no adverse impacts to the hydrology of the wetlands in the Cooper Slough due to the proposed development. Impact to Wildlife. The enclosed report by Groundwater Specialists quantifies that the water quality, water quantity, water temperature and hydrology will not adversely impact the Cooper Slough or its associated wetlands. The developer is willing to consider either permanent pool open water, wetland bottom or dry bottom detention ponds within the development or perhaps a combination in order to enhance wildlife habitat within the proposed development. April 4, 1994 Mr. Steve Olt Project Planner Community Planning & Environmental Services City of Fort Collins P.O. Box 580 Fort Collins, CO 80522-0580 Associates, Inc. w a t e r r e s o u r c a c o n s u l t a n t s 2995 Centergreen Court South. Suite C Boulder, Colorado 80301-5421 Phone (3W) 4463439 FAX (303) 4403835 REF: WATERGLEN PUD - PRELIMINARY DRAINAGE REPORT Dear Steve: This submittal package addresses certain areas of outstanding concern related to the Waterglen PUD as addressed in your letter to Eldon Ward of Cityscape Urban Design dated March 24, 1994. Item No. 5 related to the preliminary drainage report and Item No. 6 related to environmental concerns are addressed in this submittal package. Under separate cover, Karen Schneller McDonald of Cottonwood Consulting has provided documentation for the delineated wetlands that are graphically portrayed in this submittal package. This portion of the submittal will be delivered today directly to Karen Manci of the City's Natural Resources Department. We believe this submittal package addresses the primary drainage, floodplain and wetland related issues requested by the City. The following summarizes our opinions on these issues. DRAINAGE AND FLOODPLAIN ISSUES: • The attached report states that the current Cooper Slough Plan indicates a regional stormwater detention pond with a 100-year detention and release rates equal to the historic 2-year runoff. The proposed ponds for this development have been designed to this criteria and will be modeled by SWMM in the final drainage analysis to account for staging of pond discharges to historic rates. • A new box culvert has been sized at the Cooper Slough and Vine Drive to convey the 100-year Cooper Slough flow with no road overtopping. • All drainage swales have been verified to meet the City freeboard requirements of 1-foot or 33% of the flow (including the Box Elder Creek overflow swales.) • Wetlands have been delineated on the drainage basin maps. • Anheuser Busch discharges will be conveyed in a swale and culvert system to the Cooper Slough.