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Home My WebLink AboutPROSPECT INDUSTRIAL PARK, LOT 15 - PDP - 28-98 - REPORTS - DRAINAGE REPORT1 c3� / •.. � ]-ED � ►- / \ / \: r • u3 ,,. Mid oint _ o = I a° 1 1 I 1 Ll 1 C� •-- .-. 1 1 1 1 1 � 1 � i INV ® 1 1 1 East Drake Road VICINITY MAP SCALE: 1 "= 1000' pan at the North lime of Prospect Industrial Park. The pan crosses at the Southeast comer of the existing Larimer County Jail property. Therefore, 1200 feet of Midpoint Drive is carrying runoff from the high point to the Northwesterly comer of Lot 15. Three of the lots that have been developed have onsite detention. Five lots that have been developed do not have detention and eight lots have not been built on. The resultant runoff coefficient for the 14.3 acres is 0.35 Since Lot 15 is at the low end of the basin and near the discharge to the Cache la Poudre River we are not providing on site storm water detention. The rate of runoff at the Northwesterly comer of Lot 15 is Q2,,, = 6.5 c.f.s. and Q100,, = 24.1 c.fs. The capacity of the street cross section is 68.45 c.f.s. at 6 inches over crown. EROSION CONTROL: The site is located in a moderate wind erodibility zone and in a high rainfall erodibility zone. A silt fence will be required around the perimeter of the site prior to beginning any overlot grading. Immediately after grading, the concrete building foundation will be installed and gravel road base shall be placed in the driveways and parking areas. This road base shall be thick enough to handle construction traffic without failure. Straw bales will be installed after the site is graded and before the curb and gutter and asphalt is installed at the points where the runoff discharges into Midpoint Driv'.-. This is a fairly small site and it will be very busy during building construction so vegetative plantings will not be done until the building and paving procedures are nearing completion. Wind erosion control on the site will be provided by the silt fence, building foundation and gravel road base. All erosion control procedures shall comply with the City of Fort Collins Criteria. The stormwater runoff calculations, the Grading, Drainage and Erosion Control Plan and the overall Utility Plan of Prospect Industrial Park showing the stormwater flows in Midpoint Drive are enclosed as part of this report. This drainage report and the design of the drainage system for Lot 15 are in compliance with the City of Fort Collins Storm Drainage Specifications and Criteria. If you have any questions regarding this report, please call. Sincerely, GisTE'q�; p4 * 5028 Richard A Rutherford, P.E. & L.S. MF STEWART86SSOCIATES Consulting Engineers and Surveyors September 21, 1998 Mr. Basil Hamdan Storm Water Utility City of Fort Collins P.O. Box 580 Fort Collins, CO 80522-0580 Dear Basil, The following is the Final Drainage Report for Lot 15, Prospect Industrial Park, City of Fort Collins, County of Larimer, State of Colorado. The site is in the Poudre River Basin and contains 1.3724 acres. The existing site slopes from Northwest to Southeast at an approximate slope of 0.7%. The site has a very good ground cover of grass and weeds. It is proposed to divide Lot 15 into two new lots which each will have an office/warehouse building. The site will be phased with Lot 15-A being Phase I and Lot 15-B begin Phase U. The site is in the Poudre River Basin and is within approximately 1100 feet of the Cache La Poudre River. Due to this close proximity to the River, it is proposed to not have storm water detention on site. The runoff from the basin enters the outfall system to the River at the existing inlets at the comer of Midpoint Drive and Sharp Point Drive. The Westerly inlet is only 450 feet Southeasterly of the Southwest comer of Lot 15. The two inlets drain in a 24 inch R-C.P. to an existing gravel pit which drains into the Cache La Poudre River. The stormwater will be carried in the on -site curb and gutter to.the two driveways where it will enter the Northeasterly gutter of Midpoint Drive at both driveways on the site. The Phase I Building is Developed Basin-1 and the developed runoff rates for it are Qm = 1.93 c.£s. and Q,00 = 6.70 c.f.s. The second phase is Developed Basin-2 and the developed runoff rates for it are QZn = 1.56 c.f.s. and Qloo n = 4.68 c.f.s. There is not any appreciable stormwater runoff entering this site from off site. Lots 10 & 11 which are adjacent to the rear of Lot 15, drain Southeast onto Lots 13 & 14. Lot 16 has not been developed at this time and some of its historic runoff will sheet flow onto D.B.-1 and D.B.-2. The grading on both basins will accommodate the off -site flow through each basin to Midpoint Drive. The offsite flow onto D.B.-1 is Qlao = 0.37 c.f.s. and onto D.B.-2 is Qloo = 0.57 c.f s. There was some concern at the conceptual review meeting regarding the capacity of Midpoint Drive to carry the stormwater runoff that discharges into it. The flow in the Midpoint Drive South and Southwesterly gutter from Timberline Road to the North lime of Prospect Industrial Park is diverted to the East in a pan across Midpoint Drive and then to an existing pond in the Prospect East Industrial Park. The North and Northeast gutter of Midpoint Drive flows into the Specht Point Road, Prospect Parkway and the above described pan. There is a high point in Midpoint Drive 110 feet South of the James H. Stewart and Associates, Inc. 103 S. Meldrum Street P.O. Box 429 Ft. Collins, CO 80522 970/482-9331 Fax 970/482-9382 Table of Contents 1-2 Text of Report 3 Vicinity Map 4-9 Storm Water Runoff Calculations 10 Midpoint Drive Drainage Capacity 11-14 Erosion Control Calculations 15 Variance Request Pocket Utility and Grading & Drainage and Erosion Control Plan Plat of Off -site Areas Draining to Midpoint Drive n 0 11 I i FINAL DRAINAGE REPORT FOR LOT 159 PROSPECT INDUSTRIAL PARK POUDRE RIVER BASIN PREPARED FOR DOHN CONSTRUCTION, INC. SEPTEMBER 21, 1998 PREPARED BY STEWART & ASSOCIATES 103 SOUTH MELDRUM STREET FORT COLLINS, CO 80521 TEL. 970-482-9331 FAX. 970-482-9382 i