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Home My WebLink AboutDrainage Reports - 08/20/1998July 14, 1998 Project No: 1608-01-98 Basil Hamdan City of Ft. Collins Stormwater Utility P.O. Box 580 Ft. Collins, Colorado 80524 Re: 742 -746 North College; Fort Collins, Colorado Dear Basil, This letter serves as our response to your review comments concerning the Drainage and Erosion Control Report for 742-746 North College. Our responses to the comments are as follows: We have added the floodplairi requirements to the regulations section of the report. They can be found in Section III of the drainage report. This is in accordance with your written comments dated June 181 1998 and per our discussion on Thursday, July 9, 1998. The applicable City code sections are attached as well in the stuffer envelope for your reference. A copy of the pertinent section of the report is included in this letter for your convenience. 3. The cost of the cumulative improvements to the building over time has substantially improved the site. Refer to Sections 10-16 and 10-20 item 3 of the Fort Collins City code for a definition of substantially improved. These sections are attached for reference in Appendix III. Therefore, the site is subject to the requirements of the City of Fort Collins Policy for substantial improvements (Section 10 of the City Code). a. The owner has agreed to comply with City Code for substantial improvements. This compliance will consist of flood proofing the building as part of the building improvements. This concludes our Control Report for don't hesitate to call Sincerely, response to your review comments concerning the Drainage and Erosion 742-746 North College. If you have further questions or comments, please us at 226-5334. Mark Oberschmidt Shear Engineering Corporation MEO / mo cc: Ted Zibell Shear Engineering Corporation L 4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 FAX (970) 282-0311 a AUG 1 3 FA Final Drainage and Erosion Control Report for 742 - 746 North College Avenue (Will Subdivision) Fort Collins, Colorado Prepared for: Perennial Gardener Attn: Ted Zibell 154 North College Avenue Ft. Collins, Colorado 80524 PRINT DATE JUL 1 41998 SHEAR ENGINEERING CORP Prepared by: Shear Engineering Corporation Project No: 1608-01-98 Date: July, 1998 4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 FAX (970) 282-0311 April 1, 1998 Project No: 1608-01-98 Basil Hamdan City of Fort Collins Stormwater Utility P.O. Box 580 Ft. Collins, Colorado 80522 Re: 742 - 746 North College Avenue; Fort Collins, Colorado Dear Basil, Enclosed, please find the Final Drainage and Erosion Control Report for 742-746 North College Avenue. This is the old "Gabby's" and "Dimmers Brew Pub" site and is developed. The project is primarily a remodel project with little or no change on the site. This report has been prepared, primarily to document the existing surface treatments and flow patterns according to the conceptual review note requirements of the Stormwater Utility from the December 1, 1997 conceptual review meeting. The existing building will be situated on Lot 1 of the proposed Will Subdivision. Lot 2 will be retained for possible future development. This report only considers the historic conditions for Lot 2. A separate Drainage and Erosion Control Report and Plan will be required when a proposal for development for Lot 2 is made. If you have any questions or comments, please call me or Mark Oberschmidt at (970) 226-5334. Sincerely Brian W. Shear, P.E. Shear Engineering Corporation BWS / meo cc: Ted Zibell 4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 FAX (970) 282-031 1 Page 1 Final Drainage and Erosion Control Report Project No: 1608-01-98 L GENERAL LOCATION AND DESCRIPTION: A. Location 1. 742-746 North College Avenue is located in the Southwest 1/4 of Section 1, T7N, R69W of the 6th P.M., Fort Collins, Colorado. 2. More specifically, the site is located at 742 North College Avenue. 3. The site is bounded on the south by the Lake Canal, on the west by North College Avenue, on the north by Milan Minor Subdivision and on the east by undeveloped and unplatted property. B. Description of Property 1. The Project will consist of the remodel of an existing building which was formally "Dimmers Brew Pub" and prior to that, "Gabbys Restaurant". 2. The site will be platted into two (2) lots. The existing building will be located on Lot 1, Will Subdivision as shown on the Final Plat. Lot 2, Will Subdivision will be retained for future development. 3. Total site area under consideration is 77,588 square feet or 1.78 acres, more or less. a. Lot 1 is 35,468 square feet (0.81 acres). b. Lot 2 is 42,102 square feet (0.97 acres). 4. There are existing utilities which service the site. They are located in North College Avenue and within the site. H. DRAINAGE BASINS AND SUB -BASINS: A. Major Basin Description 1. The site is located within the Dry Creek Basin as defined on the City of Fort Collins Master Stormwater Basin Map. a. The Basin Rate fee for the Dry Creek Basin is $ 5,000 per acre. b. No fees are required if the development of the site increases the imperviousness by less than 350 square feet. 2. The flow pattern of this portion of the Dry Creek Basin is generally easterly and southerly. Runoff is primarily conveyed in ditches to the Cache La Poudre River. 3. The Lake Canal ditch is located immediately adjacent to this site. A portion of the ditch is actually on the southern portion of the site. Page 2 Final Drainage and Erosion Control Report Project No: 1608-01-98 H. DRAINAGE BASINS AND SUB -BASINS: A. Major Basin Description 4. All of the site is in the 100-year flood plain as delineated on the Flood Insurance Rate Map (FIRM) for the City of Fort Collins, Community Panel Number 080102-0004-C; dated March 18, 1996. Refer to the floodplain exhibit in Appendix III of this report. B. Sub -Basin Description 1. Runoff from a majority of the existing developed site, flows directly to the Lake Canal. The remainder of the site currently flows to the east to an existing drainageway, east of the site. 2. The site is extremely flat. The slope of the land is generally less than 1.0%. 3. An existing box culvert traverses the property from west to east. The box culvert appears to be for drainage purposes only. It conveys stormwater from the west side of North College Avenue to the east side of North College Avenue. The box culvert discharges into the Josh Ames ditch east of the property. a. The box culvert entry is located on the west side of North College Avenue, directly across from this site. b. The box culvert has been identified as an extension to the Josh Ames Ditch. 4. The drive located immediately north of the existing building, has an inverted crown and is utilized as a drainageway for a portion of this site and for a portion of the Milan Manor Subdivision to the north. Stormwater conveyance immediately east of this site and the Milan Manor Subdivision site, is not well defined and does not appear to reach the drainageway located east of the site. a. The Milan Minor Subdivision is fully developed and is currently utilized as an auto sales facility. b. The drive / drainageway is on the Milan Minor Subdivision property. A 24' access easement exists and was recorded in Book 103, at Page 19 in Latimer County Records. 5. No detention has been provided with this site. No detention will be provided now since the site is "Grandfathered" and there will not be an increase in impervious area over 350 square feet. Page 3 Final Drainage and Erosion Control Report Project No: 1608-01-98 III. DRAINAGE DESIGN CRITERIA: A. Regulations 1. This final report was prepared in accordance with the requirements of the current City of Fort Collins Storm Drainage Design Criteria and Erosion Control Criteria. 2. All items requested by the Stormwater Utility noted in the Conceptual Review letter, have been addressed. 3. The cost of the cumulative improvements to the building over time has substantially improved the site. Refer to Sections 10-16 and 10-20 item 3 of the Fort Collins City code for a definition of substantially improved. These sections are attached for reference in Appendix III. Therefore, the site is subject to the requirements of the City of Fort Collins Policy for substantial improvements (Section 10 of the City Code). a. The owner has agreed to comply with City Code for substantial improvements. This compliance will consist of flood proofing the building as part of the building improvements. B. Development Criteria Reference and Constraints 1. Because the site is currently developed, constraints occur around the perimeter of the site. a. Utilities and underground drainage facilities encumber the site (See Plan). M. DRAINAGE DESIGN CRITERIA: C. Hydrological Criteria 1. The Rainfall -Intensity -Duration curves for the City of Fort Collins were used (Figure 3-1, attached for reference), in conjunction with the "Rational Method" for determining peak flows. Peak flows were calculated for documentation purposes only. 2. Runoff calculations at various design points are based on the "Rational" method. The 2, 10, and 100-year storms have been analyzed. 3. Runoff coefficients utilized were as suggested by the City of Fort Collins Storm Drainage Criteria Manual. D. Hydraulic Criteria 1. Drainage channel capacities were based on the Mannings Equation. The Mannings coefficients are as suggested by the City of Fort Collins Storm Drainage Criteria Manual. Page 4 Final Drainage and Erosion Control Report Project No: 1608-01-98 IV. DRAINAGE FACILITY DESIGN: A. General Concept 1. Runoff is conveyed to the Lake Canal primarily by overland flow. Runoff is conveyed to the existing drainage channel east of this site, primarily by overland flow with minor conveyance via underground storm sewer flow. 2. No drainage facility improvements are planned with this project. B. Specific Details 1. No drainage facility improvements are planned with this project. 2. Existing surface coverage is based on an Improvement Survey provided by Hall and Associates, Inc. of Loveland. The following table summarizes the existing developed. surface cover for the project site. This table is summarized for both Lots 1 and 2. SURFACE COVER: Existing: Proposed: Asphalt 0.21 acres unchanged Concrete 0.10 acres unchanged Gravel 0.52 acres unchanged Building roof 0.16 acres unchanged Undeveloped (lawns; less than 2%) 0.79 acres unchanged TOTALS: 1.78 acres The average runoff coefficient for the existing site has been determined to be 0.49 for 2 to 10 year storms and 0.61 for the 100-year storm. V. EROSION CONTROL: A. General Concept 1. No erosion control devices are anticipated. Generally, no specific site work is planned. Possible parking lot pavement repairs may be considered. The limit of the site work will be limited to the removal and replacement of damaged concrete / asphalt. B. Specific Details 1. No Erosion Control devices will be required. Page 5 Final Drainage and Erosion Control Report Project No: 1608-01-98 VI. CONCLUSIONS: A. Compliance with Standards 1. All drainage analysis has been performed according to the requirements of the City of Fort Collins Storm Drainage Criteria Manual. B. Drainage Concept 1. The proposed drainage design for this site has not changed. 2. There will be no effect on City of Fort Collins Master Drainage Plan recommendations. VII. REFERENCES: 1. City of Fort Collins "Storm Drainage Design Criteria and Construction Standards'; May, 1984 2. City of Fort Collins "Erosion Control Reference Manual"; January, 1991 3. City of Fort Collins "STORMWATER BASIN MAP 4. Improvement Survey for 742-746 North College Avenue; Hall and Associates, Inc.; Survey dated 02/01/95. APPENDIX I Drainage Calculations PLOW SUMMARY FOR 742-746 NORTH COLLEGE AVENUE PAGE 1 DATE: 04/01/98 DESIGN CONTRIBUTING AREA C2 C10 C100 Tc Tc 22 I100 Q2 Q100 PAGE POINT SUB 2,10 100 BASIN(S) ac. min. min iph iph cfe cfa r rrrr:errrr rerr r+re rrre++++rrr+rrrtr:terr+r+•+r+++++rrrrtr•+tr+re re•+++rrrrtr rrr+rerrrrrrrr HISTORIC A 1 1.78 0.42 0.42 0.53 5.00 5.00 3.29 9.30 2.47 8.72 3 DEVELOPED. A 1 1.78 0.42 0.42 0.53 5.00 5.00 3.29 9.30 2.47 8.72 4 SHEAR ENGINEERING CORPORATION SUBBASIN BRBAKDOWN PROJECT: PERENIAL GARDENER LOCATION:FORT COLLINS PRAT. NO.1608-01-98 TOTAL SITE AREA - 1.78 ASPHALT CONCRETE GRAVEL ROOFS LAWNS,SANDY SOIL PLAT < 23 AVERAGE 2 TO 74 STEEP > 7% LAWNS, HEAVY SOIL: PLAT < 2% AVERAGE 2 TO 7t STEEP > 7t IEel kh1_! SUB BASINS HISTORIC DEVELOPED 0.02 0.02 0.09 0.09 0.64 0.64 0.16 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.87 0.87 0.00 0.00 0.00 0.00 1.78 1.78 PAGE 2 DATE 04/01/98 BY MEO PILE: RATZIB TOTAL BASIN AREA 1.78 RUNOFF COEFFICIENT SUB BASINS AND / OR BASINS HISTORIC DEVELOPED C2-C10 0.42 0.42 C100 - 1.25•C2 0.53 0.53 C100 IS NEVER GREATER THAN 1.0 NOTE: THERE WILL BE NO CHANGE TO THE SITE WITH THIS PROJECT. WORK WILL BE LIMITED TO REMODELLING THE BUILDING. PROTECT: PERENIAL GARDENER L.00ATION:FORT COLLINS FILE: RATZIB AREA (A)= 1.780 ACRES SHEAR ENGINEERING CORPORATION HISTORIC FLOW TO CONCENTRATION POINT A FROM BASIN 1 DATE 04/01/98 PROD. NO.1608-01-98 BY HBO PAGE 3 RUNOFF COBF. (C) 2 YEAR 10 YEAR 100 YEAR C = 0.42 0.42 0.53 SEE SPREAD SHEET ATTACHED ON PAGE 2 TIME OF CONCENTRATION (Tc) OVERLAND TRAVEL TIME (Ti) not applicable LENGTH -na FEET SLOPE -na k 2 YEAR 10 YEAR 100 YEAR C = 0.20. 0.20 0.25 Ti (min)= 0.00 0.00 0.00 TRAVEL TIME (Tt)=L/(60+V) FLOW TYPE L (£t) = 250 S (i) - 0.50 gutter V (fps) - 1.50 Tt(min)-. 2.78 L (ft) - 50 S (i) - 0.50 lawn V (fps) - 0.50 Tt(min)- 1.67 L (ft) _? S 00 = 0.00 none V (fps) - 0.00 Tt(min)= 0.00 L (ft) _7 S M - 0.00 none V (fps) = 0.00 Tt(min)= 0.00 L (ft) _? S (%) - 0.00 none V (fps) = 0.00 Tt(min)= 0.00 L (ft) _? S (t) - 0.00 none V (fps) = 0.00 Tt(min)= 0.00 L (ft) _7 S M = 0.00 none V (fps) = 0.00 Tt(min)= 0.00 ALL VELOCITIES TAKEN FROM FIGURE 3-2 TOTAL TRAVEL TIME (min) = 4.44 TOTAL LENGTH - 300 L/180+10= 11.67 > 4.44 =Ti+Tt CHOOSE LESSER Tc -Ti+TOTAL TRAVEL TIME 2 YEAR 10 YEAR 100 YEAR Tc (min)= 4.44 4.44 4.44 USE Tc - 5 5 5 INTENSITY (I) (iph) 2 YEAR 10 YEAR 100 YEAR I = 3.29 5.64 9.30 NOTE: INTENSITIES TAKEN FROM FIGURE 3-1 RUNOFF (Q= CIA) (cfs) 2 YEAR 10 YEAR 100 YEAR Q = 2.47 4.23 8.72 CONCLUD6:COMPARS WITH DEVELOPED FLOWS SHEAR ENGINEERING CORPORATION DEVELOPED PAGE FLOW TO CONCENTRATION POINT A FROM BASIN 1 PROTECT: PERENIAL GARDENER DATE 04/01/98 LOCATION:FORT COLLINS PROJ. NO.1608-01-98 PILE: RATZIB BY MEO AREA (A)= 1.780 ACRES RUNOFF CORP. (C) 2 YEAR 10 YEAR 100 YEAR C = 0.42 0.42 0.53 SEE SPREAD SHEET ATTACHED ON PAGE 2 TIME OF CONCENTRATION (TO ' OVERLAND TRAVEL TIME (Ti) not applicable LENGTH =na FRET SLOPS -na } 2 YEAR 10 YEAR 100 YEAR C = 0.20 0.20 0.25 Ti (min)= 0.00 0.00 -0.00 TRAVEL TIME (Tt)-L/(60+V) PLOW TYPE L (ft) = 250 S (}) - 0.50 gutter V (fps) = 1.50 Tt(min)= 2.78 L (ft) _ _ 50 S (}) - 0.50 lawn - V (fps) = 0.50 Tt(min)= 1.67 L (ft) _? S (}) = 0.00 none V (fps) = 0.00 Tt(min)= 0.00 L (ft) _? S (}) = 0.00 none V (fps) = 0:00 Tt(min)= 0.00 L (ft) _? S (}) = 0.00 none V (fps) = 0.00 Tt(min)= 0.00 L (ft) _? S (}) - 0.00 none V (fps) = 0.00 Tt(min)= 0.00 L (ft) _? S (}) - 0.00 none V (fps) = 0.00 Tt(min)= 0.00 ALL VELOCITIES TAKEN FROM FIGURE 3-2 TOTAL TRAVEL TIME (min) = 4.44 TOTAL LENGTH = 300 L/180+10= 11.67 > 4.44 -Ti+Tt CHOOSE LESSER Tc =Ti+TOTAL TRAVEL TIME 2 YEAR 10 YEAR 100 YEAR Tc (min). 4.44 4.44 4.44 USE Tc - 5 5 5 INTENSITY (I) (iph) 2 YEAR 10 YEAR 100 YEAR I = 3.29 5.64 9.30 NOTE: INTENSITIES TAKEN FROM FIGURE 3-1 RUNOFF (Q= CIA) (cfs) 2 YEAR 10 YEAR 100 YEAR Q = 2.47 4.23 8.72 VERSUS QHIST = 2.47 4.23 8.72 r CONCLUDH:NO CHANGE TO SITS THEREFORE NO INCREASE IN PLOW DUE TO PROJECT 4 APPENDIX H Charts & Figures No Text Table 3-3 RATIONAL METHOD RUNOFF COEFFICIENTS FOR COMPOSITE ANALYSIS Character of Surface Runoff Coefficient Streets Parking Lots, Drives: Asphalt 0.95 Concrete 0.95 Gravel 0.50 Roofs 0.95 Lawns, Sandy Soil: Flat < 2% 0.10 Average 2 to 7% 0.15 Steep > 7% 0.20 Lawn, Heavy Soil: Flat < 2% • 0.20 Average 2 to 7 % 0.25 Steep > 7% 0.35 Table 3-4 RATIONAL METHOD FREQUENCY ADJUSTMENT FACTORS Storm Return Period Frequency Factor years Cf ********************************************************************* 2-10 1.0 11-25 1.1 26-50 1.20 51-100 1.25 Note: The product of C times Cf shall not exceed 1.0 tables APPENDIX III Stuffer Envelope Drainage and Erosion Control Plan Portions of Section 10 of the City of Fort Collins Code Floodplain Exhibit WIN 20 /r MN El • 4961 R IIN. 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