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HomeMy WebLinkAboutSYMBIOS LOGIC PUD - FINAL - 5-94F - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTOVERALL DRAINAGE STUDY AND PHASE I FINAL DRAINAGE STUDY FOR THE SYMBIOS LOGIC SITE FORT COLLINS, COLORADO June 24,1996 Prepared for: Client: RNL Design Seventeenth Street Plaza 1225 Seventeenth Street, Suite 1700 Denver, Colorado 80202 Prepared by: 33D INC Engineering Consultants A division of The Sear -Brown Group 209 South Meldrum Fort Collins, Colorado 80521 (970)482-5922 Engineering Consultants A division o/'THe Sear -Brown Group 209 S. Meldrum Fort Collins, Colorado 80521 970/482-5922 June 24, 1996 Mr. Basil Hamdan City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Overall Drainage Study and Final Phase I Drainage Study for the Symbios Logic Site Dear Basil: We are pleased to submit to you, for your review and approval, this Overall Drainage Study and Phase I Final Drainage Study for the Symbios Logic site. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, RBD Inc. Engineering Consultants par By: Patricia Kroetch Project Engineer Denver 303/458-5526 Reviewed By: David K. Thaemert, P.E. Water Resources Project Engineer TABLE OF CONTENTS 1 • ' 1' • ► I. GENERAL LOCATION AND DESCRIPTION PAGE A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE BASINS A. MAJOR BASIN DESCRIPTION 1 B. SUB -BASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA A. REGULATIONS 3 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 3 C. HYDROLOGICAL CRITERIA 3 D. HYDRAULIC CRITERIA 3 E. VARIANCES FROM CRITERIA 4 IV. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT 4 B. SPECIFIC DETAILS 5 OVERALL SITE DEVELOPMENT 5 PHASE I DEVELOPMENT 6 V. STORM WATER QUALITY A. GENERAL CONCEPT 7 B. SPECIFIC DETAILS 7 VI. EROSION CONTROL A. GENERAL CONCEPT 8 B. SPECIFIC DETAILS 8 VII. CONCLUSIONS A. COMPLIANCE WITH STANDARDS 9 B. DRAINAGE CONCEPT 9 C. STORM WATER QUALITY 9 D. EROSION CONTROL CONCEPT 9 REFERENCES 10 171l VICINITY MAP 1 HYDROLOGY 3 INLET SIZING AND STORM DRAIN SIZING 9 EROSION CONTROL CALCULATIONS AND RIPRAP SIZING 21 TABLES AND FIGURES 31 FOX MEADOWS BASIN H DRAINAGE MASTER PLAN INFORMATION 35 EXCERPTS FROM PREVIOUS DRAINAGE REPORTS 52 UPDATED 100-YEAR SWMM MODEL INPUT DATA FOR THE SOUTH FOX MEADOWS BASIN 66 UPDATED 100-YEAR SWMM MODEL OUTPUT FILE FOR THE SOUTH FOX MEADOWS BASIN 72 SWMM MODEL FOR PHASE I INTERIM CONDITIONS 80 OVERALL DRAINAGE STUDY AND PHASE I FINAL DRAINAGE STUDY FOR THE SYMBIOS LOGIC SITE FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The Symbios Logic site is located north of Harmony Road and west of County Road 9 (Minor Road) in southeastern Fort Collins, Colorado. The site is shown on the Vicinity Map in the Appendix. More particularly, the site is situated in the southeasterly portion of Section 22, Township 7 North, Range 68 West of the Sixth P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The Symbios Logic site contains 102 acres of land, more or less, of which all of the area is currently undeveloped and being proposed for an Industrial Park for the Symbios Logic Company. The majority of the property currently consists of cultivated farm land. Topography at the site is generally sloping from west to east at approximately 0.7 %. There is a concrete irrigation ditch in the southeast corner of this site which is a portion of the Dixon Canyon Lateral. This ditch will be replaced by a pipe during Phase I construction as approved by the ditch company. There is also an irrigation lateral that runs north -south through the west portion of the site. This lateral will be maintained in its current location with the Phase I development. With future development, if the lateral is to be preserved, it will be rerouted as necessary. H. DRAINAGE BASINS A. Major Basin Description The Symbios Logic site lies entirely within the Fox Meadows Drainage Master Plan (Basin H) as shown in the Master Plan Report by Resource Consultants Inc., dated 1981. In addition, this area was studied again by Nolte and Associates in May 1990 when they prepared a master drainage plan for the Hewlett-Packard (H-P) site which lies to the East of the Symbios Logic site. This site was recently investigated in the Final Drainage Study for Hewlett-Packard Building 5 by RBD, Inc. in February 1996. Applicable portions of all of these studies are included in the Appendix. The Master Drainage Report which was done by Nolte and Associates did not alter any of the assumptions or conclusions which were made in the Fox Meadows Master Drainage Plan. In effect, this report simply incorporated the recommendations that the Master Drainage Plan for Fox Meadows had called for in the design of the Hewlett-Packard (H-P) site. These recommendations included the design of a drainage swale which runs along the North side of the H-P site and eventually drains into H-P's North pond. This drainage swale has been sized and final designed with the H-P Building 5 drainage report. The drainage swale to be constructed across the H-P site has been final designed by H-P and is anticipated to be constructed in the summer of 1996. The Master Drainage Plan for the H-P site is shown in the Appendix. The Symbios Logic site currently drains to two existing 18" RCP and onto the H-P site. According to the Master Drainage Plan done for the H-P site the Symbios Logic site falls within both basins 31 and 23. However, the shape and area of these basins does not correspond to the shape of the Symbios Logic site. It appears that Symbios Logic would have pond #215 on their site and pond #214 also. The total area draining to these two ponds on the master plan is equal to 149.2 acres. This area includes the Symbios site and the area to the west of this site. Both ponds #215 and #214 were shown as having an allowable release rate of 24 cfs each or a total release of 48 cfs. B. Sub -Basin Description Historic drainage patterns on the subject site are in an easterly direction per Figure 2 (Fox Meadows Drainage Master Plan) on page 31 in the appendix. Upstream off -site areas lying west of proposed Corbett Drive contribute storm water runoff which crosses the Symbios Logic site at the present time. With Phase I construction, the flows from the off -site areas lying west of proposed Corbett Drive will continue to sheet flow across the Symbios site as they have historically done. When the Symbios Logic site is fully developed, off -site flows will be conveyed in a drainage swale around the site and detained in the proposed detention pond at the north end of the Symbios site. The flows will combine with on -site runoff and be released at 24 cfs under County Road 9 in a proposed pipe that is to be constructed with the English Ranch construction in the summer of 1996. This storm pipe will discharge those off -site flows into the proposed drainage swale on the north side of the Hewlett-Packard site. No off -site runoff from properties north and south of the Symbios Logic site traverse through the site. �J' 11 . i 1 A. R g lations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. B. Development Criteria Reference and onctraints The Fox Meadows Basin (Basin H) Drainage Master Plan and the subsequent H-P Master Drainage Plan criteria and constraints are being utilized in this Overall Drainage Study. The recent Final Drainage Study for H-P Building 5 is also being used to determine criteria for this site. Since the Symbios Logic site is currently being utilized as agricultural land, the Fox Meadows Master Plan for the site included on -site detention facilities for the future development. As can be seen from the Fox Meadows Drainage Master Plan report (Figure 5), detention was planned for 3 locations on the West side of County Road 9. Two of those ponds, which are labeled as pond #3 and #4 in the Fox Meadows Drainage Master Plan, are located entirely within the Symbios Logic site. However, the drainage area which drains to those ponds in the Fox Meadows Master Plan does not correspond to the area of the Symbios Logic site. In fact, the area which was proposed to drain to ponds #3 and #4 is larger than the Symbios Logic site by approximately 47.2 acres. These ponds will be sized to accept runoff from the entire 149.2 acres and both ponds will have a combined restricted release rate of 48 cfs. C. Ilydrnlnuic Criteria The SWMM hydrologic model was previously used in the Fox Meadows Basin Master Drainage Plan. The Hewlett-Packard Master Drainage Plan report utilized the Fox Meadows Basin Master Drainage Plan SWMM model and simply expanded on it. The SWMM model was updated recently for the H-P Building 5 project. This SWMM model has again been updated to include the two detention ponds which are proposed for the Symbios Logic site. A copy of the SWMM model for the 100-year storm is included in the Appendix. D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of Fort Collins Storm Drainage Criteria and are included in the appendix. 3 I E. Variances from Criteria No variances from the City of Fort Collins Storm Drainage Criteria are being sought for this project. IV. DRAINAGE FACILITY DESIGN A. General Concept As development occurs within the Symbios Logic site, the drainage concepts shown on the Overall Drainage Plan in the back pocket of this report should be followed. There are three ponds shown within the site to handle the stormwater runoff. Two of these ponds are proposed as permanent wet ponds which will be fed by irrigation water and runoff from the adjacent area. Water in these ponds will be utilized for irrigating the site. The retention pond (pond #3) will need to be sized in excess of the required amount of permanent water storage to allow for the periodic inflows of stormwater and the ultimate inflow of the 100 year storm. Even though this pond is a permanent retention pond, it will need some overflow mechanism to allow for a situation where complete inundation of the pond volume occurs. The other two ponds will discharge under County Road 9 and onto the H-P site at the allowable release rate of 48 cfs combined. On -site stormwater will be conveyed to the three on -site ponds through the use of inlets, storm drain pipes, and cross pans. For the updated SWMM model, the sub -basins within and tributary to the Symbios Logic site were revised to match proposed developed conditions. This included revising sub -basin areas to match proposed site layout and revising the theoretical detention pond rating curves for ponds 214 and 215. Both of these ponds are master -planned to discharge 24 cfs each.. The sub -basin to the west of the proposed Symbios Logic site contains approximately 50.3 acres and was modeled with a restricted release rate of 0.32 cfs per acre or approximately 16.2 cfs. The release from this sub -basin is accounted for in the detention provided on the Symbios Logic site. Note that, when that area is developed, additional runoff from this sub -basin will have to be detained before releasing these flows downstream to the Symbios Logic site. Refer to the Appendix for the supporting calculations for this SWMM model update. 4 B. Specific Details Overall Site Development Per the Fox Meadows Basin Drainage Master Plan and the approved Hewlett- Packard Master Drainage Plan the Symbios Logic site must have on -site detention. The Fox Meadows Master Plan showed two ponds within the Symbios Logic site which each release 24 cfs. In addition, the Hewlett-Packard site is constructing a drainage swale which has been sized to accommodate Symbios Logic's off -site flows as well as its' own. The Overall Drainage Plan for the Symbios Logic site includes utilizing a proposed permanent pool pond within the site for retention. An additional volume above the permanent pool will be provided within this pond which allows for the permanent retention of the 100-year runoff for the drainage area which drains to it. There will however, be an emergency overflow provided for this pond. The additional stormwater volume needed in pond # 3 will be approximately 0.58 acre-feet plus one foot of freeboard. This is in addition to whatever "wet pond" volume is needed for irrigation purposes and to maintain an attractive water feature for the Symbios Logic site. The second pond (pond #2) will be located in the northeast corner of this site. This pond will outlet under County Road 9 through a proposed storm pipe which will outlet into the Hewlett-Packard drainage channel with a restricted release of 24 cfs. This pond will need a minimum volume of approximately 5.7 acre-feet plus one foot of freeboard. The third pond (pond #3) proposed on the Symbios Logic site is located to the west of County Road 9. Because of the desire which Symbios Logic has to be environmentally sensitive, this pond will contain a wetlands area which will help filter out pollutants from the site. The pond itself will be on both sides of the main entrance off of County Road 9, with a storm pipe located under the entry -way which will allow 24 cfs to pass through and access the two existing 18" RCP's (designed with the County Road 9 project, excerpts in appendix) which are located on the North side of the entryway. This pond will need a minimum volume of 6.1 acre-feet plus one foot of freeboard. The City of Fort Collins Stormwater Utility has requested that a SWMM Model be submitted and include the three proposed on -site ponds. The Hewlett-Packard site developed a SWMM Model for the entire area, and we have updated this model for the Overall Symbios Site and used this model to size the detention ponds on the Symbios Site. The SWMM Model is a conservative approach to ensure all detention ponds within the City of Fort Collins have sufficient capacity. 5 Phase I Development The first phase of the Symbios Logic site will include the construction of a portion of detention pond #1. Pond #1 will serve as an irrigation pond for Phase I as well as detention. The storm water runoff from the site will reach this pond by conveyance methods such as inlets, storm drain pipe, curb and gutter, and cross pans. The runoff from those areas which would have drained into ponds #1 and #2, is being diverted into pond #1 at this time. Therefore, detention pond #1 is being built to accommodate runoff from Phase I under developed conditions and the remainder of the site under undeveloped conditions. The irrigation volume will be in addition to the required detention volume. As this site develops, pond #3 will be enlarged and ponds #1 and #2 will be constructed to accommodate the increased runoff. The outlet culvert for pond #2 is anticipated to be constructed with the development of English Ranch to the north of the Symbios sits. The timing of this installation is unclear at this time, therefore this pond is not anticipated to be constructed with Phase I. If the pipe is installed by the time Phase I is under construction, it is possible that this pond could be constructed with Phase I. Pond #3 will be used primarily for irrigation water and as a water feature. This pond will be constructed as the site is developed around the proposed pond location. This site has been broken into eight on -site drainage basins and one off -site basin. Basin 1 includes a portion of the motor court in front of the office building and runoff from this basin will flow into an 5 foot curb inlet (Inlet 10). Basin 2 includes the remainder of the motor court and runoff from this basin will flow via curb and gutter to Inlet 20 (10' type R). Basin 3 includes half of the employee parking lot and runoff from basin 3 sheet flows across the lot to Inlet 30 (10' type R). Runoff from basins 1,2, and 3 combine and flow via a storm drain system (Storm Pipe A) into the detention pond in basin 8. Basin 4 includes a portion of the employee parking lot. Drainage from basin 4 flows into a 10 foot curb inlet (Inlet 40) and will also flows via storm drain system (Storm Pipe B) into the detention pond in basin 8. This flow will be released into basin 9 through a 36 inch RCP (Storm Pipe C) under the entrance. Basin 5 contains the north half of the loop road. Runoff from this basin will flow in the curb and gutter to the location of a future concrete pan at the entrance. Basin 6 includes the remainder of the employee parking lot and runoff from this basin will sheet flow to combine with the flow from basin 5. Basin 7 includes the south half of the loop road. Drainage from this basin will flow in the curb and gutter to combine with runoff from basins 5 and 6 at the entrance. The combined 6 flow from basins 5, 6, and 7 enters basin 9 and detention pond 1. The off -site basin 9 is a portion of the Symbios property that will remain mostly undisturbed with the Phase I construction. The area in basin 9 will be allowed to sheet flow to the east as it has historically done. The portion of detention pond #1 that lies in basin 9 will conform to the natural existing contours which will prevent disturbance in this area and minimize erosion. See the Appendix for detention pond, inlet and storm pipe sizing calculations. V. STORM WATER QUALITY A. General Concept The State of Colorado requires Stormwater Management Plans as part of their permit process. The Symbios Logic site development is anticipating construction beginning in the Fall of 1996. Therefore for this study, we have sought to find various Best Management Practices for the treatment of storm water runoff which could be implemented in the construction phase of the project. B. Specific Details Best Management Practices (BMP) for the treatment of storm water runoff have been incorporated into the design for this project. The first BMP will be in place prior to overlot grading of Phase I. This will be the construction of the irrigation pond which will also function as a water quality feature during the construction phase of this project. This pond will provide a mechanism for pollutants to settle out of the storm water runoff prior to being released into the Hewlett-Packard drainage swale and eventually into Fossil Creek. The BMP's for this site also include the installation of silt fence and gravel inlet filters during construction. After the construction is completed, the Symbios Logic site will have on -going Best Management Practices. The on -site detention area constructed with Phase I is being proposed with a wetlands area. This wetlands area will serve many purposes. Because the area is held flat, the runoff will be slowed down in these areas and this will allow pollutants and other transported materials to be filtered out. In addition, the wetlands native grass species also "treat" the polluted runoff water and allow for a much cleaner discharge from the Symbios Logic site onto Hewlett-Packard. All construction activities must comply with the State of Colorado permitting process for Storm water Discharges Associated with Construction Activity. A 6 Colorado Department of Health NPDES Permit will be required before any construction grading can begin. VI. EROSION CONTROL A. General Concept The Symbios Logic site lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. The potential exists for erosion problems during construction, and after construction until the disturbed ground is revegetated or paved. It is anticipated that construction will begin in September of 1996. B. Specific Details Erosion control for this site during construction includes the construction of the irrigation pond which will act as a water quality pond until it is filled with irrigation water. Additional erosion control measures include gravel filters for all of the inlets on the site, silt fence to be installed along the downstream perimeter of the site, and straw bale check dams installed in all of the swales and the detention area. All areas that remain disturbed for more than four weeks will require seeding and mulching to prevent excessive erosion. During the four week period, disturbed areas shall be roughened. After construction of utilities, the loop road will have a paved surface and the foundation of the office building will be constructed. The open areas will be seeded to reduce the erosion potential. Calculations for erosion control performance standards were completed per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and are included in the appendix. The erosion control performance standard for this site during construction is 74.6%. The effectiveness of the proposed erosion control plan during construction is 91.4%. The erosion control performance standard after construction was calculated to be 87.8%.The effectiveness of the proposed erosion control plan after construction is 97.5 %. Therefore, the erosion control plan will meet the City of Fort Collins criteria. 8 VIE[. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. The City of Fort Collins Stormwater Utility will not maintain the on -site storm drainage facilities within the Symbios Logic site. The owners of the Symbios Logic site will need to maintain their on -site storm drainage facilities on a regular basis. B. Drainage Concept The proposed drainage concepts presented in this study and shown on the final utility plans adequately provide for the transmission of developed on -site runoff to the proposed detention pond. The combination of on -site street capacities and the on -site storm sewer system will provide for the developed flows to reach the proposed detention pond. The size, location and release rate of this pond will allow the Symbios Logic site to develop in conformance with the Fox Meadows Basin Drainage Master Planning concepts accepted by the City of Fort Collins and the H-P Master Drainage Plan. The on -site detention ponds shall provide one foot of freeboard and an emergency overflow outlet in the event the outlet becomes plugged. If groundwater is encountered at the time of construction, a Colorado Department of Health Construction Dewatering Permit will be required. C. Storm Water Quality The wetlands area proposed within the on -site detention pond is an excellent way to allow storm water pollutants an opportunity to be filtered out of the storm water as the pollutants are carried by the storm water across the site. Periodic maintenance may be required to remove sediment deposits as they accumulate in the on -site detention pond. D. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from Symbios Logic. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standard will be met. The proposed erosion control concepts presented in this report and shown on the erosion control plan are in compliance with the City of Fort Collins Erosion Control Criteria. 9 REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. 3. Fox Meadows Basin (Basin H) Drainage Master Plan, Fort Collins, Colorado, by Resource Consultants Ind., 1981. 4. Master Drainage Report, Hewlett Packard Site, Preston Kelly Subdivision, Fort Collins, Colorado by Nolte and Associates, May 1990. 5. Final Drainage Study for Hewlett-Packard Company Building 5, Fort Collins, Colorado by RBD, Inc., February 1996. 10