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Home My WebLink AboutPVH HARMONY CAMPUS (PHASE 1) - PDP - 32-98A - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTrnl C*.Z � cl - PORSE TOOTH ROAD 9 I . Ila i ir 0 rm cw a a C.aft [AW Ld D /z Jva, Me r0 0 ckf LLI z M -i LLJ z m 0 m I;a F- VIIE ar L O ramp N� VICINITY MAP POUDRE VALLEY HOSPITAL HARMONY CAMPUS nm na SPAN BROWN GROUP VICINITY MAP 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, Revised January 1997. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991, Revised January 1997. 3. McClellands Basin 100-Year Master Plan Update, by RBD, Inc., Fort Collins, Colorado, April 1, , 1996. 4. McClellands Basin Master Drainage Plan, by Greenhorne & O'Mara, Inc., Fort Collins, Colorado, June 20, 1986. 5. Final Drainage Report for Timberline Road, by Northern Engineering Services, Inc., Fort Collins, Colorado, July 15, 1994. 6. Final Drainage and Erosion Control Study for The Hamlet at Miramont P.U.D., Fort Collins, Colorado, by RBD, Inc., March 1996. E VII. CONCLUSIONS A. B C. D. 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 Poudre Valley Hospital site. The owners of the Poudre Valley Hospital site will maintain their on -site storm drainage facilities on a regular basis. 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 ponds. 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 ponds. The sizes, locations and release rates of these ponds will allow the Poudre Valley Hospital site to develop in conformance with the McClellands Basin Drainage Master Planning concepts accepted by the City of Fort Collins. If groundwater is encountered at the time of construction, a Colorado Department of Health Construction Dewatering Permit will be required. Storm Water Quality The sediment basin traps proposed within the on -site detention ponds are excellent ways to allow storm water pollutants an opportunity to be filtered out of the storm water as the storm water carries the pollutants across the site. Periodic maintenance may be required to remove sediment deposits as they accumulate in the on -site detention pond. Erosion Control Concert The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from Poudre Valley Hospital. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standards 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. El VI. ponds, which will also function as water quality features during the construction phase of this project. These ponds will have sedimentary basin traps for pollutants to settle out of the storm water runoff prior to being released into McClellands Basin Drainageway. The BMP's for this site also include the installation of silt fence during construction. All construction activities must comply with the State of Colorado permitting process for Storm water Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required before any construction grading can begin. EROSION CONTROL A. General Concept The Poudre Valley Hospital 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 re -vegetated or paved. It is anticipated that construction will begin November of 1998. B. Specific Details Erosion control for this site during construction includes the building of two temporary detention ponds that will act as water quality ponds. Additional erosion control measures include sediment/basin traps for the ponds, gravel mulch, roughened soil, and silt fence to be installed along the downstream perimeter of the site. 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, the loop road will have a paved surface and the foundation of the office building will be constructed. The open areas will have sod grass installed to reduce the erosion potential. Calculations for erosion control performance standards have been completed per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and can be found in the Appendix of this report. 7 With this project, Basin 316 of the McClellands Basin SWMM model was modified. The area of basin 316 has been increased from 99 acres to 102.76 acres due to the addition of a portion of Harmony Road, which was not originally included in this basin. For this project, basin 316 was subdivided into three basins, 316, 317, and 318, which now have 67.1 acres, 16.14 acres, and 19.52 acres respectively. Conveyance element 39 was subdivided into conveyance elements 391 and 39. Basin 317 has an embedded conveyance that leads to Detention Pond 394, which outlets into conveyance element 391, and ultimately merges with conveyance element 39. Similarly, Basin 318 has an embedded conveyance that leads to Detention Pond 393, which outlets into conveyance element 392, and also ultimately merges with conveyance element 39. Conveyance element 39 turns at the southeast corner of the site and merges with conveyance element 38, as it did in the McClellands Basin SWMM model. The SWMM Model data for this project takes into account the dual staged release structures, and the 10 year and 100 year allowable release rates. The tailwater used in the calculations was calculated using circular channel flow, which represents the proposed future conditions as shown in the Overall Drainage Report for this site. From running the model, it was found that Pond 393 has 2.5 ac-ft of storage and Pond 394 has 2.3 ac-ft of storage. The amount of flow being released into Conveyance Element 39 from the proposed Poudre Valley Hospital site, at the 100-year release rate of 0.50 cfs/acre, is 30.2 cfs, which is less than the flow that was originally being conveyed in element 39. No downstream off -site impact is anticipated by the construction of the on -site development and detention ponds. The SWMM.models and data are located in the Appendix of this report. V. STORM WATER QUALITY A. General Concept The State of Colorado requires Stormwater Management Plans as part of their permit process. The Poudre Valley Hospital site development is anticipating construction beginning in January of 1999. Therefore this study has sought to find various Best Management Practices for the treatment of storm water runoff that 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 detention Detention Pond 393 is a detention pond as well as an irrigation pond and has a total storage capacity of approximately 7 acre-feet, where 2.5 acre-feet of this storage has been allocated for detention storage. The pond is comprised of two ponds with an equalizing pipe connecting them. In order to maintain water in the pond for irrigation purposes, the outlet structure will be placed above the irrigation high water surface. As with the outlet structure for Pond 394, there is a 10 year and 100 year staged release rate which outlets into a temporary trapezoidal swale that conveys the flows to the existing grass -lined drainage (SWMM model Conveyance Element 39) ditch at the south boundary of the site. Similar to Detention Pond 394, an emergency overflow spillway was designed for this pond with its elevation equal to the 100 year WSEL. Runoff from the northeastern portion of the site will be routed to and detained in Detention Pond 393, located near the northern boundary of the site. Developed flow from a portion of Harmony Road, Basin 1, and the eastern parking areas, Basins 15-18, is conveyed via a swale and curb and gutter toward the center of the large parking lot where the flow is intercepted by two large Type "R" inlets. The flows are then conveyed via storm drainpipes to Detention Pond 393. Also entering Detention Pond 393 are flows from the entrance road and the Main Private Road, Basins 19, 19A, 21, 23. The developed runoff off of these roads enters the pond through Type "R" Inlets and storm drainpipes. Flow from Basin 23 enters the pond through a temporary swale. Undeveloped runoff from the southern portion of the site, Basins 25-31, flows south towards the existing grass -lined drainage ditch at the south boundary of the site, as it has historically. Due to the proposed detention ponds and the staged release structures, the Swale will not receive flows greater then the historic flows previously entering it. SWMM Model In order to analyze the detention ponds within the Poudre Valley Hospital Phase I development, the Urban Drainage Districts SWMM routing computer model was used. As part of the McClellands Basin Master Plan, a SWMM model was developed for this basin and the Final Drainage and Erosion Control Study for the Hamlet at Miramont P.U.D.'s existing 100 year SWMM Model was utilized and added onto for this development analysis. Included in the back pocket of this report is a new SWMM Model Exhibit drawing for the area directly north of the Stetson Creek and Timber Creek Developments, east of the Harmony Crossing Development, and west of the Wildwood Farms Development. 5 B. Specific Details Overall Drainage Plan Please refer to the Overall Drainage Report completed by The Sear -Brown Group for information on the Overall Drainage Plan. Phase I Development The entire Poudre Valley Hospital property contains approximately 102.37 acres of which approximately 36 acres are being developed with the first phase. The site has been broken into thirty-one on -site drainage basins. Basin 2 and 24 contain a portion of Harmony Road which develops runoff that will sheet flow into the Spring Canyon Lateral, located between the project site and Harmony road, as it has historically done. Runoff from the western portion of the site will be routed to and detained in Detention Pond 394, located at the southwest corner of the site. The area contributing to Detention Pond 394 is approximately 19.52 acres and consists of Basins 3-11, and Basin 13. Runoff from the north portion of Timberline Road, Basin 3, is routed onto the project site via curb/gutter and a swale, while the south portion of Timberline, Basin 4, is conveyed south to the existing inlet and ultimately drains into the proposed detention pond 394. The majority of Basins 5- 11 consists of parking lots and a portion of the Main Private Road. The developed flow off of this area is conveyed via curb and gutter to a series of Type "R" inlets and storm drain pipes (Profile A) which outlet into the detention pond 394. One third of the building drains into a roof drain, Basin 13, that intercepts the storm drain line at a manhole located in the parking area. Detention Pond 394 has a storage capacity of 2.3 acre-feet. The bottom of the pond has a minimum grade of 0.50 % s and has concrete trickle pans that facilitate the flow southeast towards the outlet structure box. The outlet structure allows for a 10 year and 100 year staged release rate, which releases the detained flows into the existing grass -lined drainage ditch (SWMM model Conveyance Element 39) at the south boundary of the site. In the event this outlet structure box becomes clogged, a 20' wide emergency overflow spillway was designed. The elevation of the spillway is equal to the 100 year water surface elevation (WSEL). The allowable release rates were determined using the requirements from Master Plan for the McClellands Basin: 0.20 cfs/acre for a 10-year design storm and 0.50 cfs/acre for a 100 year design storm. The detention ponds for this site were analyzed using SWMM Modeling and are discussed in a later section of this report. 4 B. Development Criteria Reference and Constraints The criteria and constraints from The McClellands Basin 100-Year Master Plan and the subsequent update dated April 1, 1996 are being utilized in this Preliminary Drainage Study. The Poudre Valley Hospital site is currently being utilized as agricultural land, and the McClellands Basin Master Plan for the site does not include on -site detention facilities for the future development. C. Hydrologic Criteria The SWMM hydrologic model that was previously used in the Final Drainage and Erosion Control Study for the Hamlet at Miramont P.U.D., by RBD, Inc., has been utilized and updated in this report in order to analyze the hydrologic conditions of the proposed Poudre Valley Hospital site. 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. E. Variances from Criteria A variance from the City of Fort Collins Storm Drainage Criteria is being sought for the increase in runoff into the Spring Canyon Lateral from the additional 12' wide pavement surface on Harmony Road. IV. DRAINAGE FACILITY DESIGN A. General Concept As development occurs within the Poudre Valley Hospital site, the drainage concepts shown on the Drainage and Erosion Control Plan in the back pocket of this report should be followed. Generally, the 10 year and 100 year developed on - site stormwater flows will be conveyed to the two on -site detention ponds via curb and gutter, cross -pans, sidewalk chases, inlets, storm drainpipes, and swales. There are two proposed ponds, #393 and #394, that will be constructed with Phase I of this project and they will discharge into the McClellands Basin Drainageway at the 10-year and 100-year allowable staged release rates. The release rates are based on the requirements of the Master Plan for the McClellands Basin, which requires on -site detention using a staged release rate of 0.20 cfs/acre for a 10-year design storm and 0.50 cfs/acre for a 100 year design storm c 4 Poudre Valley Hospital is located in Basin 316. Applicable portions of these studies are included in the Appendix. Historic drainage patterns on the subject site are in a southeasterly direction per the McClellands Basin 100-Year Master Plan Update. The site historically discharges into Conveyance Element 39. Conveyance Element 39 is currently 2160 feet long i and is an open channel that runs along the southern property line of the PVH site. At the southeast comer of the site, Conveyance Element 39 turns the comer and flows south along the east property line of the Timber Creek PUD and the Stetson Creek PUD. Excerpts from the McClellands Basin 100-Year Master Plan Update can be found in the appendix of this report. The flow ultimately discharges into the McClellands Basin Drainageway. A portion of Timberline Road will be detained on the Poudre Valley Hospital Site. Sections of the Final Drainage Report for Timberline Road, done on July 15, 1994, by Northern Engineering Services, Inc., which show this area of roadway has been included in the Appendix. These sections specify the area of Timberline to be detained as well as storm flows.. No off -site runoff from properties surrounding the Poudre Valley Hospital site pass through the site. With the construction of the site, no additional flows are anticipated. Poudre Valley Hospital will have Detention Ponds #393 and #394 on site. The total area draining to these two ponds is equal to approximately 36 acres. This area is included in Phase I of the Poudre Valley Hospital Site. B. Sub -Basin Description Historic drainage patterns on the subject site are in a southeasterly direction per Appendix B, page 56 of the McClellands Basin 100-Year Master Plan Update. Excerpts from the McClellands Basin 100-Year Master Plan Update can be found in the appendix of this report. No off -site runoff from properties surrounding the Poudre Valley Hospital site traverse through the site. With the construction of Phase I of the site, no additional flows are anticipated. III. DRAINAGE BASIN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. 2 r l PRELIMINARY DRAINAGE AND EROSION CONTROL REPORT FOR THE POUDRE VALLEY HOSPITAL HARMONY CAMPUS FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The Poudre Valley Hospital Harmony Campus site is located south of Harmony Road and east of Timberline 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 northwesterly portion of Section 5, Township 6 North, Range 68 West of the Sixth P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The overall Poudre Valley Hospital site contains approximately 102 acres of land, all of which is currently undeveloped and being proposed for the Harmony Campus of Poudre Valley Hospital. The majority of the property currently consists of cultivated farmland. The site generally slopes in a southeasterly direction at approximately 2.0%. Only Phase I of this project, located in the northwest corner of the property, containing approximately 36 acres, is being covered in this report. The remainder of the property will mostly remain undisturbed until future phases of development. There is a concrete irrigation ditch along the northern property line of this site called the Spring Canyon Lateral, owned by the Warren Lake Company. This ditch is to be relocated approximately 23 feet south of the current location; however, an engineer that will be designated by the ditch company will perform the design and relocation. II. DRAINAGE BASINS A. Major Basin Description The Poudre Valley Hospital site lies entirely within the McClellands Basin. In the Final Drainage and Erosion Control Study for the Hamlet at Miramont P.U.D., completed by RBD, Inc., the SWMM Model was updated. In the update, the 1 APPENDIX PAGE VICINITY MAP 1 HYDROLOGY 3 INLET SIZING AND CURB CUTS 9 STORM DRAIN SCHEMATICS AND PIPE SIZES 23 SWALE SIZING 45 SWALE ANALYSIS — CONVEYANCE ELEMENT 39 52 RIPRAP CALCULATIONS 56 DETENTION POND DESIGN BY SWMM MODEL 61 WEIR ANALYSIS 103 EROSION CONTROL CALCULATIONS 124 EXCERPTS FROM McCLELLANDS BASIN MASTER DRAINAGE PLAN 133 EXCERPTS FROM McCLELLANDS BASIN 100-YR MASTER PLAN UPDATE 137 EXCERPTS FROM THE FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE HAMLET AT MIRAMONT P.U.D. 140 EXCERPTS FROM FINAL DRAINAGE PLAN FOR TIMBERLINE ROAD 165 TABLES AND FIGURES 177 TABLE OF CONTENTS PAGE I. GENERAL LOCATION AND DESCRIPTION A. LOCATION I B. DESCRIPTION OF PROPERTY I II. DRAINAGE BASINS A. MAJOR BASIN DESCRIPTION I B. SUB -BASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA A. REGULATIONS 2 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 3 C. HYDROLOGICAL CRITERIA 3 D. HYDRAULIC CRITERIA 3 E. VARIANCES FROM CRITERIA 3 IV. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT B. SPECIFIC DETAILS OVERALL DRAINAGE PLAN PHASE I DEVELOPMENT SWMM MODEL V. STORM WATER QUALITY A. GENERAL CONCEPT B. SPECIFIC DETAILS VI. EROSION CONTROL A. GENERAL CONCEPT B. SPECIFIC DETAILS VII. CONCLUSIONS A. COMPLIANCE WITH STANDARDS B. DRAINAGE CONCEPT C. STORM WATER QUALITY D. EROSION CONTROL CONCEPT 3 4 4 4 5 i 7 7 REFERENCES 9 y✓ ••'._.__ THE SEAR -BROWN GROUP FULL -SERVICE DESIGN PROFESSIONALS FORMERLY RBD, INC. 209 SOUTH MELDRUM FORT COLLINS, COLORADO 80521-2603 970-482-5922 FAX:970-482-6368 October 14, 1998 Mr. Basil Hamdan City of Fort Collins Water Utilities--Stormwater 700 Wood Street Fort Collins, Colorado 80521 RE: Preliminary Drainage and Erosion Control Report for the Poudre Valley Hospital - Harmony Campus . Dear Basil: We are pleased to resubmit to you, for your review and approval, this Preliminary Drainage and Erosion Control Report for the Poudre Valley Hospital - Harmony Campus. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. The Overall Drainage Report is being submitted simultaneously. We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, The Sear -Brown Group Prepared by: Reviewed by: Storm Gewirtz, E.I.T. Kevin Gingery, P.E. Project Engineer Engineering Manager Traci Downs, E.I.T. Project Engineer cc: File 823-001 Albert Kahn Associates NEW YORK•PENNSYLVANIA COLORADO•UTAH STANDARDS IN EXCELLENCE EQUAL OPPORTUNITY EMPLOYER Preliminary Drainage and Erosion Control Report Poudre Valley Hospital Harmony Campus, Fort Collins, Colorado October, 1998 THE SEAR -BROWN GROUP Standards in Excellence