The URL can be used to link to this page

Home My WebLink AboutWESTBROOKE PUD FIRST FILING FINAL - 3 90D - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT0 10 FINAL DRAINAGE & EROSION CONTROL REPORT FOR WESTBROOKE FIRST FILING (FORMERLY PLATT PROPERTIES) AT REGENCY DRIVE AND WAKEROBIN LANE JUNE 28, 1991 PREPARED FOR: THE GROUP, INC. 401 WEST MULBERRY FORT COLLINS, COLORADO 80521 PREPARED BY: PARSONS & ASSOCIATES CONSULTING ENGINEERS 432 LINK LANE FORT COLLINS, COLORADO 80524 (303) 221-2400 PROJECT NUMBER: 91.07 GRP 1 NO FINAL DRAINAGE AND EROSION CONTROL REPORT FOR WESTBROOKE FIRST,FILING AT REGENCY DRIVE AND WAKEROBIN LANE I INTRODUCTION This final report has been prepared in conjunction with the development of detailed site topography and final construction plans for Westbrooke First Filing (formerly Platt Properties). It is the intent of this report to provide additional information for those issues identified by the preliminary report as well as address the concerns outlined by the City of Fort Collins staff members. This report then will redefine drainage boundaries, determine runoff quantities and detention volumes if needed in accordance to the guidelines established by the City of Fort Collins Storm Drainage Criteria Manual. .SITE DESCRIPTION This phase of Westbrooke is located in the Southeast Quarter of section 34, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, Larimer County, Colorado. More generally described as being located North and West of the intersection of Shields Street and Harmony Road just North of Wakerobin Lane. (See figure 1.) The entire 31.9 acre parcel is bounded by Seneca Street on the west, by Troutman Parkway the north, Regency Drive and Wakerobin Lane to the south, and the Pleasant Valley and Lake Canal on the east. The preliminary project included 109 single family lots on the entire 31.9 acre parcel. The Phase I project being proposed includes 70 lots on the southerly 20 acres. The land' uses- are varied adjacent to this project. On the west adjacent to Seneca Street are two school campuses, Webber Junior High and Johnson Elementary. The area to the north of this project is master planned for a regional park, regional detention facility and multi -family development as part of the Mountain Ridge Farm. -1- PROJECT SITE VICINITY MAP N. T. S. ME No Text 0 0 On the east the Pleasant Valley and Lake Canal makes a natural buffer to the higher density and commercial uses proposed in the Pineview P.U.D. To the south is the Mail Creek Drainageway Regional detention Pond #1. This pond accepts drainage from approximately 159 acres of the Mail Creek Drainage basin. Graded channels along Harmony road and Regency Drive assure that runoff gets to this facility. I This report is intended to address final design issues for the first phase of this two phase project. Phase I will be developed as. seventy (70) single family residences as modified in the Amendment of Area B of the Master Plan of the Villages at Harmony West P.U.D. This area is currently undeveloped and covered with native grasses. The site slopes to the south with an average slope of 1% - 1.5%. HISTORIC DRAINAGE Westbrooke First Filing sits along a subbasin boundary between the McClelland Drainage Basin and. Mail Creek drainage basin. One of the criteria for selecting a phase line for the total parcel was to identify,a line which conforms with drainage boundaries. The grading and drainage plan show that this was accomplished as this phase drains entirely to the south and is totally contained in subbasin #85 as identified in a study entitled "McClellands and Mail Creek Major Drainageway Plan" prepared by Cornell consulting company and John S. Griffith in December of 1980. The location of this Phase I greatly simplifies the drainage requirements for the development of the initial 70 lots. Drainage to the north including the 39 lots proposed as Phase II flow away from this site to the McClelland basin. Flows on the east side of the Pleasant Valley and Lake Canal also flow away from Phase I through the Pineview P.U.D. area to Shields Street. Flows from the school site to the West as well as those flows in Seneca Street and Regency Drive are directed towards the channellalong the north side of Regency Drive. These flows cross under Seneca Street and Regency Drive in twin 34" X 53" horizontal elliptical reinforced concrete pipe and flow into the Mail Creek Drainageway detention Pond #1. Therefore, no offsite drainage impacts the proposed 20 acre Phase I site. In addition no flows from the project site impact adjacent areas. Drainage flow runs from north to south towards Wakerobin Lane. These flows are diverted to a 36" reinforced concrete pipe under Wakerobin Lane where they are eventually discharged into Detention Pond #1. It should be noted that as stated in the original drainage study for this area (subbasin 85) detention area was provided in the existing basin. Therefore no flows from the project area affect adjacent areas and any required detention for the entire phase I project has been provided for in Detention Pond #1. -2- M DESIGN CRITERIA The Rational Formula as identified in the City of Fort Collins Storm drainage Design criteria has been used to calculate storm water runoff flows for the developed 100 year return period. i PROPOSED DRAINAGE Proposed drainage improvements will consist of street curb and gutters and storm sewers. In no circumstance will runoff from subbasins be allowed to exceed street capacities. A summary of each of the subbasins follows: SUBBASIN A Subbasin A includes sheet runoff from back yards from the lots along the west side of'Sand Creek Court as well as adjacent Street flows. This water enters into the drainage channel along Regency Drive where it continues to the regional detention pond. SUBBASIN B Subbasin B is approximately 3.3 acres in size. Flows from Sand Creek Court drain via street curbs into the north curb line of Wakerobin Lane. These flows continue easterly to the low spot in Wakerobin Lane. A new inlet and pipe under Wakerobin Lane will convey 100 year flood flows to the detention pond. SUBBASIN C Subbasin C is approximately 5.1 acres in size. Drainage from the lots adjacent to Shadowbrooke Court run towards the street curbs and then proceed to the north curb line of Wakerobin Lane. Flows here combine with runoff from Sand Creek Court and proceed to the new inlet at the existing low spot of Wakerobin Lane. Some overtopping of Wakerobin Lane can be expected in the 100 year flood. These flows will find their way to the inlet on the south side of the street and possibly overtop the inlet and curb here and pass directly into the detention pond. -3- SUBBASINS D & E Subbasins D & E include approximately, 6.5 acres. Runoff from lots adjacent to and west of Westbrooke Drive and Westbrooke Court run towards inlets at the intersection of the two street approximately 400' north of Wakerobin Lane., Inlets at this intersection and a 36" concrete; pipe will covey 100 year flood waters to the detention pond. SUBBASINS F & G Subbasins F & G includes approximately 1.1 acres and includes the front yards along the east side of Westbrooke Court. These two basins drain into the inlet at the intersection of Westbrooke Dive and Westbrooke Court. The existing 36" reinforced concrete pipe under Wakerobin Lane will be reset to match new grades. Flows greater than the expected 100 storm will be conveyed to the east in a swale which will eventually spill into the Pleasant Valley and Lake Canal. SUBBASIN H Subbasin H contains 3.6 acres. No concentration point exists in this basin. Flows will consist of backyard runoff which. will sheet flow into the Pleasant Valley and Lake Canal. These sheet flows from grassed back yards will contribute less water into the Pleasant Valley and Lake Canal. Existing low lying areas that did not drain to the south and spilled into the Canal will be eliminated. REGENCY DRIVE CHANNEL A 50 foot easement has been provided for the existing channel along Regency Drive. This provides room for a sidewalk adjacent to Regency Drive, and also provides for a 10 foot wide flat area between the edge of the channel and proposed property lines. -4- DETENTION STORAGE Storm water generated from this project will be detained in regional Detention Pond #1. This facility will have and approximate surface area of 7..3 acres during the 100 year storm. It has been designed to detain the 100-year developed runoff from 195 acres including this project. i CONCLUSION Drainage from'. the Westbrooke First Filing' has been accomplished by means of street drainage and storm sewer conveyance to the Mail Creek Drainageway Detention Pond #1. Only developed 100-year flows were considered in the analysis since no detention will be needed on -site. The proposed 70 lot development boundary closely follows the'existing drainage basin boundaries. -5-