STORMWATER REPORT FRITO LAY SUBDIVISION NO. 3

Transcription

1 STORMWATER REPORT FRITO LAY SUBDIVISION NO. 3 May 2018

2 STORMWATER REPORT I. Subdivision Data a. The parcel is adjacent to the existing Frito Lay property in Topeka; and the subject plat application encompasses approximately 76 acres a replat of Block C, Replat of Seymour Subdivision (18 acres), and a replat of Lot 1, Block A, Frito Lay Subdivision No. 2 (58 acres). The 58 acre portion is in the south side of the plat, and it is currently undeveloped. There are no current plans or configurations for the development of this portion of the plat. The 18 acre portion is on the north side of the plat, and partially developed with a parking lot. There are plans for development of this portion of the plat. The project will be an addition to the west side of the existing Frito Lay facility south of I-335 (Kansas Turnpike) and southwest of the west termination of SW 42 nd Street. Initially, there are plans for a large warehouse, and ultimately there are plans for several warehouses and truck/trailer parking. The plat submission is accompanied by an application for A Planned Unit Development for Frito Lay Subdivision No. 3. This application shows the location of the initial warehouse addition, as well as the planned additions to the south. Also attached to this report is a schematic sketch of the planned build out. There is a stream on the site. It begins on the west side of the site, near the southeast corner of the 58 acre parcel. From there, it drains to the northwest, dividing the 18 acre parcel to the north from the 58 acre parcel to the south. Once the stream meets with the west line of the plat boundary, it orients north and runs along the west side of the 18 acre parcel. Land within the 18 acre parcel drains from east to west, and drains into the stream. Land within the 58 acre parcel drains to the north and northwest. Some of the runoff enters the same stream, although some exits the site along the west side of the proposed subdivision. The stream exits the plat near its northwest corner, and flows under I335 (Kansas Turnpike) in a large concrete box. For the south 58 acres, because this area drains towards a tributary of the Shunganunga Creek, it is anticipated that stormwater detention is required. And also, because the land is currently undeveloped, it is anticipated that stormwater quality measures will be required for any future development. The size and details of those features would be designed and submitted for review at the time of site plan development, if the 58 acre parcel were to be developed in the future. For the north 18 acres, the development plan is known. This portion of the site also drains towards the Shunganunga Creek and is partially undeveloped; and stormwater detention/stormwater quality is planned. This report will give further details on the size and configuration of those features. b. Excluding planned ROW, the tract is 17.1 acres in size. The planned warehouses cover 3.8 acres, and the planned pavement areas cover 5.7 acres for an overall future runoff factor of In the existing condition, 1.2 acres is paved, with a site runoff factor of 0.34.

3 II. Drainage Discussion a. The table below shows the Future vs Existing runoff conditions. FUTURE VS EXISTING Area c Tc k 100 I 2 I 10 I 100 Q 2 Q 10 Q 100 (ac) (min) (in/hr) (in/hr) (in/hr) (cfs) (cfs) (cfs) Existing Future Stormwater detention will be required to reduce the future flows. b. Attached to this report are two worksheets from the MARC Manual Worksheet 1A and Worksheet 2. Worksheet 1A assess the total disturbed area, total impervious in the existing and future condition, total treatment area, and required level of service. Worksheet 2 assesses the value rating of a planned extended dry detention facility, with a vegetated filter strip. The value rating provided by this BMP meets the level of service required on Worksheet 1A. c. Attached are floodrouting worksheets for the site 2, 10, and 100 year. The detention facility utilizes a small (6 ) orifice as the outlet structure. This small outlet allows the pond to take approximately 40 hours to fully drain, in order to qualify for extended dry detention as defined by the MARC Manual. The easterly side of the facility will utilize a vegetated filter strip for overland flows which enter the pond. The extended dry detention facility coupled with the vegetated filter strip should provide an adequate value rating to provide stormwater quality, as defined in the MARC Manual. The extremely long detention time results in very low outflow rates less than 2 cfs for the 100 year event. III. Conclusions a. Conclusion: The proposed development will not increase the total flow to the existing stream or box culvert under I-335. The extended detention and filter strip should provide the required stormwater quality. b. The person responsible for the maintenance of the pond will be the owner or owner s representative currently the facilities manage for the Frito Lay facility. The Parcel ID Numbers are and c. The development will encroach into an area designated as Zone A on FEMA Panel 20177C0302E. This area of the stream has not been subject to a detailed study, and no Floodway or Base Flood Elevations have been published on the map panel. Bartlett & West, Inc. has acquired the HECRAS Flood Model for this stream from the Kansas Department of Agriculture Division of Water Resources (DWR). It does include Approximate Base Flood Elevations (BFA). Prior to obtaining a building permit for a

4 building/parking lot that would include fill in the Zone A, the owner shall certify a No- Rise of these BFAs. It is anticipated that discharging fill on the easterly side of the stream will have to be accompanied by removal of material on the westerly side on the stream, in order to certify a No-Rise. The attached exhibit shows the approximate areas of encroachment into the Zone A, as well as the anticipated area of excavation on the westerly bank. The fill and cut areas will be re-modeled in the HECRAS flood model, and the revised model, along with No-Rise certification, will be submitted to DWR for approval/evaluation by FEMA, prior to obtaining a building permit. Steven E. LaCasse, P.E.

5 SCHEMATIC SITE LAYOUT

6 WORKSHEET 1A FRITO LAY SUBDIVISION NO. 3 Proposed Building Addition and Parking Existing Parking Building and Parking % APWA / MARC BMP Manual 4-17 October 2012

7 WORKSHEET 2 Bartlett & West Project: FRITO LAY N0. 3 Project No: Date: 5/4/2018 WORKSHEET 2: DEVELOP MITIGATION PACKAGE(S) THAT MEET THE REQUIRED LS 1. Required LS (From Worksheet 1 or 1A, as Appropriate) 87.8 Note: Various BMPs may alter CN of proposed development and LS; recalculate both if applicable. 2. Proposed BMP Option Package No. 1 Proposed Site Area = 17.1 ac. Cover/BMP Description Area 1 - Vegetated Filer Strip and Extended Dry Detention VR from Table 2 or Table Treatment Area (acres) (Treatment Area x VR) Total Treatment Area 2 Total LS Refer to Mitigation Instructions and Tables 2 and 3 as appropriate when determining VR. Total treatment area cannot exceed 100 percent of the actual site area. Meets Required LS (Yes/No)? YES (If No, or if additional options area being tested, proceed below.)

8 FLOODROUTING 2 YEAR STORAGE ROUTING TABLES wo # LOCATION: Frito Lay No. 3 BY: SEL ORIFICE (in): 6.00 STORM (yr): 2 Tc (hrs): dt (hrs) Qp: STORAGE - OUTFLOW RELATIONSHIP Surface Ele. Head Discharge (cfs) Storage (ac ft) 2s/dt (cfs) 2s/dt + O (cfs) STORAGE - INDICATION ROUTING TABLE t/tp Q/Qp Time (hrs) Inflow (cfs) 2s/dt - O (cfs) 2s/dt + O (cfs) Outflow (cfs)

9 E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E Peak Outflow (cfs): 1.0 Surface Elevation (ft): Storage (ac ft):

10 FLOODROUTING 10 YEAR STORAGE ROUTING TABLES wo # LOCATION: Frito Lay No. 3 BY: SEL ORIFICE (in): 6.00 STORM (yr): 10 Tc (hrs): dt (hrs) Qp: STORAGE - OUTFLOW RELATIONSHIP Surface Ele. Head Discharge (cfs) Storage (ac ft) 2s/dt (cfs) 2s/dt + O (cfs) STORAGE - INDICATION ROUTING TABLE t/tp Q/Qp Time (hrs) Inflow (cfs) 2s/dt - O (cfs) 2s/dt + O (cfs) Outflow (cfs)

11 E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E Peak Outflow (cfs): 1.3 Surface Elevation (ft): Storage (ac ft):

12 FLOODROUTING 100 YEAR STORAGE ROUTING TABLES wo # LOCATION: Frito Lay No. 3 BY: SEL ORIFICE (in): 6.00 STORM (yr): 100 Tc (hrs): dt (hrs) Qp: STORAGE - OUTFLOW RELATIONSHIP Surface Ele. Head Discharge (cfs) Storage (ac ft) 2s/dt (cfs) 2s/dt + O (cfs) STORAGE - INDICATION ROUTING TABLE t/tp Q/Qp Time (hrs) Inflow (cfs) 2s/dt - O (cfs) 2s/dt + O (cfs) Outflow (cfs)

13 E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E Peak Outflow (cfs): 1.7 Surface Elevation (ft): Storage (ac ft):

14 18 ACRE PARCEL STORM WATER EASEMENT POND TOP ELEVATION= FLOW TOWARDS STREAM BORROW AREA DRAINAGE EXHIBIT FRITO LAY SUB. NO.3 TOPEKA, KS Drawing Name: W:\Proj\15000\15400\ \Documents\Reports\Drainage\Drainage Exhibit.dwg Layout Name: Layout1 Plotted By: RCP00722 Plotted on: 5/4/ :00:54 AM INLET WITH 6" ORIFICE Z MA ON P# E A 20 PE 17 R 7C FIR 03 M 02 E FLOW TOWARDS STREAM 58 ACRE PARCEL 0 400' SCALE: 1" = 400' FLOW OFFSITE DESIGNED BY: SEL DRAWN BY: RCP APPROVED BY: SEL PROJ NO: SCALE: AS NOTED DATE: MAY 2018 SHEET NUMBER 1 OF 1