HomeMy WebLinkAbout28. West 9th Avenue Resconstruction Storm Water Services
I:\City Manager\Diane\1AGENDA PREP\2.23 word memos\28.docx Page 1 of 1
TO: Honorable Mayor and Members of the Common Council
FROM: Mark A. Rohloff, City Manager
DATE: February 18, 2021
RE: Amendment to Professional Services Agreement for West 9th
Reconstruction Storm Water Services / Brown and Caldwell ($8,727)
A professional services agreement with Brown and Caldwell for providing water quality
analysis and hydrologic and hydraulic system modeling services for the reconstruction
of West 9th Avenue was reported to the Common Council on September 8, 2020. During
the course of the project, additional services were requested by City Staff.
Brown and Caldwell evaluated various water quality practices that could be utilized
towards meeting the Total Suspended Solids reduction goals for the project outlined in
the original scope of work. The analysis identified the conversion of the Pheasant Creek
Drive Dry Detention Basin into a wet detention Basin and diverting a portion of the runoff
from the West 9th Avenue reconstruction area as a viable alternative. To further evaluate
the potential impacts and results of the dry pond conversion, additional analysis was
required. This additional analysis considered potential hydrologic and hydraulic
impacts to the Pheasant Creek Drive Detention Basin and the downstream conveyance
system between the detention basin and Sawyer Creek.
Staff has reviewed the amendment and the costs. The amount of this amendment is not
to exceed $8,727. This will raise the total agreement amount to $47,263. Funds for this
project are included in the 2021 Storm Water Utility Operating Budget (Account
#05612030-6450 Engineering & Planning-Engineering & Consulting Fees).
Chapter 12 of the Municipal Code of the City of Oshkosh provides that professional services
of a specialized nature, including engineering services, may be procured without the use
of formal, sealed quotes. In accordance with Section 12-16 of the Code, I am hereby
submitting this report regarding this professional services agreement amendment.
Please contact me if you have any questions concerning this professional services
agreement amendment.
MAR/jg
MN _'A· gr Oshkosh
RECEIVED Attachment A Amendment #1 to West 9" Avenue Reconstruction Storm Water Services Brown and Caldwell Project# 155708 City of Oshkosh Reference: City Contract 21-04 1/21/2021 This Attachment A documents additional scope and tasks requested of Brown and Caldwell (BC) by the City of Oshkosh (City) for services under the West 9th Avenue Reconstruction Storm Water Services project (City Contract 21-04; BC Project# 155708) agreement dated October 7, 2020. Background BC evaluated various water quality practices that could be utilized towards meeting the TSS reduction goals for the project outlined in the original scope of work. The analysis identified the conversion of the Pheasant Creek Drive dry detention basin into a wet detention basin and diverting a portion of the runoff from the West 9" Avenue reconstruction area as a viable alternative. To further evaluate the potential impacts and results of the dry pond conversion, additional analysis is required. The Pheasant Creek Drive dry detention basin is located south of West 9" Avenue, within an adjacent watershed. This additional analysis will consider potential hydrologic and hydraulic (H&H) impacts to the Pheasant Creek Drive detention basin and the downstream conveyance system between the detention basin and Sawyer Creek. Scope Changes Add Task 4 to the scope of work as follows: Task 4: Pheasant Creek Drive Detention Basin Hydrologic & Hydraulic Analysis 1. Execute Existing Conditions Hydrologic and Hydraulic Model (XP SWMM 2D) a. Utilize general methodology and data consistent with Task 2 of this analysis. b. A detailed analysis of all storm sewers and drainage-ways in the Pheasant Creek Drive detention basin drainage area will not be conducted under this amendment except as noted in item 1. d below. c. Hydrologic model will incorporate all runoff tributary to the dry detention basin and areas that enter the downstream conveyance system prior to reaching Sawyer Creek. Drainage areas will be delineated for each detention basin inlet (three drainage areas estimated) and for the area downstream (two drainage areas estimated). d. Hydraulic model will incorporate: i. the existing dry detention basin storage volume, ii. the detention basin outlet structure, iii. existing storm sewer within Homestead Drive, iv. grass swale located north of Homestead Drive and south of West 9" Avenue, and v. culverts under South Oakwood Road. e. Perform sensitivity analysis to determine which duration design storm is the most critical for detention basin capacity (check the 1-hour, 3-hour, 6-hour, 12-hour, and 24-hour storm events). f. Run model at the critical duration for the following design storm events: 1-year, 2-year, 10-year, 25-year, and 100-year. Run the model for the June 12-13, 2008 storm event. g. Prepare table noting the flooding depth for up to (five) 5 locations for each design storm and for the June 12-13, 2008 storm event. 2. Evaluate conversion of the dry detention basin into a wet detention basin and two alternative diversions of runoff from the West 9" Avenue reconstruction project area to the Pheasant Creek Drive detention basin. Evaluation will be completed by updating the existing conditions XP SWMM 2D model to consider scenarios described below. a. The wet detention basin conversion will assume: i. The detention basin outlet structure will remain the same. Oshkosh 9th Ave SW Analysis Amend1-2021-01-21.docx 1/21/2021 1
Attachment A Amendment #1 to West 9" Avenue Reconstruction Storm Water Services Brown and Caldwell Project # 155708 City of Oshkosh Reference: City Contract 21-04 1/21/2021 ii. The detention basin footprint remains the same and side slopes will not be modified. A permanent pool of water will be created at the elevation of the outlet structure. b. Runoff diversion #1 will assume all runoff from West 9" Avenue west of Pheasant Creek Drive will be diverted south to the detention basin. A storm sewer meeting the City's conveyance goals will be sized in Pheasant Creek Drive to divert runoff. c. Runoff diversion #2 will assume low flow runoff will be diverted to the detention basin, while high flows remain within West 9" Avenue. The diversion sizing will be based on analysis of the Win SLAMM model (developed under Task 1) to determine the diversion flow rate needed to convey runoff from water quality storm events. d. For each alternative, the model will be executed at the critical duration for the following design storm events: 1-year, 2-year, 10-year, 25-year, and 100-year. Model will also be run for the June 12-13, 2008 storm event. e. Prepare table noting the flooding depth for up to (five) 5 locations for each design storm under each alternative. 3. Conduct one (1) web-based meeting to discuss questions and document decisions as needed related to the Pheasant Creek Drive detention basin feasibility. Budget Amendment All work will be conducted under the terms and conditions as described in the West 9 Avenue Reconstruction Storm Water Services agreement dated October 7, 2020. The Amendment budget is provided below: Task Hours Budget Task 4: Pheasant Creek Drive Detention Basin Hvdroloaic & Hvdraulic Analvsis 62 $8,727 Current contract amount= Amendment #1: Amended Contract Amount: $38,536 $8,727 $47,263 2 Oshkosh 9th Ave SW Analysis Amend1-2021-01-21.docx 1/21/2021