Title
Request Authorization to Enter Into Intergovernmental Agreement with Flood Control District of Maricopa County for 27th Avenue and Olney Avenue Storm Drain Project (Ordinance S-44314)
Description
Request authorization for the City Manager, or his designee, to enter into an Intergovernmental Agreement (IGA) with the Flood Control District of Maricopa County (FCDMC) for the 27th Avenue and Olney Avenue Storm Drain Project. Further request authorization for the City Treasurer to accept and the City Controller to disburse all funds related to this item. The estimated project cost is $6 million, which includes channel rights-of-way, utility relocations, storm drain construction, construction management, post design, and materials testing.
Report
Summary
In late 2015, the FCDMC, in partnership with the City of Phoenix, initiated a study to update the Laveen Area Drainage Master Plan for the South Phoenix/Laveen area using new mapping and comprehensive flood model software. The updated study used data gathered from heavy rains and flooding that occurred in August and September of 2014. The study included analysis of existing regional drainage improvements such as detention basins, channels, storm drains and culverts, much of which had been constructed based on recommendations from earlier versions of the regional drainage master plans. Construction efforts prior to this study focused mainly on the downstream portion of the overall recommended regional system to provide an outfall for future improvements closer to the foothills. The study recommends additional regional drainage facilities extending further up into the watershed area to address neighborhood flooding issues that became more apparent during the 2014 storms.
The regional rainfall-runoff model now covers the entire study area. The new model identifies sources of stormwater flows so mitigation alternatives can be developed. Flood prone areas known as Areas of Mitigation Interest (AoMIs) were identified through the updated study. A total of 11 potential mitigation alternatives were developed and presented at two public meetings held in May of 2017, at which time, comments were received from attendees. After further technical analysis of potential mitigation alternatives, the following alternative component is proposed as one of the recommended drainage master plans for the study area.
27th Avenue and Olney Avenue Storm Drain Project
This area’s greatest flooding problems are the major washes north of Olney Avenue east of 27th and 23rd Avenues, overwhelming the drainage infrastructure of existing subdivisions to the north and west. Flooding problems occur downstream from north of the subdivisions because there is no drainage infrastructure to carry stormwater to the recently constructed regional detention basin at 27th Avenue and South Mountain Avenue.
The proposed project will construct a 72-inch diameter storm drain in Olney Avenue from about 24th Drive west to 27th Ave, then north to the existing 27th Avenue and South Mountain Avenue regional basin. This storm drain would have large inlets at multiple locations along Olney Avenue to intercept drainage as well as multiple inlets along 27th Avenue, including a large inlet for the subdivision retention basin just south of the Western Canal. The project also includes a proposed Hazard Mitigation Assistance (HMA) regional drainage basin on about 4.5 acres along 23rd Avenue north of Olney Avenue. The estimated cost for the storm drain project is $6 million. Re-construction of 27th Avenue between Olney Avenue and Gary Way may be required in conjunction with this proposed storm drain project. Portions of the existing roadway right-of-way remain within the Maricopa County Department of Transportation (MCDOT) jurisdiction. MCDOT may become a cost share partner in the IGA if the proposed project is extended to include roadway improvements to 27th Avenue between Olney Avenue and Gary Way.
Financial Impact
The estimated project cost is $6 million, which includes channel rights-of-way, utility relocations, storm drain construction, construction management, post design, and materials testing. The terms of the IGA between the City and the FCDMC will jointly cost share for project development and implementation of the 27th Avenue and Olney Avenue Storm Drain Project. The cost-share distribution between the City of Phoenix and FCDMC will maintain an overall 50/50 cost share, which is the standard cost-share allocation for projects funded by FCDMC. The projects included are: (1) Durango Regional Conveyance Channel Project, which was previously approved by the City Council on October 4, 2017, (2) South Phoenix/Laveen Drainage Projects, and (3) Rawhide Wash Project. The City's contribution of up to $3.0 million dollars is available in the City's five-year Capital Improvement Program (CIP) budget.
Concurrence/Previous Council Action
This item was recommended for approval at the Transportation and Infrastructure Subcommittee meeting on Feb. 13, 2018 by a vote of 4-0.
Location
The project is generally located along Olney Avenue and 27th Avenue going north to the 27th Avenue and South Mountain Avenue Regional Drainage Basin.
Council District: 8
Department
Responsible Department
This item is submitted by Deputy City Managers Mario Paniagua and Karen Peters, and the Street Transportation and Public Works departments.