Title
Request Authorization to Enter into Intergovernmental Agreement with Flood Control District of Maricopa County for 19th Avenue and Dobbins Road Project (Ordinance S-44315)
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 19th Avenue and Dobbins Road 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 $6.5 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 has 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 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. A total of 11 potential mitigation alternatives were developed and presented at two public meetings held in May 2017, at which time, comments were received from attendees. After further technical analysis of potential mitigation alternatives, the following component is proposed as one of the recommended drainage master plans for the study area.
19th Avenue and Dobbins Road Project
Most flooding in this area and the areas to the north and west is associated with very large flows that enter Dobbins Road from the south between 15th Avenue to about 19th Avenue. This combined flow floods Dobbins Road and adjacent properties and ponds along Salt River Project's (SRP) Western Canal. The combined flow passes through the narrow area along Dobbins Road near the Western Canal and continues west, entering the intersection at 19th Avenue and other downstream areas.
The proposed project will construct a regional detention basin on about 5.5 acres at the northeast corner of 15th Avenue and Dobbins Road, east of the existing fire station. The project will include a four-barrel, 54-inch diameter basin inlet culvert under Dobbins Road to intercept flow from the existing Humane Society channel. The project will also construct a storm drain in Dobbins Road from the new regional basin west to 19th Avenue, then north to South Mountain Avenue, then west to the existing regional drainage basin at 27th Avenue and South Mountain Avenue. The storm drain would range in size from 54-inch diameter along Dobbins Road to 72-inch diameter along South Mountain Avenue. In addition to draining the new detention basin, the storm drain would have large inlets along Dobbins Road and numerous smaller inlets along 19th Avenue and South Mountain Avenue.
Financial Impact
The estimated project cost is $6.5 million, which includes channel rights-of-way, utility relocations, 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 19th Avenue and Dobbins Road Project. The cost-share distribution between the City of Phoenix and FCDMC for this project will maintain an overall 50/50 cost share, which is the standard cost-share allocation for projects funded by FCDMC. The following projects are included: (1) Durango Regional Conveyance Channel Project previously approved October 4, 2017, (2) South Phoenix/Laveen Drainage Projects, and (3) Rawhide Wash Project. The City's contribution of up to $3.25 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 19th Avenue and along Dobbins Road, along South Mountain Avenue 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.