Granite Reef Watershed Drainage and Flood Control Improvement

PROJECT PURPOSE

The primary objective of the Granite Reef Watershed Drainage and Flood Control Improvement Project is to eliminate the risk of structural flooding, eliminate the Federal Emergency Management Agency (FEMA) floodplain along Granite Reef Wash, and reduce street and yard flooding. The project will also include a new storm drain in Pima Road that will help reduce floodwater flows in Granite Reef Wash and provide street drainage for the future Pima Road widening project. The existing FEMA floodplain is approximately 2 miles long and encompasses over 600 homes; extending from Thomas Road downstream to the City’s southern boundary at McKellips Road, generally between Granite Reef Road and Pima Road.

PROJECT AREA

The project area is bounded by the Arizona Canal on the north, Loop 101 on the east, the Salt River on the south and the drainage divide that runs between Hayden Road and Granite Reef Road on the east. The project will be designed and constructed in two segments - NORTH, the area north of Indian School Rd., and SOUTH, the area south of Indian School Rd.

PLANNED DRAINAGE IMPROVEMENTS

Drainage improvements are being planned for the project area to control the runoff from the 100-year storm in order to eliminate the FEMA-designated floodplain along Granite Reef Wash. The improvements will be implemented in two phases. 

NORTH Improvements (Phase 1) - COMPLETE

Construction of the Phase 1, North Area Improvements took place between June 2017 and June 2021.   Construction is now complete on new storm drain laterals that connect to the existing storm drains on Jackrabbit Road, Chaparral Road and Camelback Road.  The new laterals will discharge more flow to the existing storm drains allowing more runoff to be diverted to Indian Bend Wash, so it doesn’t flow south, resulting in flooding problems downstream. The proposed storm drain laterals will control all the 100-year runoff north of Indian School Road.  

SOUTH Improvements (Phase 2)

The SOUTH area implementation plan includes new drainage improvements south of Indian School Road that, which, together with the North area improvements, will hopefully eliminate the FEMA floodplain along the Granite Reef Wash.  The SOUTH area improvements will be built in two segments. The first portion will be built with the widening of Pima Road (Phase 2A), the remainder of the storm drain improvements will follow with the construction of Granite Reef South (Phase 2B).

These improvements include:

• A storm drain in Thomas Road between 82nd Street and Pima Road (2A Pima Road)

• A storm drain in McKellips Road between 82nd Street and Pima Road (2A Pima Road)

• A storm drain in the Granite Reef Wash alignment from McKellips Road to the Salt River. (2B Granite Reef)
• A stormwater detention basin in Pima Park (2B Granite Reef)
• A storm drain in Pima Road from Thomas Road to McKellips Road 

  (2B Granite Reef)

• Granite Reef Channel improvements both upstream and downstream of McDowell Road (2B Granite Reef)
  

Pima Road Improvements

A series of improvements are planned for Pima Road from McDowell Road to the Salt River Pima – Maricopa Indian Community’s (SRP-MIC) north boundary near 90th Street and Via Linda. The improvements are based on a concept report that was developed in 2009 and will include a portion of the Granite Reef Watershed Storm Drain Improvements.

The project includes widening Pima Road, intersection improvements at Talking Stick Way, Via de Ventura, and Via Linda/90th Street, as well as landscape improvements between Via de Ventura and SR Loop 202 Freeway. The project will increase safety, mitigate flooding impacts, add traffic capacity and improve multimodal and pedestrian features, and add consistency to the overall corridor.

Pima Road is co-owned by SRP-MIC and City of Scottsdale, and SRP-MIC is the lead agency completing this project in partnership with the City and other funding partners. Other funding partners include the Flood Control District of Maricopa County (FCDMC) and the Maricopa Association of Governments (MAG). 

NEW HYDROLOGIC AND HYDRAULIC ANALYSIS & APPLICATION TO FEMA FOR FLOODPLAIN REDUCTION

The project includes the development of a two-dimensional hydrologic and hydraulic computer model, utilizing new technology, to analyze storm water runoff in the project area.  An analysis is complete based on the recently completed Phase I Improvements and the future Phase II Improvements. This analysis will be included in the City’s application to FEMA to reduce the size of the current, effective floodplain, as well as the 100-year flood elevations. The application is titled  A  Conditional Request for Letter of Map Revision (CLOMR) for the Granite Reef Wash Drainage and Flood Control project. The city plans to submit the CLOMR application to FEMA soon.  Approval of the CLOMR application may take up to 12 months.