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North Ranch Wash Floodplain Remapping

Study status: 
Completed - Existing conditions local floodplain delineations
Under Development - FEMA floodplain map revision

Study/Project Purpose

For more information contact:
Evan Canfield, PE, PhD, CFM Project Manager
(520) 724-4600

The purpose of this project is to perform a floodplain study for the portion of the North Ranch Wash starting at the Oasis Road alignment and continuing upstream (north) to a point located north of W. Tortolita Mountain Circle. Segments of the study reach are located in both the Town of Oro Valley and unincorporated Pima County. The information provided by the study will provide the technical support for a potential Letter of Map Revision (LOMR) to be submitted to, and approved by, FEMA.

Project Location

The contributing watershed for the study reach of North Ranch Wash is bounded at the downstream limit by the Oasis Road alignment and extends northerly to the headwaters within the Tortolita Mountains. The watershed is located within portions of the following Townships and Range in Pima County, Arizona:
The study reach for the floodplain mapping corresponds to the existing FEMA floodplain boundaries beginning downstream at the Oasis Road alignment and continuing to the upstream limit where the FEMA mapping terminates at a point located north of W. Tortolita Mountain Circle. The study reach is shown on the attached map provided by the RCFD. The study reach is approximately 7 miles in length. The existing FEMA Special Flood Hazard Areas (SFHA) mostly consist of Zone A (approximate mapping), with a local area of Zone AE (detailed mapping) located just south of Tangerine Road.


Project Location and Boundary Map

Project Description

The Pima County Flood Control District is undertaking this project in partnership with the Town of Oro Valley. FEMA has identified Special Flood Hazard Areas (100-year floodplains) associated with the washes which encompass homes and businesses. The North Ranch Wash floodplain is complex and exhibits two-dimensional flow patterns, and the District and Town of Oro Valley have determined that the existing floodplain maps do not accurately reflect risk. New two-dimensional floodplain assessment techniques with improved topographic information were used to develop new detailed mapping that will better reflect risk.

FEMA Floodplain Map Revision

The North Ranch Wash floodplain limits as shown on the Flood Insurance Rate Maps (FIRMs) are outdated. The Pima County Regional Flood Control District submitted a Letter of Map Revision (LOMR) application to the Federal Emergency Management Agency (FEMA) to modify the floodplain boundaries. Click in the map boundary boxes in the image below to compare the exiting FIRM flood hazard boundaries to the proposed boundaries submitted with the LOMR. See this brochure for more information on LOMRs.