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Upper Santa Cruz RiskMAP Study

Study/Project Purpose

The purpose of the Upper Santa Cruz RiskMAP Project is to identify flood risks along the Santa Cruz River within Pima County from the Santa Cruz County line, north to Interstate 19.

For more information contact:
Terry Hendricks, Chief Hydrologist
River and Basin Management Studies
Pima County Regional Flood Control District
210 N. Stone Ave, 9th Floor
Tucson, Arizona 85701-1207
(520) 724-4600
Terry.Hendricks@Pima.gov

Cooperative Technical Partnership with FEMA

The Pima County Regional Flood Control District (District) entered into a Cooperative Technical Partnership (CTP) in August 2014. The CTP allows for greater participation for communities to collaborate with FEMA on floodplain mapping projects. It also provided cost sharing between FEMA and the District to produce the RiskMAP data.  

Project Location

The Upper Santa Cruz River RiskMAP project follows the Santa Cruz River. It starts just upstream (south) of the Santa Cruz County Line and ends at Interstate 19. See the map below.
revised map

Project Description

The Upper Santa Cruz River RiskMAP project is a cooperative effort with the Federal Emergency Management Agency (FEMA) and utilizes the latest HEC-RAS computer riverine model developed by the Hydrologic Engineering Center of the U. S Army Corps of Engineers. The program is a 2-dimensional model that more accurately computes flow depths, velocities and areas of inundation. The current FEMA Flood Insurance Rate Map (FIRM) data for the Santa Cruz River is based on computer punch card technology and does not accurately reflect flood flow distribution. The RiskMAP products are not replacing the FIRM data or the current effective floodway delineations.

On July 17, 2018, there was a change the Scope of Work for the project to extend the modeling downstream to Interstate 19. The scope change also included revising the hydraulic model by upgrading to the newer version of the U. S Army Corps of Engineers HEC-RAS hydraulic program (version 5.05). The revisions produced slightly different results than the products previously shown on this website. Please contact the District if you need to view or obtain a copy of the initial product (12.3 Giga Bytes).

The Santa Cruz River was analyzed for the following discharge-flow return frequencies.

Return Frequency  Percent Annual Chance Exceedance  Peak Discharge in cubic feet/second (cfs) 
10-year
10%
15,570
25-year
4%
24,750
50-year
2%
33,750
100-year
1%
45,000
500-year
0.2%
100,500

 

Project Schedule

Activity
Completion Date
Comments
LiDAR and Aerial Photography
August 15, 2015
Explanation of LiDAR
RiskMAP report

Completed

Stakeholders Meeting
January 25, 2018
Town of Sahuarita Mayor and Council Office
Sahuarita Town Council presentation
February 26, 2018
 
Town of Sahuarita Mayor and Council Office
Public Open House
March 13, 2018
 
Town of Sahuarita Mayor and Council Office

 Change order to extend the mapping north to Interstate-19

December 19, 2018

 Upgraded the riverine computer model to HEC-RAS Vs 5.05 and extended the model downstream to Interstate-19

 Project Completion

 March 26, 2019

 The project was approved to be used as “Best Available Data”.  This means District staff will compare the RiskMap data to the Flood Insurance Rate Map information and make regulatory decisions based on the greatest flood risk. 

 The federal grant expired April 21, 2018.

Products

This project will create a report and flood hazard maps for five different flood frequencies. A copy of the Technical Data Notebook report (100 MB) on the Upper Santa Cruz RiskMAP Project is available for review.

There are five sets of 22 maps showing the flood risks along the upper Santa Cruz River for the 10-, 25-, 50-, 100-, and 500-year events. Go to the Maps tab to view the maps.

Flood Depth Maps

Click on the map number below to view the Flood Depth maps. 
Clickable index map linking to 10-, 25-, 50-, 100-, and 500-year flood depth maps for each panel of the Upper Santa Cruz River Risk Map Study.

Click for Panel 1 Maps Click for Panel 2 Maps Click for Panel 3 Maps Click for Panel 4 Maps Click for Panel 5 Maps Click for Panel 6 Maps Click for Panel 7 Maps Click for Panel 8 Maps Click for Panel 9 Maps Click for Panel 10 Maps Click for Panel 11 Maps Click for Panel 12 Maps Click for Panel 13 Maps Click for Panel 14 Maps Click for Panel 15 Maps Click for Panel 16 Maps Click for Panel 17 Maps Click for Panel 18 Maps Click for Panel 19 Maps Click for Panel 20 Maps Click for Panel 21 Maps Click for Panel 22 Maps

100-Year Flood Comparison Maps

Floodplain administrators are required to use is the 1% chance flood for permit regulations, according to local floodplain ordinances and state statutes.  The 1% chance flood is often referred to as the 100-year flood.  Although this RiskMAP project does not involve revising the Flood Insurance Rate Maps (FIRMs) approved by FEMA, they are an additional tool that floodplain administrators can use to assess flood risks and hazards. The most common question will be “What is the difference between the floodplains shown on the FIRMs and areas of inundation shown on the Flood RiskMAPs?"  By clicking on the map below, users will be able to see the FIRM AE and AO flood zones and Floodway for the Santa Cruz River on top of the 100-year Flood RiskMAPs.  Please note this comparison does not extend into Santa Cruz County and that the FIRMs do not show the 100-year limits inside Tohono O’Odham tribal lands. 

Click on the map number below to view the Floodplain Comparison maps. 
Clickable index map linking to 100-year flood comparison maps for each panel of the Upper Santa Cruz River Risk Map Study.

Click for Panel 1 Maps Click for Panel 2 Maps Click for Panel 3 Maps Click for Panel 4 Maps Click for Panel 5 Maps Click for Panel 6 Maps Click for Panel 7 Maps Click for Panel 8 Maps Click for Panel 9 Maps Click for Panel 10 Maps Click for Panel 11 Maps Click for Panel 12 Maps Click for Panel 13 Maps Click for Panel 14 Maps Click for Panel 15 Maps Click for Panel 16 Maps Click for Panel 17 Maps Click for Panel 18 Maps Click for Panel 19 Maps Click for Panel 20 Maps Click for Panel 21 Maps Click for Panel 22 Maps

Videos

The District generated a map video showing depths and flow paths for the 100-year (1% annual probability) data. The MP4 video is a little under 3 minutes long and shows color coded flow depths and moving velocity vectors. Due to their size, you may be required to download the video and play it locally from your device.

Documents

Reports, Frequently Asked Questions and other documents will be placed here as they become available. Below are the currently available documents.