Pima County Flood Control District (PCFCD) has recently published three important documents:
Tortolita Alliance (TA) has provided comments on all three documents and you can download TA's comment letter at the link below:
TA's comments cover primarily the Tortolita Fan Watershed and the key supportive comments in the letter are:
Watershed Management Plan-provides important documentation regarding the unpredictable nature of alluvial fan flooding in the Tortolita Fan Watershed and the inherent flooding risks associated with any proposed development in this watershed.
Floodplain Management Plan-identifies successes and improvements necessary to protect the public from flooding risk with public involvement and inter-governmental coordination an integral part of the Plan.
Technical Policy-TECH-010-Rainfall Input For Hydrologic Modeling-PCFCD is rightly concerned that the warmer climate has and will result in more intense precipitation events. Accordingly, new Intensity-Duration-Frequency (IDF) curves have been developed using climate models and precipitation data. The new IDF curves indicate the need to increase the NOAA Atlas 14-90% upper confidence level by 15%. This results in a new 100-year storm return frequency that is approximately equivalent to the current 500-year storm return frequency. This is significant and will ensure that hydrology/hydraulic analysis will now include the impacts of climate change.
TA supports TECH-010 and the same technical policy should be adopted by the Town of Marana Flood Plain Administrator.
All existing development with flood protection and stormwater facilities approved utilizing NOAA Atlas 14 (or earlier) should be re-modeled to ascertain any flood protection issues under the new TECH-010 standard.
You can learn more about these proposed documents and policies by going to the Pima County Flood Control District-Newsroom. The PowerPoint (cover page shown below) describing the development of the new IDF curves and TECH-010 is quite interesting.
