Stormwater System Maintenance

Pg.9 Rio de Flag
Pg.9 Milton flooding

Objective 4: Upgrade Stormwater System and Increase Maintenance

Relevant Standards

  • Protect public health, safety, and the local environment
  • Stormwater system resilient to the impacts of climate change
  • Reduce stormwater drainage complaints


Flagstaff’s stormwater system is separate from the sanitary sewer system and is comprised of open channels (both natural and manmade) that convey large amounts of stormwater through culverts/ pipes that allow stormwater to cross under roads and catch basins that capture and guide stormwater into an underground network of pipes. For the system to function properly, it must be well maintained (clear of debris) and be sized to meet the type and magnitude of storms that occur in Flagstaff. The Stormwater Section is the delegated authority managing the National Flood Insurance Program for the City.

Timing Concerns

All indications are that “100-year” storms are now regular occurrences and may get worse in the near term. Damage will increase if this issue is not addressed expeditiously. Identifying and addressing the greatest vulnerabilities should be a high priority.


Consistent with climate change models, the intensity of rainstorms in Flagstaff has been increasing.  Flagstaff has experienced “100Year” storms in 2014, 2016, 2018, and a “1000-Year” storm in 2018. Clearly, storms that were considered very unlikely may now be much more frequent or even the norm. Storms are typically categorized in terms of likely frequency, for example a 10-Year or 100-Year storm Also, wildfires increase the risks of flooding. These conditions highlight a variety of problems, Including:  

  • Flagstaff’s current stormwater control system is under-sized, and in certain areas cannot meet the requirements of what was previously defined as a 10-Year storm, let alone a 100-Year storm.
  • Over the last 5 years, the number of drainage complaints has reached 350, and overall damage estimates/insurance claims are unknown.
  • Maintenance is a problem. Many drainage complaints are due to a clogged system.
  • Floodplain policies and regulations need updating. Both old and new construction do not meet current grading and drainage regulations, which increases damage during storms. To the dismay of owners, some new homes are being flooded.
  • The existing stormwater system is not completely documented, which makes it difficult to administer the National Flood Insurance program.
  • These concerns are above and beyond the downtown flooding being addressed by the Army Corps of Engineers’ Rio de Flag project.

Specific Responses

  Champion Action Items Timing
1.    Continue data collection to improve understanding of               Flagstaff hydrology on the configuration and condition of         the stormwater system __________________ _______________________
2.    Ensure that system maintenance is adequately specified           and funded      
3.    Update current policies, process and enforcement of                 grading and drainage regulations for new construction.             Ensure sufficient staffing to review plans, permits and               final inspections.      
4.    Re-set the storm categorization system to reflect the                 changing reality of climate change      
5.    Conduct a risk analysis of the stormwater system based           on recent storms and damage      
6.    Develop a comprehensive stormwater infrastructure                   computer model to enhance decision-making      
7.    Prioritize upgrades to the stormwater system based on             risk analyses      

Provide your public comment here.