Stormwater System Maintenance

Pg.9 Rio de Flag
Pg.9 Milton flooding

Objective 4: Upgrade Stormwater System & 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

Step Champion Action Items Timing
1. Continue data collection to improve understanding of  Flagstaff hydrology on the configuration and condition of  the stormwater system Stormwater Manager, Program Manager 1. Collecting data at numerous stream gauges. 2.  RDF Hydrology grant ongoing.  Collected USGS historic gauge information to be used to create statistical hydrology for Flagstaff.
New gauges (9) installed throughout city. 2.  Finish rating tables and geomorphological assessment.
2. Ensure that system maintenance is adequately specified  and funded Stormwater Manager, Open Channel Manager 1. Stormwater System Maintenance Program moved under Water Services 2. Adopted CMMS to plan, manage and track.
​ 3. Employed technicians to verify, correct and add stormwater assets to GIS mapping system.
1. Hire 2 MSWs.
​ 2. Complete SOP and work with PW and WSD Operations to define responsibilities.
​3. Assess workload and effectiveness of program using data collected in CMMS
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. Stormwater manager, Program Manager 1. Worked with Building Safety Department to draft new SFD / residential grading permit requirements to address current shortcomings.
​ 2. Working with DE and Legal for updates to City Code and certifications in regards to Registrant requirements for grading activities from grading plans to final grading certifications.
1.  Work with Building Safety to finalize grading ordinance. 2.  Continue in early phases of Stormwater Management Design Manual.
4. Re-set the storm categorization system to reflect the   changing reality of climate change Stormwater Manager,Program Manager 1. Administering FEMA grant for upgraded flood ALERT system to estimate flows when connecting to the new Rio de Flag stormwater system.
​ 2.  Summarized rainfall runoff relationships in Upper Lake Mary.
1. Use information gathered to update rainfall-runoff curve numbers.
​ 2.  Use results of meteorological design study to guide the revision to hydrology section of the SW Design manual.
5. Conduct a risk analysis of the stormwater system based  on recent storms and damage Stormwater Manager, Program Manager 1. Administering FEMA grant for upgraded flood ALERT system to evaluate flood damage. 1. Use information gathered to assess needs for improvements to system.
6. Develop a comprehensive stormwater infrastructure  computer model to enhance decision-making Stormwater Manager 1.  Completed preliminary infrastructure inventory mapping. 1.  Continue mapping. 2. Continue collaboration with NAU Smart City project.
7. Prioritize upgrades to the stormwater system based on  risk analyses Stormwater Manager 1. Updated CIP project priorities to complete improvements to Spruce Ave. Channel at Linda Vista 1.  CIP Ranking updates
​2. Completing additional improvement project at Dortha to address elevated risk from Linda Vista project.