City Council approval of staff's proposed funding option and to move the timing of the project forward. 

The Water Services Division has two upcoming projects that are located adjacent to one another along Linda Vista Drive: the Stormwater Culvert Upsizing by Community Development, and the replacement of the Water Pressure Reducing Valve (PRV) by Water Services.  These two projects can be constructed simultaneously this Spring/Summer prior to the Monsoons.  Constructing these two projects simultaneously not only will save project costs but will reduce impacts to the community by combining necessary road closures.  The need to upsize the culvert is a result of last year's Museum Fire and is not funded in this fiscal year's Stormwater Enterprise Fund Capital Improvement Program (CIP).  Staff initially anticipated partially funding the Linda Vista Culvert Upsizing project using a grant through FEMA's Hazard Mitigation Grant Program of approximately $187,000. Waiting for this grant would require the City to delay construction on this project until after the 2020 Monsoons.  With the U.S. Army Corps of Engineers (USACE) recently announcing the Rio de Flag Flood Control Project will be funded in the next Federal Fiscal Year, staff believes we can reallocate current funding to complete this project. The USACE's announcement has a profound impact on Stormwater's CIP freeing up funding for other drainage projects that are needed in the event the Rio de Flag Flood Control Project was further delayed for lack of funding.  Specifically, the solution to the repair/replacement of the Phoenix Avenue Bridge near Beaver Street becomes less expensive since this structure will no longer have to accommodate the entire flows within the Rio de Flag in the future.  The Phoenix Avenue Bridge project is funded in FY2019-2020 at $999,995 and staff is proposing the anticipated savings from this project be re-directed to fund the Linda Vista Stormwater Culvert Upsizing at a cost of $322,000.  

The Museum Fire started in July 2019 and burned approximately 1900 acres of steep slopes in the Dry Lake Hills. Preliminary flood models, completed while the fire was still active, indicated that post-fire flooding is possible in Spruce Wash, the predominant drainage of the fire footprint. Potential flood impacts the Flagstaff neighborhoods of Grandview and Sunnyside and would be exacerbated by an undersized culvert at Linda Vista Avenue. The City hired a consulting firm who completed the engineering design for a culvert upsizing at Linda Vista, the design calls for an additional arched corrugated metal pipe that will increase the capacity of the road crossing to match that of the next downstream culvert at Cedar Avenue. The total capacity would increase from 184 cubic feet per second to 325 cubic feet per second. As a reference, the new 25-year flood is predicted by the 2019 flood model to be 1,329 cubic feet per second. This project will not mediate large floods but will provide neighborhood protection for medium-sized flow events.
Additionally, the flood model has not been updated since summer 2019. There are several factors that may have changed the predicted flows. These include:

• Low severity burn areas are largely re-vegetated with native grasses.
• Some high severity burn areas are now mulched (168 acres)
• Some channel conditions have been improved (“detention” basin at Elden Road and channel crossing, RAC mitigation efforts on the alluvial fan)
• Updated soil infiltration measurements from NAU/COF/AZGS.
• Planned snag removal and soil stabilization awarded to FWPP
• The model does not take into account infiltration across the alluvial fan. Observed infiltration during rain events in 2019 was substantial with one flow event seeing a drop from 200 cubic feet per second upstream from Mount Elden Road to approximately 2 cubic feet per second at Paradise Road near the City limits.

While being conservative on flood flow calculations helps communities be better prepared, it should also be noted that there has not been an extensive geophysical or geotechnical survey of the alluvial fans that impact Spruce Wash flow and soil infiltration. The pre-fire FEMA flood study predicts a 10-year flood of 60 cfs at Linda Vista, a 50-year flood of 180 cfs (at culvert capacity), and a 100-year flood of 230 cfs. The largest recorded flow near Linda Vista was 5 cfs (USGS report) and the water has never been recorded to overtop Linda Vista Drive.  Traditional hydrologic models have struggled to calculate flood flows for the headwaters of Spruce Wash due to the high infiltration rates mixed conifer forests and the in the alluvial fan reach. The magnitude of the flood threat is yet unknown and may be considerably less than either the Schultz Fire or the 2019 hydrologic model.
 
The cost of the Linda Vista culvert upsizing is approximately $322,000 according to Community Development who is delivering this project on behalf of Water Services - Stormwater.  Water Services had initially planned to partially fund this project using a Hazard Mitigation Grant Program (HMGP) grant through FEMA that is in review at the State level. This funding source is secured for state and federally declared disasters and as such is assured funding for the City. HMGP will provide approximately $187,000 of federal funds for the Linda Vista culvert. The FEMA funding, however, is not available until the grant is awarded, likely in late summer 2020. Waiting for this funding does have potential drawbacks including missing the 2020 monsoon season. Community Development has worked with Eagle Mountain Construction under a Job Order Contract (JOC) on costing and planning for both the PRV and Linda Vista Culvert projects. There is a time and cost savings by moving forward with both projects in the spring at the same time, The City will save approximately $24,000 by combining projects. Doing the projects separately will cost more now and cause more interruptions to the community with multiple road closures.  Eagle Mountain estimates that the PRV project will take 5 days of road closure and the culvert replacement will take 10 days of closure. Combining these projects will reduce the closure time to 10 days total, which is 5 days less than doing the projects separately.

By combining the PRV replacement and the culvert upsizing projects this Spring/Summer will disqualify the City from receiving the federally funded grant. The Federal funds identified for this project will be released, and the next highest HMGP priority is a Coconino County Flood Control District proposal for fuels reduction on Bill Williams Mountain, a project outside of the Flagstaff community.