2020 Issue

33 following the prior river channel and came through the Starvation Dam outlet at more than 1000 NTU. This type of flow through the reservoir had never been observed histor - ically. See Figure 6 . During this condition, the water near the intake, 2 meters above the bottom of the reservoir, was 61 NTU, with approximately 6 to 8 NTU coming into the plant. The CUWCD mobilized a sampling and moni- toring team to evaluate turbidity within the lake. The team sampled several areas at several depths on various days. Figure 5 shows the locations and the turbidity at various depths in the reservoir at one of the sampling locations. The turbidity was impacted by thunderstorms that washed down significant sediment during a storm that produced over 2,000 cubic feet per second in the Strawberry River. Figure 6 shows the flows coming out of Starvation Reser - voir when the high turbidity water was channeling through the reservoir and coming out of the dam. This sediment has the potential to shut down this water supply to parts of the Duchesne Valley. Figure 6 - Turbid Water Channeled Through the Reservoir and Flowed Through the Outlet of the Dam at >1000 NTU Ben Willardson, Ph.D., P.E., D.WRE, ENV SP, QSD/P Dr. Ben Willardson has 19 years of pro- fessional experience in the development and review of hydrologic, hydraulic, and sediment transport models. During that time, he has managed roadway and pavement improve- ment projects, pedestrian facility upgrades, and drainage improvement projects. Ben has worked for both the public and private engineering sectors. While working for the Los Angeles County Flood Control District, he oversaw the operation of 14 dams and 27 spreading ground facilities for flood control and water conservation within the com - plex flood control system serving Los Angeles County. He has conducted asset assessment for programs related to flood-control channels and pavements. Mike Rau, CUWCD Mike Rau is the Water Quality Manager for Central Utah Water, where he has been employed since 2009. He has a B.S. in Physiology and Developmental Biology from Brigham Young University, and has grade IV certifications in drinking water treatment and distribution. He is from Mapleton, Utah where he enjoys all things outdoors and spending time with his wife and 5 children. As discussed above, watershed recovery takes five to 10 years to complete. The size of the fire limits the effective - ness of erosion mitigation measures. The ability of the CUWCD to deploy standard mitigation measures is ham- pered by geology, terrain, and highly erosive soil. There will be some seeding this year to encourage revegetation within the burned area. Water quality impacts could likely continue for the fore- seeable future as the watershed slowly recovers. Although there were a few thunderstorms after the fire, there is still sediment within the watershed with no vegetation to hold it in place. Due to the nature of burned watersheds, it is expected that average storms will produce higher flow rates with larger loads of sediment, organics, and debris. These impacts will taper off as the watershed recovers. The DVWTP process is not designed to treat high turbidity and is restricted by law. The current process was designed based on past water quality, which was stable for 40 years, and has now been impacted for years to come. These changes will require changes in the treatment process to meet the impacted conditions. The changes may include clarification, with flocculation/sedimentation processes, and may also require alternative water sources. There may be a potential for emergency funding through the Federal Emergency Management Agency to implement watershed recovery programs or fund plant upgrades to handle the changed conditions. Civil engineers will be con- sidering many of these choices to come up with the solu- tion that will best meet the needs of the community served by the DVWTP in the coming years. Wildfires are natural disasters that cause impacts to the communities we live in and work with. They increase the chances of flooding, debris flows, and impacts on utility systems like the WVWTP. Civil engineers need to consider the risks of fire and after-effects when designing the sys - tems that serve our communities. No picture available