Water Resources Research Act Program

Details for Project ID 2019UT256B

New design and analysis guidance regarding potential scour of hydraulic structures located in canals, rivers, dams, and levees

Institute: Utah
Year Established: 2019 Start Date: 2019-02-28 End Date: 2020-02-27
Total Federal Funds: $28,394 Total Non-Federal Funds: $41,053

Principal Investigators: Brian M. Crookson

Abstract: Many communities today rely heavily on engineered water distribution systems for potable water, irrigation, and flood control. These systems contain hydraulic structures, critical operational elements that have often been in service for decades. While in service, a structure might deteriorate or experience damage, local scour might compromise stability, demands from the local community might increase, or its purpose might change. Indeed, many hydraulic structures have been identified that do not meet public safety or performance standards and are in need of rehabilitation. A small selection of recent dramatic examples in Utah and the USA include: Montello Dam near the Utah border (embankment failure February 2017); Oroville Dam Crisis in California (spillway damage, Feather River communities evacuated February 2017); South Carolina Flooding (24 high and significant hazard dams failed October 2015); Divers Dam near Salida, Colorado (4 fatalities June 2014); local scour and road damage in the Santa Ana River, and South Creek Dam failure and flash flooding on the Virgin River, Utah (Town of Rockville evacuated December 2010). Looking at the immediate future, Utah is at a crossroad with historic growth, requiring significant changes in the State’s water infrastructure. Many communities that have been historically centered around agriculture are being urbanized, and Utah has a growing high-population density corridor. In addition to increased demands on water infrastructure, the number of incidents related to flooding in Utah and the USA are increasing. Additional understanding regarding hydrologic risks is being provided by a detailed extreme precipitation study of Utah (currently underway) through Utah Dam Safety. However, a critical component to a structure is foundation protection during operation and floods. Local scour can undermine footings and slabs, which could potentially result in structural failure and instability. According to Utah Dam Safety Engineer Everett Taylor, the State of Utah is in need of additional guidance for predicting local scour at structures. This information would be useful for estimating eroded volumes, scour hole geometries, and equilibrium scour depths. Knowing a maximum depth of scour is particularly useful for sizing cutoff walls where concrete structures terminate. In addition to Utah, various entities are also involved in this infrastructure crisis. The Federal Emergency Management Agency is working closely with the National Dam Safety Review Board (NDSRB) at this critical time to increase public safety by raising the standard of practice of hydraulic structures. This effort specifically includes a new FEMA best practices manual for concrete spillways, corresponding hydraulic failure modes, and communicating new applied research to practitioners involved in the rehabilitation of hydraulic structures. Also, a new ASCE task force was created in 2018 to prepare a guidance monograph for practitioners focused on scour at in-stream hydraulic structures. This effort has identified various research needs that includes prediction methods for the temporal evolution of local scour at structures and estimating maximum scour depths in non-cohesive alluvium, which is commonly found in Utah. Sediment movement, particularly undermining scour, can affect public safety and the performance of hydraulic structures located in canals, channels, rivers, and at dams and levees. Insufficient information is available on this topic to practitioners involved in water infrastructure rehabilitation efforts. If granted the USGS 104B funding for 2019, this applied research study would provide new information for practitioners regarding scour potential at drop structures. As part of this effort, we anticipate development of a new design and analysis tool, new insights regarding scour processes, and a theoretical approach based on shear stress and scour depth equilibrium. Study results will directly benefit the State of Utah and current ASCE, FEMA and NDSRB efforts (previously mentioned).