RIPARIAN CORRIDOR STUDY FINAL CITY CREEK MANAGEMENT PLAN 3.0 BASELINE ASSESSMENT RESULTS Watershed Conditions Bonneville Boulevard, drains cover of 9.2% (SLCO 2009). 11,189 acres of wooded Much of this impervious cover is Size and Land Use mountainous terrain ranging in associated with the paved City elevation from 9,400 to 4,300 Creek Canyon Road which City Creek is the northernmost feet. Upper City Creek flows for extends 5.75 miles up the significant mountain stream a total length of 10.3 miles canyon to Rotary Park. More drainage in Salt Lake City (SLCO 2009). The majority of than 99% of the upper (Figure 3.1). The upper the upper subwatershed is subwatershed is public land subwatershed, which includes the forested and undeveloped, with owned by Salt Lake City and RCS study area above an estimated overall impervious managed for drinking water Figure 3.1. City Creek watershed (map from SLCO 2009). SALT LAKE CITY OCTOBER 2010 DEPARTMENT OF PUBLIC UTILITIES3-1 BIO-WEST, INC. RIPARIAN CORRIDOR STUDY FINAL CITY CREEK MANAGEMENT PLAN source protection and open east and the State Capitol supported by groundwater space/recreation. The City Creek complex on the west. An inputs, and flows in the channel Water Treatment Plant (CCWTP) additional 2.3 miles of lower City recover rapidly below the is located about 3 miles up the Creek south and west of the RCS CCWTP diversion point. canyon; access to the area above study area is conveyed in the CCWTP is subject to engineered conduits to the Average annual precipitation restrictions designed to limit Jordan River (Figure 1.1). ranges from 32–42 inches in the potential water supply Estimated existing impervious highest portion of the upper contamination. Recreational cover is 19.7% within the lower subwatershed, from 22–32 opportunities in the upper subwatershed (SLCO 2009). inches in the mid-elevation subwatershed include biking, portions of the upper jogging, hiking, fishing, Hydrology subwatershed, and from 11 to 22 picnicking at designated picnic inches in the valley/lower sites, skiing, and snowshoeing. The hydrology of City Creek is subwatershed (SLCO 2009). altered by flow diversions at the Above the CCWTP City Creek is The lower City Creek CCWTP, which commonly classified as having perennial sub-watershed is much smaller, removes all available flows from flow; below the CCWTP the draining 4,621 acres of mixed the creek. Typical withdrawal creek is classified as use land below Bonneville rates average about 4.6 cfs, but “perennial-reduced,” indicating Boulevard. Lower City Creek rates as great as 23 cfs are that flows are artificially reduced flows approximately 1.5 miles sometimes diverted during the by the stream diversions for through Memory Grove, an area spring runoff period (F. Reynolds municipal water supply (SLCO owned and managed by the 2010, pers. comm.). In the 2009). City’s Parks Division. The vicinity of the CCWTP, the corridor is bordered by the stream is a “gaining reach” No significant water storage Avenues residential area on the where surface flows are reservoirs are currently present on City Creek, although Below: City Creek debris basin above Bonneville Boulevard shortly historically reservoirs were after dredging. constructed in the canyon to store water for municipal supply. Two debris basins located immediately above and below the Bonneville Boulevard crossing provide some degree of flow regulation and capture a significant portion of the creek’s coarse sediment loads. These debris basins are maintained by Salt Lake County and require dredging approximately every two to three years. Additionally, the formal portion of Memory Grove Park adjacent to study reach LCC_R02B is designed to function as a flow regulation SALT LAKE CITY OCTOBER 2010 DEPARTMENT OF PUBLIC UTILITIES3-2 BIO-WEST, INC. RIPARIAN CORRIDOR STUDY FINAL CITY CREEK MANAGEMENT PLAN basin that would control flood flows entering the downstream engineered conduits. This current system for flow and sediment regulation was constructed to prevent damages similar to those sustained during the major flood event in 1983. City Creek’s hydrology is characterized by a distinct springtime peak typical of snowmelt-driven systems. Based on analysis of flow data recorded at the County gage in Memory Grove from 1980–2005, mean Figure 3.2. Monthly flows at Salt Lake County’s gage at Memory annual flow is 8.3 cfs, average Grove. monthly flow is highest in May (Figure 3.2 ), and base flows average about 3 cfs. Peak daily flow occurs on May 21st on average (SLCO 2009), and average annual high flow is 67 cfs based on analysis of the 1980–2005 time period. Urbanization and development in the lower subwatershed have affected surface water- groundwater patterns. These influences affect the study reaches from LCC_R01B downstream, which receive water from urbanized areas via storm drain outfalls. As contributing watershed areas become converted to impervious surfaces, a greater proportion of storm water runs off as surface flow rather than infiltrating into the ground, leaving less groundwater available to supply baseflow to the creek during the summer dry Figure 3.3. Relationship between impervious cover and surface period (Figure 3.3). The runoff. Impervious cover in a watershed results relatively high proportion of in increased surface runoff. Diagram and caption text from FISRWG 1998. SALT LAKE CITY OCTOBER 2010 DEPARTMENT OF PUBLIC UTILITIES3-3 BIO-WEST, INC. RIPARIAN CORRIDOR STUDY FINAL CITY CREEK MANAGEMENT PLAN surface flow during storm events fishery). Below the CCWTP, the Jordan River, several new E.coli can also lead to a “flashy” designated beneficial uses monitoring stations have been hydrologic pattern with rapid, include 2B and 3A. City Creek’s recently established on City brief rises in flow during storms water quality is considered good Creek by DWQ and Salt Lake (Figure 3.4). On City Creek, and fully supports all of its County. Samples are being however, these influences are beneficial uses (DWQ 2006). collected monthly at these sites, limited only to the downstream- but data have not yet gone most study reaches because the Potential nonpoint sources of through quality assurance/control majority of the contributing contamination in the City Creek procedures and have not been watershed area has been watershed include fertilizers and released to the public or protected as undeveloped open herbicides from managed parks, comprehensively analyzed. As space. runoff from roads/urbanized additional data are collected and areas (e.g., automotive fluids), analyzed and as DWQ’s new E. Water Quality and waste from wildlife (e.g., coli work group becomes more deer, ducks) and pets. established, it is anticipated that a Above the CCWTP, City Creek’s Bacteriological contamination is better understanding of beneficial use classifications as of particular concern because the bacteriological contamination designated by the Utah Division Jordan River, the receiving body sources within City Creek will of Water Quality (DWQ) include for City Creek water, is currently develop. 1C (high quality drinking water), listed as impaired for E. coli 2B (secondary contact (DWQ 2006). To help inform Geology and Soils recreation), and 3A (cold water ongoing TMDL studies on the Within the upper subwatershed, City Creek flows primarily through Pennsylvanian and Mississippian age sandstones and limestones. Within the RCS study area, the channel flows through Miocene conglomerates, Oligocene and Eocene tuffs and other volcanics, and quaternary landslide deposits. Below reach UCC_R10C, these formations are surrounded by Pleistocene Lake Bonneville deposits ranging from finer-grained silt and clay deposits to coarser sand and gravel deposits. Within reach LCC_R01C and downstream, the channel flows directly through these Lake Bonneville deposits Figure 3.4. A comparison of hydrographs before and after and other quaternary alluvial urbanization. The discharge curve is higher and steeper deposits (Bryant 1990). for urban streams than for natural streams. Diagram and caption text from FISRWG 1998. SALT LAKE CITY OCTOBER 2010 DEPARTMENT OF PUBLIC UTILITIES3-4 BIO-WEST, INC. RIPARIAN CORRIDOR STUDY FINAL CITY CREEK MANAGEMENT PLAN In the upper City Creek Fish, Birds, and Wildlife surveys in this portion of the subwatershed, approximately creek (D. Wiley 2010, pers. 20–35 % of the soils have severe Above the CCWTP City Creek comm.). to very severe soil erosion supports a confirmed potential. In the lower conservation population of native During the Audubon Society’s subwatershed, 35–50% of the Bonneville cutthroat trout, the 2005 Christmas bird count, soils have severe to very severe state fish of Utah and a state- which included City Creek erosion potential (SLCO 2009). designated special status species Canyon and Memory Grove, 19 Several significant hillslope that evolved as the top predator different bird species were slumps are evident adjacent to within ancient Lake Bonneville observed (Carr 2009). Scientific the south/east side of the channel (Lentsch et al. 2000). City Creek data describing detailed within the study area. Slumps also supports rainbow trout, information about mammal have also occurred recently on brown trout, and rainbow- populations are limited. the steep hillside west of the cutthroat hybrid crosses (SLCO However, general observations channel within areas adjacent to 2009). During the RCS field suggest that wildlife populations reach LCC_R01B and assessments, trout (species in the canyon include deer, downstream. In some