The City of Sacramento is the state capital of California in the United States of America. Situated in the Central Valley in Northern California, Sacramento is blessed with direct access to surface water from the Sacramento River that flows south from Lake Shasta and the American River that flows west from the Sierra Nevada snowpack. Unfortunately, the city also faces certain challenges that affect its’ water quality and daily activity. Sacramento experiences wide precipitation variability each year, which leads to multi-year droughts or major rainfall events during El Niño seasons. The city’s low topography and poor soil drainage along the Sacramento River cause the city to have major flooding events and combined sewage overflows in the historic core of the city. Based on these conditions, the City has opportunity to collect stormwater to reduce flooding and combined sewage overflows. This opportunity for implementing Green Stormwater Infrastructure (GSI) in Sacramento will be identified after reviewing Sacramento’s geographic context, existing water infrastructure and vulnerabilities.
Site Context:
Sacramento is currently the sixth largest city in California with 501,344 residents (2018) and the fastest growing major city in the state with an annual growth rate of 1.43%. However, the region is more suburban than urban as the city population is only 21% of the Sacramento-Roseville-Arden-Arcade MSA population of 2.3 million (2018). The city sits at the confluence of the Sacramento and American Rivers. The Sacramento River is the largest river and watershed system in California. The 27,000 square mile basin drains from the Coastal Range, Mount Shasta, the Cascades and the Sierra Nevada mountains. Urban development is buffered from the river by the Sacramento levee system. The American River is buffered from urban development by the levee system and the riparian park system known as the American River Parkway. Since the city is approximately 44 miles north of the Sacramento-San Joaquin Delta and 65 miles from the San Francisco Bay, the city’s water supplies do not face issues with saltwater intrusion.
Sacramento is a relatively flat city along the Sacramento River. Elevations in Greater Sacramento increase moving east toward the Sierra Nevada range. The original city settlement experienced many floods based on its low topography. The City recognized that the confluence of the two rivers were a flooding threat for the growing city, so they decided to construct the levee system to protect the neighborhoods south and east of the two rivers. The downtown area was also raised 12 feet to rise above the water mark.
The city has poor soil drainage along the Sacramento River, which makes the city more susceptible to flooding. Most of Downtown Sacramento is under Sailboat-Scribner-Consumes soil, which is defined as poorly drained soils that have a high seasonal water table. The southwestern portion of the city along the river features Egbert-Valpac soil, which is also defined as poorly drained soils with a high-water table. Without the protection of the levee system, each of these areas would be extremely vulnerable to flooding.
Water Rights & Supply:
The Greater Sacramento region is fragmented by 24 water purveyors but is united through a joint-powers authority known as the Regional Water Authority. The agency coordinates responsible water planning in the region. The City of Sacramento’s Department of Utilities is responsible for providing and maintaining drinking water, sewer collection, storm drainage, and flood control services for the city. Sacramento’s water supply comes from surface water (80%) and groundwater sources (20%). Surface water is collected and treated from the Sacramento River at the Sacramento River Water Treatment Plant, which can support 160 million gallons per day (MGD). Diverted American River is treated at the E.A. Fairburn Water Treatment Plant, which can also support 160 MGD. There are 22 groundwater wells used in Sacramento, with 20 wells located north (North American Subbasin) and 2 wells located south (South American Subbasin) of the American River. Groundwater can support 20.6 MGD for the city and is treated at the wells.
The City has appropriative rights to diverting river water. The City can divert from the Sacramento River through the Pre-1914 Appropriative Right that allows the City to divert 75 cubic feet per second (cfs) from the river and Post-1914 River Permit 992 that enables the City to divert up to 81,800 acre-feet per year (AFY) with a maximum flow of 225 cfs within city limits. The City can divert from the American River through River Permits 11358 and 11361 which allows the City to divert 675 cfs from the river and River Permits 11359 and 11360 which allows the City to re-divert river water that was previously diverted by the Sacramento Municipal Utility District (SMUD)’s Upper American River Project (UARP). Re-diversion can be up to 1150 cfs and up to 589,000 AFY of UARP stored water.
The City also has access to Folsom Reservoir water through a Settlement Contract with the US Bureau of Reclamation. Through this contract, the City must limit its total combined diversions of the Sacramento River and American Rivers and must make an annual payment to the USBR for storage capacity. In return, the USBR must always make water available pursuant to the City’s water rights. The City is also held accountable by the regionally-based Water Forum Agreement, which limits the quantity of water diverted from the American River during consecutive dry years (Conference Years) and when river flows are below Hodge Flow Criteria. The Agreement does not impact the amount of diverted water from the American River unless either of the conditions occur.
The North American and South American Subbasins are managed by regional authorities because their boundaries cross many cities, water districts, and water agencies within Greater Sacramento. Both subbasins are monitored by the Sacramento Water Forum and the Regional Water Authority. As of 2014, the Sustainable Groundwater Management Act ensures that local agencies properly manage their groundwater through the creation of Groundwater Sustainability Plans.
Water Distribution:
Sacramento maintains 1,600 miles of transmission and distribution system mains with pipe diameters between 2 and 72 inches wide. There are 17 storage facilities throughout the city, including 12 reservoirs and 5 water clearwells at the water treatment plants. Treated water is provided to 480,105 retail customers within the city limits or to 362,731 customers in 4 other water districts through wholesale trade.
The city consists of 2 sewage systems that were constructed in different time periods. The historic core utilizes a Combined Sewer System (CSS) that has been in operation since the late 1800s. The CSS serves 11,240 acres (40% of the city) and features 2 primary pumping stations and 3 stations for large storms. The CSS has 275 miles of wastewater and stormwater pipes that are periodically discharged into the pumping stations if over 60 MGD is reached. The primary wastewater treatment plants in this zone is the Pioneer Reservoir that can treat 250 MGD and the Combined Wastewater Treatment Plant that can treat 130 MGD. In the case of large storms, the Sacramento Regional Wastewater Treatment Plant can treat 60 MGD for the CSS. The Sacramento Regional Wastewater Treatment Plant is owned and operated by the Sacramento Regional County Sanitation District. The plant treats and discharges wastewater into the Sacramento River for 5 cities in the region. The rest of the city is served by a Separate Sewer System which features 482 miles of pipes from 4 to 36 inches. The primary treatment plant for this system is the Sacramento Regional Wastewater Treatment Plant.
The city does not currently employ any active stormwater recovery measures, which enables more susceptibility to flooding and Combined Sewage Overflows (CSOs).
Vulnerabilities:
The Sacramento region faces precipitation variability and is susceptible to either droughts or heavy rain seasons. Sacramento has a Hot-summer Mediterranean climate, which means that the city experiences ‘hot and dry’ summers and ‘mild and wet’ winters. The El Niño precipitation cycle also provides higher levels of precipitation to the Sacramento Valley depending on the strength of the cycle. This, along with the city’s low topography and poor soil drainage, shows that flooding is the greatest natural hazard to Sacramento.
Sacramento has the greatest flood risk of any urban area in America. Most federal and state emergency declarations in Sacramento County were for flooding, including 12 of 17 Federal Emergency Management Agency (FEMA) declarations and 8 of 11 California Office of Emergency Services (Cal OES) declarations. Since most of the residents live within the levee-protected area, heavy flooding years have broken the levees and eventually caused property damages.
High amounts of flooding in the CSS zone also have contributed to an increase of CSOs, with over 80 sewage spills between 2012 and 2015. As heavy precipitation events are expected to occur more often according to California’s Fourth Climate Change Assessment, the city needs to employ active stormwater recovery measures to filter rain away from the sewer systems and to drain to maintain daily activities in the city.
Solution:
The best solution to reducing flooding risk during heavy rain storms in Sacramento is to install Green Stormwater Infrastructure (GSI) in areas with the greatest flooding risk in the city. Although the City does not currently have stormwater recovery measures, city employees will be performing pilot studies and evaluating storage projects to determine the best practices to maximize capacity during storms and provide flood reduction benefits. The benefits of GSI in Sacramento would be that it would capture more stormwater in flood-prone areas and protect the Sacramento River from CSOs.
As defined earlier, areas along the Sacramento River are the most susceptible to flooding based on their low topography and poor soil drainage. Although these areas are protected by the levee system, the City has determined that repetitive flooding areas occur from within the levee-dependent zone. Residents living within the levee-dependent areas are still strongly recommended to purchase flood insurance for their properties based on the possibility of levee breaks or river overflows. The City has identified that over half of the CSS area is at risk for flooding, which is where GSI should be specifically implemented in Sacramento.
In search of applicable precedents, GSI in Melbourne would be an appropriate example to Sacramento since the Australian city faces similar flooding and drought conditions. The Kalkallo Stormwater Harvest project utilizes street drains along the main corridors of an office park to transfer to a wetland and 65 milliliter per day (MLD) storage basin. A 1 MLD water treatment plant treats the harvested water to be distributed back into the drinking water supply of the catchment area. The Elizabeth Street Catchment Plan for the Elizabeth Street area in the heart of Melbourne analyzed the existing flooding conditions and stormwater storage capacity to identify opportunity zones for implementing GSI. Strategies included new open spaces with underground cisterns, permeable surfaces in large plazas, rain collectors on roofs (blue stormwater infrastructure) and tree trenches with small dispersed storage tanks.
Some of these ideas can be transferred into Sacramento’s CSS area by defining which public rights-of-way capture the most stormwater based on low topography. Downtown and Midtown Sacramento, which make up the historic core of the city, feature a series of short hills that push stormwater into pockets of low elevated areas. As most of these low-elevated areas run along some the historic core’s north and south streets, GSI could be implemented as bioswales that run along these corridors. Like the city’s Complete Street projects, the GSI corridors can be designed with pedestrian bump-outs and medians to collect stormwater. Dryland perennial grasses that are native to the region could be planted to provide low maintenance during the hot and dry summer months.
Another method of stormwater collection is the creation of new stormwater collection wetlands along the levee system that can retrieve water from selected GSI corridors and to filter water from river overflows. These wetlands can be built where land is available along the levee to act as a second buffer from urban development. These areas could have a combination of wetland perennial grasses and dryland perennial grasses based on their contact with rivers and creeks. Together, these two strategies could filter stormwater and floodwater away from urban development and the CSS.
Sources:
- US Census, American Community Survey, Age & Sex: ACS Estimates 2018. Sacramento city, CA.
- US Census, American Community Survey, Annual Estimates of the Resident Population: April 1, 2010 to July 1, 2018: 2018 Population Estimates. Sacramento-Roseville-Arden-Arcade, CA Metro Area.
- Sacramento River Watershed Program, “Sacramento River Basin“. 2019. http://www.sacriver.org/aboutwatershed/roadmap/sacramento-river-basin
- West Yost Associates. 2015 Urban Water Management Plan. City of Sacramento. Draft June 2016.
- Topographic-Map.com, Sacramento Topographic Map. 2019. http://en-us.topographic-map.com/
- Sacramento Area Flood Control Agency, “Sacramento Area Flood History”. 2008. http://www.safca.org/history.html
- United States Department of Agriculture Soil Conservation Service, General Soil Map: Sacramento County, California.
- Climate-Data.org, “Climate Sacramento“. AM OP. https://en.climate-data.org/north-america/united-states-of-america/california/sacramento-1460/
- Timothy Werth, “Heavy California Rains Determine El Nino Weather in Pacific”. LA’s the Place.com. February 2019. https://lastheplace.com/2019/02/15/heavy-california-rains-determine-el-nino-weather-in-pacific/
- Eric Escalante, “Sacramento County Flood Risk | What every person should know“. ABC 10. March 2019. https://www.abc10.com/article/news/sacramento-county-flood-risk-what-every-person-should-know/103-044b392d-285d-4ce8-a5a5-bd278f759de9
- Michael Mott, “Dirty money: Sacramento sewer district to pay $225,000 after spills“. Newsreview.com. April 2017. https://www.newsreview.com/sacramento/dirty-money-sacramento-sewer-district/content?oid=24128188
- State of California Office of Planning and Research, State of California Energy Commission & California Natural Resources Agency, California’s Fourth Climate Change Assessment. 2018.
- Cooperative Research Centre for Water Sensitive Cities Ltd., “Kalkallo Stormwater Harvesting and Reuse“, Australian Government Department of Industry, Innovation and Science. 2018.
- Cooperative Research Centre for Water Sensitive Cities Ltd., “Elizabeth Street Catchment: Integrated Water Cycle Management Plan“, Australian Government Department of Industry, Innovation and Science. 2018.
- LocalWiki: Sacramento, “Native Grasses and Grasslike Plants“. https://localwiki.org/sac/Native_Grasses_and_Grasslike_Plants