PROJECT PROFILES
salton sea
SALTON SEA LAKEBED PROJECT
California’s largest lake, the Salton Sea, was once flourishing as a sport-fishing and recreational area as well as a habitat for endangered wildlife. Now, it is quickly turning into a pungent-smelling, desolate, lake dying from enemies such as salt, fertilizer, California water agencies, and the sun. The Salton Sea straddles Riverside and Imperial Counties and is located only 35 miles north of the Mexican border, in the middle of a hot and dry desert area. This feat of nature was created in 1905 when a silt build up blocked the Colorado River’s flow to the Gulf of California. The river diverted from its course and flowed into the Salton Sink. The lake that resulted was five times larger than it is now and attracted over 400 species of birds, some now endangered. Numerous species of sport fish were introduced and the lake flourished. When the river’s silt closed off in-flow to the lake, the water level began to decrease due to evaporation under the intense desert sun. Since the lake has no out-flow channel, the minerals and salts remain and increase in concentration as the water level is depleted.
How does the lake maintain its current level?
At 227 feet below sea level, the sea is officially designated as a sump for agricultural drainage. Agricultural runoff from farms throughout the Imperial and Coachella valleys drain into the lake, replenishing water lost due to evaporation. This results in more salts, nutrients and contaminants retained by the lake as pure water is removed by evaporation. The Salton Sea is currently 25% saltier than the Pacific Ocean and boasts large amounts of fertilizer and minerals. The nutrients fuel plant and algae growth which at first, allowed the fish population to boom, but now is causing their demise. Fertilizers cause large algae blooms, which deplete the water of oxygen when they die and decompose. In summer, oxygen levels in the water disappear in all but the top few inches due to the heat, high salt content, and decomposing algae. This causes massive fish die-offs, affecting birds and wildlife surviving in the area. Salt itself also aides fish extinction because an increasing content will soon hinder the ability for fish to reproduce. To add to these problems, representatives of Southern California’s largest water agencies agreed on September 5th, 2003 to transfer 65 million gallons of water from the Imperial Irrigation District to the San Diego County Water Authority. If approved by the agencies’ boards, this would reduce the inflow of water that maintains the Salton Sea. This will, in effect, only add to the problems outlined above by speeding up the process.
Is there hope?
Yes! The Salton Sea Authority, which is a coalition of Riverside and Imperial county governments and water districts, decided in January 2003 to take restoration plans into their own hands. A number of ideas were proposed to improve water quality and preserve the valuable habitat. It was also important that all designs account for possible seismic movement since the east side of the lake borders the San Andreas Fault. The plans revolve around creating a dike or dam to separate the lake into north and south sections. Desalination plants would reduce the salt content in the north lake, providing a recreational area and marine lake environment. The southern section would also benefit from water quality improvement, and could be turned into shallow wetlands for water birds and other wildlife. The plan would entail dam construction, wildlife preserves and one of the world’s largest desalination plants. Initial estimates come in at almost $2 billion due to the hefty price tag on desalination. To assist with the cost of implementation, some of the water could be sold to California residents at $470/acre-foot. This is half the cost of desalinating ocean water but 60% more than just transferring water from the valley and not improving the Salton Sea. Enough water for 1 to 2 million people could be provided by this project, creating a win-win situation for the water agencies and the environmental conservationists. There are still some opponents to the plan who say that it is too centered on reducing the sea’s salinity and stabilizing its elevation instead of other, more serious, water quality factors.
Action is taken
Regardless of this opposition, in June 2003, Congress gave the Salton Sea Authority $10 million for feasibility studies and design efforts. After more than 30 years of research, the Authority was eager to take action. They contracted Tetra Tech and URS Corporation, environmental and engineering firms, to conduct investigations. Before engineers could get started on possible designs, exploration of the seabed for strength, stability and possible building materials had to be conducted.
The specialized nature of the project required engineers to engage Gregg Drilling & Testing of Signal Hill, California to perform the over-water drilling operation. Gregg used a jack-up boat with a deck load capacity of 25,000 as a stable platform upon which they mounted their drilling rig. The benefit of the jack-up boat is that it is easily maneuvered to different locations across the lake and can be raised off the water surface to avoid disturbance by large waves. The jack-up boat was used to successfully drill and test sub-bottom soil in water up to 50 feet deep. A total of 28 locations were tested and sampled using standard penetration tests (SPT), cone penetration tests (CPT), and Shelby tube samplers.
The boreholes and CPT ranged from 30 to 50 feet in depth with one borehole extending to 200 feet below mudline. Cone Penetration Tests (CPT) conducted in 15 locations provided a continuous soil behavior type profile of the sub-bottom environment. This was accomplished by pushing a cone penetrometer, attached to a data acquisition system, into the subsurface using a hydraulic ram. The cone penetrometer contains electronic sensors to measure tip resistance and sleeve friction, while a small filter behind the tip measures pore water pressure. The CPT provides a rapid, reliable, and economical means of determining soil stratigraphy, relative density, strength, and hydro-geologic information without generating soil cuttings. Geologists and engineers looked for strong and stable soils in the planned construction area to support large structures, and around the lake for possible fill materials for the proposed earthen structures (to reduce material importing costs). If the sub-bottom sediments are found to be soft fine-grained soils, extensive excavation and backfilling will be required to support construction of a dam.
Drilling and testing was completed in just over four weeks with samples sent to a URS geotechnical laboratory for further study. The data and information collected will provide valuable information for Salton Sea restoration designers and planners.
Salton Sea - Map courtesy of Salton Sea Database Program, University of Redlands, Redlands, California
Jack-up boat used for Salton Sea project by Gregg Drilling & Testing, Inc.