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Land Use and Resource Management Plan for the Primary Zone of the Delta — Environment

The Delta is a unique geographic area in the State of California, a low-lying region of rich mineral and peat soils, composed of islands created largely by humans, as they diked and drained the prehistoric marshes of the region.

The lush wetland habitats surrounded by riparian woodlands have been replaced by agricultural lands, both cultivated and irrigated croplands, and irrigated and unirrigated pasture lands. Remnants of natural habitat are located largely along some sloughs and rivers and on small channel islands. Pockets of wooded or wetland habitat exist on some islands.

The aquatic habitats were historically brackish and home to both resident and migratory fish. Modern aquatic habitats are affected by flows released from upstream dams, seasonal drainage from agricultural lands, and year-round drainage from sources outside the Primary Zone, such as sewage treatment plants. Several large, freshwater lakes are located on the eastern edge of the Delta, providing year-round wetland habitat.

At all levels of the ecosystem, native plants and animals are now competing with exotics. Of particular concern are the Asian clam, which is competing for phytoplankton at the bottom of the food chain, and popular introduced game fish, such as the Striped bass, which are declining in numbers and in health. The native winter-run Chinook salmon and Delta smelt are designated endangered and threatened, respectively.

Large mammals, such as bear and elk, which historically lived in and around the Delta have been eliminated. Aquatic mammals including beaver and otter still remain. Both year-round and migratory birds have adapted to the agricultural practices in the Delta, particularly the small grain fields which are flooded in fall and winter months. Migratory birds include ducks, geese, swans, cranes, and shorebirds. Hawks and eagles forage in the Delta fields; Swainson's Hawk is designated "threatened" by the Department of Fish and Game.

The geology of the region created this unique "delta". Sediments trapped inland of the rocky neck of the Carquinez Straits resulted in the creation of the 1,100 square mile area known as "the Delta". The Delta exists in a State known for earthquake faults; the probability of seismic activity remains constant. A zone of buried thrust faults is located along the western edge of the Delta.

The peat soils of the central and western Delta have oxidized in great part due to drainage. Losses of soil due primarily to such oxidation have resulted in subsidence of land surfaces of up to 20 feet. Original peat soil depths varied substantially from area to area and even within a given island. Current studies show the only effective way to stop subsidence is to reflood the peat soils. Subsidence has slowed to about one-third of an inch a year in many areas. About 60% of the lands in the Delta are designated prime agricultural lands.

The low elevations of the Delta, exacerbated by subsidence, result in a constant threat of flooding. Twice in each approximately 25 hour period the tides raise and lower the elevation of the Sacramento River about three feet. The threat of flooding is generally associated with periods of high winter rainfall and periods of rapid spring snow melt in the watersheds draining into the Delta. The most critical conditions occur when upstream dams are full and the resulting high rates of river flow combine with high tides

Goal: Preserve and protect the natural resources of the Delta, including soils. Promote protection of remnants of riparian habitat. Promote seasonal flooding and agriculture practices on agricultural lands to maximize wildlife use of the hundreds of thousands of acres of lands in the Delta. Promote levee maintenance and rehabilitation to preserve the land areas and channel configurations in the Delta.

Environment Findings:
  • F-1. The physical environment which existed prior to 1850 has been permanently and irretrievably modified through levee construction, drainage of wetlands, and introduction of agriculture.
  • F-2. Human activities in the central Delta have contributed to subsidence of much of the area. Some areas are now more than 20 feet below sea level.
  • F-3. Most of the soils in the central Delta are designated "prime" and of statewide value for agriculture.
  • F-4. The peat soils have subsided largely through oxidation; other activities resulting in subsidence include cycles of drain and flood, wind, and burning.
  • F-5. While over 95% of all wetlands in the Delta have been lost, the Delta area is used by 10% of the wintering waterfowl traveling within the Pacific Flyway.
  • F-6. Valuable habitat for many birds and mammals is included on linear riparian corridors along levees and small isolated areas located on the islands and small channel islands, and Delta wetlands. Agricultural lands also provide high quality wildlife habitat and foraging areas, depending on agricultural practices. The levees keep flooding from occurring, which would destroy habitat. Levees are manmade structures which have no initial habitat value when constructed. The value of wildlife and habitat on the levees is dependent on the maintenance of the levees.
  • F-7. The value to wildlife of levee habitat and habitat within the levees is lessened by on-going human impacts such as levee maintenance, farm practices, human habitation, and recreational use of the levees and waterways. Activities such as water transport and boating use have eroded Delta channel islands, berms, and levees destroying habitat areas. Without levee maintenance, the habitat on the levees and within the islands will be lost.
  • F-8. The native population of fish and other aquatic species has been modified by hydromodification including water diversion, etc., through introduction of exotic species and other causes. Numbers of both native and of some introduced fish have dropped dramatically since the late 1960's; numbers have dropped so low that winter-run Chinook salmon and Delta smelt have been listed as endangered and threatened, respectively. However, the population of some introduced species of fish and other introduced aquatic species throughout the aquatic food chain has substantially increased.
  • F-9. There is no Delta regionwide management plan for wildlife resources.
  • F-10. Most of the Delta is located in the 100-year flood plain. While the levee system is constantly being maintained and upgraded, many Delta islands have been temporarily flooded; at least four have remained flooded. Permanent flooding, such as seen on Frank's Tract, would adversely impact utility infrastructure, residential and recreational facilities, farmlands, wildlife habitat, transportation, commerce, and fisheries. Evaporation from flooded islands consumes substantially more water than is needed to farm those islands.
  • F-11. The Primary Zone, with its large open expanses of farmland, mosaic of small grain crop residues and shallow flooded fields, permitting wildlife to feed and rest, provides extremely high quality wildlife habitat.
  • F-12. Seasonal flooding in fall and winter has traditionally been carried out to serve several purposes: weed control, leaching of soils, control of oxidation of peat soils, provision of seasonal habitat, and hunting.
  • F-13. Delta channel islands and levees serve as habitat for several burrowing species, including beaver and muskrat. Some species have created burrows large enough to endanger levee stability.
Environment Policies:
  • P-1. The priority land use of areas of prime soil shall be agriculture. If commercial agriculture is no longer feasible due to subsidence or lack of adequate water supply or water quality, land uses which protect other beneficial uses of Delta resources, and which would not adversely affect agriculture on surrounding lands, or viability or cost of levee maintenance, may be permitted. If temporarily taken out of agriculture production due to lack of adequate water supply or water quality, the land shall remain reinstateable to agricultural production for the future.
  • P-2. Agricultural and land management practices shall minimize subsidence of peat soils. Local governments shall support studies of agricultural methods that minimize subsidence and shall assist in educating landowners and managers as to the value of utilizing these methods.
  • P-3. Lands managed primarily for wildlife habitat shall be managed to provide several inter-related habitats. Deltawide habitat needs should be addressed in development of any wildlife habitat plan. Appropriate programs, such as "Coordinated Resource Management and Planning" (Public Resources Code Section 9408(c)) and "Natural Community Conservation Planning" (Fish and Game Code Section 2800 et seq.) should ensure full participation by local government and property owner representatives.
Environment Recommendations:
  • R-1. Seasonal flooding should be carried out in a manner so as to minimize mosquito production. Deltawide guidelines outlining "best management practices" should be prepared and distributed to land managers.
  • R-2. Wildlife habitat on the islands should be of adequate size and configuration to provide significant wildlife habitat for birds, small mammals, and other Delta wildlife.
  • R-3. Undeveloped channel islands provide unique opportunities for permanent wildlife habitat in the Primary Zone. A strategy should be developed to encourage permanent protection and management of the channel islands. Protection may include: acquisition, conservation easements, or memoranda of understanding. Management may include: protection from erosion, controlling human access, or habitat management, such as planting native plants and removing exotic plants. Some larger, reclaimed channel islands may be suitable for mixed uses, such as recreation and habitat. Any development on channel islands must ensure long-term protection of the wildlife habitat.
  • R-4. Feasible steps to protect and enhance aquatic habitat should be implemented as may be determined by resource agencies consistent with balancing other beneficial uses of Delta resources.
  • R-5. Publicly-owned land should incorporate, to the maximum extent feasible, suitable and appropriate wildlife protection, restoration and enhancement as part of a Deltawide plan for habitat management.
  • R-6. Management of suitable agricultural lands to maximize habitat values for migratory birds and other wildlife should be encouraged. Appropriate incentives, such as conservation easements, should be provided by nonprofits or other entities to protect this seasonal habitat through donation or through purchase.
  • R-7. Lands currently managed for wildlife habitat, such as private duck clubs or publicly-owned wildlife areas, should be preserved and protected, particularly from destruction from inundation.