Inadequate instream flows and sometimes the complete absence of water due to irrigation withdrawals have severely affected Columbia basin salmon. For example, within Idaho, inadequate instream flows and localized de-watering are significant problems in the Lemhi and Pahsimeroi rivers, the Salmon River mainstem, and several Salmon River tributaries.
Other significant Snake River tributaries include the Grande Ronde River in Oregon and the Tucannon River in Washington. In the Grande Ronde, except during spring run-off, water appropriations exceed average flow in all major streams of the basin. Studies have shown that salmonid production is directly related to the level of summer and fall flows in juvenile rearing streams. Although water rights for minimum stream flows for fish have been set at various locations in the Grande Ronde, the priority dates for these rights are too recent to provide any real protection for fish. Inadequate instream flows are also a significant constraint on fish habitat productivity in the Tucannon River basin. Other important Washington rivers in the Columbia basin where instream flows do not meet the needs of fish include the Methow and Okanogan, the Entiat, the Wenatchee, and the Yakima. Within Oregon, important rivers accessible to salmon where habitat productivity is significantly impaired by inadequate instream flows include the John Day and Umatilla.
Stream withdrawals for irrigation are not the only land use activities that adversely affect instream flows. Not surprisingly, groundwater pumping often reduces summer low flows (Rhodes et al. 1994). In addition, cattle grazing increases spring peak flows, while decreasing summer low flows. Cattle grazing decreases low flows by de-watering wet meadows by incised channels, increased overland flow due to compacted soils and reduced water storage in compacted soils (Rhodes et al. 1994). In general, mining, road construction, grazing, and tractor logging in wetlands disrupt wetland functions and reduce contributions to summer low flows (Rhodes et al. 1994).
Fish populations evolved, flourished, and provided large harvestable surpluses in watersheds with natural riparian areas and hydrologic regimes, including periodic flood events. Instream flows in the late summer were often fed by groundwater inputs, wetlands, and vegetated uncompacted riparian areas.
Establishment of instream flows and protection of riparian vegetation, wetland preservation, and prevention of soil compaction would provide sufficient water to maintain fish habitat for adult and juvenile passage, spawning, rearing, and maintain channel structure and riparian areas necessary for fish habitat to persist over time.
- Mandate utilization of most efficient irrigation methods.
- Halt any additional consumptive withdrawal of water from salmon subbasins until adequate instream flows and tribal instream flow reserved water rights are protected.
- Assure that no consumptive uses are occurring in excess of the amount permitted.
- Meter groundwater and surface water withdrawals.
- Halt any further impairments of wetlands.
- Prevent additional soil compaction.
- Prevent removal of riparian vegetation.
- Prohibit activities that would contribute to the creation or maintenance of peak flows earlier or greater than those that would occur naturally.
- Establish instream flows designed to provide the full range of habitat conditions needed to provide healthy, naturally reproducing salmon populations.
- Identify, through negotiation or adjudication, instream flow water rights reserved by tribes’ treaties.
- Implement actions to create wetlands, e.g., re-introduction of beavers.
- Implement actions needed to promote re-vegetation of riparian areas and de-compaction of soils where recovery is not occurring naturally.
- If necessary, initiate land management designed to return a watershed to a natural hydrologic regime, e.g., re-vegetation of areas adversely affected by past land-disturbing activities.
Short-term: Halt the ongoing incremental losses of instream flows due to consumptive use or from land management activities that adversely affect natural watershed water storage and release processes.
Long-term: Gradual improvements in the level of tributary instream flows. Increased spawning success and improved egg-to-smolt survival. As natural watershed processes are restored, more water will be available for instream and consumptive use year-round. Increased water use efficiency by existing consumptive users will, in some cases, result in greater water availability for additional consumptive uses.
Federal and state water managers are called upon to enforce existing water rights, implement moratoria on all additional withdrawals of water, meter water withdrawals.
Federal and state water managers must identify and assure implementation of best available water conservation methods.
Federal and state land managers must implement watershed protection measures to protect and improve natural watershed water storage processes. These efforts should be coordinated with federal and state water managers.
Federal and state water managers, along with federal, state and tribal fish managers must establish instream flows adequate to sustain healthy naturally reproducing salmon populations.