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200731800 - Entiat River - UPA - Knapp-Wham Hanan Detwiler Irrigation System Consolidation Project

Sponsor: Chelan County Conservation District (SWCD)

Budgets: FY07: $364,077 | FY08: $9,313 | FY09: $0

Short description: Consolidation of the Knapp-Wham and Hanan Detwiler irrigation systems will eliminate partial fish passage barriers associated with 2 surface water diversions, add instream habitat within the lower Entiat River, and enhance instream flows via water saved.

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Final Council recommendation (Nov 2006)

Funding category: Expense

Recommended budgets: FY07: $365,000 | FY08: $10,000 | FY09: $0

Comment: ISRP fundable qualified: Address ISRP concerns during contracting.

ISRP final recommendation: Fundable (Qualified)

Comment:

This proposal would (1) eliminate one of the two main river irrigation diversions in the lower Entiat River (Hanan Detwiler), (2) move the expensive, high capacity rotary screen from this diversion to the upper diversion (Knapp-Wham) which has an undersized screen, (3) replace the two existing push-up dams with full channel-spanning rock cross-vanes to impound water and create holding pools, and (4) replace a 3.4 mile open irrigation ditch with a pipe network to distribute irrigation water to farmers. The ISRP is not requesting a response, but the proposal would be improved by addressing the following comments: Two large irrigation diversions have been identified as high priority sites for restoration, which makes this project attractive. A stronger case for the work could have been made that included a better estimate of how much water will actually be saved in the river during irrigation season, and what species and life stages are likely to benefit from these incremental flows and presumably improved water quality. Although the theoretical increase in flow in the lower Entiat during the irrigation season is claimed to be 2-6 cfs, the proposal admits that the realized incremental flow savings will be less. In addition to re-engineering the water intake, new wells are being added to the system, and the contribution of those wells to flow savings is also uncertain. The proposal states that these two irrigation systems are the largest in the Entiat subbasin and have been assigned highest priority for improvement in the Entiat Watershed Planning Unit, which underscores the value of this project. However, regardless of the amount of water being conserved, it is important that instream flows not be appropriated by junior water right holders downstream. Therefore, project managers should provide some evidence that conserved water will remain in the river. Alternatively, it might be cost-effective to purchase water rights. The engineering aspects of the proposal were adequately described, but the habitat and fish population benefits were less clear. Since both existing diversions are screened, how much will the consolidation really lead to a reduction in juvenile salmonid entrainment? Will the flow savings primarily benefit spawning, rearing or both -- and to which species? Have pesticide residues been identified in irrigation return water of the existing canal systems that this project will help reduce? It is stated that "both physical and biological changes will be noted post-implementation", but there was no elaboration of what this meant. The budget includes a request for a dry suit for snorkel surveys in 2008-2009 during March, May, and September, but additional details were not provided. Monitoring water quality (temperature, pesticide residues) in irrigation return water would help verify the effectiveness of this project.

State/province recommendation:

Review group:

Recommended budgets: FY07: (n/a) | FY08: (n/a) | FY09: (n/a)

Comment: