The Knapp-Wham and Hanan Detwiler irrigation systems lie within the Lower Entiat River Assessment Unit (RM 0.0-16.2) of the Entiat subbasin.  The systems run along the left-bank (looking downstream) of the lower Entiat River from about RM 3.7-RM 2.0.  The surface water points of diversion for the Knapp-Wham and Hanan Detwiler systems are RM 5.8 and RM 5.0, respectively.  The ESA listed salmonids that utilize the mainstem Entiat River within the Lower AU and project portion of the subbasin include endangered Upper Columbia River spring Chinook (Oncorhynchus tshawytscha), as well as endangered steelhead (Oncorhynchus mykiss) and threatened bull trout (Salvelinus confluentus).  Non-listed salmonids such as summer Chinook and Coho, and resident fish species such as westslope cutthroat trout are also found here.  

The primary goals of the Knapp-Wham Hanan Detwiler Irrigation System Consolidation are to eliminate two low flow passage barriers, add instream pool habitat, reduce fish entrainment, conserve water for instream flows, and improve overall water quality.  The preferred design will result in Hanan Detwiler water users being served by the piped Knapp-Wham system, with augmentation by wells in some areas.  The objectives of the contract include: 1) Eliminating the Hanan-Detwiler surface water diversion and associated unlined irrigation ditch to improve instream flow conditions in the lower river, particularly during the late-summer/fall period, and 2) Enhancement of the Knapp-Wham system and surface water diversion to eliminate low flow passage issues and provide additional large pool habitat complexity within the lower Entiat River.  

The Knapp-Wham Hanan Detwiler Irrigation System Consolidation proposes to maintain the K-W system as is and put five H-D users on ten new groundwater wells and serve remaining H-D users from the K-W system.  The existing side channels at the K-W and H-D POD, which currently support spawning and rearing, will remain.  A new consolidation weir will be built at the K-W POD to provide irrigation flows and reduce annual maintenance, and to provide pool habitat.  A new boulder weir will also be built at the H-D POD to provide resting pool habitat for ESA listed salmonids.  The surface water diversion into the H-D ditch will be removed, eliminating low-flow passage barrier concerns for listed and other fish species.  The H-D headworks and screen will be removed, and, as is currently done, users along the K-W system will be provided with main pipeline flow by use of a gravity system.  A new consolidation pipeline will be installed at the end of the K-W system to connect some H-D users to the K-W system below Crystal Springs, located just above Mills Canyon. These users on the H-D system would be provided with gravity water.   The K-W consolidation flow, as estimated at the beginning of the main pipeline, would remain the same as the present diversion, as the additional K-W users would take advantage of the current wasteway flow, approximately 1.5 CFS (minimum).