MS-1 is the first PA in the Lower Mainstem Touchet Reach and is 1.0 RM in length with an average channel slope of 0.39%. The Lower Mainstem Touchet reach runs from the Highway 125 bridge just below the city of Prescott that marks the downstream end of this assessment, to the downstream end of the Waitsburg levee. This reach includes six project areas from MS-1 to MS-6. Two significant tributaries enter the system in this reach: Coppei Creek, which enters at the upstream end of the reach on the left bank, and Whetstone Creek, which enters at the downstream end on the right bank. These tributaries provide the only significant changes in hydrology through the reach.