Moses Coulee course southward past the Frenchman Hills and turning west to run along the north face of the Saddle Mountains and rejoin the previous and modern course of the Columbia River just above the main water gap in the Saddle Mountains, Sentinel Gap. Although the Columbia River flowed only for a short period through Moses Coulee, this period included one or more of the tremendous flows from the Missoula Floods. As the Okanogan lobe melted, the upper portions of Moses Coulee were littered with clear evidence of its passing in the Withrow Moraine. The glacier left behind a blanket of glacial
Grand Coulee Dam the year. For example, while the dam may generate at nameplate-capacity in the spring, decreased river flow in the fall means less power can be generated the rest of the year, resulting in a lower capacity factor. The proposal to build the dam was the focus of a bitter debate during the 1920s between two groups. One group wanted to irrigate the ancient Grand Coulee with a gravity canal while the other pursued a high dam and pumping scheme. The dam supporters won in 1933, but for fiscal reasons the initial design was for a "low dam" tall which would