Each winter the District removes accumulations of woody debris from the Boise River to maintain a clear channel to reduce property damage during high river flows. Trees, snags and debris can get caught up on bridges and other channel obstructions during high flows and cause localized flooding damage. Once an obstruction causes the water to overtop the banks, it’s difficult to predict where the flood water will go.
Generally, the District only removes trees that have already fallen in the river or are about to fall in the channel. If a tree is ready to fall, the District often cuts the trunk 2 to 3 feet above the ground and leaves the root in place to help keep the bank stable. Woody debris is disposed of by burning, chipping or hauling away.
The District clears different areas each winter with the goal of clearing the entire length of the river within District boundaries every 3 years. However, the pace of work depends on river conditions each year - we only work in the river when flows at Glenwood Bridge are below 500 cubic feet per second. While we're out there working, we also remove and dispose of tires, trash and other debris.
Channel maintenance is completed under permits from the Idaho Department of Water Resources and the Army Corps of Engineers. The Idaho Department of Environmental Quality approves debris burning each week based on weather conditions and stops burning any time air quality is potentially at risk.
Rivers naturally move laterally over time. Sometimes this movement can put property at risk when banks destabilize and erode. The District works with property owners to stabilize eroding riverbanks by placing rock and vegetation along the banks to redirect flows and reduce erosion. Generally, this work is requested and largely funded by the property owner, but guided by the District to ensure an effective outcome and permit compliance.
From time to time, the District removes gravel at key locations. Accumulated gravel can alter river flow and present a significant risk during a flood. Accumulated gravel is removed from the channel and used by adjacent landowners or other public entities for project work.