b'Pit CaptureGravel pits and other pond features in river oodplainsrain on snow, resulting in water depths that spread may result in pit capture, which occurs when there is aacross the landscape persisting until the water nds a dierence in water elevation between the river and adrainage channel or is pumped out. Sheet oods can pond, leading to the pit lling and altering the streamimpact homes, roads, businesses, and agriculture.2bed and gradient of the river, both upstream andOther Flood Typesdownstream of the event. The result of a pit capture is that a portion of a river channel may be abandoned asRain on snow increases the snowmelt rate, which can the river reinforces its new ow path.2 cause ooding. This type of ooding can be especially dangerous in the spring and has aected the entire Ice Jam Floods state in areas with snowpack. Next, debris jam oods occur when foreign material (soil, rock, vegetation, Floods can also occur when a buildup of ice createsor snow) forms a dam and blocks water ows along a an ice jam that acts as a natural dam that restricts andstream. Another ood hazard, groundwater ooding, redirects the ow of a body of water. Damage fromoccurs in low-lying areas near streams and rivers, ice jam ooding usually exceeds that caused by openwhich ll as the water table rises with the river. Lastly, water ooding. Ice jam oods can occur during fallooding can occur due to dam, levee, or canal failure freeze-up from the formation of needle-shaped frazilwhen an uncontrolled release of impounded water ice, during midwinter periods when stream channelsor waste due to a catastrophic collapse, breach, or freeze solid to form anchor ice, and during springovertopping of the structure, resulting in downstream break-up when rising water levels from snowmelt orooding. As of 2018, the Idaho Department of Water rainfall break the existing ice cover into large oatingResources (IDWR) regulates nearly 600 water storage masses (or oes) that amass at bridges and otherdams and more than 20 mine tailings impoundment constrictions.2 structures located throughout the state. Compared to Sheet Flooding other ood hazards in Idaho, these structural failures are rare, but can cause signicant damage and loss Sheet ooding, or areal ooding is a type of oodof life when they occur, causing high ows in river event with shallow depths of one to three feet owingchannels with little or no advance warning, much like overland. These oods occur because of heavy rainsash ooding. The destructive failure of the Teton on relatively impervious surfaces, rapid snow melt, orDam in 1983 is an example of this hazard.2104 I D A H O I N F R A S T R U C T U R E G U I D E B O O K'