Floods are a natural occurrence in every river system and can damage valuable infrastructure and buildings located in flood zones. Despite the risks, humans have inhabited floodplains in order to capitalize on ease of travel, commerce and access to food sources since the beginning of human history. In the Mohawk River watershed there are four main types of flood events for which management strategies are required:
- Spring breakup, Snowmelt and Winter Rains - The annual breakup and thaw produces regular flooding associated with rising temperatures and thaw of stored waters from winter-accumulated snow. While March has been the most typical time for this flooding, the current window is January through April. This is the one of the leading causes of flooding in the watershed. Ice jamming during these events provides a unique component to this hazard. Historically, some of the most significant floods in the basin have been winter rain on snow events (such as January 1996 which is the second highest recorded peak flow on the Schoharie Creek at Burtonsville - records dating back to 1939). As climate change brings warmer spring temperatures, snow melt is predicted to occur earlier and more rapidly. Further, more late-winter precipitation is likely to fall as rain, rather than snow. Both phenomena will increase the risk of flooding.
- Cyclonic disturbances - Precipitation from large-scale atmospheric systems such as hurricanes, remnants of hurricanes, and stalled frontal systems can produce enormous quantities of rain in the watershed. Damages to public infrastructure from the June-July 2006 floods, which resulted in Presidential Disaster Declaration DR-1650, approached $400,000,000. FEMA estimates public infrastructure damages from Hurricane Irene and Tropical Storm Lee in 2011 (Presidential Disaster Declarations DR-4020 and DR-4031, respectively) will surpass $1.7 billion. Climate change is projected to increase the frequency of severe cyclonic events and may permit more northward tracking of hurricanes.
- Localized summer outburst events - Thunderstorms and other summer disturbances that result in intense local precipitation may cause severe flooding in small tributaries. The July 2008 event caused intense scour, sediment transport, and over $3 million in damage to infrastructure in Schenectady County. Climate change is projected to lead to an increase in the potential for formation of conditions conducive to summer outbursts and flash flooding.
- Catastrophic release of impoundments - The failure of upstream impoundments (i.e., reservoirs) could cause devastating floods in the watershed. A catastrophic event of this type has not occurred yet, but dam-break analyses have shown how problematic such an event would be.