How are floods predicted?

July 15, 2008 6:58:40 AM PDT
article| David Murphy| In the Delaware and Lehigh Valleys, as in most regions of the U.S., a flood gauges have been installed at varying locations along local creeks, streams, and rivers. Hydrologists at the National Weather Service office in Mount Holly, New Jersey, monitor all of these gauges, recording stream flow and water levels and noting whether the levels are rising or falling. Over the years, the hydrologists have observed how different portions of waterways react to injections of extra water from storms or snow melt. Armed with a rich historical record, the hydrologists have devised charts that predict how much additional water a given waterway can absorb over various periods of time, before flooding begins. They use these charts and gauge readings to predict the timing and extent of flooding. Adjustments are made occasionally, based on changes in the local landscape, most notably new development which increases run-off and reduces the region's natural ability to drain water. By the way, these same hydrologists also monitor underground wells to account for the level of water in aquifers (natural, underground water storage channels) that run beneath our region, determining whether there is room for additional water there. The hydrologists also use these underground measurements to make drought predictions and declarations.