In August 2011, Tropical Storm Irene battered the eastern coast of the United States. The town of Stowe in Vermont experienced extensive damage to roads, bridges, and culverts due to flooding caused by the storm. To prepare for future flood events, Stowe's town government wants to know the level of rainfall needed to cause the nearby Little River to flood. Because observed data about the river's flow patterns is sparse, the town intends to estimate runoff characteristics using unit hydrographs. Unit hydrographs are line graphs that determine how much water a stream outlet will discharge over time during a predicted rainstorm. They can be created by analyzing the time it takes for rainfall to travel through a watershed to the stream.
In these lessons, you'll create the unit hydrographs for an outlet on the downstream end of the Little River. First, you'll prepare elevation data and use it to determine the watershed area for the outlet. Based on your watershed and terrain data, you'll create a velocity field, which determines how fast water tends to move in your study area. Using this velocity field, you'll create an isochrone map, which assesses the time it takes for water to travel to the outlet from anywhere in the watershed. Lastly, you'll use the isochrone map to derive a unit hydrograph and interpret what it says about the potential for floods in Stowe.
|Precondition the elevation model||Fill sinks in your elevation model to remove small imperfections in the data.||20 minutes|
|Delineate the watershed||Find the contributing area above a set of cells in an elevation model.||25 minutes|
|Create a velocity field||Determine how fast water flows with a spatially variant, time- and discharge-invariant velocity field.||25 minutes|
|Create an isochrone map||Assess the time it takes water to follow the flow path.||25 minutes|
|Create a unit hydrograph||Use the isochrone map to create a unit hydrograph for the outlet.||20 minutes|