Students will learn about Hydrology. Porosity, Permeabilty, Salt Water Intrusin along with Hydrographs & types: A hydrograph is a graph or plot that shows the rate of water flow in relation to time, given a specific point or cross-section. These graphs are often used to evaluate stormwater runoff on a particular site considering a development project.A natural landscape with no development or impervious surfaces will have high levels of rainfall abstraction and produce less runoff due to the vegetation and infiltration capacity of the soils, which produces a gradually sloped hydrograph (1). In this scenario, rainwater will meet multiple obstacles while flowing towards a stream in the form of rainfall interception by vegetation, transpiration by plants, evaporation from land surfaces, infiltration into soils, and ponding of water in surface depressions. When the natural landscape is altered by development, trees and other vegetation are replaced by impervious surfaces such as roofs, driveways, gutters, and parking lots. These impervious areas curtail the landscapesability to filter and infiltrate water, and results in higher peak flows and greater runoff volumes as seen inhydrograph (2). Stripping the landscapes ability tonaturally manage stormwater results in increasederosion, sedimentation, and nutrientsentering our waterways. So how can we prevent this from happening? LowImpact Development (LID) is a design strategy that strives to mimic the pre-existing site hydrology using a variety of best management practices (BMPs). If a site planner knows what the hydrograph for a site lookedlike prior to development, they can amend their site plan to accommodate increased runoff onsite using practices such as rain gardens and bio-swales. This will produce a hydrograph (3).What if my home is already built? LID can be used in redevelopment or retrofitapplications as well. Forpreviously developed sites, best management practices can beinstalled within the confines ofexisting site conditions. Simple practices, such asdisconnecting a downspout and redirecting runoff into a lawn or garden, will have positive impacts on a sites hydrograph and help prevent pollutants from entering your local stream. Stream discharge hydrograph. . Hydrographs are charts that display the change of a hydrologic variable over time. Here are several examples from the US Geological Survey’s gaging station on the Tioga River near Mansfield, Pennsylvania. Physical factors affecting flood hydrograph dynamicsShape. A circular-shaped drainage basin leads to rapid drainage whereas a long drainage basin will take time for the water to reach the river. Topography & relief. Heavy Storms. Lengthy rainfall. Snowfall. Vegetation. Rock type. Comparing hydrographsSteep Slopes. Deciduous trees. An urban area in its catchment. Clay soils that stop water soaking in. Permeable ground. Heavy sudden precipitation. Long periods of steady rainfall. Lots of streams gathering water in the basin.
