Visualizing the effects that a future development may have on downstream areas, as well as the influence of additional or existing developments upstream.After a watershed is delineated, useful determinations can be made that can aid in the land use planning process such as: Such a map can be used to determine the cumulative effects of land development or land use changes on both water quantity and water quality. To begin this process, one of the primary tools required is a map of the watershed. ![]() Stormwater Management from a Watershed PerspectiveĮffective stormwater management to protect and preserve nearby and downstream water resources can be conducted on a watershed level. This can cause flooding, erosion and scouring problems downstream. Without proper stormwater management, urbanization affects the water quantity, velocity, peak flow rates, and flow frequency in the watershed's tributaries and river system. Stormwater that once soaked into the soil now runs off in greater quantities and at higher velocities to the smaller tributaries and ponding areas, which in turn convey the water to the wetland, river or lake of that watershed. Water Quantity Concerns: When agricultural and natural areas become urbanized, vegetation (grasses, trees, etc) and base soils are replaced with impermeable materials such as asphalt and concrete. The sediment from stream bank erosion can alter stream bed characteristics, thereby affecting benthic habitat, and reducing light transmission. In addition to these water quality concerns from increased urbanization, water quality also degrades when stream banks erode due to changes in water quantity. ![]() The degradation of water quality can cause immediate (acute) and long term (chronic) negative effects on aquatic and terrestrial plant and animal species and their habitat, while also degrading drinking water supplies, and limiting other uses of the water resource such as swimming and recreation. As a result, the quality of the water resource tends to degrade within the immediate vicinity of the urbanized area, as well as in areas further downstream. Also, the temperature of the stormwater increases as it passes over these surfaces. When stormwater runs off the urban landscape, it carries the pollutants with it into the receiving waters. Urban surfaces also act as heat collectors. Water Quality Concerns: As development and urbanization increase within the watershed, various pollutants (e.g., nutrients, bacteria, pesticides, heavy metals, sediments, organic matter, trash) will be deposited. This runoff can have negative effects on water quality and quantity within the watershed. Stormwater is created when rain falls on impervious surfaces and runs off the surface. One such environmental issue which challenges many local and municipal officials today is stormwater management. Thus, the quality of a wetland, stream or lake often reflects the land use and other activities being conducted in the upstream areas.īecause the relationship of cause and effect can extend for distances throughout the entire watershed, it is important to address environmental management issues from a watershed perspective. It is through this linkage that the upper portions of a watershed can effect downstream areas. Rainwater and snowmelt that does not evaporate or infiltrate into the soil runs off into a nearby tributary or ponding area, and then flows to the main wetland, river or lake within the watershed. Depending on the size of the area and the topography, a watershed can contain numerous tributaries, such as streams and ditches, and ponding areas such as detention structures, natural ponds and wetlands. Contour lines are curved, straight or a mixture of both lines on a map describing the intersection of a real or hypothetical surface with one or more horizontal planes.A watershed is an area of land that drains to an associated water resource such as a wetland, river or lake. A level set is a generalization of a contour line for functions of any number of variables. When the lines are close together the magnitude of the gradient is large: the variation is steep. The gradient of the function is always perpendicular to the contour lines. More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value. ![]() The contour interval of a contour map is the difference in elevation between successive contour lines. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness of slopes. In cartography, a contour line joins points of equal elevation above a given level, such as mean sea level. Contour line A contour line of a function of two variables is a curve along which the function has a constant value.
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