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Watersheds

 

Watersheds are basin-like landforms defined by highpoints and ridgelines that descend into lower elevations and stream valleys. Even in the relatively flat topography of East Baton Rouge Parish, there are ridgelines that form boundaries between watersheds. The East Baton Rouge Parish is within the Lake Pontchartrain Basin, and the Lower Mississippi Basin.

Within a watershed, the natural and built systems capture and move precipitation, filter and store water, and control its release over time. Impervious surfaces – anything that prevents rainfall from soaking into the ground, such as buildings, roads, or parking lots – have a significant impact on the watershed functioning because they prevent infiltration and increase stormwater runoff. Watersheds are nested systems meaning that many small watersheds make up the larger regional watershed. The hydrology of the Parish naturally divides into three main watersheds, which are subdivided into a total of 704 micro-watersheds.

The eastern part of the Parish drains into the Amite River and the southern part of the Parish drains into Bayou Manchac. The northwest portion of the Parish drains into the Mississippi River. Water management and management of biodiversity and other natural systems, is best handled at the watershed level. Remediation or mitigation of such changes, therefore, should take place within the same watershed to achieve ecological benefits and maintain the integrity of the watershed.

Under the Clean Water Act, waterways on the Impaired Waterbodies List must undergo watershed modeling to assess the loads of each pollutant for which they are listed. Termed “Total Maximum Daily Loads” (TMDLs), these models calculate the reduction in the pollutant that will be necessary for the waterway to be removed from the Impaired Waterbodies List. TMDL calculations performed in the Pontchartrain Basin so far have resulted in substantial reductions in pollutant loads.

In addition, under the Clean Water Act, urban areas are mandated to meet standards of the Environmental Protection Agency (EPA) Municipal Separate Storm Sewer Systems (MS4) Program. The MS4 Program requires that urban areas eventually monitor their stormwater discharges as a point source of pollution. Water quality limits must be set on these discharges and urban areas are responsible for meeting the limits.