Basin Watersheds
The Pontchartrain Basin Watershed Map has the following data layers:
Pontchartrain Basin Boundary
On the map, the red dashed line illustrates the Pontchartrain Basin Boundary. The Pontchartrain Basin is a 10,000 square mile watershed encompassing 16 Louisiana parishes. Lake Pontchartrain is actually an estuary is a partially closed coastal body of water where freshwater and saltwater mix. The Basin’s topography ranges from rolling woodlands in the north to coastal marshes in the south, with the 630 square mile Lake Pontchartrain as its centerpiece. Land use of the region is both rural and urban and is the most densely populated region in Louisiana, including metro New Orleans and the state capital, Baton Rouge. It is one of the largest estuarine systems in the Gulf of Mexico containing over 22 essential habitats.
Basin Waterways (Northshore Rivers on Map)
The waterways that make up the Pontchartrain Basin include different types. Two major rivers form the approximate east and west boundaries of the basin. The Mississippi River is on the western side of the basin and the Pearl River is on the eastern side. Many smaller rivers drain into the estuary. The Amite, Tickfaw, Natalbany and Comite Rivers drain into Lake Maurepas while the Tangipahoa, Tchefuncte, and Bogue Falaya Rivers drain into Lake Pontchartrain. The Pearl and West Pearl Rivers drain into the top of Lake Borgne. Smaller more sluggish marshy waterbodies called bayous also drain into Lake Pontchartrain. Bayou Castine, Cane Bayou, Bayou Liberty and Bayou Bonfouca flow into Lake Pontchartrain from the north shore.
Lake Pontchartrain has two sister lakes, Lake Maurepas to the west of Lake Pontchartrain and Lake Borgne to its east. Pass Manchac, Chef Pass, and the Rigolets Pass connect the lakes. The three lakes ultimately connect out into the Gulf of Mexico. They receive fresh water from north shore streams, rivers and bayous as well as rain and are influenced by tidal action from the gulf bringing in saltwater.
Additional sources of water into the estuarine system include Bayou St. John and Bayou LaBranche entering the lake from the south shore. Bayou Bienvenue flows into Lake Borgne to the east. The final source of water into the system is the manmade canals, which drain the low land of the metropolitan New Orleans area. Stormwater in these canals is pumped into Lake Pontchartrain during rain events.
Finally, the water bodies of the Pontchartrain Basin connect to the Gulf of Mexico through the Mississippi, Chandeleur, and Breton Sounds. A sound is a wide relatively shallow inlet of a gulf, sea or ocean that parallels a coast, frequently inside a barrier island. Gradually the water’s salinity increases, as it mixes more with seawater in the Gulf of Mexico.
Impaired Waterways: Primary and Secondary Contact Recreation
The federal Clean Water Act (CWA), Section 305(b) requires states to assess and report on the overall quality of waters in their state. In Louisiana, this is accomplished through Louisiana Department of Environmental Quality’s Integrated Report (IR). The IR is produced biennially (every even year), reporting of the status of Louisiana waters and is made up of the 305(b) Water Quality Inventory Report and the 303(d) List of Impaired Waterbodies. The IR covers the use of five categories and three subcategories in which waterbodies or waterbody/impairment combinations can be given. The attainment of the CWA goals is measured by determining how well waters support their designated uses. For the purposes of the 305(b) water quality assessments, seven designated uses are evaluated: fish and wildlife habitat (aquatic life use); drinking water supply; shellfish consumption; shellfish controlled relay and depuration; fish consumption; primary contact recreation; and secondary contact recreation. According to the EPA, “categorization under IR guidance allows for a more focused approach to water quality management by clearly determining what actions are required to protect or improve individual waters of the state.”
On the map, the waterways highlighted in orange are considered impaired for secondary contact recreation. The waterways highlighted in red are impaired for primary contact recreation according to the 2012 IR.
Urban Areas
The grey shaded areas located on the Pontchartrain Basin Watershed Map illustrate the U.S. Environmental Protection Agency’s 2010 Urbanized Areas as defined by the U.S. Census Bureau. Once an area is designated as an urban area by EPA, it falls under special storm water regulations called PC works with municipalities in the Pontchartrain Basin to meet the Municipal Separate Sewer System (MS4) requirements.
Please note: The urbanized area and urban cluster are both outlined in green on the reference maps, so it’s difficult to distinguish them, however the urbanized areas are labeled in regular font and the urban clusters are italicized. EPA’s small MS4 program applies in the urbanized areas.
Subbasins, Watersheds, Subwatersheds & Pontchartrain Conservancy-Defined Watersheds
The layers on the map are also referred to as Hydrologic Unit Codes (HUCs), which are sequences of numbers that identifies a hydrological feature like a river, river reach, lake, or area like a drainage basin/watershed. Subbasins are categorized as Level 4 or 8-digit HUCs. Watersheds are Level 5 or 10-digit HUCs. Subwatersheds are Level 6 or 12-digit HUCs. The PC Defined Watersheds are used to describe PC project areas and are a combination of both Watersheds and Subwatersheds. Click on these layers to find information including: Name, HUC level, U.S. Acres, and the data layer source.