If you care about our coast or fishing, you should know about Hydrocoast!

By John Lopez, Director, Coasts & Community

Louisiana’s coast is dynamic. This simple but profoundly important trait of coastal Louisiana is largely due to the fact that water is always moving around our coast.

This plays out in a variety of ways in our coastal estuaries, where fresh water from the Mississippi River mixes with salty water from the Gulf. Rain falls, and rivers flood fresh water areas. An east wind blows, and an extra high tide pushes salty Gulf water inland. Every day, the tides driven by the moon give the coast a pulse, and while there are many rhythms along the coast, more often there are “a-rhythms” of these constant changes and fluctuations.

These dynamic variations have different implications on coastal habitats and the critters that depend on them. While some need salty water, others will die from it and the same holds true for fresh water. However most species in our estuaries need a mix of both.

Monitoring these conditions for salinity and fishing can be quite challenging when circumstances are constantly changing at different rates, but Hydrocoast maps allow us to do exactly that. Like a photo finish of NASCAR race cars taken by a high-speed camera, Hydrocoast maps provide continuous snapshots of the coast in southeast Louisiana. Every two weeks, five Hydrocoast maps capture tons of information about the coast that provide us a detailed look among all the fluctuations in conditions.

The Lake Pontchartrain Basin Foundation releases Hydrocoast maps every other week on our website. The week in-between is when we observe and collect data on five different themes: salinity, weather, biology, water quality and habitat.

All five maps depict salinity across the entire Pontchartrain Basin, using salinity values near the water’s surface and a standard mapping method of “contour lines.” Here we call the lines “isohaline lines,” and salinity remains constant along the isohaline. A line labeled 10 parts per thousand (ppt) means that everywhere that line is located has a salinity is close to 10 ppt. By drawing all the possible isohalines (lines of equal salinity) from freshwater (0 ppt) to seawater (35 ppt), we can show salinity levels throughout the estuary.

Generally, the isohalines increase from west to east as they get closer to the Gulf of Mexico. If the lines are close together, that means salinity is changing quickly. The isohalines use salinity data, the known freshwater discharges from all the rivers, diversions or outlets whose flows are also updated on the maps. Isohalines also use the most recent satellite image of the water (MODIS), which can show water flow influence or patterns of flow. (See our report for complete details.)

Six to ten times per year, Hydrocoast logs another important activity – oyster and shrimp boat traffic. A professional spotter flies over the coast to identify actively fishing commercial oyster and air shrimp boats in aerial surveys orchestrated around the regulated seasons for fishing. Hydrocoast portrays the survey results on its “biology” map when they are available.

The Hydrocoast maps have been produced since 2013, and all of these 600 or so maps are archived on LPBF’s website.  These maps provide a longer-term of observations that can reveal to coastal scientists much about the changes in our basin. (Check back for a future blog on how scientists are using this information to help inform their work around the coast.)

The Hydrocoast maps are not a perfect snapshot, but they are provide enough of an overview to help guide commercial and recreational fishers who want to understand how salinity, fishing activity, rainfall and other conditions might be important to their particular business or recreational activity or for anyone who wants to learn more about our ever-changing coast. 

To register to receive Hydrocoast map updates by email, please click here.