Ecology of the Mississippi River Delta Region

It is easy for non-Louisianians to wonder why anyone would settle in a dank, sinking subtropical area full of alligators, snakes, and insects. Bienville chose the French Quarter area for his settlement because it met certain economic needs. Before the settlement of New Orleans in 1718, all shipping coming down the Mississippi River and destined for Mobile had to exit the mouth of the river and sail across Breton Sound. During good weather, this was no problem. However, southeast Louisiana is known for its storms of various types. These storms make a crossing of the very shallow Breton Sound very treacherous.

It is said that Bienville landed at a point where Iberville meets the river today. He chose this place because it was the nearest place to transfer cargo from the river to Bayou St. John, a sheltered waterway to Lake Pontchartrain (see adjacent figure "Carlos Trudeau's map of New Orleans . . ."). Once cargo was portaged to ships waiting at the head of the bayou, it was shipped down the bayou, through Lakes Pontchartrain and Borgne, then along the Mississippi coast to Mobile. Obviously, this was successful because New Orleans flourished, becoming the richest and second largest city in America at one point.

In the area of the French Quarter, the natural levee was about 15 feet above sea level. This would give protection during most years, but the fledgling city was flooded out in 1719. The citizens added to the height of the levee until flooded again. For two hundred years, new levees were built in response to floods. Plantation owners protected their water's edge, but this did no good if the landowner upstream did not. Over the years, a rather safe levee system was developed.

So what adversities did the settlers of New Orleans have to overcome? There were four major obstacles.

1. How to keep flood waters away. This was done by the levees discussed above, but was not finalized until the great flood of 1927 stimulated Congress to protect the entire lower Mississippi River by an elaborate federally funded system of levees. Today, the levees along the river are 25 ft above sea level and those around the lake are 17 ft.

2. How to keep dry behind the levees. Even with the levees, water would fall from the sky and seep through the soil from below. For decades, New Orleans was a very wet place to live. It was not unusual for the city to be under two or three feet of water, with locals having to wade or pirogue about to conduct business. Many of the older homes were built up, having the first living floor 5-10 ft above the ground. If they were closed around the base, they had windows of various types to allow the humidity to escape.

   Several canals were built or augmented (Dublin Avenue, Bayou St. John, and London Avenue) to collect water. Each of these had a steam driven paddle wheel that endeavored to push the city's water into the adjacent swamps and marshes. During the last quarter of the 1800s, several attempts were made to acquire funding to build a sewer system to remove the water, but each failed due to lack of funding.

   During the very late 1890s and in response to new outbreaks of yellow fever, a group of ladies waged a public information campaign to pass taxes to develop a better drainage system. They were successful and in 1900, the Sewerage & Water Board had a system in place that allowed them to daily drain the canals, thus allowing New Orleans to dry out with an immediate decrease in the number of mosquitoes and an increase in property values!

   When the going gets tough, a hero usually arises. In 1899, the New Orleans Sewerage & Water Board hired a young engineer named A. Baldwin Wood. He tackled the issue of lifting large quantities of water over the levee so that it could be flushed into the surrounding lakes. In 1912, he developed his 12 ft screw pump (a large propeller specially designed to lift water) that is still in use today.

   The system is very elaborate today. There are 90 mi of covered canals and 82 mi of open canals. The total pumping capacity (1993) is 24 billion gallons per day.

3. How to build on the soils. The soil layers of the delta (thus New Orleans) are varied. Remember that the sea came and went, the river has frequently changed its course, swamps and marshes have grown and them been displaced, etc. Each of these events have left a mark in the soil profile (the layers found in a cross-section of the soil). See the adjacent figure "Engineering geology of New Orleans".

   The best way to see these layers is to visit a construction site. When the wetlands around the Louisiana Nature Center were built, the holes that were dug revealed alternating layers of sand and silt, evidence of the changing surface of the land over time.

   Sand, of course, is the most stable and compacted soil type and is thus preferable for building. When the sand is at the surface, as on a ridge (like the Metairie or Bayou Sauvage ridges), a foundation can be laid on the surface with no support. The sand supports the foundation and does not subside.

   Silty and clayey soils are much less sturdy. When building a house on these soils, pilings must be driven into the ground to support the foundation so that the forgiving soils do not settle unevenly and tilt or crack the foundation.

   

   The pilings (see the adjacent figures "Section of typical slab-on-piling construction before differential subsidence has begun" and "Section of slab-on-piling construction after differential subsidence") either hit a sand layer and were directly supported by it or they were driven into clay layers and the friction around the pile held it up (the so called friction pile). If these slip, it is disastrous for the slab at the surface.

   

   Some of the older buildings in the city (such as the city's first sky scraper, the three story [now four] Yves LeMonnier House at the corner of Royal and St. Peter) were constructed on floating cypress log mats that distributed the weight over a larger area. It is always rumored that the Custom House on Canal Street is constructed on bales of cotton; this is untrue and it is also on cypress mats.

   The worst soils of all are the peats that exist where marshes existed before being drained. Peat is truly organic soil and when it is drained, it oxidizes rapidly, returning to its component minerals and occupying much, much less space. In some places in the region (such as northern Williams Blvd. in Kenner, Academy Drive and environs in Metairie, and Michoud Blvd. in eastern New Orleans) have experienced as much as 3-4 ft of subsidence, leaving enough space under some slabs so that an adult can bend over and walk underneath.

   For several views of the impact of subsidence, click here.

   During the 1970s, several houses have been destroyed when they exploded due to subsidence. All were concrete slab houses and used natural gas. As the soil shifted and subsided, it cracked the gas pipes that entered the slab. This allowed gas to accumulate in air pockets under the slab until some spark caused the trapped gas to explode. In order to avoid this accident today, all new construction uses flexible pipe at bends under the slab.

4. How to design buildings for the local environment. Early settlers built simple, wooden Creole cottages on the ground. Since the buildings rapidly rotted due to constant contact with the wet ground and frequent flooding, locals built their creole cottages out of brick.

   

   

   

   When subjected to floods, they raised them so that flood waters would not get into their living quarters. Eventually, these raised Creole cottages were the dominant house type, with the living quarters about ten feet above the ground. This allowed for flood protection, storage underneath, and, during hot weather, the doors could be opened and the wind blowing under the house would help cool it. Many, such as Madame John's Legacy, part of the State Museum on Dumaine, have large covered porches to provide useful space during frequent rains.

   Virtually all construction used French doors. They were managed for the temperature: they could be left open for a breeze; when the night air cooled down, they could be closed to keep the cool air in and the morning hot air out for a while; they could be left closed on the east side in the morning to prevent the rising sun to heat the room (during the winter the opposite could be done - opening them early to allow the rising sun to warm a cool room); the same options were available for the western side in the evenings.

   The great fires of 1788 and 1794 burned out all the Creole cottages and they were replaced with the town houses that are so characteristic of the French Quarter today (the many ground level creole cottages that exist today have been built in the last 150 or so years). Their galleries were decorative, but they also protected pedestrians from rain and windows from direct sunlight. There were originally almost never galleries or awnings on windows that face east (to allow the early morning sun in) but they were almost always present on the west (the afternoon sun is much hotter).

   The typical French Quarter town house was perfectly designed for its location in New Orleans (see the adjacent figures "New Orleans town house and courtyard" and "House at 725 Ursulines Street"). First, the rooms were usually arranged so <that air could move from the street directly to the courtyard. Of course they had French doors so they could control air movement (plus security). They had the kitchen in an outbuilding across the courtyard from the main house to remove the cooking heat from the living quarters. For those who owned slaves, this is where they lived (slave quarters); many used this for their adolescent sons (it was then called a garçonniere) so they could come and go without disturbing the family. The alley leading from the street to the courtyard served many purposes. If it was narrow, it was a walkway; if wide, it was called a carriage way since the family carriage would enter here for security and so that the ladies could step down without being in the normal muddy street.

   

   The walls were constructed of local bricks and mortar (both of which were relatively soft). In order to structurally strengthen the walls, the bricks were usually placed between upright cypress posts and then covered with stucco.

   
   

   There were usually plants and a fountain in the courtyard to reduce the temperature.

   

   If viewed from above, almost all buildings were the same height (look at the French Quarter proper today).
   
   French Quarter, viewed through highrise buildings on Canal Street.

   So how did all this help with living in the sultry New Orleans Environment? Winds blowing over the Quarter off the river and lake would literally suck the air out of the courtyards via Bernoulli's Principle. This sucked-out air had to be replaced, so a breeze was created down the carriage way when cooler air was pulled off the street and from under the galleries. The stucco covered walls allowed water to be absorbed inside of them. As the air moved passed the walls, the water in the walls evapo-cooled the air. The same happened as the air passed over the plants and fountains. If the windows were opened in the main house, a breeze passed through the living quarters. All of this worked very effectively. The next time you are in the French Quarter on a hot day, simply step into a carriage way and feel the cool breeze.

   Remember the earlier discussion regarding placement of sleeping room to take advantage of summer evening breezes. Many other types of New Orleans houses duplicate many of the concepts discussed above. Look around as you drive around town. You will see many good examples.

THINGS TO CONSIDER WHEN BUYING A HOUSE IN THE NEW ORLEANS AREA

What type of soil is on the property? It should be sand or sandy-loam. This consolidates well and can support the weight of your home. If too organic, you will have constant subsidence problems.

What is the flood history? Obviously, one doesn’t want to settle in a flood prone area. If there has been flooding in the past, has there been recent flood protection that will do the job?

Is any neighboring property higher than that which you are considering? If any are, rain will run into your yard and keep it flooded or too moist.

Is there any undeveloped (but developable) property within a mile or so? If so, code requirements may well dictate that the developments will be higher than your property, so you may have to deal with more water in the future than now.

Is the sidewalk level? If so, is it lower than the neighbor's; if so, is it new? Is it lower than the grass? This tells you something about on-going subsidence.

Does the last section of the sidewalk slant up to the porch? Driveway to garage? If it does, this clearly means that they have subsided and the slant was retrofitted.

Is the street level well below the living level of the house? Water runs downhill!

Is the street cracked? More evidence of subsidence in the neighborhood.

Do the street drains appear workable? If not, you will surely flood due to back up of rain water.

Is there subsidence around the edge of the slab? Is soil (even if grassed over) steeply stacked around the slab? A bad sign. The soil will probably continue to subside.

If the house has natural gas, is there proof that the connection under the slab is not rigid? If not, slight subsidence may crack the rigid connection and leak natural gas into the subsided pocket under your house. A spark can cause a devastating explosion.

If a marble is dropped in the center of a room, does it stop or roll to a corner? This means that the floor is not level, probably due to subsidence that one can’t see.

Are there any cracks visible (or repaired) on inside and/or outside walls? If so, these probably resulted from subsidence.

Is there hurricane strapping? If not, then a hurricane may cause the house to collapse.

What is the orientation of the house? Is it designed to absorb morning sun and is it protected from the west? Is it landscaped with deciduous trees on the south and west? A house with the “living spaces” facing west or south may well get so hot during the summer that either the air conditioner must run constantly (very expensive) or the room will be so hot that nobody wants to relax there. A workable solution is to plant deciduous (leaves fall off in winter) trees and bushes along the west and south sides of the building. This way, the leaves block the heat in summer (when one wishes to keep cool) and lets it through in winter (when one wishes to keep warm). Obviously, this can be planted after a house is purchased.

For new construction, are metal studs used instead of wood? Termites eat wood. Why tempt them?

How is the roof ventilated? There are many ways that this can happen. The fans ventilate heat, but the energy cost for the fan motor seems to be about the same as the energy savings from ventilating. Ridge vents are passive and cost nothing after instillation.

Is the house well insulated? Insulation in the attic and the outside walls are extremely important in the hot south.

Are there lots of windows on the north side? Are they double pane glass? In winter, the cold winds blow from the north, especially the northwest. If there are windows on the north, they should be double pane glass.

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