The Vermilion is a unique, meandering river that has long been used to carry people and products to and from Lafayette Parish and points beyond. Despite decades of indifference and abuse that left it a stinking, polluted waterway in the middle of the 20th century, efforts to improve the river's water quality have succeeded to the extent that some of the finest homes in the area line its banks.
But the transformation of Lafayette from an agricultural parish to a fast-growing metro area has placed increasing emphasis on the Vermilion's original role as the main source of drainage for the parish, and there are very real questions about whether the river is up to the now greatly expanded task.
Based on records produced by the Surrey Street gauge, incidents of the Vermilion reaching flood stage there (10 feet on the gauge) have been steadily increasing since the early 1950s, which corresponds with the start of the period of rapid growth in the parish. The population in Lafayette Parish in the 1940 census was 43,941. It almost doubled by 1960 (84,656) and nearly doubled again by 1980 (150,017). Population growth has continued steadily since then, albeit at a slower rate.
Growth brought changes in land use. Farm land was converted to commercial and residential uses. That brought the need to move water away from those homes and businesses rather than let it sit in fields. Most stormwater in the parish is bound for the Vermilion. As development has continued, so too has the amount of water the Vermilion is tasked with moving.
[caption id="attachment_2830" align="alignnone" width="1500"] An Oregonian by birth, Gary Kinsland has looked deeply at the history of the Vermilion River, his interest piqued by the Vermilion's peculiar habit of flowing backwards when flooding.[/caption]
Gary Kinsland has been a professor in UL's School of Geosciences since the 1970s. The Oregon native started looking more deeply into the history of the Vermilion River when flooding in the 1990s — particularly the reverse flow of the river from south to north — caught his eye.
In a 1998 paper on river flooding in Lafayette, Kinsland writes that the increased flooding was the result of growth amplified by how the parish developed: "Many housing projects with slab construction houses on well drained lots (as opposed to houses on piers requiring less drainage) were developed in and around the city. Streets were drained and sewers were installed. After this period, development continued with concreting of coulees beginning in the 1960s and continuing (along with increases in population, housing, commercial buildings, parking lots and roads) until the present. Whenever natural terrain is covered with impervious surface (pavement, concrete, or roofs) or is more efficiently drained via grading of lots, addition of ditches or improvement of coulees, the demand on the Vermilion River to accommodate runoff water is increased."
As a result, small, intense storms tend to produce more flash flooding. Kinsland writes, "The effect of impervious surface is worse for the smaller rainfalls than for the major storms because the major storms soon overcome the ability of the soil and topography of uncovered terrain to retain water, forcing much of the rainfall to runoff regardless of whether the soil is covered with impervious material."
Kinsland and others who have studied the Vermilion note that it is a tidal river. That is, water levels as far north on the river as Lafayette are affected by daily tidal action in Vermilion Bay and the Gulf of Mexico. High tides in Vermilion Bay produce higher river levels. The river's current is not strong.
The Vermilion is only about 70 miles long from its headwaters in St. Landry Parish to the spot where it enters Vermilion Bay. It's a short distance, but it is not a simple journey.
The Vemilion flows from the confluence of Bayou Fuselier and Bayou Bourbeux just west of Arnaudville. From there, it meanders south into the northeastern part of Lafayette Parish. That route keeps it inside what is the western edge of the Mississippi River Valley. The ridge is apparent from the air and at ground level from roads in certain parts of the parish.
Just east of the Lafayette airport, the Vermilion enters what is geographically known as the Prairie Terrace before making its way south to the Gulf of Mexico through the parish and bay that bear its name.
[caption id="attachment_2852" align="alignnone" width="1676"] The flow of the Vermilion River from Bayou Fuselier to the Vermilion Bay south of Abbeville[/caption]
When it rains real hard, the water goes both ways
The headwaters of the Vermilion are about 25 feet lower than the land it moves through, starting on the east side of the Lafayette Regional Airport. The airport, Lafayette and most of the rest of the parish are on the terrace — high, flat ground.
Kinsland says the fact that the river cut a valley for itself through the Prairie Terrace puzzled him for years until access to better measurement and imaging tools revealed the river's secret.
"The Vermilion flows through a valley that actually cuts through the prairie terrace," Kinsland explains. "But the question was how did that happen."
The answer, he says, is tied to the history of the Mississippi River and the hydrology of the alluvial plain that is the lowland area off the escarpment. That plain was once a valley that the Mississippi River careened through for centuries before settling into its current course.
"The Mississippi River changed courses a number of times within a 45-mile wide valley that existed between Lafayette and Baton Rouge," Kinsland says. "That valley was as much as 325 feet deep. That's the Atchafalaya Basin now. Bayou Teche was once a channel of the Mississippi, as were the Atchafalaya and Bayou LaFourche."
The Vermilion flowed into that valley but from the south — the opposite direction in which it now normally flows.
"LIDAR imaging shows the area where the Vermilion entered the valley just behind the airport," Kinsland says. "When sea levels fell, the northward flows stopped, but the channel that it had cut in the plain reversed its flow, taking it south into Bayou Tortue."
[caption id="attachment_2901" align="alignnone" width="669"] LIDAR imaging shows where the Vermilion River flowed into a valley just behind where the Lafayette Regional Airport is today.[/caption]
According to Kinsland, the Mississippi raised water levels in the valley again later, which allowed the Vermilion to return to the valley it had cut for itself earlier. Only this time the flow was southward, which it has maintained for the approximately 4,000 years since. All of that geographic and hydrologic drama took place along that section of the escarpment that runs from the Lafayette Airport south to Broussard on the eastern side of U.S. 90.
The Vermilion's bi-directional flow history reappears periodically when intense rains in the parish send water rushing through coulees to the river.
The Vermilion flows north when the input from tributaries in and below the city overwhelm the river's currents.
"When it rains real hard on Lafayette, drainage in the Coulee Mine causes the river to flow both ways," Kinsland explains. "The coulee comes into the river twice — near South College and at Rotary Point. The channel to Rotary Point is a man-made ditch to get the water out quicker. Stand on the deck there and watch the water come out. The water goes north from there, and whatever trash is there sits between the directions."
On the southern stretch of the Vermilion above Milton, the south end of Isaac Verot Coulee empties into the river from the east, and Coulee Iles des Cannes does the same from the west. Coulee Iles des Cannes drains a large swath of western Lafayette Parish stretching from north of I-10 southward. Near Maurice, the coulee serves as the Lafayette-Vermilion parish boundary.
Kinsland says the combined infusion of water from those two tributaries pushes water northward all the way through Lafayette back into Cypress Island Swamp, which sits in the plain east of the Lafayette Airport. When that happens, Lafayette experiences flooding along the river.
He compares the impact of the tributaries on the Vermilion to putting a water hose in the middle of the gutter on a house with small slope. "If you stick the hose in the middle, the water will water flow both ways. Those tributaries put more water in than the river can handle in one direction, so it flows both ways."
Kinsland sees a version of class warfare playing out in flood fights in Lafayette.
"The people living on the terrace want drainage," Kinsland continues. "That means putting the water in the Vermilion. Look at the houses along the river and look at the people with political sway there. It's a form of class warfare."