- COME THE FLOOD: Riverdale levees built for 500-year surges.
With broken levees helping drown more than 80 percent of New Orleans in the wake of Hurricane Katrina, one couldn’t help but be reminded that Little Rock is a city by a river — a river that has, in the not-too-distant past, risen up and waylaid the city with Biblical-scale destruction.
Holding back that river when it decides to swell are more than 50 interconnected levees in the Little Rock area, most of them built by the Army Corps of Engineers and then turned over to private levee boards for administration.
Though there are some concrete floodwalls in the area most of the levees around the city are of the “dirt embankment” style: a wide earthwork set back some distance from the edge of the river.
Though these levees may look like artless mounds of earth, Charlie Tobin with the Army engineers said that building one isn’t as simple as getting a load of fill dirt and piling it up. While not designed to withstand constant water against them like a dam, at flood stage, levees show their careful engineering by doing battle with everything the river can throw at them: “piping” (the seepage of water underneath the surface, which can cause the levee to be undermined), changes in water pressure and depth, alterations in the river’s channel, and currents that can grind the legs out from under a levee in a process called “scouring.”
Tobin said there are levees of various strength throughout the Arkansas, most of them maintained by private owners. They’re graded by the strength of the flood they would likely be able to withstand — from small berms to withstand the kind of flood that might occur every five years, all the way up to massive earthworks engineered to fend off a 500-year deluge.
Tobin said the New Orleans levees that failed bear little resemblance to the dirt levees around Little Rock.
“The levee down there that had the big problem was a structure — a concrete floodwall,” Tobin said. “As the water came over the top, it scoured out the foundation. On the levee systems that we have, you have a slope, so you’re not going to get the scouring effect on most of the levees we have.”
Tobin said that in addition to blending better with the environment, dirt embankment levees are much cheaper to build than concrete structures like floodwalls.
Largely foolproof when maintained and inspected properly (Tobin said the Corps inspects both federal and privately maintained levees in the state either annually or biannually, and makes recommendations for repair) there are dirt levees in the Delta region that routinely save cropland from flooding two or three times a year. Given enough rain, however, Tobin said even the highest levee can be “overtopped,” with water pouring over — something he said is not technically considered a “failure.”
One place that knows about the threat of overtopping is North Little Rock. Unlike Little Rock, the city has a prominent system of floodwalls, gates and levees running through its downtown. Bobby Ward, the North Little Rock Public Works director, who oversees the city’s floodwall and levee system, said the reason is simple.
“The elevation on both sides of the river is not the same,” Ward said. “That’s the reason why we have levees on our side of the river and Little Rock doesn’t.” Because their downtown area is closer to sea level than Little Rock’s — 267 feet above sea level, compared to 335 feet for Little Rock, according to the U.S. Geologic Survey — North Little Rock has historically seen more than its share of overtopping scares. During heavy flooding in 1990, Ward said, the city had to put up the gates in the floodwall to protect the downtown area, with the river rising to within “two to three feet” of overtopping the floodwall.
On the other side of the river, Marion Burton is one of three commissioners on the private Riverdale Levee Board. Built in the 1960s when the low-lying Riverdale area was developed for commercial businesses, the 500-year-rated levee that Burton helps oversee encloses 250 acres between Cantrell Road and the Arkansas River. It’s all dirt, except for a very small portion of concrete around a lock near the marina.
Burton said that the largest expense in keeping up the levee in the past was making sure the grass got mowed. In the last few years, however, the Corps has grown more and more concerned about a number of trees on the Riverdale levee. Burton said the removal of the trees — from top to root ball — has led to considerable expense
“There are two problems with [trees on the levee],” Burton said. “If the river side of the levee was ever exposed to high current, a tree could dislodge and create a weak spot on the levee, or if a tree died, and the roots decayed, of course that would create an avenue by which water could migrate into the levee.”
Burton said he has seen the levee weather what were called hundred-year floods. As for sweating the worst-case scenario — the 500-year monster flood that might overtop the Riverdale levee — Burton agreed that we’ll all have bigger problems than Riverdale being flooded out if the Big One ever comes.
“Yes we will,” Burton said, chuckling. “We sure will.”