My current homesite sits just outside of the floodplain of the Tangipahoa River, but it’s subject to flooding in any heavy rain event and the road is even more susceptible than our land. In the past few downpours, the ditches at the end of the road have become essentially useless, as the water just travels over the road in a stream about 6 feet wide and 4-6 inches deep.
The photo above shows how clean the ditch is upstream– an apparently desireable condition for people with extensive lawns because anyone who manages a strict lawn seems to have clean ditches. “Clean” in this sense means lacking vegetation or being overmaintained, rather than being free of trash. The result? There is nothing to trap the debris as it moves downstream. The water moves faster, the soil erodes, and debris travels quickly until it reaches a point where it becomes trapped– a culvert, perhaps. The culvert acts as a dam in this case, allowing debris to build up and thus pushing the water up over the road instead of through the pipe.
Contrast that ditch with the one below:
See that lovely greenery right there? That’s a ditch, but it doesn’t look like one does it? This is my neighbor, the cattleman’s ditch. He’s got one of the loveliest ditches in the neighborhood, rich with native bog plants (button bush, pickerel weed, sagittaria, lizard’s tail and others) that make habitat for frogs, crawfish and minnows. These plants are most likely benefitting from a lot of nutrient runoff from the farm and thus they are growing more densely than they would without all of those nutrients, but at least they are acting to reduce the runoff that gets carried downstream– so I still consider this a more ideal ditch for this area than the bare ditches in the other images.
In heavy rains, water travels slowly through this area because of the vegetation, apparently reducing the speed and quantity of the output downstream. Debris can get trapped in this area and has time to deteriorate naturally, becoming food for insects, microbes and other creatures. The water evaporates more slowly, being protected by vegetation, and therefore has time to seep into the ground to replenish the groundwater. Though the water is ponding here to some extent, the presence of fish and frogs and other creatures tend to reduce the amount of mosquitos that successfully reproduce. The ponding is desireable as long as the conditions upstream are not contributing to an excess of water reaching this area before it can be adequately drained.
The ditch above no longer exists. It has been converted to something more like this:
- The deep groove in front of this culvert is a symptom of downcutting; water travels too quickly to this point and is pushed downward when the volume is too large for all of the water to enter the pipe. This is a result of both too small of a culvert, as well as nothing to slow down the water upstream.
Although this isn’t in the same location, the cattleman’s beautiful ditch has been dredged to look much like this, with bare mud walls and bottom vegetation tossed up to dry out on the banks. The photograph above is actually a segment of ditch further downstream that occurs after about 100 feet of unvegetated ditch. You can see the result of having no vegetation to slow the flow of water, and that is downcutting– described in the caption above (check out the NRCS guide “Stream Visual Assessment Protocol.”)
As for the undercutting, I believe this is the segment of ditch that is responsible. This is the area where a neighbor of mine seems so insistent on a clean ditch that he sprayed Round-Up along about 100 feet of ditch to maintain this lovely aesthetic:
Now look at that– ain’t it pretty? Hmm… the clay brown sedimentation, thick green algae, stagnant water and eroded banks emphasize everything “bad” about a poorly managed ditch. The water that ponds here may promote mosquitoes because fish and frogs are less likely to control the populations here where there is so little habitat for them. The bare banks promote higher water speeds, which increase erosion, undercutting and movement of debris to be deposited downstream.
Modern cities in the US typically move closer and closer to clean ditches and further away from natural wetlands andswales. The practice of this clean ditch philosophy results in overall degradation of waterways. When a ditch that provides habitat for wildlife, slows water movement, reduces erosion and filters runoff is dredged to look more like the upstream ditch that caused the problem, this is inappropriate drainage practice. This fits well with the clean ditch philosophy– because vegetation that SLOWS runoff is naturally going to slow the emptying of water from the stream overrunning the road– but it fails to address the overall problem and fails to actually IMPROVE conditions both upstream and downstream.
The big failure in this logic is that they did not take into account the ditch conditions upstream. The clean ditch from the first photo and the one in the photo below are the two inputs to the clogged culvert at the end of our lane. With these two inputs, of course there will be large quantities of fast-moving water depositing debris in the culvert and overrunning the road. It doesn’t matter what the conditions are downstream if the upstream conditions are causing the problem. Thus, degrading the downstream conditions to accommodate inadequate water behavior upstream is probably NOT the best solution.
- The ditch is compromising the roots of this live oak tree, and the surface of the ground beneath the trees canopy is also being compacted by rainfall. The death of this tree would likely speed erosion, because the roots would no longer hold the soil back. A decrease in mowing in this area, as well as the use of mulch, retention walls and shady vegetation could reverse this condition and would likely prolong the life of the tree.
Ultimately, this is a matter for the parish drainage board, or perhaps the Army Corps of Engineers. Who’s responsible for this mess? Are landowners responsible for proper stewardship of their ditches, and are they entitled to maintain clean ditches for fear of water snakes, or an unkempt landscape? Whose ditches are these?
Another thing to ask is: if heavy, highly efficient drainage from ditches contributes to poor water conditions in the larger streams and rivers, and increased flood risk downstream, do ditch managers have an obligation to reduce these conditions for the benefit of their neighbors? Who is responsible when sick drainage degrades the overall condition of the environment for everyone?
I’m a ditch-lover and a ditch-hater, both. Digging ditches at all gets the blood under my skin boiling because natural drainage in this area results in wide, boggy floodplains and slowly-moving swamps further south– not deep channels of fast-moving water. However, when the ditches are dug and managed like storm drains it is especially frustrating. The perfect solution, some are probably thinking, are CONCRETE ditches! Concrete= less dredging, fewer poisonous snakes, quick emptying, no erosion.
Let me just throw this in there, for those of you who think concrete is the solution: the speed with which water travels through a concrete storm drain is often enough to pose a serious hazard to children and animals, and perhaps even adults if the ditch is travelling downhill. I’ve seen water in my mom’s open, concrete ditch rushing like whitewater rapids down to the little stream behind her neighborhood.
Concrete is not the answer. Pipes and tubes that discretely remove water is not the answer. Water retention is key to reducing environmental problems. Water retention is key to reducing toxic runoff, recharging groundwater, and ironically, reducing the impact of flood events. The water is always going *somewhere* when we choose to drain it, and the hazards imposed on others for our drainage choices are our responsibility.
As a final, personal note, I almost rescinded my disgust with my neighbor’s ongoing muckworks (I’m passive-aggressive about this stuff) because they actually kept a nice strip of native vegetation growing in the boggy soil where a pipe drains on their property (instead of converting it to bare mud, like they’ve done everywhere else). I walked by today, and the vegetation had been scraped up, and now there’s a big ugly tunnel carrying the water away to some unknown destination.
That’s my ditch philosophy.
Look out for upcoming posts on management alternatives for communities and individual property owners.
The Granite Garden. Anne Whiston Spirn, 1984.
Cities and Natural Process. Michael Hough, 1994.
Principles of Water Resources, 3rd Ed. Thomas V Cech, 2010.
Urban Forestry. Robert W Miller, 1997.