grass Archives - Reduce Flooding

“Backslope interceptors” help prevent erosion that can clog drainage ditches and contribute to flooding. Most people have probably seen them, but never paid much attention to them. Nor do they understand can reduce ditch maintenance costs by lengthening maintenance intervals. This photo essay shows what a difference they can make. All three counties in the Lake Houston Area require them, but Liberty County doesn’t enforce its own regulations. So the visual differences are dramatic.

What Are They? How Do They Work?

We’ve all observed water flowing through drainage ditches. But how does it get into the ditch? Broadly speaking, it can get into the ditch by a) flowing down the banks or b) through pipes. Option A increases erosion. Option B decreases it. B also reduces flood risk and the long-term cost of ditch maintenance.

What is a backslope interceptor? Imagine a small ditch (or swale) parallel to but offset from the main ditch. The swale captures runoff and overland sheet flow before it gets to the main ditch. The swale then funnels the flow into pipes that run under the banks of the main ditch. Keeping large volumes of water off those banks reduces erosion which could otherwise quickly fill the ditch with dirt and reduce its carrying capacity. If erosion reduces carrying capacity enough, water can flood nearby homes and businesses. The illustration below shows how backslope interceptors work.

Real-Life Examples

On 3/3/2021, I flew over three counties: Harris, Montgomery and Liberty. The “with/without” photos below illustrate the difference that properly constructed backslope interceptors can make. I shot the first one over the new Artavia development in southern Montgomery County. Note how the backslope interceptors let the developer establish grass on the banks of the ditch despite construction still in progress.

Ditches WITH Backslope Interceptors

*Artavia ditch in Montgomery County. Note series of backslope interceptors behind the maintenance roads that flank the ditch.*

*Drainage ditch in Atascocita in Harris County. Again, backslope interceptors let grass establish on the sides of ditches, reducing erosion.*

Ditches WITHOUT Backslope Interceptors

The rest of these examples came from Colony Ridge in Liberty County.

*Lack of backslope interceptors has led to severe erosion. Runoff goes straight down the banks of ditch and into the East Fork San Jacinto.*

Role in Establishing Grass

The next two photos show the role of backslope interceptors in establishing grass. By preventing bank erosion from sheet flow, the interceptors give grass time to establish and grow, reducing erosion even more.

*Ditch in Artavia, a still-developing area in Montgomery County, where developer has recently hydromulched to establish grass.*

Liberty County ditch in newly developing part of Colony Ridge, also recently hydromulched. Without backslope interceptors, hydromulch has washed into bottom of ditch and will eventually wash away, leading to more severe erosion.

How Enforcing Regulations Can Reduce Costs, Flooding

Ironically, Liberty County drainage regulations updated in 2019 require developers to install backslope interceptors and plant grass on the banks of drainage ditches.

Page 100 states: “Erosion Control: All drainage facilities must be designed and maintained in a manner which minimizes the potential for damage due to erosion. No bare earthen slopes will be allowed. [Emphasis added] Various slope treatments, including turf establishment, concrete slope paving, and rip- rap, are accepted. Flow velocities should be kept below permissible values for each type of slope treatment. Interceptor structures and backslope swale systems are required [Emphasis added] to prevent sheet flows from eroding the side slopes of open channels and detention facilities.”

Unfortunately, Liberty County does not enforce its own regulations.

When the developer eventually tries to turn Colony Ridge over to Liberty County, the county will inherit as massive maintenance burden because of non-compliance with these regulations. But even before then, the developer is creating rivers of mud that reduce the conveyance of ditches, and thus contribute to flooding nearby residents in Plum Grove.

*This Colony Ridge drainage ditch in Liberty County is rapidly filling in. Residents use it for joy-riding in their ATVs, which further contributes to erosion.*

The sediment also contributes to dredging and water purification costs for people downstream in Harris County.

Posted by Bob Rehak on 3/6/2021

1285 Days since Hurricane Harvey and 534 since Imelda

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

While Imelda brought untold heartache and suffering to hundreds, it did have one bright spot.

Shortly before Imelda, KSA had the meadows mowed in East End Park. Since then, thanks to the heavy rains, a bumper crop of fresh new green grass has attracted large numbers of deer. The grass is already knee high. On my evening walk in the park tonight, we circled the large meadow and saw more deer than I have ever seen in one place in 35 years of living in Kingwood. We counted a total of four families and twenty deer in total: bucks, does, and fawns.

The best time for viewing deer, if you are so inclined, is near sunset.

Video courtesy of John Knoezer. Deer are pretty skittish. You probably won’t get closer to them than 20 or 30 yards. But it’s inspiring to watch such graceful creatures, even from a distance. Bring binoculars for the best viewing. Many deer will remain near the edge of the meadow where they can retreat into the forest if they feel threatened.

Why KSA Mows the Meadows

KSA mows the meadows occasionally to discourage the spread of invasive species and halt the spread of the forests into meadow areas. The meadows also provide grass seed for migrating species of birds in the fall and spring.

Even though KSA got a late start mowing this year, heavy rains from Imelda made the grass grow quickly. It has already started going to seed, ensuring that migrating birds will have a satisfying rest stop and that birders will have have one of the best seasons ever.

The deer this year? Purely a bonus.

Meadow Trails Still Passable

While flood waters destroyed trails and wetlands in other parts of the park, the main meadow near Kingwood Drive seems to have benefited. Meadow trails are still passable unlike other trails. And at sunset there is a refreshing breeze that seems to keep mosquitos away.

*Three of 20 deer spotted in East End Park’s main meadow near sunset on 10/9/2019.* *Photo courtesy of John Knoezer.*

Posted by Bob Rehak on 10/9/2019

771 Days since Hurricane Harvey and 20 since Imelda

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Photo Essay: How “Backslope Interceptors” Reduce Erosion, Ditch Maintenance, Flood Risk