Bentley-DePue Drain

One of the topics of neighborhood discussion is the performance of the upper reaches of the Bentley-DePue drain.

Last year, Columbia Highway was impassible for 37 days due to flooding.

The dashed portion of the drain, shown here, is underground. It is of an age where it is clay tile, butted end-to-end. The inside is rough and it is vulnerable to cracking and to tree roots intruding.

Another factor exacerbating the situation is that there is only 4' of drop over the half a mile of buried drain.

This chart is a sensitivity study. Numbers from this website.

In the nominal condition (18" drain, roughness coefficient of 80, 6" rain and 4' of head) it would take 53 days to move all of the water that falls on the square mile drained by the upper reaches through that drain.

12" diameter tile was evaluated to simulate degraded performance due to sediment, roots and partially collapsed tile. 24" diameter was looked at as an upgrade.

Increased head, the height of the water in the swamp, was also evaluated.

 

Smooth plastic pipe was also looked at. Plastic pipe comes in much longer lengths than clay tile so there are fewer joints. The inside is smoother. The walls are impervious to roots.

In the nominal condition (18" drain, roughness coefficient of 150, 6" rain and 4' of head) it would take 28 days to move an all of the water through that drain.

Obviously, much of the water percolates through the soil as the estimated times shown on the charts are WAY longer than observed.

My take-away is that drains are very sensitive to increasing diameter (good) and smoother walls (good).

This image added in response to comment by B.