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Our office of environmental
services is looking to install weir structures, shown in the attachments, in
ditches to research retention and flow. These structures would be in the clear
zone. Do you know of anything like this that has been analyzed or tested in the
past?

Any thoughts would be
appreciated!

I am not aware of any previous testing or analysis of weirs in the clear zone. I do have a couple of thoughts.

1.       First, before one considers the weir itself, one would need to consider if the waterway needed to be shielded. If the waterway has slope and depth such that it would not be considered traversable or is deep enough to pose a hazard to an encroaching vehicle, then it would likely be recommended to shield the waterway if it was in the clear zone. The RDG provides guidance on both foreslopes, backslopes, and transverse slopes. Additionally, guidance in the RDG for culverts and cross-drainage structures may apply here as well.

2.       In terms of the weir itself, there may be concerns with placement of these structures in the clear zone. First, the structure may pose a deceleration hazard to encroaching vehicles depending on the type of structure used. The examples you sent did not appear to be extremely strong structures, but this is still a consideration. Similarly, depending on the orientation and structure of the weir, it could pose a vehicle stability risk if placed in the clear zone. However, the extent of these concerns is difficult to determine without further study and details of the various potential weir installations.

3.       MwRSF did do some research on erosion control features for WisDOT. This research looked at recommendations for rock ditch liners and check dams. The scope was limited, but it may provide additional insight on the concerns associated with structures in the clear zone and best recommendations for slopes and placement that may be applicable here as well. I have attached the report.

Thanks