Design of a modular baffling system to enhance sediment basin settling
A common way of protecting streams and rivers from damage by sediment is to trap
that sediment before it comes off of disturbed land areas, and one of the most
common methods of doing that is through use of a sediment basin. The idea behind a
sediment basin in simple; we force the sediment-laden runoff through ponded tranquil
water, giving the sediment time to gently settle to the bottom before it reaches the
basin outlet. In practice things are much more complicated, as the turbulence and
momentum of the incoming flow set up circulation patterns in the basin, carrying
some of the sediment directly to the outlet and “short-circuiting” its ponded volume.
Two techniques are commonly used to limit this short-circuiting: 1) baffles—barriers
made of wood or of plastic mesh—are attached to stakes driven into the basin bottom,
forcing the flow through a more circuitous route; and 2) double basins are used, where
rather than a single large basin the water is routed through two smaller basins, thereby
at least reducing the magnitude of the short-circuiting effect. Though these
techniques help, the literature shows that basins are still not as effective as hoped.
This raises an idea: what if we carry this approach to its logical extreme? Can we
construct a sediment basin as we normally would, but then install within it some sort
of open cell structure that forces the runoff to flow through a large number of small
cells in order to reach the outlet? Won’t this give us the ultimate in the effect
afforded by the baffles and multiple basins?
The goal of this project is to design, build a prototype, and lab test a modular cellbased system for placement in sediment basins to aid in settling. If successful, such a
design has strong development potential.
A successful design must address the following issues:
1) it can require at most minimal alterations to the standard sediment basin design
2) it will force the runoff to pass through as many cells as possible on its way to the
outlet. It may not allow the runoff to bypass the system and cause more damage
3) it will handle very large runoff rates through some sort of “emergency spillway”
approach, perhaps not providing the best treatment under such conditions, but at
least avoiding system failure.
4) it will be modular, with module size depending on the following:
- easy transport of the modules on normally-available trucks, perhaps including
folding or easy dismantling
-with the structure in place and the cells filled with sediment, the module will need to
be lifted by readily-available equipment (say, a tractor-mounted backhoe) to allow
the sediment to be scraped out of the basin. This will not lift the sediment itself,
but will pull the module out of the sediment.
5) the system will withstand rough handling and multiple uses
6) it will be built of materials that resist degradation and cause minimal environmental
impact
7) it will be inexpensive
Design expectations:
- the design reports (including presentations) will address all the issues either listed
above or additional ones that come into consideration through the background
literature review and analysis. These reports will include not only ideas on how
the issues will be approached, but details on materials used, drawings, calculations,
etc. In other words, the reports will convincingly make the case for this as the
best possible design.
- once the design is approved, the team will propose a testing protocol to prove that
the design successfully addresses as many these issues as possible. This testing
will be based on a full-scale but very small prototype, as full-scale testing in large
sediment basins would be an excellent post-graduate study but is beyond the scope
of the current effort. The proposed testing protocol should make optimum use of
existing facilities, but may require additional testing equipment design and
construction, so consideration of this should occur in concert with the design.
- once the testing protocol is approved, the team will oversee its construction
- the team will carry out the testing protocol as approved
- the team will add to their report the findings of the testing, including especially
proof of successfully addressing the design issues, recommendations for design
improvements if the design did not prove to adequately address an issue, or
recommendations for further testing if that seems most appropriate.
You may wish to take or audit the ENCI648 course (offered during Term 1). A
special permit to overcome GPA restrictions to attend the class may be considered.
Figure 1. Sediment basin showing long baffle. The inlet is on the bottom left, and the outlet is
through the taller pipe on the bottom right. Source: North Hampton Cons. Dist.
Figure 2. Standard sediment basin design. Source: Clean Water Services
Figure 3. Active sediment basin. The primary inlet is at the far right end. Source: Cumberland
Cons. District