Current Research

Tillage and Amendments to Improve Construction Site Soil Properties

Soils on construction sites are usually made up of subsoil materials with low fertility and organic matter and which may have been compacted.  This creates problems with vegetation establishment and can lead to poor infiltration and root growth.  We’ve been experimenting with various levels of tillage and different amendments to alleviate these problems, with the added benefit of reducing runoff into stormwater systems.  Our studies have demonstrated that tillage can improve infiltration 3-5X and that this is maintained for at least several years, the longest we’ve measured it.  Vigorous vegetation is needed to maintain this effect, and incorporating compost can be beneficial.  Infiltration rates of 20-30 cm per hour have been common in a variety of soils around North Carolina, but mower traffic can greatly reduce this within the wheel track.  Current research is focused on potential benefits of using wildflowers instead of grass in strips of high-infiltration areas along roadsides.

Preparing plots with different combinations of tillage and amendments.
Tilling lime into an experimental plot.
Taking digital images to assess vegetation coverage.
Wildflowers planted adjacent to grassed area.

Tackifiers for Straw Applied for Erosion Control

There have been a number of recommended products to replace the asphalt that used to be commonly used to hold straw in place, but no testing of their effectiveness.  In this project we tested a wide variety of products, including various

hydromulches, glues, and polyacrylamide for their ability to withstand winds up to 50 mph in a wind tunnel.  The hydromulches and plantago glue worked well, holding the straw to close to the maximum wind speed.  The paper-based hydromulch would be recommended primarily because it is the least expensive.



Advanced Best Management Practices for Maximum Erosion, Sediment, and Turbidity Control

We have developed and tested a number of approaches to reducing sediment in construction site runoff and are deploying these on construction sites to determine how well they work.  Active construction sites are particularly challenging because of the constant changes as grading and building progresses, so this “real world” project will provide guidance on the best approaches to successful designs and installations.

Evaluation of Ground Covers on Construction Sites

There are a wide variety of products used as ground covers, including blown materials (mostly straw), hydraulically applied fibers, and erosion control blankets.  In addition, applying polyacrylamide along with these ground covers has great potential for further erosion reduction.  We have a continuous program of  evaluating this for both erosion reduction and vegetation establishment.

Image of road ditch lined with coir wattles used to reduce to velocity of water.







Image of basin with baffles and slope drain inlets.







Continuation of basin above showing baffles installed as well as skimmer as drain down device.








Evaulation of various types of erosion control blankets, mulches, and hydraulically applied fibers.








Channel Lining for Erosion Control

When construction site stormwater is collected into temporary channels, some form of lining is needed to prevent erosion in them. We are testing several options to achieve channel stabilization: jute netting, jute netting with polyacrylamide applied underneath, excelsior blankets, and a spray-on concrete product. Tests are being conducted both under controlled conditions (a simulated channel) and in the field on active construction site

Example of erosion in the unlined test ditch.
Field testing of a spray-on concrete product for its potential in stabilizing temporary ditches.


Alternative Methods for Dosing Construction Site Stormwater with Polyacrylamide

Applying polyacrylamide (PAM) powder to fiber check dams is a well-proven method of reducing turbidity in construction site stormwater. We are also exploring alternative methods which may provide more control over the dosing process. Two examples are shown below, one using a simple float valve system and a weir, and the other is a rain-driven system developed in New Zealand. Both involve dissolved PAM, which is good because it reacts quickly with the suspended solids. The drawbacks are that the solutions can freeze and have to be replenished after each storm. We are interested in determining if the benefits are worth the effort

A float valve is positioned behind the square-notch weir and releases PAM solution in proportion to the height of the pool behind the weir.
With the rain-driven dosing system, the rain is collected on the roof and directed to a tank floating in a larger tank filled with PAM solution. As the rain water accumulates in the floating tank, it sinks, displacing the PAM solution into a hose that discharges into the ditch. As a result, dosing is proportional to rainfall.