Full-Scale Performance Evaluation of Slash Mulch Berms as a Sediment Barrier Practice

This topic focuses on the large-scale testing of slash mulch berm installations as a method of preventing sediment-laden stormwater from leaving a construction site and carrying harmful substances and sediment into stormwater. A twenty-foot section of a trapezoidal mulch berm with a 6 ft wide base and a height of 3 ft will be tested using Alabama hydrological conditions based on the peak 30 minutes of a 2 year-24 hour storm that carries sediment from a representative drainage area of 0.1 acres. Participants will learn how three mulch berm installations performed as a sediment barrier using impoundment data, water quality upstream and downstream of the practice, and sediment deposited upstream of the practice.

Full Presentation Abstract
Sediment barriers are the final line of defense to prevent sediment-laden stormwater from leaving construction sites and carrying sediment as well as other waterways. Most of the commonly used sediment barriers contain artificially fabricated components, including silt fences, wattles, and other geotextile products. These have had extensive research and testing completed on them, including full-scale laboratory testing.
One sediment barrier practice that is approved for use as a standard practice in multiple states, including Minnesota and Georgia, and is naturally occurring, is slash mulch berms. Slash mulch berms, after installation and the completion of construction work, can be left on a site, as they are composed of biodegradable material. Due to this, these installations can continue providing protection to the surrounding areas from sediment-laden stormwater.

There is very little research or testing that has been completed on the effectiveness of slash mulch berms as a sediment barrier practice. There has especially been little to no full-scale testing completed for slash mulch berms to provide evidence of their effectiveness as a practice.
For the full-scale testing, a 20-foot-wide section of a pine slash mulch berm that is 6 feet wide at the base, 3 ft tall, and having a 6-in. key cut into the earth at the upstream section was tested 3 times per installation to show the long-term effectiveness of slash mulch as a sediment barrier practice. Flow rates and Sediment Introduction rates were calculated based off of local Alabama conditions, to best test the effectiveness of the practice as an option for the state of Alabama; however, the results would also be relevant to other states in the region that have similar hydrological conditions.
Testing is currently ongoing. Data that will be collected during testing includes water quality up and downstream of the installation, impoundment upstream of the installation, and amount of sediment retained upstream of the installation. This data will be collected over the 30 min. test and through the dewatering practice up to 90 min. after the conclusion of the test. Water quality data and sediment retained will be used to evaluate the performance of the slash mulch berms as a sediment barrier.