Hydraulic Performance Evaluation of Wattles Used for Erosion and Sediment Control

Abstract

Land disturbing construction activities can become nonpoint sources of pollution, particularly due to suspended sediment, if erosion and sediment control measures are ineffective. Wattles have become popular practices among many governing agencies and contractors because of the variety of wattle materials available and their vast array of applications, such as ditch checks, inlet protection practices, and perimeter controls. As technologies continue to emerge, quantifying wattle performance can be a difficult and daunting task. To better understand hydraulic performance, flume experiments were conducted on eight manufactured wattles using a testing regime that used four inflow rates of 0.007, 0.021, 0.035, and 0.057 m3/s (0.25, 0.75, 1.25, and 2.00 ft3/s) and three longitudinal channel slopes of 3.50%, 4.25%, and 5.00%. Hydraulic measurements to assess wattle performance were taken for each trial after flow stabilization. Six different fill materials (excelsior wood fiber, wheat straw, coconut coir, recycled synthetic fiber, chipped wood, and miscanthus fiber) and four containment systems (natural netting, synthetic netting, synthetic socking, and polyester socking) were evaluated. Test results indicated that wattles fall into one of four developed classes based on correlations between hydraulic depth ratios and subcritical length ratios identified in the study. Class 1 wattles are considered the least hydraulically favorable, and Class 4 wattles are considered the most favorable at reducing supercritical flows when compared to the performance of an impervious weir control test. Two-way (flow rate and channel slope) ANOVA analyses were conducted to evaluate the degree of wattle performance variations for each wattle type, and a multiple linear regression model was developed to quantify performance characteristics based on fill material, slope, and flow rate from a base case (i.e., impervious weir) scenario. The ANOVA analyses indicated that synthetic fiber and miscanthus filled wattles had superior hydraulic performance capabilities when subjected to various flow rates and longitudinal slopes based on no statistical difference across flow rates and slopes. The multiple linear regression model suggested that excelsior fiber was the least effective fill material for establishing flow velocities favorable for soil particle settlement, while miscanthus fiber created the most favorable conditions. Lastly, water absorption evaluations suggest that saturated wattle density, as opposed to dry density, can be used to link the wattle fill type to hydraulic performance.