Field Evaluation of Hydromulches for Water Quality and Vegetation Establishment.

The North Carolina Department of Transportation’s (NC DOT) current practice for erosion control, using straw ground cover, has relatively high erosion rates with common failure. We are testing hydromulch, a natural fiber mulch material applied hydraulically as a slurry, as a potential alternative. Five treatments were evaluated on a 3:1 sandy fill slope in Kinston, NC. Treatments (4 replications) included: (1) straw + tackifier; (2) straw + polyacrylamide (PAM) + tackifier; (3) 70/30 wood and paper fiber blend; (4) wood fiber; and (5) hydroblanket bonded-fiber matrix. Runoff TSS values ranged from 135 to 201 mg∙L-1, relatively low due to the high infiltration rates on this sandy soil, and were not affected by mulch treatments. Treatments 1 and 3 elicited the most vegetation (315 and 322 kg∙ha-1, respectively). Hydromulch testing will continue on two sites in the Piedmont and two in the Mountains to evaluate site condition effects. We also conducted tests of PAM solution treatments using a rainfall simulator and packed soil boxes at a 5% slope. Preliminary results indicated that increasing the volume of application while keeping the PAM rate the same tended to reduce runoff turbidity. The effectiveness of the PAM was improved in proportion to the amount of straw mulch applied, suggesting that raindrop impact on the soil could reduce PAM effectiveness by exposing untreated soil. The higher application volumes may have provided deeper penetration, partially offsetting the raindrop impacts.