The discharge of sediment-laden stormwater from active construction sites, such as highway construction projects, is a growing concern in the construction industry [
1]. The United States Environmental Protection Agency (USEPA) labels such discharge as nonpoint source (NPS) pollution, which is defined as land runoff, precipitation, atmospheric deposition, seepage, or hydrologic modification that does not meet the legal definition of ‘point source’ in Section 502 (14) of the Clean Water Act [
2].
Soil erosion is considered the largest contributor to NPS pollution in the U.S. [
3]. Construction sites are known to be a significant contributor to soil erosion by exhibiting soil loss rates that are 20 times greater from construction sites than agricultural lands, and 1000 to 2000 times greater than forest lands [
4,
5]. Studies have shown that erosion rates on cut slopes of roadways has varied from 5.93 mm/ha (0.09 in./ac. or in./ac.) up to 70 mm/ha (1.12 in./ac.) [
6]. When soil is eroded from construction sites, other harmful particulates such as fertilizers, pesticides, metals, and fuels attach to the soil and are transported into municipal separate storm sewer systems (MS4s) [
7,
8]. Polluted MS4s transport construction site runoff directly to surface waters, ultimately causing sedimentation. In the U.S. alone, “sedimentation impairs 84,503 river and stream miles (12% of the assessed river and stream miles and 31% of the impaired river and stream miles)” [
9]. Sedimentation of surface water can lead to deterioration of aquatic habitats, rapid loss of storage capacity of reservoirs, eroded streambanks, and increased turbidity of the waters thereby reducing photosynthesis, and clogging fish gills [
10]. An annual estimate of
$17 billion is spent in the U.S. alone in an effort to control onsite sedimentation, bringing the national total to nearly
$60 billion in erosion and sediment control activities [
11]. Thus, the combination of environmental and economic downfalls related to erosion and sedimentation in the construction industry has developed a need for scientific research to be performed to understand the overall performance of erosion and sediment control (ESC) practices used at the federal, state, and local levels.
Within the construction industry, there are numerous types of erosion controls. The focus of this research effort is to test the performance of the following surface cover treatments: (1) conventional straw, crimped, (2) conventional straw, tackified, (3) wood fiber hydromulch (HM) (Excel® Fibermulch II), (4) straw and cotton hydromulch (Geoskin®), (5) cotton fiber reinforced matrix hydromulch (FRM) (HydraCX2®), and (6) bonded wheat fiber matrix hydromulch (FM) (Hydrostraw® BFM).
1.1. Mulching as an Erosion Control
Mulching is defined as an erosion control practice that uses materials such as shredded paper, grass, hay, wood chips, wood fibers, straw, or gravel to stabilize exposed or recently planted soil surfaces [
12,
13]. Surface mulch has been found to be one of the most effective, practical means of controlling runoff and erosion on disturbed land prior to vegetation establishment; however it is most effective when used in conjunction with vegetation [
12,
14,
15]. Researchers [
16,
17,
18,
19] have reported that mulches used to control erosion have a two-fold advantage: (1) reduce soil loss and (2) protect grass seeds and soil amendments from being washed away. Additionally, mulches are capable of reducing solar radiation, suppressing fluctuations of soil temperature, reducing water loss through evaporation, increases interception storage capacity, dissipating the kinetic energy from the raindrops impact, and helping to prevent soil crust formation [
17,
18,
20,
21,
22,
23]. Research has also shown that mulching can reduce sediment yields by over 80% when applied at a rate of 2000 kg/ha (1784 lb./ac.) [
23,
24].
The purpose of testing conventional straw was to have a traditional, low-cost, widely used erosion control practice to compare to the performance of hydromulch products. Straw is one of the most widely used ground covers used to reduce erosion on construction sites [
25], and has been reported to reduce erosion rates by more than 90% if applied at sufficient rates [
22,
26,
27,
28]. Turgeon [
21] states that straw is also capable of encouraging grass establishment by reducing runoff, increasing infiltration, and improving soil conditions.
Straw crimpers are typically used to crimp or punch straw into the soil when the soil is not too sandy [
29]. If crimpers are not available or necessary, liquid mulch binders are used to ‘tack’ mulch by spraying the tack on top of the straw [
15].
There are advantages and disadvantages to using straw mulch for erosion control. The advantages are that it is inexpensive, quick, and easy to apply using a straw-blower, capable of achieving efficient grass growth, and water is not needed for application. Straw mulch has also been found to perform as well as or better than hydromulch products when applied at sufficient rates [
30]. Other studies have shown straw mulch to not only reduce soil erosion in the short term, but also by aiding in vegetation establishment through the long-term reduction of soil erosion [
31]. Conversely, disadvantages of conventional straw include that it does not prevent soil loss as well as more expensive erosion products (e.g., erosion control blankets, compost, etc.), is susceptible to wind if not properly anchored, may introduce weed seeds, and fines from straw blowers can drift long distances [
29].
1.2. Hydraulically Applied Mulch (As Known as Hydromulch)
Hydraulically applied mulches, referred to herein as ‘hydromulches’, have shown continuous evolution and improvement over the past 50 years. Advancements in technology have resulted in the production of equipment and materials that offer enhanced performance and greater productivity over many traditional methods of erosion control. Hydromulch has been shown to meet the required planting depth for small seeded species [
32]. In other studies, hydromulch has been shown to reduce the sediment yield by about 75% when compared to bare plots [
33]. There is a knowledge gap between the cost-effectiveness and performance benefits of new products [
18,
34,
35,
36] such as hydromulches, largely due to newly evolving technologies as well as a lack of research involving hydromulch products.
The introduction of water, refined fiber matrices, tackifiers, super-absorbents, flocculating agents, man-made fibers, plant biostimulants, and other performance enhancing additives to hydromulching practices on slopes has forced federal, state, and local governments to develop hydromulch guidelines. ASTM International (ASTM) has proposed new standards for testing hydraulically applied erosion control products (HECPs). Additionally, the Erosion Control Technology Council (ECTC) has divided HECPs into five distinct categories, relevant to their corresponding functional longevity, erosion control effectiveness, and vegetative establishment [
29,
37]. Specific to this study, the addition of a tackifier to a hydromulch has been shown to increase the effectiveness of the hydromulch as a soil cover due to the tackifier bonding with the soil particles and creating a more hydrophobic environment [
38]. Prats et al. [
23] determined that the initial reduction in soil erosion on a plot treated with hydromulch was attributed to the initial protective cover provided by the mulch to minimize splash erosion.
McLaughlin and Brown [
27] conducted large- and laboratory-scale tests on four ground cover practices: straw mulch, straw erosion control blanket, wood fiber, and a mechanically bonded fiber matrix (MBFM) hydromulch. In their study, it was reported that the ground covers reduced runoff turbidity by a factor of four or greater when compared to bare soil. More specifically, on the controlled, laboratory-scale tests, the MBFM reduced average turbidity by approximately 85% and sediment loss by about 86% in comparison to a bare soil control.
Holt et al. [
39] performed laboratory-scale tests on six hydromulch treatments using 0.6 m (2 ft) wide by 3.05 m (10 ft) long by 7.62 cm (3 in.) deep trays at a 15.7% slope. The following six hydromulches were applied by hand at 1120 kg/ha (1000 lb./ac.) and 2240 kg/ha (2000 lb./ac.): wood hydromulch, paper hydromulch, cottonseed hulls hydromulch, cotton byproduct (COBY) hydromulch produced from stripper waste (COBY Red), COBY produced from picker waste (COBY Yellow), and COBY produced from ground stripper waste (COBY Green). COBY is a term used in Holt’s report to represent a patented cotton by product of cottonseed hulls [
40]. The respective soil treatments with an application rate of 1120 kg/ha (1000 lb./ac.) achieved soil loss reductions of 35%, 58%, 84%, 90%, 80%, and 80% for wood, paper, cotton-seed hulls, COBY red, COBY yellow, and COBY green. When the application rate was increased to 2240 kg/ha (2000 lb./ac.), the respective soil treatments achieved soil loss reductions of 19%, 32%, 79%, 88%, 88%, and 68% for wood, paper, cotton-seed hulls, COBY red, COBY yellow, and COBY green.
In 2002, Landloch [
41] studied the performance of four hydromulch treatments using 15 plots that were 5 m long by 1.5 m wide (16.4 ft long by 4.9 ft wide) at a 25% slope. The four hydromulches tested were paper hydromulch, flax hydromulch, flax plus paper hydromulch, and sugar cane hydromulch, applied at a rate of 1000 (893 lb./ac.), 2500 (2232 lb./ac.), 3250 (2900 lb./ac.), and 5000 kg/ha (4464 lb./ac.), respectively. The respective treatments achieved soil loss reductions of 80%, 85%, 96%, and 96% for paper, flax, flax plus paper, and sugar cane.
Benik et al. [
42] developed a study comparing the effectiveness of five treatments, including Soil Guard
® which is a bonded fiber matrix (BFM). In their experiments, the BFM was applied at a minimum rate of 3360 kg/ha (3000 lb./ac.). The BFM reduced average sediment yield by approximately 94%.
Buxton and Caruccio [
43] evaluated 19 soil stabilizing and erosion control treatments, four of them were hydromulches without tackifiers. The plot sizes used were approximately 1.5 m (5 ft) wide by 3 m (10 ft) long at a 12% to 15% slope. The four hydromulches tested were Conwed wood fiber mulch, Superior wood fiber mulch, Silva wood fiber mulch, and Pulch; each hydromulch was applied at a rate of 1344 kg/ha (1200 lb./ac.). In the study of Buxton and Caruccio [
43], effectiveness of the hydromulches were measured using a vegetative maintenance (VM) and erosion control value, which in 1979 was a new parameter in the Universal Soil Loss Equation (USLE), and represented total loss ratio expressed as a decimal. These values ranged from 0.0 to 1.0, where a value of 1.0 means the erosion control practice had no effect in reducing erosion. The VM values for Buxton and Cauccio’s [
43] report were translated below in
Table 1 to measure erosion control performance in soil loss reduction percentage.
Babcock and McLaughlin [
25] evaluated straw mulch, with and without polyacrylamide (PAM), and a wood fiber hydromulch, with and without PAM, on the effectiveness of reducing erosion and improving the water quality of the runoff. The plot sizes used were 1 m by 2 m (3.3 ft by 6.6 ft) on a −33% slope. The plots were subjected to a total rainfall of 3.05 cm (1.2 in.) at an intensity of 3.7 cm/h (1.5 in./h). The mulch was applied at a rate of 2240 kg/ha (1998 lb./ac.), while the hydromulch was applied at two separate application rates: 1970 kg/ha (1758 lb./ac.) and 2940 kg/ha (2623 lb./ac.). This study found that hydromulch applied at a rate of 2940 kg/ha (2623 lb./ac.) provided a soil loss reduction of 8% and hydromulch applied at a rate of 1970 kg/ha (1758 lb./ac.) provided a soil loss reduction of 19% when normalized to a straw mulch application of 2240 kg/ha (1998 lb./ac.).
Robichaud et al. [
44] developed a study to evaluate the performance of wheat straw mulch and wood hydromulch when used in a post-fire condition to reduce erosion. This study utilized natural rainfall over several years to evaluate the products. Two separate tests were performed in two different locations. At the first location, the application rate of the wheat straw was 2200 kg/ha (1963 lb./ac.) and the hydromulch was 1100 kg/ha (981 lb./ac.). The soil loss reduction rates of the wheat straw mulch and the hydromulch were found to be 97% and 65%, respectively, for the first year of the study. At the second location, the application rate of the wheat straw was 4500 kg/ha to 6700 kg/ha (4015 lb./ac. to 5978 lb./ac.) and the hydromulch was 600 kg/ha (535 lb./ac.). The soil loss reduction rates of the wheat straw mulch and the hydromulch were found to be 99% and 19% for the first year, respectively.
This research aims to evaluate the effectiveness of six different ground cover treatments, normalized to a control treatment, when evaluated under simulated rainfall on laboratory scale plots. The process will include a standard and repeatable methodology that is consistently applied across the treatments under evaluation. The expected outcome is to confirm the effectiveness of the treatments.