Erosion Control Vital on Transportation Infrastructure Projects
The impact of runoff can be felt on many levels. Just a few of the negative effects include:
- Eroded soils can enter water bodies and channels, raising water levels and blocking culverts. This can increase the chances for inundation of surrounding land.
- Sediment in water bodies can cover the eggs of fish and other organisms, preventing them from reproducing.
- Excess sediment that is suspended in streams and rivers acts like sandpaper on fish and other organisms. Suspended sediment can also abrade the tissues of plants that live in the water.
- Excess sediment can increase the cost of treating drinking water and negatively affect the equipment used in the drinking water treatment process. This increases the cost of treating drinking water.
- Other pollutants such as pesticides, herbicides and oil, can become attached to eroded soils and enter water bodies along with the soil. These contaminants can make swimming unhealthy for children and adults.
Temporary sediment control practices include those that intercept and slow or detain the flow of stormwater to allow sediment to settle and be trapped. These practices can consist of installing temporary linear sediment barriers (such as silt fences, fiber rolls, sandbag barriers, and straw bale barriers); providing fiber rolls, aggregate bag berms, or check dams to break up slope length or flow; or constructing a temporary desilting basin, sediment trap, or sediment basin. Linear sediment barriers are typically placed below the toe of exposed and erodible slopes, downslope of exposed soil areas, around temporary soil stockpiles and at other appropriate locations along the site perimeter.
Erosion control plans have been designed just like the roadway and structure plans and they must be given the same attention and importance. Many factors must be taken into account, such as topography, hydrology, desired trapping efficiency for a certain designed storm, sensitivity of the site, etc. Using inspections of the site and knowledge of the erosion and sediment control devices; construction engineers and designers can work hand-in-hand to determine what measure is best for each location.
One of the most important factors for a successful erosion and sediment control plan is the timeliness of its installation. In order to contain sediment on-site, the timing of erosion control device installation must be coordinated with the progress of construction. Devices should be installed before the area draining to them is disturbed, if possible. As grading progresses and as drainage structures and inlets are installed, it is important that erosion control devices be constructed in intermediate phases to protect them from off-site sediment. This ensures that all new outlets and/or modified drainage patterns are protected from causing off-site sediment.
However, installing controls to slow erosion and control sediment is only the first step. These controls must be maintained and replaced if disturbed, an occurrence not uncommon at active work sites. The needs of a project may necessitate the movement of erosion control measures during a particular phase of work. It is important for designers and supervisors to make sure these controls are replaced as soon as possible. In most states regular inspections are required at job sites. When possible, designers should include final or temporary vegetation measures in their staging plans. The most effective erosion control measures include installing final seed/sod to eliminate the need for temporary erosion control devices.
For instance, in Illinois, permits from the Illinois Environmental Protection Agency require weekly inspections of these controls and inspections whenever there is a .5 inch of rain or more. The intensity of a rainfall can be more important than the actual amount of rain that falls however as severe rainstorms can overwhelm even well designed and installed erosion controls. Effective monitoring can prevent a small problem from growing into a costly issue requiring a delay in work and additional measures being installed.