As in most things, the key to controlling an unfavorable consequence is to prevent it from happening in the first place. Excess sediment in rivers is typically related to runoff from nearby agricultural areas and urban development. Erosion within a river bed also produces excess sediment, and it is exacerbated by loss of wetland buffer areas, channeled water courses that produce high energy flows, and uncontrolled flow into a river from stormwater or dam releases and industrial activity. Mitigation of any or all of these contributors on a large scale can reduce or even eliminate sediment problems at the outset.
On a smaller scale, sediment pollution can be reduced naturally by encouraging the establishment of riparian buffers and restoring wetlands. Designed solutions include controlling disturbances from artificial outlets, nearby construction sites, and dredging activities. Turbidity (or silt) curtains are one of the primary tools in these applications. They interrupt the flow of water loaded with sediment from construction sites, stormwater outlets, etc. and keep it contained within a specific and limited area, allowing sediment to settle. Turbidity curtains are used on a temporary basis to control sediment until local construction is completed, or until a longer term solution is applied. Typically, a turbidity curtain consists of a series of floats supporting a curtain of geotextile fabric suspended in the water. In very calm conditions, the fabric may be impermeable and simply contain the water while the silt gradually settles to the bottom. In more active conditions, permeable fabric actually filters the water, retaining tiny particles of silt and debris within the containment area while permitting clear water to pass. Once silt has settled to the bottom of a riverbed, it generally will remain safely in place unless another large disturbance (uncontrolled stormwater flow, for example) stirs things up again. Even with short-term solutions like turbidity curtains, sediment control in rivers requires that water flow from human activities be effectively controlled.
