The importance of sediment Sediment is an important part of river health. Sediment is carried by rivers from the erosion of hills and land in the upper watershed, nourishes downstream areas, and is an important part of estuary function, replenishing beaches and areas at the coast. A healthy river system is one that is in equilibrium the sediment is in balance between erosion in high-energy areas and deposition in other areas without too little or too much sediment. The removal of suspended sediment accounts for a large portion of the cost to treat water for public consumption, and can be devastating for spawning of various fish species.
Sediment can clog or irritate fish gills, so that they are unable to function.
Different fish species prefer different size spawning gravels, which can be covered by finer sediment from soil erosion. Sediment can also smother eggs once they have been laid, and can smother the aquatic nymphs of many invertebrate species such and stoneflies and mayflies. Erosion is a natural process, but can be sped up by clearing land for development and agriculture. A typical construction site can erode at a rate up to 100,000 tons per square mile per year, and can damage up to three miles of waterway below the site. In contrast, forest land erodes at rates up to 50 tons per square mile per year, and agricultural crop land erodes up to 500 tons per square mile per year.