What is the best way to conduct a sediment survey? Areas with higher amounts of impervious surfaces or areas which are under construction generate higher levels of pollutants and sediment. The frequency of how often a sediment survey should be done depends on the size of the pond and the land use that is tributary to the wet pond. Most of the time, you’re not going to immediately know that you have an issue that you need to address and that is when a sediment survey comes in handy. Cattails tend to grow in about one to two feet of standing water and the permanent pool in a wet pond is designed to be deeper than that. Another visual sign that there is too much sediment in your pond is when you begin to see cattails growing. Sometimes you can visually see accumulated sediment above the water surface in or near an inlet structure. How do I know if there is too much sediment accumulated in my pond?
Scouring and reduced functionality begins to happen when your pond has 3 feet or less of permanent pool depth left. This likely means that your pond is no longer meeting the pollutant reduction requirements that it was originally designed to meet. Additionally, when there is too much sediment on the bottom of the pond, storm water flow through the pond may scour the accumulated sediment and pollutants and carry it directly out the outlet structure. Depending on where the sediment is accumulated, it may reduce the storage capacity above the permanent pool of the pond. When too much sediment accumulates, the quality and functionality of the pond begin to decrease. In some cases, it may reduce the capacity of the inlet pipe, leading to flooding upstream. When sediment accumulates near an inlet, it may impede flow into the pond. The accumulation of sediment often begins near the inlet to the pond. What happens when too much sediment accumulates in my pond?
It may be time to evaluate how much sediment has accumulated in those ponds and whether or not it is time to dredge them to remove the accumulated sediment. Most municipalities and older developments own wet retention ponds that were built in the early 2000’s. The pollutants and sediment settle to the bottom of the wet pond where they often remain until they are removed. The permanent pool of a wet retention pond helps settle out those nasty pollutants that are often carried in storm water runoff. Wet retention ponds are a great way to effectively meet pollutant reduction requirements while also controlling peak discharge release rates during storm events. As the world of storm water management continues to evolve and municipalities face new requirements for the treatment and control of storm water runoff, storm water wet retention ponds are becoming a regular fixture for new and re-developments.
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