Storm Sewer & Road Culvert Basins: Sediment basins (or catch basins) have been used for many years to intercept run-ff water and trap/retain any sediment before it can get into a watercourse. For instance, storm sewers that drain large parking lots near a river should have a connected sediment basin to collect sediment, since parking lots typically flush toxic pollutants such as fuel oils, lubricants and gasoline into a river. Road culverts should never directly outlet to a stream or lake. Ideally, this run-off should be directed into a vegetated area. But that is not always possible, especially in steep watershed areas or near bridges.
Of course, if there is a basin it must be cleaned periodically. An uncleaned catch basin might actually worsen water quality conditions, since pollutants can concentrate in the accumulated sediments and become washed into a lake or river during one flush of a sudden storm. With prudent planning a basin can be designed to make cleaning more easy and less costly. Rather than digging out accumulated sediments by hand, a clamshell bucket or modified piece of equipment might scoop material from the basin quickly into a waiting truck. Or, a "silt sack"–whether purchased or constructed–could trap sediment and be lifted into a truck for emptying in an upland location.
Pre-Cast In-Channel Basins: Another type of sediment basin has also been used for several years, but this basin in constructed in a stream channel in order to trap sand and fine sediments that might otherwise smother stream insects and fish eggs. This kind of basin must also be cleaned before it becomes 40% full, or water velocity will scour out all the trapped fines. These in-channel basins can be a dug hole into which is placed a concrete structure, or simple a dug pit in the streambed. The former is typically installed in urban areas or in parts of a watershed undergoing development and land use changes. Pre-cast concrete slabs, of 6" minimum thickness reinforced with steel, are poured off-site, joined together, then set into place by a special crane. This is costly. For just the setting of a 7' wide, 17' long and 7' tall basin in Saratoga County the bill was $10,000.
In-Channel Dug Basins: Dug holes in a streambed have only the cost of digging and removal. BRASS has been interested in the possibility of an in-channel sediment basin for several years as a way of quickly improving fish habitat in a selected area of the Boquet while the organization works at stabilizing eroded embankments. We knew, from our 1993 attempt at collecting and measuring sediment from miniature plywood boxes we positioned in the streambed, how quickly sandy sediments "drop out" of the water column given an opportunity. We thought a large basin could help clean sand from a section of the river so insects could recolonize and trout and salmon have a chance at natural reproduction.
From a professional journal article about in-channel basins, we assumed Michigan scientists were using dug pits so we called to get particulars about slope, depth, sizing, and the siting of basins. They were/are using dug pits of all sizes. But, BRASS got information it wasn't expecting. Basins to improve trout and salmon habitat in Michigan are on streams with less than 1% gradient. (Most of the Boquet and its tributaries have a higher percentage gradient.) Michigan streams with basins have a streambed movement of primarily sand; the majority of their water is from groundwater seepage; and there is only slight variation in discharge rates. (The Boquet is highly impacted by rain and snow melt. Average discharge is about 315 cubic feet per second, but can be as low as 9 cfs and as high as 12,000 cfs.) It doesn't look like in-channel sediment basins are going to be of assistance on the Boquet River.