A water and sediment basin is an earth embankment—or a combination of ridges and channels—that is generally constructed across a slope to develop minor water courses that trap sediment and/or detain water. A sediment basin is a basin constructed specifically to collect and store debris or sediment. A water and sediment basin is considered an edge-of-field practice.
Water and sediment basins have similar functions to sediment basins, and are used to reduce or prevent sediment (soil) moving downstream from a land surface activity such as urban development, mining, or agriculture.
This practice applies to sites where:
- The topography is generally irregular.
- Watercourse and gully erosion are a problem.
- Sheet and rill erosion levels are reduced in the watershed to minimize operation and maintenance requirements.
- Runoff and sediment damage land and improvements.
- Soil and site conditions are suitable.
- Adequate outlets are available or can be provided.
- The basins are part of a planned conservation system.
Depending on the application, there are a multitude of regulations that might apply to the construction of these structures. Small basins for agricultural purposes are often exempt from many of these requirements. It is recommended to check on requirements with your local SWCD.
Figures 26a and 26b. Established water sediment control basin within a field (26a). Credit: SWCD, Fairfield County Ohio. Newly seeded water sediment control basin establishing a grassed area to provide additional filtering (26b). Credit: USDA-NRCS.
A water and sediment basin should be installed to control the stage, discharge, distribution, delivery, or direction of flow of water in open channels or water use areas. NRCS Conservation Practice Standard 638 is used to reduce watercourse and gully erosion; trap sediment; reduce and manage onsite and downstream runoff; improve downstream water quality; and improve the ability to farm sloping land. A water and sediment basin is usually small enough that the sediment can be excavated and placed back on fields.
NRCS Conservation Practice Standard 350 is used where physical conditions or land ownership preclude treatment of a sediment source by the installation of erosion control measures to keep soil and other material in place, or where a sediment basin offers the most practical solution to the problem. A sediment basin is often larger than a water and sediment basin. Typically, it has legal size requirements and is not commonly used in Ohio as an agricultural sediment management practice.
The effectiveness and water quality benefits of sediment control structures are very site-specific. In most applications, the primary purpose of a sediment control structure is to reduce downstream exports of sediment. It is not designed specifically to remove nutrients. However, total phosphorus loads are related to sediment transport so sediment control structures do help reduce total phosphorus exports from fields.
- Water and sediment control basins can be part of the treatment needed to protect a soil resource base. In addition, other practices such as terraces, contouring, a conservation cropping system, conservation tillage, and crop residue management can also be used to control erosion.
- Water and sediment control basins should not be used in place of terraces. When a ridge and channel extends beyond the detention basin or level embankment, the system should be designed as a terrace.
- The planned conservation management system should reduce sheet and rill erosion in the watershed to minimize operation and maintenance requirements.
- If used with terraces, water and sediment control basins should generally be spaced at terrace intervals. The grade of the watercourse between basins should be considered, and the spacing should be set to prevent watercourse or gully erosion.
- The drainage of each basin should be limited so that the duration of flooding, infiltration, or seepage does not damage crops or create other problems. The maximum drawdown time for cropland should be 24 hours, but it should be 48 hours for pastureland.
- The system of basins and row arrangements should be parallel, when possible, and spaced to accommodate the widths of farm machinery. Consideration should be given to embankment slope lengths, top width, and inlet location when determining spacing.
- Water and sediment control basins can be used as part of a terrace system to control small watersheds. They are intended to be used in a watershed and not at the outlet of a watercourse. Reference NRCS Conservation Practice Standard 410 or NRCS Conservation Practice 350 for this purpose.
- The uncontrolled drainage area to each basin should not exceed 30 acres.
- Reference NRCS Conservation Practice Standard 350 and your local SWCD for details on sediment basins.
Costs are site-specific and depend on the size and type of sediment control structures needed at a location. These costs might range from a few hundred dollars to several thousand dollars. In some cases, cost-sharing funds might be available.
Water and sediment control basins are hydraulic control structures used to manage water flows in channels and pipes. They act like dams, slowing water down with sediment dropping out of suspension.
Periodically, basins should be cleaned out and the soil placed back on the land. Without removal of the deposited sediment, they act as temporary traps, where much of the deposited material might be washed out during future severe storm events. In this situation, they might do more harm than good. The amount of sediment removed depends on the size of the sediment control basin, properties of the area draining to the basin, and the size of the sediment particles.
- Once designed and constructed, sediment control structures need to be checked with necessary maintenance performed after major storms— including the removal of debris and sediment. Clogging of an outlet is a common problem. A single large storm event can fill a sediment control structure.
- Contact your local SWCD or NRCS engineer if you have frequent problems with your sediment control structure. It might be undersized and in need of modification, or it might have only part of the flow of your drainage area discharging into it. Partial control is better than no control!
Extensive design details are provided in