Check Dams & Gully Plugs

A check dam (also called gully plug) is a small, temporary or permanent dam constructed across a drainage ditch, swale, or channel to lower the speed of concentrated flows for a certain design range of storm events. A check dam can be built from wood logs, stone, pea gravel-filled sandbags or bricks and cement (RUFFINO 2009). Reduced runoff speed reduces erosion and gully erosion in the channel and allows sediments and other pollutants to settle out. Check dams are inexpensive and easy to install. They may be permanent if designed properly and can be used where it is not possible to otherwise divert flow and stabilise the channel (POLYTECHNIC n.y.). Furthermore, they allow groundwater recharge (RUFFINO 2009). While gully plugs are able to retain soil moisture, to harvest runoff water, sand dams (which are similar in appearance) might be the better solution.

The size and shape of a drainage area, as well as the length and gradient of its slopes, have an effect on the run-off rate and amount of surface water. Therefore, all topographic characteristics should be studied in detail before gully-plugging work begins. There are several designs for how check dams should be constructed. The kind of gully plug that should be constructed depends on the local situation (what kind of material is available, slope gradient, is it a permanent solution, what tasks are intended). In gully control, temporary structural measures such as woven-wire, brushwood, logs, loose stone and boulder check dams are used to facilitate the growth of permanent vegetative cover. Check dams are constructed across the gully bed to stop, as already described, channel and lateral erosion. By reducing the original gradient of the gully channel, check dams diminish the velocity of water flow and the erosive power of run-off. Run-off during peak flow is conveyed safely by check dams. Temporary check dams, which have a life span of three to eight years, collect and hold soil and moisture in the bottom of the gully. Tree seedlings, as well as shrub and grass cuttings planted in gullies, can grow without being washed away by flowing water. Thus, a permanent vegetative cover can be established in a short time (FAO 1986).

General construction guidelines

(adapted from AKVOPEDIA 2012)

• The sides of the check dam must be higher than the centre so that water is always directed over the centre of the dam (this avoids the dam being outflanked by the flow).
• The dam can be made of temporary or permanent materials in natural gullies on the land surface. Materials used are concrete, earth, vegetation, stone and brushwood. Where earth is used, erosion or destruction of the structure needs to be avoided – to do this, a concrete spillway is often constructed. As they use the existing drainage system, no design of trench is needed (as with contour trenches).
• Do not construct check dams in watercourses or permanently flowing streams without specific design (because of possible restrictions to fish passage).

In the following section, several check dam methods are introduced (FAO 1986):

Brush fills

Brush fill is a continuous filling of small gullies with brush, branches of trees, stems of bushy vegetation, etc. This method is also called brush plug and is especially economical where brush is plentiful.

Earth plugs

Earth plugs, which are small structures, are constructed across the gullies. Their main purpose is to hold water and let it percolate into the ground (see also surface groundwater recharge). In non-humid regions, small gullies which are not deeper than 2 metres, with a gully bed gradient of less than 10 per cent, can be stabilised by a series of earth plugs. In humid regions, earth plugs must be combined with small diversions. Distribution of earth plugs depends on the gully channel's gradient.

Woven-wire check dams

Woven-wire check dams are small barriers which are usually constructed to hold fine material in the gully. They are used in gullies with moderate slopes (not more than 10 per cent) and small drainage areas that do not have flood flows which carry rocks and boulders.

Brushwood check dams

Brushwood check dams made of posts and brush are placed across the gully. The main objective of brushwood check dams is to hold fine material carried by flowing water in the gully. Small gully heads, no deeper than one metre, can also be stabilised by brushwood check dams. Brushwood check dams are temporary structures and should not be used to treat ongoing problems such as concentrated run-off from roads or cultivated fields. They can be employed in connection with land use changes such as reforestation or improved range management until vegetative and slope treatment measures become effective.

Log check dam

Log check dams made of logs and posts are placed across the gully. They can also be built of planks, heavy boards, slabs, poles or old railroad ties. The main objectives of log check dams are to hold fine and coarse material carried by flowing water in the gully, and to stabilise gully heads. They are used to stabilise incipient, small and branch gullies generally not longer than 100 metre and with catchment areas of less than two hectares. The maximum height of the dam is 1.5 metres from the ground level. Both its downstream and upstream face inclination is 25 per cent backwards. Its spillway form is rectangular. In general, the length and depth of its spillway are one to two metres and 0.5 to 0.6 metres.

Loose stone check dams

Loose stone check dams made of relatively small rocks are placed across the gully. The main objectives for these dams are to control channel erosion along the gully bed and to stop waterfall erosion by stabilising gully heads. Loose stone check dams are used to stabilise the incipient and small gullies and the branch gullies of a continuous gully or gully network. The length of the gully channel is not more than 100 metres and the gully catchment area is two hectares or less. These dams can be used in all regions.

The cost in India is reported to be between US $200-400 for temporary dams (made from brush wood, rocks, soil) and US $1,000- 3,000 for permanent dams (made from stones, bricks, cement), depending on the length and height. Variation depends on materials used and size of gully (AKVOPEDIA 2012). To stop gully erosion, early interventions are far more economical than late ones. A small gully or rill can be repaired with basic gully plugs (e.g. brush fills) (FAO 1986).

Check dams should be inspected regularly for sediment accumulation after each significant rainfall. Sediment should be removed when it reaches one-half of the original height or before. Check to ensure that the flow is over the centre of the dam and not either under or around the dam. Check that there is no erosion at the outfall (AKVOPEDIA 2012).