Checkdams are of the following types;
- Brushwood check dams: constructing brushwood checkdams conserves small gullies up to 1.2 m to 2.1 m deep. These are classified into;
- Single row brushwood checkdams: it consists of a single row of posts erected across the channel with brushwood laid along the flow of water. The brushwood is kept in position by tying it to the posts.
- Both row brushwood checkdams: it is used for 7 or 8 feet deep and about 29 feet wide gullies. The posts about 6’’ diameter are driven in two rows across the flow of water and brushwood are tied with galvanized wire.
Semi permanent dams: these dams ar emore stable than brushwood checkdams. These are following types;
Dry stone checkdams: it is made up of dry stones without mortar. It is constructed in the form of an arch with convex side facing the current. The walls are built leaving a step of 6’’ on the down streamside without deviating from the arch so that the top width is gradually reduced. After reaching 2 ft above bed level, a notch is left I the middle. Notch is half the span long and 1 ft, deep. Apron and windwalls are also built of stones. At the back of checkdames, earth brushwood and stones are piled upon the notch.
Log Dams: when timber is available it is used for making log dams. Logs of at least 10 cm in diameter and 2 m. in length are driven in side by side to form a wall of logs. If the gully has steep sides, a rectangular notch is made in the center. Lashing and bolting crossmembers to vertical posts obtain some extrarigidit.
Permanent checkdams: they are built in deeper and wider gullies where no other measures can stop erosion. They are of following types;
- Drop spillway: it is an efficient structure for cotrolling relatively low head upon 3m and discharge capacity of 3m3/ sec.
- Chute spillways: it is useful in high overfalls where a full flow structure is required and where site condition do not permit the use a detention type of structure.
- Gabions: it uses pre- fabricated rectangular basket called gabion made up of galvanized wire netting. The basket is placed in position and filled with stones, and then the lid is wired down. Basket has size of 4m * 1m*1m. Baskets are built up on top of each other and can form large and small structures. The main advantage of these structures is that there is sufficient flexibility for the structure to adjust to settlement resulting from scouring of foundation.
|Loose stone checkdams||2.0m|