*4.2.2 Gully plugs*

*Slope Engineering*

flows into sub critical flows [10].

*4.1.3 Contour and peripheral bund*

cross section of 0.9 to 1.3 m2

*4.2.1 Composite check dam*

grass cover. The grass filter strips is able to reduce the sediment concentration in runoff water by 5 times (from 3.6 to 0.72 g/lit). The *Para* grass filter in waterways is able to reduce the flow velocity of runoff water by converting the super critical

The management of shallow ravine by contour and peripheral bund has shown improvement in value of land and crop yield due to soil moisture retention within the field, prevention of soil and nutrient losses from the crop field. The different cross sections of contour and peripheral bunds were tested in ravine lands of Western India [11]. The design cross sections of the bunds were fixed on the basis of the area of the catchment, slope of the land and its location. The bunds were designed on the basis of the vertical interval or horizontal spacing [11]. Usually one bund could only be located in each field approximately on contour so that it can also serve as peripheral control of gully heads. These bunds were sodded with *Dichanthium annulatum* and *Cenchrus ciliaris* grasses. In ravine lands an average

best [11]. Grass ramps and pipe outlets were provided in the bunds for the safe disposal of excess runoff water. It is further stated that the effectiveness of the bunds would be for a longer period, as with passage of time the rate of reduction of bund height is expected to be slow and can be maintained indefinitely with good stabilized grasses [12]. It is also found that the area lost under bunds could fetch revenue from grasses, which is sufficient as comparable to production in rainfed area [12].

**4.2 Engineering measures for management of medium and deep ravine land**

soil loss, associated nutrients and stabilize the steep slopes with time.

About two third of the ravine lands in the country are deep ravines 3–9 m or more with varying width and slope and cannot be easily reclaimed with simple earth moving machinery for cultivation of crops. The management of deep ravines instigates with designing and instituting a series of composite check dams in the gully bed. The construction of gully plug at regular interval with provision for safe disposal of runoff assists in stabilization of gully bed, which can be alternatively utilized for raising crops tolerant to water logging. The easing of gully is required in deep gully to prevent caving action against steep slope due to runoff and protect the adjoining marginal land to collapse inside the gully due to unstable slope. The medium and deep gully can be reclaimed by terracing and or trenching for conservation of runoff,

A large number of earth cum brick masonry check dams were constructed in Mahi ravines of Western India for reclamation of medium and deep gullies in ravine [10]. These check dams were found to be very effective to check erosion, detaining the sediment and runoff water behind the structure which ultimately resulted in ground water recharge. The deposition of sediment against the check dams was measured by fixing a series of angle iron poles on concrete level of the structure. The average sedimentation from these ravine sub catchments having agricultural crop in table lands as well as in gully beds was 24.51 cu. m./ha/year during year 1961 to 1963 [10]. The average sediment deposition from watershed having agricultural crop in tablelands and natural regeneration in gully beds was 4.20 cu. m. /ha/year during year 1964 to 1977 [10]. After the siltation of these composite check dams the level terraces formed in the gully beds were stabilized and was put under cultivation

spaced at 0.90 to 1.20 m vertical interval was found

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Gully plugs protect the gully beds by reducing the runoff velocity, distributing the water spread, increasing infiltration opportunity time and improving the soil moisture regime for improving the vegetation cover. Gully plugs made of various materials i.e. brush wood, live hedges, earth, sandbags and brick masonry, loose boulder were evaluated in Western India [10]. The size and materials for the gully plug depends on the width, length and bed slope of the gully and anticipated runoff. In narrow gullies whose width did not exceed 3 m, live hedges consisting of Euphorbia species were planted across the gully beds in three rows spaced 90 cm apart and the stems at 90 cm in each row alternatively staggered [11]. It was found that all types of gully plugs were effective either in retaining or retarding the runoff. The earthen gully plugs were found to be the cheapest. Brick masonry gully plugs are constructed at the confluence of all gully branches of a compound gully. The gullies where no runoff is expected from the top, earthen gully plugs of 1.1 m2 cross section with a grassed ramp of 22.5 cm below the top level and spaced at 45–60 m horizontal interval were found suitable. However, for gullies in which excess runoff from the top was expected an earthen gully plugs of 2.2 m2 cross section with a pipe outlet was to be provided. The earthen gully plugs are required to be constructed for a life expectancy of 10 years. During these periods it is estimated that the vegetative growth of forest species will be sufficient to take care of soil erosion as well as their root system will be sufficiently developed to extract the moisture from deep soil layers [11].
