Review of Efforts to Combat Desertification and Arrest and Reverse Land Degradation in Myanmar - Combating Desertification in Asia, Africa and the Middle East - page 279

Fig. 14.5 Earthworks such as these can reduce runoff and soil loss and retain moisture in situ

Gully erosion can result in the loss of considerable areas of productive cropping
or grazing land. It causes significant increases in farming costs, because it makes
the operation of farm machinery and the management of livestock more difficult. It
also produces serious off site effects, resulting from the movement and deposition
of sediment, as described below. Because of their size and areal extent, eroded
gullies can remove and transport downslope very large quantities of material. If
a stream or waterway does not exist downstream to transport this material further
down the watershed, a sediment fan will be deposited at its lower end. This can
render a substantial area of agricultural land unproductive and may damage farm
infrastructure and public facilities such as roads and irrigation or drainage channels.
Disturbed flow across the fan deposit may initiate further instability lower down
the slope, leading to extended multi-channel or compounded gully development. If
the gully discharges into main watershed drainage system, movement of sediment
into stream channels will occur, to be eventually deposited further downstream
causing river sedimentation or accumulating silt in lakes and artificial reservoirs,
with consequential adverse effects on flooding, river and lake productivity and
reservoir storage capacity and a general impairment of downstream water quality.
A wide variety of structural and non-structural options is available for the
solution of watershed management problems. These may be employed either to
control or to rehabilitate land degradation, to control or mitigate the occurrence
or effects of water-based natural disasters, or to achieve both concurrently. The
more commonly used of these options are briefly described below (Fig. 14.5 ). More
detailed information about them can be obtained from a variety of textbooks and
manuals, some of which are listed in the Bibliography which follows this chapter.
Land management measures for the control of land degradation and the miti-
gation of natural disasters may include a variety of structural and non-structural
approaches. The structural approaches comprise a number of small and relatively
low-cost mechanical devices whose function is to reduce run-off rates or volumes,
to control or retard overland flow or to give protection against erosive or scouring
forces. The non-structural measures comprise a variety of farming, cropping and