The floods take place more and less at dry lands and they are less visible, because they take place very fast.
The flood is an important problem and a serious decay factor for roads, bridges and buildings. What the flood appears as a disaster, it is a lack of plant cover at soils of one region. The floods often are an unstable and short-time (one day) and are less visible.
The flood not only degrades every ting at it's route, but also with the sudden water flowing with a high volume.
First it causes the earth surface erosion and an agriculture soils annihilation and then the suspended materials and mud sedimentation at down stream regions.
The anticipation and avoidance of the flood occurance is a very difficult, particularly, there are a few recorded data at a dry regions. The occurance speed makes a difficult for avoiding a flood, and in practice, it is impossible or almost impossible.
In one river, the water surface determination is recorded by a hydrograph A hydrograph measures the passed water from one point of river on the time scale, that it is stated as m3/s. The passed water volume from one point of a river in a second is said a river discharge.
The most important of measures for avoiding from a flood occurance are as follows:
1- To maintain the plant cover and increase it's amount at a drainage basin.
2- To cle4ar the channels and rivers from a sediments and muds that have been filled from a foam and caused their volume decline.
3- To avoid from establishing the houses and villas and entertainments places having a building at a waterways and rivers bed.
4- To make a levees and protective walls at a rivers margin.
5- To build dams and weirs at a rivers route that often become a diluvial.
6- To make a small weir at a waterways route, as we can make an approtunity for penetrating water behind these walls inside earth with establishing a small stone walls.
Flood risk survey
We must inform about a river discharge variation at different days of the year for doing this, and we must be have an estimates from a damage and degradation amount caused from previous floods, and be informed from a weather position, and it must be possible the meteorology anticipations.