| Abstract: | The currently enforced Bulgarian water legislation the Water Act (1999),the Environmental Protection Act (2002),etc.] requires conducting special studies for accurate assessments of sand and gravel flux along the rivers,prior to the issue of the license for operation of the quarries,where they will be dredged. The activity of a quarry necessitates special investigations because of the large dimensions of the damages inflicted on the environment. Ours studies have shown that there are two types of river reaches,in which abstracion of sand and gravel is performed. The first one refers usually to the plain area river reaches. The other type is mountainous with high rate of sediment load,which consists of coarse solid matter. The "on-the-spot" study on the environmental impact of the sand and gravel dredging has revealed that in the area of the quarry the riverbed cuts into the alluvial sediments to about 6-7 m and this ditch has spread by attenuation at a distance of more than 25 km upstream. Downstream the pit the picture is replicated and at the 8th km a local scour on the riverbed,amounting to more than 1.80 - 2.00 m,has been measured near the foundation of a massive bridge in the centre of city of Plovdiv. Such assessments of dynamic resources of sand and gravel materials are expected to serve for the purposes of gradual limitation of this activity in river sections close to renewable resources. The amount of sediment load,which may be abstracted in the area of the Orizare quarry in Bulgaria on a yearly basis has been calculated as 6000 m3/a. It ensures that the resources will not be exhausted and irreversible distortion of the riverbed will be prevented. This is an environmentally safe limit. |
