Dry river beds

Habitat The chul and adyr zones. A weed and ruderal found on hills, among unirrigated winter wheat fields, along roads, in dry river-beds and on stony slopes of the lower mountains. 

Habitat The adyr and tau zones. On clay bluffs, stony slopes and in dry river beds with rocky debris. 

Conjoined MHOrOXJiaBBIH Dry river-bed cyxoe pycjio peicH... 

Often the flow of water in the river bed is accompanied by a subsurface flow through the aquifer below and beside the surface flow. Although this flow is much slower than the surface flow, its cross section can be very large and its discharge rate can exceed the discharge of the surface flow, especially in dry areas. The interaction of water and chemicals between surface flow and aquifer is called hyporheic exchange. Here we will not deal with the influence of the hyporheic flow on the surface flow. The opposite, the impact of the river water on the chemical characteristics of the groundwater will be discussed in Chapter 25. 

The cysts of the microalga Haematococcus pluvialis occasionally cause a spectacular blood-red appearance to drIed-out lakes, ponds, river beds or even the stoups in churches, and can be associated with the natural phenomenon described as "blood rain" (left). - Algae production plant in the kibbutz Ketura in the Negev desert In Israel (right). 

Studies of Mars by spacecraft have indicated that it was once a wetter, more habitable world than the cold desert planet of today. Dried stream beds and river channels attest to liquid water flow on the surface. There is even evidence that the northern lowlands may have held an ocean. The geological data indicate that the main epoch of liquid water activity was very early in Mars history, although some limited level of liquid water activity may have continued even to the present time. 

The most interesting facts lie in the Pacific Ocean, where the anomalies are seen with the dotted areas, i.e., areas warmer than they should be. These hot bodies of water are the consequence of the U.S. Navy rejecting excessive quantities of wastes, chemicals, and exhausts. The mud carried down by Californian rivers reaching the sea could explain the phenomenon, but I doubt it, knowing all too well how desperately dry the beds of these rivers are. 

Diamonds were first discovered in India as early as about 800 BC. The early diamond mines were the alluvial gravel in the banks or beds of active or dried up rivers in which diamond and other heavy and hard crystals had been concentrated by the action of the flooding water. The most famous Indian mine was at Kollur near Hyderabad where several historical diamonds (the chief among them being the Koh-i-Nur) were found. Although most of the Indian diamond mines dried up by the 18 century, the mines at Panna in Madhya Pradesh are still operational and some new fields in the vicinity are soon to be opened for commercial exploitation. 

Where a flooding risk exists, cofferdams/caissons may need to be installed with pumps of suitable capacity. A cofferdam or caisson is a watertight box-like iron structure which is normally sunk in the bed of a river. It is pumped dry and filled with concrete and used in the construction of underwater foundations for structures such as bridges or quay walls. Cofferdams must be inspected by a competent person on the same day as it is used by a worker. A permit to work system may also have to be used. 

Dry valleys are characteristic of the limestone and chalk downland. The few rivers rise from underground streams and the deliberate flooding of water meadows in the river valleys used to be a common practice. Watercress beds flourish along some chalk streams. The farms and fields on this type of land are usually large, especially on the thinner soils. There are very few hedges and the trees are mainly beech and conifers. Walls of local stone form the field boundaries in some limestone areas. 

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