Shortages of fresh water, e.g. portable water and/or water for agricultural uses, are being encountered more often due to increasing demands from an increasing population and the concentration of people in large metropolitan areas. It has been estimated that by the year 2050 some four billion people will be facing severe water shortages. Such water shortages are not limited to underdeveloped countries. It is estimated that people living in southwestern states in the United States, for example, could be facing severe freshwater shortages even earlier. Even though most of the Earth’s surface is covered by water, it is estimated that less than two percent of the surface water is fresh water. Shortages of fresh water are further compounded by waste and poorly managed water supplies.
Despite the many constructive uses of fresh river water everywhere, a large amount of fresh river water flows in the world’s oceans every day. Many regions, municipalities, agricultural users, and the like divert or otherwise contain large quantities of fresh river water in reservoirs, which are typically located near the source of the water. However, large fresh water reservoirs are very expensive to build and maintain, and require large regions of land that could be put to other productive uses. Moreover, suitable locations for such large reservoirs are clearly limited.
A significant proportion of the population is located near the ocean or other major bodies of salt water. The salt water is generally not potable, of course, although large quantities of fresh water regularly flow into the bodies. Typically, the flow of fresh water in rivers is very seasonal, and seasonal flow forecasting is an important undertaking for most water supply systems. The seasonality of river flows is due to the seasonality of rainfall, as well as the availability of other watershed resources such as snow accumulations.
Typically, during times of high water flow, fresh water is abundantly available to fill local needs, but when the water flow drops off, severe fresh water shortages can occur. It would be useful to store fresh water river effluent from periods of high water flow, for use during times of low water flow.
In addition, in certain regions near bodies of salt water and without an adequate fresh water source, water desalination plants are used to extract fresh water from the salt-water body. In order to run the desalination plants at peak efficiency while ensuring a stable supply of fresh water, it is desirable to have a reservoir to store fresh water that is produced, for purposes of load leveling and to accommodate periods of equipment maintenance.
This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
An offshore fresh water reservoir is disclosed that includes a flotation member, for example and annular foam and/or air-filled bladder, that defines a closed perimeter, and a pliable, tubular skirt that extends downwardly from the floatation member, to define a volume. A density interface assembly in disposed in the volume, and is formed from one or more members having a gross density such that the members float in salt water and sink in freshwater. For example, the density interface member(s) may be formed by filling a container with a mixture of seawater and freshwater. An anchor system is provided to fix the location of the offshore fresh water reservoir.
In an embodiment of offshore fresh water reservoir is sized to contain at least ten million cubic meters of fresh water, and the density interface assembly comprises a large plurality of intermediate buoyancy spherical containers filled with salt water.
In an embodiment, the offshore density interface assembly includes an impermeable sheet that is configured to degrade over time.
In an embodiment, the reservoir further comprises a system for supplying fresh water to the reservoir, for example a conduit system that extends from the mouth of a river to the offshore reservoir. The conduit system may comprise a floating blanket system with a U-shaped bladder and/or a wave-powered pumping station for pumping fresh water into the reservoir.