The reservoirs can serve several purposes, included are the supply of water to communities, e. g. in water compromised areas and the safe accumulation of flood waters, especially in built up areas such as cities.

BACKGROUND OF THE INVENTION Reservoirs for water, whether for drinking and/or washing and/or cooking purposes are commonly made as reinforced concrete structures above ground or as dams which dam natural water courses such as rivers. Water purification and sterilization techniques are applied before supply of water, as required. A rare source is underground water raised to storage dams or reservoirs.

A key economic factor is the cost of such storage means such that commonly they can only be provided to communities which have attained a reasonable degree of wealth production. In countries that have attained a reasonable degree of wealth often is nevertheless difficult to economically justify or obtain willing investors for a bulk water storage facility, whether for supply purposes or flood control purposes, or both.

Flooding in cities has become more common than can easily be dismissed. This is due to the fast runoff times resulting from extensive paving of ground surfaces which is the norm in cities and the increasing number and size of cities. For example, 100 years ago New York, London and Paris were the three largest cities, but now they are all smaller than Tokyo, Mexico city, Sao Paolo, Beijing, Los Angles, Rio de Janeiro and Buenos Aires. Coupled with this factor is a tendency for large falls in catchment areas upstream of cities and cloudbursts over cities resulting form topographical effects. Sometimes failure of dams are a cause, a"domino"effect on a series of dams along a river have occurred. Storm water drainage systems are not capable of dealing with storm water and flood damage in cities which have a concentration of high quality infrastructure reaches many millions and even billions of dollar levels. Examples of floods in cities in the last twelve months are Wilmington and Jacksonville (USA), Paris, Maputo, Edinburgh, Moscow, Sao Paolo, York, Buenos Aires, Valencia and Caracas and many others.

SUMMARY OF THE INVENTION A key feature of this invention is to link the need to provide solutions for these problems with market forces in the economy, a procedure whereby the cost of providing reservoirs which have the capacity to deal with such flooding events can be justified by linking another economic value with the reservoir.

In accordance with a first preferred embodiment of the invention, a reservoir is provided preferably underground (or elsewhere convenient) preferably in (or near) a city or town which is adapted also to be capable of serving one or more functions selected from parking areas for vehicles which have entered the city, storage of water for desired or required purposes, shelter for populations in the city from disasters including earthquakes, fires and nuclear or other attack and providing economically viable extraction of an ore body.

In accordance with another preferred embodiment of the invention a reservoir is provided in a space left after open cast mining operations, alternatively open cast mining operations are conducted with a view to providing a reservoir after extraction of economically viable ore bodies, preferably near a city or large town and located between a catchment area which leads to the city or on a river which leads to the city or downstream of the city, for accumulation of water. One or more of the additional functions referred to like parking etc. may be added if appropriate.

In both the embodiments the preferred location of the water below ground level provides less vulnerability to high temperatures and resulting evaporation losses and to low temperatures which have potential for freezing the water.

The invention also provides avenues which can be exploite to resolve environmental protection requirements which arise when such major works are undertaken as are implied by this invention. For example, storage volumes measured in giga litre or even tera litre (e. g. 400 to-1 000 MI or more) are contemplated.

In some applications of the invention mining operations which are not economic by themselves can be justified by application of one or more of the additional functions listed, like parking etc.

In accordance with an aspect of the invention the method inclues placement of engineering installations which allow the parking of vehicles in parts of the reservoir volume which are above stored water and/or parts which are temporarily empty of water, means of monitoring water level in the reservoir and a method of moving parked vehicles upwards to higher levels when water levels rise and conversely allowing more vehicles into a reservoir for parking at lower levefs when water levels recede.

Materials used must be capable of withstanding immersion without undue deterioration. Pump systems can be installed as well as pipe work and/or viaducts for removal of water to adjacent reservoirs, rivers or dams.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is more fully described by way of examples with reference to the drawings, in which:- Figure 1 is a schematic block diagram of a new technical method of constructing reservoirs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 assists in the explanation of an example of application of the invention in an area of South Africa. The cities of Witbank and Middelburg are expected to expand into a mega city along the Maputo corridor. In this area are large near-surface deposits of low grade coal, some of which is smouldering underground. All of this area is located at altitudes which will permit supply of water from rives and dams, as well as from storms and rainfalls especially heavy rainfalls. The technical method of construction of reservoirs in this example of application of the invention comprises excavation of ore bodies in three localities which will be in and around the mega city in the following manner. The extent of excavation of the ore bodies is selected to provide excavated volumes below ground level which are suitably adapted, according to the application of civil engineering principles, to lining with water containing floors and walls (optionally to be roofed over, e. g. in locations where city infrastructure is planned to take place above the reservoir).

The excavation is progressed at a rate that allows refining and sale of the coal ore to a consumer such as large thermal power stations which have furnaces suitably adapted to burn the grades of coal produced for sale. Transportation by road and/or rail is facilitated by the staged rate of excavation. Civil engineering design will precede each excavation at least to the level of design of basic parameters of the final purpose of the reservoir of water storage and vehicle parking and/or natural disaster shelter, etc. As excavation progresses and income from ore sales funds investment costs civil engineering design proceeds into further detail. The final product of the reservoir water is contracted for sale to two major customers, the purification works of the mega city and the power station at mass transfer rates which match the mass transfer rate of the solid ore material excavated, i. e. the coal ore in this case. The detail civil engineering design will include provision for partial use of the reservoir for water storage at lower levels and parking at upper levels.

Provision will be made in the civil design for evacuation of vehicles at a sufficient rate in the event of flooding causing rising levels. Ventilation and humidity control aspects are also dealt with. Temperature stability is achieved through a mass of water located in the reservoir.

The method includes amortising the accumulating costs which arise as the project develops over a period of time against the costs of the ore extracted, the water later stored, the parking facility provided, the electricity which is to be generated using the coal that is processed out of the excavation and other possibilities.

Apart from coal, other mineral deposits can be exploited according to the invention.

The reservoirs constructed according to this invention can also be used to contain substances other than water, for example gas, e. g. natural gas.

Figure 1 shows an example of a possible case where the new technical method of construction of reservoirs is utilized. The sketch is not to scale and is primarily a functional flow diagram to show the layout of structures, construction process, cash flow and other aspects.

The development of a mega city 1 is predicated, arising out of growth of Witbank city 2 and Middelburg city 3. In and around the growth areas of the two cities are coal fields which can be mined by open cast mining (some are smouldering). The mega city will straddle the Maputo corridor freeway (motorway) 5 which is a major freeway around which industrial and commercial development is supported by government policy. The Maputo corridor stretches from rich platinum group metals mines and ultimately the city of Gaberone 6 in the West, linking en route with the Witwatersrand gold mining and industrial complex, to the East at the sea port of Maputo 7 which links with the ports of Richards bay 8 and Durban 9. An existing water supplier to the Witwatersrand industrial complex and surrounding areas is the Rand Water Board 10 which is supplied primarily by a major dam 11, the Vaal dam, which in turn is supplemented by a pump water storage scheme 12 which draws water from dams 13,14 and 15 in the Lesotho highlands. A smaller town 27, Bronkhorstspruit, is planned to be absorbed into the mega city in the course of time.

The method or procedure by which the reservoirs are constructed and integrated into the mega city complex is planned and co-ordinated by a Reservoir Consortium 16.

Four reservoirs 17, 18,19 and 20 are constructed over a planned period of time, co- ordinated with other aspects of the development of the mega city. The reservoirs are linked with each other by pipelines 21 or preferably, subject to suitable altitude relationships and terrains, aquaducts, of sufficient capacity to absorb and distribute water flows up to flood rates of flow. The reservoirs are variously connected in the same ways with the cities Witbank and Middelburg by pipes/aquaducts 22 and in the course of time at 23 with the mega city. For example, the reservoirs can have capacities of 3 giga litre, 2 giga litre, 1 giga litre and 500 mega litre. The reservoirs are constructed in voids left by open cast mining of coal and other mineras, either pre-existing mines or planned mines, using base and wall support techniques in the design provided by backfill in the mine.

Existing and future thermal power stations 24,25 and 26 are supplied with the mined coal and with the stored water, becoming thus customers for these products.

A major oil-from-coal industrial complex also producing valable downstream products from Fisher-Tropsch process 28, Sasol I and Sasol II, is connected to the cola mines/reservoirs at appropriate timings, to become another customer for the coal that is mined and for the water that is stored. Sasol products, e. g. fuels and chemical products are cycled back to customers 30, including in the mega city area.

These customers also become consumers of water from the reservoirs-arrow 31.

Licence fees of the consortium can be built into these revenue flows-arrow 32, to sustain an income for the consortium, which can receive finance from other sources.

Existing and developing industry, including steel works 29, Columbus Steel and Middelburg Steel, are connected to the reservoirs for supply of water and can also become customers of coal from the excavations as well as of water.

Local governments can also be included in the scheme.

The Lesotho highlands water scheme can be linked, arrow 33 can be linked to supply into the reservoirs.

The engineering of the reservoirs is designed to facilitate other uses for the reservoirs, e. g. parking and/or shelter, when there is no water in the reservoirs or at levels above the water level in the reservoirs, in the cases of reservoirs that are suitably located in relation to the high density development of the mega city, e. g. for "park and ride"schemes to manage traffic flows, etc. The reservoirs are engineered for this purpose by use of materials which are unaffected by water immersion and subsequent drying out, i. e. concretes are suitably specified, steel reinforcement within the concrete is suitably protected, steels and other materials exposed to water and humidity are selected and/or treated to protect them. In addition, detectors are provided to detect rising water levels, preferably computer inputted to calculate rising rates and evacuation timing when necessary. Bulkheads and doors, seals and barriers are specified optionally to manage water and possible risks associated with the water.

Link between water storage means can be by pipeline and/or ducts, using pumping stations where necessary.