DESCRIPTION

Technical Field

The present invention is in the field of construc- tion and more specifically relates to a technique for controlling the amount of underground moisture supplied to a surface layer, while simultaneously stablilizing the surface layer. The technique of the present inven¬ tion is particularly suitable for the construction of clay tennis courts, although it could equally well be applied to agricultural use.

Background Art

In building railbeds- for railroad tracks, it is known to place a layer of ballast stone on the ground as a first layer. The ballast stones are more or less of the same size. The ballast layer permits surface water to flow under the railroad tracks so that the railbed does not act to dam the flow of surface water. In other structures, a layer of finer rock is sometimes placed on top of the ballast layer, and no effort is made to keep the layers separated. With the passage of time, and under the action of the elements, it is not unusual for the finer upper layer to work its way into the coarser lower ballast layer, thereby filling in the interstices of the ballast layer and thereby reducing its ability to pass the surface water.

In a different field of prior art, it is known to bury perforated pipes in the earth to provide irriga¬ tion for the soil. The water supplied to the pipes escapes through the perforationsand is released into the soil. This drip irrigation technique, as cur-

rently practiced, is an excellent way to supply mois¬ ture to a pair of adjacent parallel rows of crops, but the current technique would prove to be hopelessly uneconomical and impractical for creating and main- taining an artificial water table.

In the event of a heavy rain, such an underground watering system can cause flooding because it includes no way of removing water from the ground.

Finally, the use of a system of buried pipes has the disadvantage that if a pipe should break it is ver difficult to locate the break, and repair can be effected only by digging up the surface area.

Thus, it is seen that previously known undergroun watering systems have a number of defects that limit their usefulness.

Disclosure of Invention

The present invention overcomes many of the pro¬ blems associated with underground watering systems tha are known in the prior art and permits a much greater degree of control in the application of water.

The present invention permits an artificial water table to be established beneath a level surface, and permits the depth of this artificial water table to be raised and lowered at will, and in response to rain, heat, wind and other environmental conditions.

In accordance with the present invention, a basin like excavation is dug in the earth at the plot that is to be irrigated. The bottom of this excavation is carefully leveled, and then the floor and walls of the excavation are covered with a watertight membrane, such as stout plastic, to form a shallow watertight basin.

A ballast layer of rock is then laid down on the

watertight membrane to a typical depth of 10.16 cm. The ballast layer consists of a myriad of rocks having approximately the same size. That size typically is in the range from1.27 to 2.54 cm. In alternative embodiments, the ballast layer may consist of man-made materials such as glass marbles or even foraminous pipes of steel or plastic. The purpose of the ballast layer is to provide a medium for the lateral flow of water and to provide a firm support or foundation for the layers above it.

In accordance with the present invention, there is placed upon the ballast layer a permeable membrane that entirely covers the exposed upper surface of the ballast layer. The permeable membrane may consist of a durable fabric, such as denim, while in other embodi¬ ments, a metal or plastic screen is used. The inclu¬ sion of this permeable membrane is an important aspect of the present invention. The permeable membrane should provide only low resistance to the passage of water, but prevents finely divided rock from passing through it.

In accordance with the present invention, a layer of finely divided material is deposited on top of the permeable membrane. In a preferred embodiment, this fine layer consists of scoria or crushed volcanic ash. That material is very porous and because the material is finely divided, the surface tension of the water is broken and the water can disperse through the layer by by capillary action "wick effect" . The particles of the fine layer cannot penetrate downwardly through the permeable membrane because the particles are larger than the passages through the permeable membrane. For this reason, particles from the fine layer cannot get into the ballast layer and thereby clog up the ballast

layer, which interfere with the desired flow of water through the ballast layer.

Finally, a finish layer is deposited on the fine layer, and the nature of the finish layer depends on the use to be made of the installation. If the installation is to be a tennis court, the finish layer might consist of crushed granite or crushed basalt. On the other hand, if the installation is to be used for agricultural purposes, the finish layer may consist of top soil. In an alternative embodiment, the finish layer is omitted.

In accordance with the present invention, the watertight membrane extends upwardly at the perimeter of the installation so that all of the layers dis- cussed above lie within the watertight basin formed •by the watertight membrane.

A water supply pipe extends into the ballast layer and is used for supplying water to that layer. As the water level in the ballast layer rises, no irrigation of the fine layer or the finish layer takes place until the water level reaches the permeable membrane. Once the water level has risen above the permeable membrane, the water wets the scoria in the fine layer, and this layer acts like a wick or blotter so that the water penetrates upward through the fine layer by capillary action. Similarly, moisture is drawn into the finish layer by the same effect.

If the water level is permitted to continue to rise above the permeable membrane, moisture is supplied to the finish layer at an even faster rate. A suction pipe also extends into the ballast layer, and reaches almost to the bottom of that layer, but is spaced slightly from the watertight membrance. This suction pipe is used for withdrawing water from

the ballast layer, and this may be accomplished most readily through the use of a pump attached to the suction pipe. As water is removed from the ballast layer by the suction pipe, the artificial water table falls, at first merely reducing the rate at which water is supplied to the finish layer. However, when the water table has fallen below the permeable membrane, water will no longer flow into the fine layer, and the irrigation is terminated. It is a feature of the present invention that the ballast layer readily conducts the water in all direc¬ tions, so that an area the size of a tennis court can be irrigated through the use of only one water supply pipe, and only one suction pipe is required to remove the water. This action results from the uniformity of the stones in the ballast layer thereby resulting in interstices that cannot become clogged. Unlike systems that employ buried foraminous pipes that can break, the ballast layer is practically indestructible and trouble-free.

In the following detailed description, the tech¬ niques for constructing the irrigated plot and the techniques for controlling the artificial water table will be described in greater detail. The novel features which are believed to be characteristic of the invention, both as to organiza¬ tion and method of operation, together with further objects and advantages thereof, will be better under¬ stood from the following description considered in connection with the accompanying drawing in which a preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only and is not intended

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as a definition of the limits of the invention.

Brief Description of the Drawing

Figure 1 is a diagramatic cross-sectional elevation view of an irrigated plot constructed in accordance with a preferred embodiment of the present invention.

Best Mode of Carrying out the Invention

The method, materials and structure of the installation will now be discussed in detail with reference to Figure 1. For purposes of illustration, it is convenient to think of the installation as bein a tennis court, but the structure and method remain substantially the same, with possible changes in dimensions, when the installation is to serve some other use.

For example, the construction of the present invention is particularly well suited for the irriga¬ tion of crops that are sown broadcast as contrasted with row crops, because it provides moisture uniformly to the entire plot.

In Figure 1, the line 12 represents the ground level before the construction has been started.

A basin is then excavated in the earth 14. The depth of the basin is determined from the description given below, and typically the basin might be 15. ^' 24 c to 30.48 cm in depth. The area and shape of the basin should be substantially the same as the area an shape of the exposed tennis court surface 16, and the walls of the excavation are preferably vertical. It is extremely important that the floor 18 of the basin be level with variations across the width o the basin not exceeding 2.54 cm. This degree of

accuraσy is desirable to permit substantially all of the water to be drained from the structure if desired.

In the preferred embodiment, a watertight membrane 20 is laid down on the exposed floor and walls of the basin so as to form a watertight and water- containing liner for the basin. In the preferred embodiment, the watertight membrane 20 consists of a sheet of heavy gauge plastic of a type commonly used for providing moisture barriers in construction work. In an alternative embodiment, the watertight membrane is a sheet of tar paper. In another embodiment, the basin may be rendered watertight by the application of a coating that cures to form a watertight liner. At some location on the perimeter of the tennis court, an excavation is made for a reservoir 22.

Typically, the reservoir, as seen from above, may have an area of no more than one square meter. It is not necessary that the reservoir extend along the entire length of one of the sides of the tennis court. The reservoir 22 serves to contain the apparatus that is used to regulate the depth of the artificial water table.

As shown in Figure 1, in a preferred embodiment the reservoir includes a floor 24 and walls 26, 28. A baffle 30 extends across the interior of the reservoir to set off a portion of it. That portion debouches into a sewer pipe or drain 32. Further description of the reservoir and the apparatus associated with it will be given below. Returning now to the structure underlying the surface 16 of the tennis court, in the preferred embodi¬ ment, a ballast layer 34 is laid down upon the water¬ tight membrane 20. In the preferred embodiment, the ballast layer consists of a myriad of rocks that are

approximately the same size. The exact size of the rocks is immaterial as long as they are all of appro mately the same size so that the voids between the rocks remain open to permit water to move freely through the layer. In the preferred embodiment, the size of the rocks is in the range of 1.27 cm to 2.54

In an alternative embodiment, the rocks of the ballast layer 34 could be replaced by foraminous pip but these have the disadvantage of being more expens and also subject to breakage.

In a typical installation, the ballast layer is 7.62 cm to 17.78 cm thick. It is desirable that the top of the ballast layer be level, and in accordance with the method aspect of the present inv tion, this may be accomplished by partially filling the basin with water to a depth approximately equal to the depth of the ballast layer 34. When this has been done, high spots in the layer will extend above the exposed surface of the water, while low spots in the ballast layer will lie below the surface of the water. Once the high spots and low spots have been detected in this manner, the high spots can be raked down to the level of the surface of the water and the low spots can be filled in. Once the top of the ballast layer 34 has been made level, a permeable membrane 36 is laid on top o the ballast layer 34. The permeable membrane 36 is permeable to water, but prevents the overlying mater in the fine layer 38 from penetrating into the balla layer 34 and thereby clogging the voids in the balla layer through which the water is intended to move freely. In the preferred embodiment, the permeable membrane consists of a heavy durable fabric like denim. In alternative embodiments, the permeable

membrane may consist of a fine screen of plastic or metal.

A fine layer 38 is laid down on top of the permeable membrane 36. In the preferred embodiment, the fine layer consists of crushed volcanic ash, called scoria. In other embodiments, cinders or porous rock are used. The material of the fine layer is in the form of small particles, like sand, and the voids between the particles are extremely small so that water is rapidly dispersed through the fine layer 38. This rapid dispersion of water throughout the layer resembles the action of a blotter and is referred to herein as a "wicking action" .

It should be understood that the fine layer 38 maintains its thickness and load-bearing ability whether moist or dry.

The top of the fine layer 38 is leveled by increasing the water level in the basin until the water level is approximately equal to the elevation of the top of the fine layer. At this condition, the high spots and low spots in the fine layer can be identified, and the variations can be smoothed. Thereafter, the water level within the basin may be reduced. The final step in construction of the tennis court is to lay down a finish layer 40 on the top of the fine layer 38. The finish layer has the color and texture desired for the tennis court. In a pre¬ ferred embodiment of the invention, the finish layer consists of crushed granite or crushed basalt. After the finish layer 40 has been laid down, it may be leveled by once again raising the level of the artificial water table in the basin to a level approximately equal to the elevation of the exposed

surface 16 of the tennis court. Thereafter, the variations may be evened out to render the exposed surface 16 level and smooth.

Now that the construction of the installation has been described, the method and apparatus used for raising and lowering the depth of the artificial water table will now be explained. It must be remembered that the porous nature of the finish layer 40, the fin layer 38, the permeable membrane 36 and the ballast layer 34 permits rain or melting snow that falls upon the tennis court to enter the watertight basin defined by the watertight membrane 20. Normally, it is desirable to maintain the water talbe at a particular depth beneath the exposed surface 16. The wall 26 includes a passage 42 near the floor 24 of the reservoir which permits the reservoir to communicate with the basin defined by the water¬ tight membrane 20. As a result, the water level in the reservoir accurately indicates the level of the water table beneath the tennis court. An optimum level for this water table is maintained by the apparatus now to be described.

The incoming water line 44 includes a shutoff valve 47 that can be used if one chooses to drain the water from the basin. The incoming water line 44 also includes a manually operated fill valve 46 that permi the water table to be raised at will. A float valve 4 adds water to the reservoir 22 automatically when the water table falls below a preset level. If the level of the water table is at the desire preset level maintained by the float valve 48 and thereafter a heavy rainfall occurs, the water table will begin to rise. As the water table rises, it may eventually reach the sensor 50 that will close an

electrical circuit indicated by the wires 52 thereby starting the drain pump 54 that removes water from the reservoir 22 and deposits it in the drain pipe 32, thereby lowering the water table. Normally, the action of the float valve 48 and the drain pump 54 are adequate to maintain the water table between preset limits. These preset limits are chosen by selecting the height of the float portion 56 of the float valve 48 and by adjusting the height of the sensor 50. In this way, any desired water table level can be selected and automatically maintained.

On occasion it may be desirable to raise tem¬ porarily the water table. This may be done by unplugging the source of electrical power to the pump 54 and opening the fill valve 46. When it is desired to lower the water table again, the pump 54 is reconnected to its source of electrical power and the valve 46 ^' or the valve 47 is enclosed. The system of the present invnetion further includes protective features to guard against too high a level of the water table, as might happen if during a rain storm the electrical power for driving the pump 54 were to fail. The height of the baffle 30 is equal to the height of the maximum water table that is to be permitted. If a severe rainfall were to raise the water table above the height of the baffle 30, the water would then pour over the baffle 30 and be disposed of in the drain 32. ^" A switch 58 is provided for selectively con¬ necting under control of the user the wires 52 together, thereby overriding the action of the sensor 50 (which does the same thing) and thereby causing the pump 54 to operate. If simultaneously the shutoff

valve 47 is closed, all of the water can be removed from the installation.

Thus, there has been described a structure for producing an artificial water table, a method for constructing the structure and installation, and an apparatus and method for controlling both auto¬ matically and manually the level of the artificial water table.

Industrial Applicability Although the installation has been described as a tennis court for purposes of illustration, it must be remembered that the installation could equally wel be used for the growing of crops, either in fields or in a greenhouse or for the maintenance of a lawn. ^' The foregoing detailed description is illustrative of several embodiments of the invention, and it is to be understood that additional embodiment thereof will be obvious to those skilled in the art. The embodiments described herein together with those additional embodiments are considered to be within the scope of the invention.