BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a typical river basin illustrating a perimeter of an underground porosity reservoir for use with an embodiment of the present invention.
FIG. 2 is a section view of the porosity reservoir taken substantially along the line 2-2 in FIG. 1, illustrating the details of an extraction/recharge well and a bedding configuration for an air ventilation conduit.
FIG. 3 is a section view of the porosity reservoir taken substantially along the line 3-3 in FIG. 1, illustrating the details of a vertical air vent providing atmospheric air to the air ventilation conduits shown in FIG. 2.
DETAILED DESCRIPTION
FIG. 1 illustrates an exemplary underground reservoir system in accordance with the present invention. In particular, FIG. 1 illustrates a plan view of an exemplary river system or basin 20 comprising a riverbed 22 that flows along the top of alluvial deposits 24 (FIG. 2) formed within the boundary 26 of a floodplain that extends to either side of the current riverbed 22. An arrow 28 in FIG. 1 illustrates a direction of flow of the groundwater through the alluvial deposits 24. An underground porosity storage reservoir 30 is typically formed with a regular geometric boundary 32. FIG. 1 further illustrates the position of a plurality of extraction/recharge wells 40, air ventilation conduits 50, and air vents 60 within the porosity reservoir 30, as described in greater detail below. Additional details regarding the design, construction and technical aspects of underground reservoirs are disclosed within U.S. Pat. No. 6,840,710, incorporated by reference above.
FIG. 2 provides a section view of the underground reservoir 30 shown in FIG. 1 and illustrates that the reservoir is created by bounding a volume of alluvial deposits 24 with sidewalls 36 that follow the perimeter 32 shown in FIG. 1. The walls 36 are substantially water impermeable and are preferably vertical in orientation. In the embodiment shown, the walls 36 are bounded by an aquiclude 44 that extends below the floodplain boundary 26, although other materials and construction techniques may be used. The underground reservoir 30 encloses a volume of natural alluvium 24, and the water storage provided by the reservoir 30 is in the form of porosity storage within the pore spaces of the alluvial material (e.g., sand and gravel). Depending on the specific type of alluvial material, the usable water storage volume may range from 10% to 40% of the total enclosed volume of the reservoir 30. In an alternative embodiment, a different material, such as imported sand, gravel or recycled concrete, may be used in place of the natural alluvium 24.
In the embodiment shown in FIG. 2, a well 40 is utilized to withdraw the stored water from the porosity reservoir 30 during emptying operations. In another embodiment, the same well 40 may be utilized as a recharge well to help refill the porosity reservoir 30. In various embodiments one or more recharge wells may provide the sole means for filling the reservoir, while in other embodiments a series of surface features (e.g., recharge ditches or holding ponds) may be used in conjunction with (or instead of) the well 40 to provide top-down filling of the reservoir 30. Additionally, a French drain system buried near the topsoil-alluvial interface (as described in U.S. Pat. No. 6,840,710) may also be used to provide top-down gravity filling of the reservoir.
In order to alleviate the problems associated with entrapped air (i.e., during the filling of the porosity reservoir 30) and/or the formation of a vacuum within the reservoir (i.e., during extraction of water from the reservoir 30), the present invention provides for ventilating the pore spaces of the alluvial materials (e.g., to atmospheric pressure as described below). Ventilation of the porosity reservoir 30 provides pressure-relief during reservoir filling operations, and further provides a vacuum-break (i.e., allows for the introduction air within the pore spaces) as water is emptied from the reservoir 30.
In particular, one embodiment of the present invention utilizes one or more air ventilation conduits 50 (FIG. 1) that are arranged near the top of the alluvial material 24 within the porosity reservoir 30 (as shown in FIGS. 2 and 3). Each air ventilation conduit 50 preferably comprises a perforated pipe 52 (e.g., a PVC pipe) bedded within coarse gravel or a similar material. In one embodiment, each perforated pipe 52 is preferably wrapped in a geo-textile fabric to minimize the potential for clogging the pipe perforations. FIG. 2 illustrates that each pipe 52 is positioned within a trench 54 that is excavated through the topsoil layer 56 and into the uppermost region of the alluvial material 24. In one embodiment, a layer of the coarse bedding material 58 (e.g., gravel) is placed along the bottom of the trench 54, and the perforated pipe 52 is then positioned atop the bottom layer of bedding material 58. Additional bedding material 58 is then added to completely cover and surround the pipe 58. The remainder of the trench 54 is then preferably backfilled (e.g., with topsoil) as shown in FIG. 2.
While a perforated pipe 52 is illustrated as a preferred embodiment of air ventilation conduit 50 in FIG. 2, those skilled in the art will understand that alternative means for supplying an atmospheric interface at the appropriate depth within the reservoir (e.g., ditches or a series of vertical pipes) may be used in place of the perforated pipe 52. Thus, as noted below, the present invention is not limited to the use of perforated pipes 52 to ventilate an underground porosity storage reservoir.
In order to provide atmospheric pressure to each air ventilation conduit 50, one or more vertical air vents 60 are connected to each length of perforated pipe 52, as shown in FIG. 3. Each air vent 60 preferably comprises a non-perforated pipe (e.g., PVC pipe) having an interior volume and a first end that connects to the perforated pipe 52. A second end of the air vent 60 extends vertically through the topsoil layer 56 and terminates a predetermined distance above the top of the reservoir surface. A top end 62 of each air vent 60 is open to the atmosphere, and a conventional screen/deflection structure 64 is utilized to prevent precipitation, small animals, insects or other contaminants from entering the air vent 60. In the event that the air ventilation conduit 50 comprises means other than a perforated pipe 52, the air vent 60 similarly provides a path between such alternate means 50 and atmospheric air above the surface of the reservoir.
By connecting one end of the air vent 60 to a conduit 50, the interior volume of the air vent communicates with the interior volume of the conduit 50 (e.g., the perforated pipe 52). The air vents 60 thus provide atmospheric air to the air ventilation conduits 50, which in turn allow air to move into and out of the porosity reservoir 30. That is, the conduits 50 and air vents 60 provide a path for air to travel to and from the pore spaces of the alluvial material 24 during reservoir filling and emptying operations. Specifically, during a reservoir recharge operation, water typically travels downward through the pore spaces of the alluvial material 24 and forces entrapped air upward toward the top of the reservoir 30. This entrapped air enters the conduits 50 (e.g., through the perforations in the pipes 52) and travels along the conduit 50 until it exits the reservoir 30 through a vertical air vent 60. Similarly, during an extraction operation, a partial vacuum would normally be formed as water is removed from the pore spaces of the reservoir 30. The presence of atmospheric air within the conduits 50 allows air to travel downward through the pore spaces of the alluvial material 24 to take the place of the newly evacuated water and thereby prevent the formation of vacuum.
Thus, the provision of the air ventilation conduits 50 and vertical air vents 60 provide both a pressure-relief mechanism and a vacuum-break during recharge and extraction operations, respectively, within the porosity reservoir 30. In one embodiment, the position of the ventilation conduits 50 is selected so that a perforated pipe 52 runs adjacent to each well 40 to maximize both the vacuum-break and pressure-relief benefits of the present invention.
While FIGS. 1-3 illustrate one embodiment of the ventilation system of the present invention, those skilled in the art will recognize that alternative materials and configurations may be used to ventilate the porosity reservoir 30. For example, the precise depth of the air ventilation conduits 50 within the reservoir 30 may be varied to both ensure that the perforated pipes 52 are neither positioned too deep (i.e., to prevent the pipes from being flooded with water when the porosity reservoir 30 is at maximum capacity) nor too shallow (i.e., to ensure that the pipes 52 are surrounded by the porous alluvial material 24 as opposed to the substantially air-impermeable topsoil layer 56).
Additionally, while FIG. 1 shows an exemplary configuration of the extraction/recharge wells 40, air ventilation conduits 50, and vertical air vents 60, the present invention is not limited to any particular number or arrangement of these elements. Indeed, alternative embodiments of the present invention may connect each of the conduits 50 to take advantage of centrally located air vents 60 (i.e., reduce the overall number of vents). These vents could be located in designated areas where accidental damage is less likely, or where the appearance of the vents will not affect the overall aesthetic of the surface area above the porosity reservoir. In one embodiment, the vents 60 may be located in a building or “decoy structure” that further protects the vent from damage, insects and other contaminants. Alternatively, instead of comprising separate conduits attached to perforated pipes 52, the air vents 60 may comprise a non-perforated end of the perforated pipe 52 that is turned upward to extend above the surface level of the reservoir. As a further alternative, the ventilation conduit 50 and air vent 60 may be combined into a single pipeline having a lower portion (conduit 50) that extends into the alluvial deposits, and an upper portion (air vent 60) that extends above the top surface of the porosity reservoir 30. In this manner, the ventilation conduit 50 need only define at least one opening (e.g., at the end of the conduit) in lieu of a number of perforations extending along a length of the conduit.
It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. Thus, the various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. Those skilled in the art will readily recognize various modifications and changes that may be made to the present invention without departing from the true spirit and scope of the present invention, which is set forth in the following claims.
Patent Application
20080073087
