Abstract:
Natural soils and underlying bedrock typical of channel banks near a river and floodplain system are utilized to improve the economics and efficiency of constructing an underground porosity storage reservoir. A man-made barrier, typically a slurry wall, is keyed into these banks and forms a first portion of a closed boundary for the reservoir. The channel banks between the two ends of the slurry wall form a substantially impermeable natural barrier defining a second portion of the closed boundary for the reservoir, thereby reducing the construction costs on sites appropriate for such a design. Locating the bank-sided porosity storage reservoir over naturally occurring scour regions in the bedrock can greatly increase the storage capacity. By building an embankment and extending the slurry walls higher, an open water storage area can be created on top of the reservoir that is bounded by the elevated slurry wall and the channel bank.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/906,848 filed on Mar. 14, 2007 titled “POROSITY STORAGE RESERVOIRS UTILIZING FLOODPLAIN BANKS FOR PARTIAL ENCLOSURE” which is incorporated herein by reference in its entirety for all that is taught and disclosed therein. 
     
    
     BACKGROUND 
       [0002]    Technical Field—The invention relates generally to storing water in underground reservoirs and, more particularly, to a method for storing an isolated supply of water in the voids found in numerous alluvial deposits. 
         [0003]    It is becoming increasingly difficult, both in terms of cost and availability, to construct conventional open reservoirs for the storage of water. Such reservoirs typically require the construction of a dam across a river, thereby flooding vast expanses of land upstream of the dam while severely curtailing the flow of water downstream from the dam. In light of the increasing value of water and the complexities of the various water laws across different jurisdictions, it is becoming prohibitively difficult to form an open reservoir in this manner. Open reservoirs may also be formed by first mining a large gravel pit and then filling the pit with water, provided that the reservoir is properly lined to isolate the privately owned water from potential commingling with the public domain water in the same general alluvial deposit. Previously, such open reservoirs could be formed by purchasing the rights to abandoned gravel quarries. However, due to the current high demand for water storage, such storage areas created by mining activity are insufficient to keep pace with society&#39;s needs. While it is possible to excavate a large pit for the specific purpose of forming an open water reservoir, such a technique requires a great expense of time and money to purchase the land, form the pit and dispose of the excavated material and soil, assuming that the excavated materials have no intrinsic economic value. 
         [0004]    One major disadvantage to open reservoirs is that they preempt any current or future use of the land other than to store water. That is, as additional land surface is devoted to the storage of water in open reservoirs that same land surface is unavailable for alternative uses such as farming or open space. A further disadvantage of storing water in open reservoirs is the high degree of evaporative losses experienced by such reservoirs due to the relatively large air/water interface. Specifically, in arid climates (such as those found in the Western United States) open reservoirs are subject to extremely large evaporative losses. 
         [0005]    A further unfortunate disadvantage to open reservoirs is that the reservoirs are highly susceptible to contamination. While previous concerns have been limited to accidental chemical spills, petroleum leaks, polluted surface-water runoff, and the like, a more immediate threat is that of intentional contamination as part of a terrorist act. Most municipal water reservoirs comprise unfenced bodies of waters in remote areas and are extremely difficult if not impossible to guard. Furthermore, the construction of fences around existing reservoirs would be expensive and time consuming, the fence could be easily breached and thus does not guarantee safety, and even if the fence is not breached, the open reservoirs would be susceptible to contamination from the air. 
         [0006]    One proposed solution to the above-described disadvantages of open reservoirs is the construction of underground reservoirs where water is stored in the voids or interstices found in alluvial deposits. One such method is described in U.S. Pat. No. 4,326,818, issued to Willis and titled “Techniques for the Storage of Water.” The Willis patent describes forming an enclosed flexible wall extending vertically downward toward a natural aquiclude or stone base that is impermeable to water. The wall is formed by a grouting process where a grout pipe is first inserted through the soil until the pipe reaches the aquiclude and is then withdrawn while a grout material is injected under pressure from the end of the pipe. The grout material moves away from the injection zone and fills the pores of the formation where it hardens to form a grout “column.” This process is repeated numerous times to form a closed perimeter wall around a defined reservoir boundary. That is, adjacent grout columns are positioned so that there is little or no space between the columns. A second and third round of grout columns are then formed adjacent the first round of columns to form a wall that is said to be substantially impermeable to water. Conventional wells and feed lines are then constructed within the boundary of the grout wall to withdraw and supply water to the reservoir as needed. 
         [0007]    The specific reservoir described in the Willis patent suffers from a number of drawbacks. Initially, the grout wall construction technique described by Willis (i.e., pressure-grouting clay or other “flexibilized” materials and allowing the grout to “gel” into place) does not typically form uniform subsurface columns. Rather, the grout material disperses from the end of the grout pipe in an uneven and haphazard manner (i.e., permeating different radial distances away from the grout pipe) as the grout pipe is retracted toward the surface. The uneven nature of the grouting process tends to form vertical sand seams between the grouted columns at the outer boundary of the pressure injection. These sand “lenses” or areas of high permeability formed between adjacent grout “columns” result in grout walls that do not form substantially impermeable water barriers and that are susceptible to relatively high levels of water leakage or seepage. Additionally, it is not possible to key the grouted in-situ “columns” into the bedrock or other impermeable basement rock that defines a bottom surface of the underground reservoir. Rather, a small horizontal layer typically remains between the bottom ends of the various grout columns and the bedrock so that water may escape the underground reservoir through this gap between the wall and the bedrock, where the hydrostatic pressure is at its greatest level. Indeed, between the inability to form a solid impermeable wall using the grout technique, and the inability to firmly tie the grout columns to the bedrock defining the lower surface of the reservoir, the water leakage rates of a reservoir built according to the technique of the Willis patent would be prohibitively high. 
         [0008]    A further problem associated with the underground reservoir described in the Willis patent is that there is no recognition of the problems associated with the construction of the massive subsurface walls. Specifically, the installation of any subsurface wall on the scale of that required to form an underground reservoir tends to form a dam to the normal flow of groundwater so that water levels on the upstream or “high” side of the reservoir wall will tend be higher than historic average levels, while the opposite condition (i.e., lower than average water levels) will be found on the downstream or “low” side of the reservoir. Such artificial changes to the historic water table can have severe adverse impacts on neighbors in the region. For example, neighbors on the high side of a subsurface, or underground, reservoir may experience flooded basements, while neighbors on the low side will experience a dearth of water such that alluvial wells may run dry. 
         [0009]    Thus, while the Willis patent describes one design for an underground reservoir, the specifics of the Willis reservoir are not feasible due to the inability to form a water-tight reservoir. Additionally, the grout wall construction techniques described in the Willis patent are prohibitively expensive (costing $40-$200 per square foot of barrier), particularly when used on the scale required for an underground reservoir. Furthermore, the Willis patent does not account for the environmental impact that will be caused by the construction of the potentially massive subsurface walls. Thus, an improved underground reservoir and method for storing water is needed that will address the shortcomings of the Willis design. 
         [0010]    U.S. Pat. No. 6,840,710, issued to Peters et al. and titled “Underground Alluvial Water Storage Reservoir And Method” presents a marked improvement over the Willis design. Peters et al. describes underground porosity reservoirs that are constructed by totally enclosing a portion of an alluvial deposit with a substantially impermeable man-made barrier, such as such as slurry walls keyed into the underlying bedrock formation. However, the economic efficiency depends on the alluvial material enclosed and the amount of slurry wall needed for the enclosure. For alluvial deposits of uniform thickness, generally the larger reservoir sites have a higher enclosure efficiency ratio (the area enclosed by the slurry walls divided by the linear length of the slurry wall that defines the perimeter of the area enclosed) expressed as acres/mile. The two-dimensional enclosure efficiency is also affected by the aspect ratio (the length divided by the width) of the porosity reservoir perimeter. Porosity reservoir sites with approximately equal length sides (substantially square-shaped) are more efficient to enclose an area than are long and narrow sites (substantially rectangular-shaped) that require more slurry wall perimeter to enclose an area. It is with respect to these and other background considerations, limitations, and problems that the present invention is directed. 
       SUMMARY 
       [0011]    This Summary is provided to introduce in a simplified form a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
         [0012]    In accordance with the present invention, the above and other problems are solved by an underground porosity reservoir for storing water in alluvial deposits that is formed by a combination of: one or more segments of an underground substantially impermeable man-made barrier, such as a slurry wall, pilings, hangar wall, or any other suitable structure that can be keyed into the underlying bedrock formation and partially enclosing an area and extending from a surface level to an aquiclude (e.g., bedrock) beneath the reservoir so that a bottom surface of the slurry wall is keyed into the aquiclude; and keying the two ends of the slurry wall into the natural soils and/or bedrock typical of channel banks near a river and floodplain system where the channel bank between the two ends of the slurry wall form another segment of an underground naturally occurring substantially impermeable barrier. The man-made segments and the naturally occurring segments establish the boundaries of the underground porosity reservoir. The combination of the one or more segments of slurry wall extending from the surface downward and keyed into bedrock on its bottom surface with the two ends of the slurry wall keyed into the natural soils and/or bedrock of the channel bank, and the channel bank between the two ends of the slurry wall, together provide an underground substantially impermeable barrier for the underground porosity reservoir. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]      FIG. 1  shows a top view of an embodiment of a substantially square-shape bank-sided porosity storage reservoir of the present invention. 
           [0014]      FIG. 2  shows a cross section of the embodiment of the bank-sided porosity storage reservoir shown in  FIG. 1 . 
           [0015]      FIG. 3  shows a top view of an embodiment of a substantially rectangular-shaped bank-sided porosity storage reservoir of the present invention. 
           [0016]      FIG. 4  shows a cross section of an embodiment of a bank-sided porosity storage reservoir where the underlying bedrock is substantially flat or slopes away from a riverbed. 
           [0017]      FIG. 5  shows a top view of an embodiment of an oval-shaped bank-sided porosity storage reservoir with multiple man-made and natural segments of the present invention. 
           [0018]      FIG. 6  shows a top view of an irregularly-shaped bank-sided porosity storage reservoir of the present invention shown with bedrock depth contours. 
           [0019]      FIG. 7  shows a cross section of the embodiment of the irregularly-shaped bank-sided porosity storage reservoir shown in  FIG. 6 . 
           [0020]      FIG. 8  shows a cross section of an embodiment of a bank-sided porosity storage reservoir in combination with an open reservoir. 
           [0021]      FIG. 9  shows a top view of a bank-sided porosity storage reservoir in combination with an open reservoir shown in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring now to the Figures, in which like reference numerals and names refer to structurally and/or functionally similar elements thereof,  FIG. 1  shows a top view of an embodiment of a substantially square-shape bank-sided porosity storage reservoir of the present invention, and  FIG. 2  shows a cross section of the same bank-sided porosity storage reservoir. Referring now to  FIGS. 1 and 2 , an exemplary river system or Basin  10  comprising a Riverbed  11  that flows along the top of Alluvial Deposits  23  (e.g., sand and gravel) formed within the Floodplain Limits  15  of a floodplain that extends to either side of the Riverbed  11 . An underground Bank-Sided Porosity Reservoir  14  is preferably formed on three sides with a Substantially Impermeable SIMM Barrier  18  (hereinafter referred to as SIMM Barrier  18 ), such as a slurry wall, and bounded on a fourth side by utilizing the Native Soil  26 , Bedrock  22 , and Topsoil  27 , sometimes delineated by a Bedrock Scour Line  19  below Native Soil  26  and Topsoil  27 , that may be located approximate to Floodplain Limits  15 . Usually, the perimeter of Bank-Sided Porosity Reservoir  14  delineated by SIMM Barrier  18  and Bedrock Scour Line  19  are contained within the bounds of one or more property lines where rights to the water and water storage rights have been obtained. 
         [0023]    Basin  10  is seen in cross-section along line  1 A- 1 A′ in  FIG. 2 , showing Riverbed  11  and the lateral and vertical limits of Bank-Sided Porosity Reservoir  14 .  FIG. 2  further illustrates that the Bank-Sided Porosity Reservoir  14  is preferably formed by a SIMM Barrier  18  that is keyed into Bedrock  22  or a similar aquiclude where SIMM Barrier  18  extends into Bedrock  22  below the boundary between Alluvial Deposits  23  and Bedrock  22 , forming a substantial seal that prevents water migration from within Bank-Sided Porosity Reservoir  14  to the surrounding soils. It can be seen in  FIG. 2  that Bedrock  22  and the overlying Native Soil  26  and Topsoil  27  rise in elevation relative to Riverbed  11 . Bedrock Scour Line  19  was formed thousands of years ago when the river flowed along a different course, scouring Bedrock  22  to form Bedrock Scour Line  19 . By keying the two ends of SIMM Barrier  18  into Bedrock  22  and through Native Soil  26  and Topsoil  27 , water trapped inside Bank-Sided Porosity Reservoir  14  cannot rise high enough in elevation to migrate around the two ends of SIMM Barrier  18  or over/through Bedrock Scour Line  19 . 
         [0024]    Initially, it is noted that SIMM Barrier  18  may be formed in a variety of manners and JO with a variety of materials. One construction technique forms a slurry wall with a trenching technique that involves excavating a narrow trench that is immediately and concurrently filled with a fluid “slurry” that exerts hydraulic pressure against the trench walls to prevent the trench from collapsing as it is formed. While different materials may be used to form the slurry, bentonite clay mixed with water is a very good slurry for use in constructing SIMM Barrier  18 . This is because the bentonite tends to coat the walls of the trench, thereby preventing the water from being absorbed through the trench walls during and after the formation of SIMM Barrier  18 . Additionally, the bentonite coating helps to enhance (i.e., reduce) the final permeability of SIMM Barrier  18 . 
         [0025]    Slurry wall trenches may be several feet wide and can be dug in excess of 100 feet deep with the use of specialized excavation equipment. Shallower trenches may be formed with conventional backhoes. It is important to remember that the trench must extend down so that it is “keyed” into Bedrock  22  or other confining layer (such as clay) that lies below Alluvial Deposits  23 . In one embodiment, the trench is keyed at least three feet deep into Bedrock  22 . In other embodiments, key depths of four or five feet or more may be required. The slurry-filled trench is then backfilled with a mixture of the previously excavated topsoil and alluvial material, mixed with additional quantities of bentonite. That is, the soil-bentonite mixture is used to fill the open trench where the mixture displaces the water-bentonite slurry and hardens to form the final SIMM Barrier  18 . Care must be taken with this technique to ensure an even backfill and avoid the presence of any voids in the wall or the collapse of any of the untreated soil back into the trench, either of which can form “windows” of relatively high permeability within the wall. With a carefully controlled backfill, soil-bentonite slurry walls having average permeability rates on the order of 1×10 −6  centimeters/sec (“cm/sec”) are obtainable, although permeability rates as low as 1×10 −8  cm/sec may also be obtained with a proper soil-bentonite mixture. 
         [0026]    An alternative construction technique is to use a single-step excavation and in situ mixing process where the bentonite-water slurry is mixed with Portland cement so that the slurry itself hardens to form a “cement-bentonite” SIMM Barrier  18 . While a cement-bentonite slurry wall is formed more quickly than the two-step (backfill) soil-bentonite slurry wall, such one-step walls typically have slightly higher permeability levels (on the order of 1×10 −5  cm/see). However, the permeability of both the soil-bentonite and the cement-bentonite slurry walls may be improved by adding liners or membranes during the trenching process and prior to forming the hardened SWIM Barrier  18 . These liners or membranes may be high density polyethylene or polyvinyl chloride sheets that are added to the slurry-filled trench either prior to the backfill step of the two-step soil-bentonite slurry wall process, or prior to the hardening of the cement-bentonite wall in the one-step cement-bentonite process. The addition of such liners or membranes further enhances the substantially impermeable nature of the slurry walls where necessary to prevent leakage. 
         [0027]    Generally, a plurality of water extraction/recharge means are distributed about the interior area of the underground porosity reservoir to provide for rapid and substantially even filling and draining. A plurality of wells may be distributed about the underground reservoir, each well connected to a pump to direct water under pressure through the plurality of wells and into the alluvial deposits of the underground reservoir. Alternatively, a series of perforated pipes may be buried at a predetermined depth within the underground reservoir so that the perforated pipes are connected to a central pressurized well that is operated to recharge and extract water from the alluvial deposits through the perforated pipes. Such filling and draining systems are disclosed in the Peters et al. patent. 
         [0028]      FIG. 3  shows a top view of an embodiment of a substantially rectangular-shaped bank-sided porosity storage reservoir of the present invention. Referring now to  FIG. 3 , river system or Basin  30  comprises a Riverbed  31  that flows along the top of alluvial deposits (e.g., sand and gravel) formed within the Floodplain Limits  35  of a floodplain that extends to either side of Riverbed  31 . An underground Bank-Sided Porosity Reservoir  34  is preferably formed on three sides with a Substantially Impermeable Man-Made Barrier  38  (hereinafter referred to as SIMM Barrier  38 ), such as a slurry wall, and bounded on a fourth side by utilizing native soil, bedrock, and topsoil. In this instance, SIMM Barrier  38  has two substantially straight short end portions, and the middle portion is fairly long in comparison to the two short end portions, and is irregular in shape as viewed from above. By keying the two ends of SIMM Barrier  38  into the underlying topsoil, native soil, and bedrock, water trapped inside Bank-Sided Porosity Reservoir  34  cannot migrate around the two ends of SIMM Barrier  38 . 
         [0029]    For alluvial deposits of uniform thickness, generally the larger reservoir sites have a higher enclosure efficiency ratio (the area enclosed by the slurry walls divided by the linear perimeter length of the slurry walls), usually expressed as acres/mile. This two-dimensional enclosure efficiency is also affected by the aspect ratio (length to width) of the reservoir boundaries. Reservoir sites with approximately equal length sides are more efficient to enclose a volume than are long and narrow sites that require more linear slurry wall perimeter to enclose a given volume for a porosity reservoir. 
         [0030]    Table 1 below indicates the improved enclosure efficiencies provided with a bank-sided reservoir, for both smaller reservoir sites and ones with poor aspect ratios. This improvement with bank-sided reservoirs is important since most properties suitable for underground porosity reservoirs are typically longer than they are wide, since the length of the river valley is usually much longer than the floodplain is wide. Thus, a bank-sided reservoir not only increases the efficiency of a normally efficient square property (aspect ratio of 1:1), but it improves the efficiency of “long” parcels (aspect ratios of 4:1) to actually equal the improved enclosure efficiency of square bank-sided reservoir sites. Uniform thicknesses of alluvial deposits are assumed in these calculations. It should be noted that the widths of the slurry walls with keys into the natural soils/bedrock and the width of the reservoir are not the same, but they are typically approximately equal due to the scale. For example, a 1,000 foot wide reservoir may have a side key width of 50 feet. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Aspect 
                 Four-Sided 
                 Bank-Sided 
               
               
                 Property Description 
                 Acres 
                 Width 
                 Length 
                 Ratio 
                 Acres/Mile 
                 Acres/Mile 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Square, Quarter Section 
                 160 
                 ½ 
                 Mile 
                 ½ 
                 Mile 
                 1:1 
                 80 
                 107 
               
               
                 Long, Quarter Section 
                 160 
                 ¼ 
                 Mile 
                 1 
                 Mile 
                 4:1 
                 64 
                 107 
               
               
                 Half Section 
                 320 
                 ½ 
                 Mile 
                 1 
                 Mile 
                 2:1 
                 107 
                 160 
               
               
                 Square Section 
                 640 
                 1 
                 Mile 
                 1 
                 Mile 
                 1:1 
                 160 
                 213 
               
               
                 Long Section 
                 640 
                 ½ 
                 Mile 
                 2 
                 Miles 
                 4:1 
                 128 
                 213 
               
               
                 Square, Four Sections 
                 2560 
                 2 
                 Miles 
                 2 
                 Miles 
                 1:1 
                 320 
                 427 
               
               
                 Long, Four Sections 
                 2560 
                 1 
                 Miles 
                 4 
                 Miles 
                 4:1 
                 256 
                 427 
               
               
                   
               
             
          
         
       
     
         [0031]    For example, for a four-sided reservoir covering a long quarter section, the perimeter of the slurry walls is ¼+1+  1 / 4 + 1  which equals 2.5 miles. The acres/mile is then derived from the area, 160 acres, divided by the perimeter length, 2.5 miles, yielding 64 acres/mile. For a long quarter section bank-sided porosity reservoir, the perimeter length of the slurry walls is ¼+1+¼ which equals 1.5 miles. The acres/mile is then calculated by dividing the area, 160 acres, by 1.5 miles, yielding 107 acres/mile. It can be seen for all property descriptions, square or rectangular, and with aspect ratios ranging from 1:1 up to 4:1, a bank-sided porosity reservoir is more efficient than any four-sided porosity reservoir due to the increased acres/mile. 
         [0032]    In comparing economic efficiencies of one reservoir site and size to another, the thickness of the alluvial deposit compared to the depth of slurry wall must also be considered. The slurry wall needs to be constructed through native over-burden materials as well as keyed into the underlying bedrock formation. However, slurry walls constructed in these materials is more of an overhead cost to the reservoir. Hence depth efficiency (the depth of alluvium compared to the total depth of slurry wall) is greater with deeper alluvial deposits and/or shallower overburden material, given a required key depth. Hence, a final three dimensional enclosure efficiency can be evaluated as the product of the two-dimensional enclosure efficiency with the depth efficiency. 
         [0033]    As an example, consider a typical or “normal” alluvial deposit of five feet of overburden and top soil, forty feet of alluvial sand and gravel, and a required bedrock key depth of five feet. This site has a depth efficiency of 80% (forty feet of alluvium divided by fifty feet total depth of slurry wall). Compare that to a different “shallow” site with only half the alluvial thickness, or twenty feet and the same five feet of overburden and the same key depth of five feet. This site has a depth efficiency of 67% (twenty feet of alluvium divided by thirty feet total depth of slurry wall). Assuming a “long, quarter section” property in a “normal” depth area and 20% net porosity (which means that only 20% of the volume can store and drain water), a four-sided enclosed porosity reservoir would require 516 square feet of slurry wall to produce one acre-foot of water storage. This is calculated as follows: The perimeter length of the slurry wall from the example above is 2.5 miles, which equals 13,200 linear feet of slurry wall. 13,200 linear feet of slurry wall times a slurry wall depth of fifty feet equals 660,000 square feet of slurry wall. Forty feet of alluvium at 20% porosity equals an equivalent of eight vertical feet of water storage. Eight feet multiplied by 160 acres equals 1,280 acre-feet of water storage. 660,000 square feet of slurry wall divided by 1,280 acre-feet of water storage equals 516 square feet of slurry wall per acre-foot of water storage. 
         [0034]    If the deposit was “shallow” having twenty feet of alluvial material, 619 square feet of slurry wall would be required, calculated as follows: 13,200 feet times a slurry wall depth of thirty feet equals 396,000 square feet of slurry wall. Twenty feet of alluvium at 20% porosity equals an equivalent of four vertical feet of water storage. Four feet multiplied by 160 acres equals 640 acre-feet of water storage. 396,000 square feet of slurry wall divided by 640 acre-feet of water storage equals 619 square feet of slurry wall per acre-foot of water storage. For these same property dimensions and thicknesses, a bank-sided porosity reservoir design would only require 309 square feet and 371 square feet of slurry wall per acre-foot of water storage respectively. Hence, the bank-sided reservoir design even overcomes the depth efficiency disadvantages of “shallow” alluvial deposits. These efficiency ratios easily convert to the cost of slurry walls per acre-foot once the cost per square foot is known. 
         [0035]    Alternately, the three dimensional efficiency of a porosity storage reservoir can be described one-dimensionally as the ratio of volume of water stored (in cubic feet) to the area (square feet) of man-made barrier constructed to effect proper isolation and containment. With the same quarter section of and enclosed by both square and long reservoir configurations, with both normal and shallow alluvial depths as described in the example above, the efficiency of bank-sided porosity reservoirs is 33% to 67% more efficient than four-sided reservoirs, as shown in TABLE 2 below: 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Property 
                   
                 Four-Sided, 
                 Bank-Sided, 
                 % In- 
               
               
                 Description 
                 Depth 
                 Feet 
                 Feet 
                 crease 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Square (1:1) 
                 Normal (40 feet) 
                 106 
                 141 
                 33% 
               
               
                 Long (4:1) 
                 Normal (40 feet) 
                 85 
                 141 
                 67% 
               
               
                 Square (1:1) 
                 Shallow (20 feet) 
                 88 
                 117 
                 33% 
               
               
                 Long (4:1) 
                 Shallow (20 feet) 
                 70 
                 117 
                 67% 
               
               
                   
               
             
          
         
       
     
         [0036]    For a long property with normal depth (40 feet of alluvium) the calculation for a four-sided porosity reservoir is as follows: An acre-foot is defined by the volume of one acre of surface area to a depth of one foot. Since the area of one acre is defined as 66 by 660 feet (a chain by a furlong) then the volume of an acre-foot is exactly 43,560 cubic feet. Eight vertical feet of storage multiplied by 160 acres multiplied by 43,560 cubic feet, then divided by 660,000 square feet equals 85 feet. For the same property the calculation for a bank-sided porosity reservoir is as follows: eight feet multiplied by 160 acres multiplied by 43,560 cubic feet, then divided by 396,000 square feet equals 141 feet. 
         [0037]    If the square configuration porosity reservoir with normal depths is considered as the baseline of the best efficiency (106 feet) for four-sided porosity storage reservoirs, (with long configurations and/or shallow alluvial deposits decreasing efficiency of enclosure to 70% to 90%), Table 2 above illustrates that bank-sided reservoirs can significantly increase the one-dimensional enclosure efficiency over four-sided porosity reservoirs. This improvement is especially important considering the aspect ratio of most alluvial river valleys tends to be rather long, making normally-efficiently square-configured reservoir sites difficult to come by on a large scale. 
         [0038]      FIG. 4  shows a cross section of an embodiment of a bank-sided porosity storage reservoir where the underlying bedrock is substantially flat or slopes away from a riverbed. Referring now to  FIG. 4 , Basin  40  is seen in cross-section, showing Riverbed  41  and the lateral and vertical limits of Bank-Sided Porosity Reservoir  44 .  FIG. 4  further illustrates that the Bank-Sided Porosity Reservoir  44  is preferably formed by a Substantially Impermeable Man-Made Barrier  48  (hereinafter referred to as SIMM Barrier  48 ) that is keyed into Bedrock  42  or a similar aquiclude where SIMM Barrier  48  extends into Bedrock  42  below the boundary between Alluvial Deposits  43  and Bedrock  42 , forming a substantial seal that prevents water migration from within Bank-Sided Porosity Reservoir  44  to the surrounding soils. It can be seen in  FIG. 4  that Bedrock  42  falls in elevation and the overlying Native Soil  46  and Topsoil  47  stays level or rises in elevation relative to Riverbed  41 . In this situation, the two ends of SIMM Barrier  48  are keyed into Bedrock  42  and through Native Soil  46  and Topsoil  47  at a distance that takes into account the permeability of Native Soil  46  such that water trapped inside Bank-Sided Porosity Reservoir  44  will not move laterally in significant amounts and then migrate around the two ends of SIMM Barrier  48 . The distance that two ends of SIMM Barrier  48  are extended may be primarily determined by a cost/benefit ratio of the amount that the percent of water migration around the two ends of SIMM Barrier  48  is reduced compared to the costs of extending the two ends of SIMM Barrier  48 . It may not be cost effective to achieve zero percent migration, where migration may be fixed at say five percent for a nominal linear extension of the two ends of SIMM Barrier  48 . 
         [0039]      FIG. 5  shows a top view of an embodiment of an oval-shaped bank-sided porosity storage reservoir with multiple man-made and natural segments of the present invention. Referring now to  FIG. 5 , Basin  50  comprises a Riverbed  51  that flows along the top of alluvial deposits (e.g., sand and gravel) formed within the Floodplain Limits  55  of a floodplain that extends to either side of the Riverbed  51 . An underground Bank-Sided Porosity Reservoir  54  is preferably formed on a first side with a Substantially Impermeable Man-Made Barrier  58  (hereinafter referred to as SIMM Barrier  58 ), such as a slurry wall formed in the shape of an oval or an arc, and bounded on a second side by utilizing the native soil, bedrock, and topsoil, sometimes delineated by a Bedrock Scour Line  59  below the native soil and topsoil, that may be located approximate to Floodplain Limits  55 . In this example, Bedrock Scour Line  59  falls in elevation between the first and second ends of SIMM Barrier  58 , and thus, would not provide the consistent substantially impermeability needed to trap water within the bounds of Bank-Sided Porosity Reservoir  54 . In this situation, an additional Substantially Impermeable Man-Made Barrier  58 ′ (hereinafter referred to as SIMM Barrier  58 ′) is constructed in the gap. The first and second ends of SIMM Barrier  58 ′ are keyed into the topsoil, native soil, and down to the bedrock level. The bottom surface of SIMM Barrier  58 ′ is also keyed into the bedrock as described above. One skilled in the art will recognize that in certain basin areas, bank-sided porosity storage reservoirs may be multi-segmented, having one or more substantially impermeable man-made barriers connecting with one or more natural substantially impermeable barriers in order to encompass the underground alluvial deposit of interest. 
         [0040]    Usually, the perimeter of Bank-Sided Porosity Reservoir  54  delineated by SIMM Barrier  58  and Bedrock Scour Line  59  are contained within the bounds of one or more property lines where rights to the water and water storage rights have been obtained. One skilled in the art will thus recognize that the substantially impermeable man-made barrier may be formed in a number of shapes, including arcs, ovals, irregularly shaped, one-sided, two-sided, three-sided, and up to n-sided depending upon the topography and property boundaries and other site-specific considerations. 
         [0041]      FIG. 6  shows a top view of an irregularly-shaped bank-sided porosity storage reservoir of the present invention shown with bedrock depth contours, and  FIG. 7  shows a cross section of the same embodiment of the bank-sided porosity storage reservoir. Referring now to  FIGS. 6 and 7 , Basin  60  comprises a Riverbed  61  that flows along the top of Alluvial Deposits  73  (e.g., sand and gravel) formed within a floodplain that extends to either side of the Riverbed  61 . An underground Bank-Sided Porosity Reservoir  64  is preferably formed on a first side with a Substantially Impermeable Man-Made Barrier  68  (hereinafter referred to as SIMM Barrier  68 ), such as a slurry wall formed in an irregular shape, and bounded on a second side by utilizing the Native Soil  66  and Bedrock  72 . 
         [0042]    Basin  60  is seen in cross-section along line  6 A- 6 A′ in  FIG. 7 . Bank-Sided Porosity Reservoir  64  capitalizes on a Scour Region  700  formed by the river path thousands of years ago, where the flow of the river scoured out a depression in Bedrock  72 . Various Contour Lines are shown in  FIG. 6 , indicating the depth below the surface of Alluvial Deposits  73  that the upper surface of Bedrock  72  is located. Contour Line  602  shows that Bedrock  72  is at a depth of twenty feet. Contour Line  604  shows that Bedrock  72  is at a depth of forty feet. Contour Line  606  shows that Bedrock  72  is at a depth of sixty feet. Contour Line  608  shows that Bedrock  72  is at a depth of eighty feet. Greatly increased volumes of water storage are obtainable by taking advantage of such scour regions when they are presented. 
         [0043]      FIG. 8  shows a cross section of an embodiment of a bank-sided porosity storage reservoir in combination with an open reservoir.  FIG. 9  shows a top view of the bank-sided porosity storage reservoir in combination with an open reservoir shown in  FIG. 8 . Referring now to  FIGS. 8 and 9 , combinations of open water and underground porosity water storage are also possible with the bank-sided porosity reservoirs. Embankments constructed above the slurry wall permit traditional open water storage above the porosity storage reservoir. River system or Basin  90  comprises a Riverbed  81  that flows along the top of Alluvial Deposits  83  (e.g., sand and gravel) formed within the Floodplain Limits  95  of a floodplain that extends to either side of the Riverbed  81 . An underground Bank-Sided Porosity Reservoir  94  is preferably formed on a first side or segment with a Substantially Impermeable Man-Made Barrier  88  (hereinafter referred to as SIMM Barrier  88 ), such as a slurry wall, and bounded on a second side or segment by utilizing the floodplain banks comprised of Native Soil  86 , Topsoil  87 , and/or Bedrock  82 . Embankment  802  is formed on top of where SIMM Barrier  88  will be constructed. Material for Embankment  802  may come from utilizing Topsoil  87  and Alluvial Deposits  83  over the surface of Bank-Sided Porosity Reservoir  94 . Topsoil  87  is often excavated within the interior of SIMM Barrier  88 , and may also be utilized to build Embankment  802 . SIMM Barrier  88  is then constructed through Embankment  802  as well as Native Soil  86 , Topsoil  87 , and/or Bedrock  82 . When Topsoil  87  is removed from the top of Bank-Sided Porosity Reservoir  94 , Alluvial Deposits  83  are directly exposed to water injected into Open Water Storage  800 , greatly increasing the percolation rate of water into Alluvial Deposits  83 , which increases the ability to rapidly fill Bank-Sided Porosity Reservoir  94 , as well as increases the volume of open water storage possible. A layer of relatively impervious materials can also be layered on top of Alluvial Deposits  83  should the reservoir operator desire to manage Open Water Storage  800  separately from Bank-Sided Porosity Reservoir  94 . Long-term settlement build-up in Open Water Storage  800  of the combination reservoirs may be removed if needed, while the underlying Bank-Sided Porosity Reservoir  94  could continue in operation. Embankment  802  has Inside Toe Of Slope  804  under water (shown in dashed lines in  FIG. 9 ) and Outside Toe Of Slope  806 . The boundary between Embankment  802  and Open Water Storage  800  is Shoreline  808 . 
         [0044]    A Bank Liner  810  could also be installed along the inside face of Embankment  802  and along Flood Plain Bank  902  to retard lateral water migration of Open Water Storage  800 . Bank Liner  810  is typically covered with rock or bric-a-brac to secure it in place. On the Embankment  802  side, Bank Liner  810  would extend from Inside Toe Of Slope  804  to a short distance above Shoreline  808 . On the Flood Plain Bank  902  side, Bank Liner  810  would extend from Inside Toe Of Slope  812  to a short distance above Shoreline  808 . In an alternate embodiment, SIMM Barrier  88  would not extend through Embankment  802 . Instead, Embankment  802  would be constructed to the left of the position shown in  FIG. 8  so that Inside Toe Of Slope  804  of Embankment  802  coincides with the top of SIMM Barrier  88  at the juncture of Topsoil  87 /Alluvial Deposits  83 . Bank Liner  810  would be installed and extending from the top of SIMM Barrier  88  on the inside face of Embankment  802  to a short distance above Shoreline  808 . 
         [0045]    Basin  90  is seen in cross-section along line  9 A- 9 A in  FIG. 8 , showing Riverbed  81  and the lateral and vertical limits of Bank-Sided Porosity Reservoir  94 .  FIG. 8  further illustrates that the Bank-Sided Porosity Reservoir  14  is preferably formed by SIMM Barrier  88  that is keyed into Bedrock  82  or a similar aquiclude where SIMM Barrier  88  extends into Bedrock  82  below the boundary between Alluvial Deposits  83  and Bedrock  82 , forming a substantial seal that prevents water migration from within Bank-Sided Porosity Reservoir  94  to the surrounding soils. By keying the two ends of SIMM Barrier  88  into Bedrock  82  and through Native Soil  86  and into Floodplain Bank  902 , water trapped inside Bank-Sided Porosity Reservoir  94  cannot rise high enough in elevation to migrate around the two ends of SIMM Barrier  88 . Water contained within Open Water Storage  800  also cannot rise high enough in elevation to migrate around or over the two ends of SIMM Barrier  88  and over Floodplain Bank  902 . 
         [0046]    By varying the height of the Embankment  802  (increased at the lower elevation end of the site), the water storage on the property can be increased. In high-evaporative climates, the operator would typically use Open Water Storage  800  for shorter time periods, and maintaining Bank-Sided Porosity Reservoir  94  for long-term drought protection, since normal evaporative losses are avoided. As depicted in  FIG. 9 , surface water upstream could enter Open Water Storage  800  via Pipe(s)  904  (with control valves) which penetrate Embankment  802 , while passive outflows could occur via similar penetrating Pipe(s)  906  (with control valves). Elevated or submersible Well Structures  908  could be used to inject and extract stored water within Bank-Sided Porosity Reservoir  94  portion of the combination reservoir. 
         [0047]    Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. It will be understood by those skilled in the art that many changes in construction and widely differing embodiments and applications will suggest themselves without departing from the scope of the disclosed subject matter.