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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a regular application filed under 35 U.S.C. §111(a) claiming priority, under 35 U.S.C. §119(e)(1), of provisional application Ser. No. 61/175,582, previously filed May 5, 2009 under 35 U.S.C. §111(b). 
     
    
     BACKGROUND 
       [0002]    Flooding caused by melting snow and ice has become an unfortunate fact of life for populations along northern rivers. When the threat arises, the usual procedure is to emplace temporary dikes or levees to restrain the rising rivers from flooding valuable buildings. 
         [0003]    Four current solutions exist. One is to simply give up, and abandon sites subject to flooding. This is expensive and unpopular with the residents of these at-risk areas. 
         [0004]    Houses are sometimes built on stilts or pilings so that the valuable portions of the structure are at all times above the highest level of flooding. This solution leads to structures with very little esthetic appeal. The necessity of climbing stairs every time one enters the occupied space is also inconvenient. 
         [0005]    Another is to install permanent levees, which is extremely expensive. Permanent levees also destroy views of the river involved. When the river is within its banks, the view of the river is of course, an important amenity for selecting the site for the structure. 
         [0006]    A fourth solution is to install temporary dikes or levees comprising piles of sandbags. This solution requires filling these sandbags with sand and one by one, heaping them onto each other to form the levee. 
         [0007]    The process of filing the bags and then emplacing them to form the required dikes is extremely time-consuming, expensive, and labor intensive. People from hundreds of miles away are recruited to help with the sandbagging activities. The bags are heavy and huge numbers of them are required. For example, Fargo, N. Dak. used 350,000 sandbags to, as it turns out, successfully repel the 2009 flood on the Red River of the North. 
         [0008]    After the river recedes, all of the bags must be removed and emptied. The sandbags themselves are usually destroyed because drying them is more expensive than replacing them. 
         [0009]    A particularly harmful aspect of this process is the procession of heavy trucks carrying the sand from its source to the levee sites. These trucks travel over roads that are vulnerable to heavy loads and are normally subject to spring load restrictions. Often, the roads are damaged so badly as to require complete reconstruction. In addition, the process for handling the sand and sandbags requires much other heavy equipment. 
         [0010]    It is fair to say that all of these existing technical solutions are primitive and unsatisfactory. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0011]    A hollow block in the form of a rectangular parallelepiped can be joined with a plurality of similar blocks, all of which are then filled with water to form a flood barrier. The block has first through fourth sides, a top, and a bottom. The first and third sides have connection features that connect with features on the first and third sides of adjacent similar blocks to form a wall of connected blocks. The top and bottom of each of a plurality of said blocks has an inter-tier connection feature mating with one of the adjacent top and bottom of a similar block to allow stacking of a plurality of these blocks into tiers to form a flood barrier taller than the height of a single block. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a hollow block forming a container to connect to a plurality of similar blocks to form a flood barrier. 
           [0013]      FIG. 2  is a side elevation view of two containers in different tiers that shows one form of the connecting feature between two such blocks. 
           [0014]      FIG. 3  is an end elevation view of an improved temporary levee wall having as its components, a relatively small number of relatively large containers comprising integral or unitary blocks  11  filled with water. 
           [0015]      FIG. 4  is a top elevation view showing the relationship between the containers in a bottom tier and a tier immediately above it, for a portion of a levee wall. 
           [0016]      FIG. 5  is a top elevation view of a single block  11  with annotations and suggested dimensions. 
           [0017]      FIG. 6  shows a side elevation of a levee wall comprising the blocks of  FIG. 1  assembled on a sloping surface. 
           [0018]      FIG. 7  is a side elevation view of a number of blocks assembled to form a flood barrier with a nominal 75% overlap of blocks from one tier to the next. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    The invention here involves a fifth solution that has substantial cost and time advantages over every one of the other solutions. 
         [0020]      FIGS. 1-7  show one form of the invention.  FIG. 3  is an end view of an improved temporary levee wall or flood barrier  10  having as its components, a relatively small number of relatively large containers comprising integral or unitary blocks  11  filled with water. In  FIG. 3 , arrows from reference numbers indicate a number of components designated by that reference number. Reference numbers  12  and  16  respectively designate the dry and wet sides of levee wall  10 . 
         [0021]      FIG. 1  is a perspective view of a hollow block  11  forming such a container. Blocks  11  have connection features that bind or attach adjacent blocks  11  in a levee  10  to each other to maintain the structural integrity of the temporary levee  10 . 
         [0022]    Block  11  is in the general form of a parallelepiped having a substantially square footprint, although a rectangular footprint may also provide the necessary functionality. “Parallelepiped” in this context means a polyhedron consisting of six faces that are rectangular parallelograms. 
         [0023]    Block  11  has an upper wall or top  17  and a floor or bottom  18 . The lead line indicates an edge of floor  18 . Block  11  has sidewalls  12 A- 12 D intersecting edges of upper wall  17  and floor  18 . Only the upper edges of sidewalls  12 C and  12 D are visible in  FIG. 1 . 
         [0024]    Each sidewall  12 A- 12 D has a connection feature  14 ,  20 ,  13 , or  19  respectively and running between wall  17  and floor  18 . Each connection feature  14 ,  20 ,  13 , and  19  is arranged to interlock with a complementary connection feature carried on an adjacent sidewall of a block  11 . 
         [0025]    Connection features  14  and  20  comprise tenon projections of constant trapezoidal cross section. Connection features  13  and  19  comprise mortise grooves of constant trapezoidal cross section into which features  14  and  20  on adjacent blocks  11  slide to form a joint similar to that of a dovetail such as used in furniture manufacture. Features  14  and  20  should fit relatively loosely within features  13  and  19  so that a number of blocks  11  can be assembled into a levee wall  10  without binding. Other types of cross sections may provide similar results. 
         [0026]    Each block  11  has a filler hole  27  near one corner of the upper wall  17 . Sidewalls  12 B and  12 D near the intersections with floor  18  each have a drain plug  15 . Two drain plugs are preferable for reasons to be explained. 
         [0027]    Internally, each block  11  has stiffening walls  23  and  24  running between opposite sidewalls  12 A- 12 D and to the top and bottom of the block  11 . Opening  33  provides communication between the four chambers that stiffening walls  23  and  24  define so that water flowing into filler hole  27  distributes among all of the internal chambers. Bottom blocks  11  ( FIG. 3 , tier  10 A) in a levee wall  10  may bear as much as 8000-10000 lb., so resistance to crushing is important. 
         [0028]    The floor of each block  11  has at least one recess  30  that will align with a filler hole  27  when the block  11  is incorporated into a levee wall  10 . A pin  37  is sized to fit into both recess  30  and filler hole  27 . A flange  37  on pin  36  prevents pin  36  from falling into a block  11 . 
         [0029]      FIG. 5  is a top elevation view showing dimensions and construction details of an individual block  11 . The height of block  11  may be 2 ft. and the footprint is shown as 3 ft.×3 ft. A block  11  of these dimensions when filled with water will weigh slightly over 1000 lb. Unfilled, each block  11  will weigh 50 lb. or less, light enough for two people to lift and maneuver. 
         [0030]    The material properties of the plastic from which block  11  is made should include relative stiffness and resistance to cold weather deterioration. Note that each additional tier adds roughly 28 lb./in. 2  of compressive stress on the material comprising a block  11  having the 0.25 in. wall thicknesses shown. The block  11  material must be able to easily support such loads under what are often mechanically stressful conditions. 
         [0031]      FIG. 3  shows details of the structure of a levee wall  10  constructed on a ground surface  54 . Surface  48  shows the level of restrained water on the wet side  16  of levee wall  10 . For 2 ft. high blocks  11 , wall  10  as shown in  FIG. 3  is 14 ft. high. 
         [0032]    Wall  10  of  FIG. 3  has seven tiers  10 A- 10 G, although more or fewer tiers may be present. Each of the tiers  10 B- 10 G has one less row of blocks  11  than the tier on which it sits. Each of the tiers  10 B- 10 G overlaps one half of each of the two outside rows of blocks  11  in the tier on which it sits. (A row of blocks  11  extends perpendicular to the plane of  FIG. 3 . Tier  10 A has eight rows, for example.) 
         [0033]    To prevent seepage of water through a levee wall  10 , plastic sheeting  45  may lie along the wet side  16  of wall  10 . The top end of sheeting  45  may fit under the top tier  10 G. 
         [0034]    A pile of sandbags  51  lies on a part of the plastic sheeting  45  on surface  54  and extending away from levee wall  10 , and also against the wet side  16 , which provides support for sandbags  51 . This construction requires many fewer sandbags  51  for a given levee wall  10  height than does a levee wall comprising only sandbags. Sandbags  51  stabilize the base of levee wall  10  and reduce seepage of water under the base of levee wall  10 . 
         [0035]      FIG. 4  shows the relationship between the blocks  10  in tier  11 A and in tier  11 B for a portion of a levee wall  10 , and how a tier  11 A, etc. comprises a plurality of interconnected blocks  11  extending along both the length and width of a wall  10 . One sees the filler holes  27  in each of the blocks  11  forming tier  10 A. Dotted line squares  42  indicate the position that the blocks comprising tier  11 B occupy. The recess  30  of each block in tier  10 B vertically aligns with a filler hole  27  in a block in tier  10 A. A pin  37  ( FIG. 2 ) fits into the recess  30  of one block  11  and the filler hole  27  of the block beneath that recess  30 . Pins  37  collectively cooperate to maintain the position of each tier  10 B- 10 G with respect to the tier on which it rests. Pins  37  and filler holes  27  form cooperating inter-tier connection features on the bottoms and tops respectively of blocks  11  to connect the successive tiers  10 A, etc. of blocks  11 . 
         [0036]    It is likely that the outside blocks  11  of successive tiers  10 B- 10 G need not overlap by 50% as shown in  FIGS. 3 and 4  to provide sufficient mass to resist the pressure of water standing along a side of wall  10 . By properly sizing the depth of one row of blocks  11  along the length (as opposed to the depth) of each tier  10 B- 10 G, the overlap on the outside blocks  11  of the overlying tier can be increased to 67% or 75% for example. This will likely require special positioning of the inter-tier connection features as well. 
         [0037]    Increasing the overlap to 67% or 75% eliminates a number of unneeded interior blocks  11  for a given number of tiers  10 B- 10 G.  FIG. 7  shows a 75% overlap from tier  10 A′ to tier  10 B′. This increased overlap arises from a void  58  in tier  10 B′. Note that this design provides four tiers  10 A′- 10 D′ using only eight blocks  11  rather than 10 blocks  11  as shown for tiers  10 E- 10 H in  FIG. 3 . 
         [0038]    Overlaps of greater than 50% require differences in the positions of inter-tier connection features to align them in upper and lower adjacent tiers  10 A′- 10 D′. It is possible that efficiency will require that tops and bottoms of each block  11  have a number of sets of inter-tier connection features, but that only one set is used, depending on the tier  10 A′- 10 D′ in which the block  11  is used. For example,  FIG. 7  shows two features  62  in the nature of recesses  30  shown in  FIG. 4  in the bottom of each block  11 , and three features  64  in the top of each block  11 . Pins  37  fit in one feature  62  of one block  11  and an aligned feature  64  of another block  11 . 
         [0039]    Construction of a levee wall  11  may start at one end by positioning unfilled blocks  11  forming a portion of several rows for tier  11 A. Each block  11  of course must interlock with the adjacent blocks  11  to connect all of the blocks  11  in tier  10 A together. 
         [0040]    After a block  11  has been position in tier  10 A, it may be filled with water. As soon as several blocks  11  have been laid in the row of tier  10 A nearest to the side on which restrained water is expected, plastic sheeting  45  is positioned and sandbags  51  placed on the sheeting. After all of the rows forming tier  10 A have been started, then placement and filling of the blocks  11  forming tier  10 B can start. 
         [0041]    This process continues for as many tiers as are required. One can see that this process lends itself to a number of workers simultaneously constructing such a levee wall  10 . Some can be placing blocks  11 , while others handle filling of blocks  11  and placement of the sheeting  45  and sandbags  51 . 
         [0042]    The weight of upper tiers  10 F and  10 G for example, distort blocks in the lower tiers  10 A and  10 B for example, reducing gaps between individual blocks  11 . Such distortion further limits infiltration and leakage of water through wall  10 . 
         [0043]    Additional tiers can easily be added on the dry side of levee  10  should water level projections warrant. Workers can climb up the blocks  10  already emplaced to place the empty blocks  10 . Then as blocks  10  are placed, water is pumped into the placed blocks  10  through their filler holes  27 . 
         [0044]    Workers disassemble a wall  10  when water level  48  recedes by substantially reversing the wall  10  assembly steps. Workers remove individual drain plugs  15  from blocks  10  on the top tiers and then remove individual blocks  10  after draining ends. Two drain plugs  15  allow access to one or the other of drain plugs  15  in blocks  11  from either side of a tier  10 A- 10 G. If a drain plug  15  is not accessible on either side, then a wall  10  can be disassembled from only one side of each tier  10 A- 10 G. 
         [0045]    Blocks  10  can be stored outside if desirable awaiting another threatened flood. Both assembly and disassembly of a wall  10  is less labor intensive than a sandbag wall. 
         [0046]      FIG. 6  shows a wall  10 ′ having a construction suitable for use on a sloping surface  54 . Sandbags  51  level the surface  54  on which tier  10 A′ sits. 
         [0047]    Proper esthetic design of blocks  11  may allow their use as a permanent, inexpensive retaining wall. This is likely to be truer in more temperate climates where freezing is infrequent or nonexistent.

Summary:
A hollow block in the form of a rectangular parallelepiped when filled with water, is joined with a plurality of similar water-filled blocks to form a flood barrier. Two opposite sides of each block have connection features that connect with features on the first and third sides of adjacent blocks to form a wall of connected blocks. Top and bottom walls of each block each have an inter-tier connection feature that mates with a block in each adjacent top or bottom wall. Each block includes on each of its top and bottom walls, inter-tier connection features structured to mate with an inter-tier connection feature of a similar block in the adjacent tier.