Aqua Dams are environmentally safe stable water barriers used to contain, divert, and control the flow of water.  The design consists of two polyethylene liners contained by a single woven geo-tech outer tube.  When the two inner tubes are filled with water, the resulting pressure and mass create a stable, non-rolling wall of water.

A single tube filled with water will not provide a stable wall or dam as the water builds up on one side of the tube the pressure on the wall of the tube begins to increase.

As a result of the building pressure, the water is pushed from one side of the tube to the other side where the pressure remains low. As the water continues to move from one side to the other, the tube begins to roll.

As water builds up on one side of the Aqua Dam, the pressure displaces the water in the inner tubes. However, because the inner tubes are unable to roll the Aqua Dam assumes a position of equilibrium and behaves as a solid barrier.

In order to roll a filled Aqua Dam, it must be tipped over.  This would require lifting all of the water mass in the first column up and over the second column.  Even if the water builds to the top of   the Aqua Dam, the pressure is far too low to provide enough force to lift the water mass and tip the Aqua Dam.  The result is a stable, non-rolling barrier forming a solid dam.

Two water filled tubes or columns placed side by side will assume their natural shapes.  If pressure is applied to one side, the water is displaced in the first tube and causes it to roll. As the first tube rolls, it pushes on the second tube moving the water from one side to the other and the two tubes roll together.

The Aqua Dam is able to offer a stable wall by containing two water columns in a single outer tube.  The contained water columns are unable to assume their natural position and form a vertical wall in the middle as they press against each other.  The pressure inside the tubes applies a substantial force to both sides of this vertical wall

As water begins to build on one side of the structure the inner tube naturally tries to roll.  However, the friction between the vertical waves and between the inner and outer tubes opposes the rolling tendency and the structure remains fixed.

In order for the Aqua Dam to move as a result of the pressure exerted on one side, it must either be tipped over or slide across the surface on which it rests. In order to tip, the water pressure must lift the first inner tube up and over the second.

The following calculation shows the Aqua Dam's resistance to tip:

Assumptions:
We will assume that the inner tubes are generally rectangular when filled to facilitate the calculations. We will also assume that the water level on one side has reached the top of the Aqua Dam as a worst case scenario.

P = Pressure
h = water depth
D = width of Aqua Dam
l = length of Aqua Dam
Þ = mass density of water
g = gravitational acceleration
y = specific weight of water
F = Force exerted on the face of the Aqua Dam due to pressure (P)
A = area of the side face of the Aqua Dam
W = weight of water in the inner tube
V = Volume of the inner tube
P = Þgh = yh
Pavg = y(h/2)
A = hl
F = PA = Pavg A
W = yV

The force exerted on the side of the water structure is then:

Having determined the force on the side of the Aqua Dam, we can evaluate the tendency of the Aqua Dam to tip.  We assume point A as the pivot point and sum moments about this point.  The moment created by each force, is a measure of how much the force contributes to rotating the first column of water around point A.

or

Simplifying the expression we see that the stability of the Aqua Dam is dependent on the relationship between its width (D) and the depth of water it must resist.

The relationship above indicates the minimum width of the Aqua Dam to prevent it from tipping when resisting water with a depth (h) equal to the height of the Aqua Dam itself. The design height for the water structures to prevent tipping would be described as:

D>(.82)h

In order to quantify the stability of the Aqua Dam we substitute the actual dimensions of the standard Aqua Dam for D and h into the equation above.  The results are expressed in terms of a safety factor.   The safety factor indicates how many times greater the water pressure or water depth must be in order to roll the Aqua Dam.

Based on the current Aqua Dam designs, the safety factor against tipping when water levels are to the top of the structure are as follows:

If the recommended maximum water depth is maintained, the safety factor against tipping is improved.  The following table illustrates the improvement when recommended water depths are observed.

The second method for moving for the Aqua Dam is to slide the entire structure. The resistance to sliding is provided by the friction between the ground and the structure. Although any type of barrier could slide along the ground if the pushing force were great enough, we will present the calculations for sliding the Aqua Dam in order to quantify its tendency to slide:

Assumptions:
We are assuming that the supporting surface is smooth and flat. Any deviation from a smooth surface will add greater opposition to sliding. Again, we assume that the inner tubes are generally rectangular to facilitate the calculations:

                    or

The coefficient of friction that will allow sliding if the recommended maximum water depths are observed as follows:

Coefficients of friction ranging from. 10-.20 indicate that the surface must be quite slippery.  For example, the coefficient of friction between two pieces of greased or folded steel is .10-.20. Again we have assumed that the surface under the Aqua Dam is smooth.  In most cases, surface under the Aqua Dam will be comparatively rough and with pose even greater opposition to sliding than indicated in the calculations above.

The principles used to create the Aqua Dam are simple yet effective.  The stable non-rolling wall of water conforms to the surface beneath it creating a tight seal.  The Aqua Dam will not tip or move even if water levels rise to the very top of the structure. Aqua Dam provides a lightweight, reusable, and ecologically safe method of temporary water control.