Other formulas are used to calculate ponds that are circular and triangular. Even if your pond is not an exact shape, it maybe possible to get a reasonable estimate of its area by using one or a combination of these formulas.
Circular pond areas are estimated by the formula: Area = 3.14 x radius2 (Radius is one-half the diameter.)
For example, a circular pond with a radius of 75 feet has an area of 17,663 square feet (3.14 x75x 75) or 0.4 acres. The radius can be measured directly or the diameter can be divided by 2. A measurement of the diameter in several directions will help to determine if the pond is truly circular.
Triangular pond areas are estimated by one of two formulas depending on whether the triangle has a square or 90° angle for one of its corners. If a 90° angle is present the formula is:
Area = 1/2 x length x width For example, a triangular pond with a length of 250 feet and a width of 220 feet has an area of 27,500 square feet (250 x 220 ÷ 2) or 0.63 acres.
It is important to remember that the longest side (the hypotenuse) is not needed for the calculation, instead the two sides that touch the 90º angle are used.
If no 90° angle is present and the sides are unequal, the formula is:
For example, a triangular pond with’ three sides of 80,90 and 130 feet has an area of 3,549.6 square feet (where S = 150; and
Irregularly shaped ponds:
Many ponds in the Southeast are watershed ponds that have been built by damming valleys. These ponds are usually irregular in shape. Check first with your county SCS office for records on your pond, or for aerial photos in the SCS or ASCS office. If no good records exist then a reasonable estimate can be made by chaining or pacing off the pond margins and using the following procedures to calculate area.
- Draw the general shape of the pond on paper (graph paper works best).
- Draw a rectangle on the pond shape that would approximate the area of the pond if some water was eliminated and placed onto an equal amount of land. This will give you a rectangle on which to base the calculation of area (See Figure 2 below).
- Mark the corners of the rectangle (from the drawing) on the ground around the pond and chain or pace its length and width. For example, a length of 350 paces and a width of 125 paces would be equal to 896 feet (350 paces x 2.56 feet/pace [pace length, from above]) by 320 feet.
- Multiply the length times width (see example above) to get the It approximate pond area. For example, 896 feet x 320 feet = 286,720 square feet or 6.58 acres (286,720 ÷ 43,560).
It is a good idea to repeat this procedure two or three times and compare your results. You may want to average these results if they differ. If a single rectangle does not fit the pond drawing then try to fit some combination of rectangles, circles, and/or triangles.
If some combination seems to fit, then calculate the areas of the different shapes, and add the corresponding areas together to get the total pond area.
Authors:
Michael P. Masser and John W. Jensen
