Eric R. Norland
Implementing pond management practices necessitates knowing the surface area and volume of the water impoundment. Aquatic herbicide applications, fish stocking rates and fertilization treatments are prescribed on the basis of area and/or volume of the pond.
There are several sources for information about the size and volume of your pond. If a Natural Resources Conservation Service technician or civil engineer designed and supervised the pond construction, that person should be able to provide you with the necessary measurements. Additionally, the local Farm Services Agency office may have an aerial photograph that shows your pond; the surface area can then be calculated from the photo. A surveyor can also be hired to determine the surface area.
Another practical alternative is for you to make your own pond measurements by following the steps listed below. To assure accuracy, take all measurements carefully and carry all calculations to at least four or five decimal places (i.e., 0.11478 acres). After the final calculation has been performed, round the number to one decimal place.
Shoreline measurements are made with a tape measure or by pacing, and are then used in the appropriate formula below.
If the pond is rectangular or square, use the following formula:
Surface area, in acres = length, in feet X width, in feet __________________________________ 43,560 sq ft per acre
Example: (Figure A)
80 feet X 140 feet _______________________ = .2571 A, or approximately 1/4 acre 43,560 sq ft per acre
If the pond is circular or nearly so, use this formula to determine surface area:
Surface area, in acres = (total feet of shoreline) squared __________________________ 547,390
Example: (Figure B)
(520 feet) X (520 feet) _______________________ = 0.4939 acre, or approximately 1/2 acre 547,390
Many ponds are irregularly-shaped, which makes the area measurements more difficult. In this case, approximate the pond shape as either a square, rectangle or circle by measuring boundary lines that most nearly represent the actual shoreline.
Example: This pond shape can be approximated as a rectangle (Figure C).
Surface area, in acres = length, in feet X width, in feet __________________________________ 43,560 = 250 X 120 _________ = 0.6887 acre 43,560
Calculating the total volume of water in the pond is a two-step process:
Step 1: Determine average depth of the pond by taking uniformly-spaced soundings over the entire pond surface. This can be done from a boat, or during the winter when ice covers the entire surface. The measurements can be taken with a long pole, chain or weighted rope marked off in feet. At least 15 measurements should be taken. Add the measurements and divide by the number of measurements taken.
Example: Average depth =
2 + 3 + 5 + 8 + 9 + 1 + 4 + 6 + 9 + 0 + 1 + 2 + 3 + 3 + 8 _________________________________________________________ 15 64 = ______ = 4.27 feet 15
Step 2: Once you have determined average depth and surface area, acre-feet are determined by multiplying the two measurements:
Volume, in acre-feet = Surface area, in acres X Average depth, in feet Example: A 1.5-acre pond has an average depth of 4.27 feet. Acre-feet = 1.5 acres X 4.27 feet = 6.405 acre-feet
Pond measurements should be re-taken whenever there is an appreciable change in either surface area or average depth. Significant changes in surface area occur when existing ponds are enlarged. However, average depth changes very gradually over a period of years as a result of natural processes. Sediment inflow and the accumulation of decomposing vegetation will cause a pond to gradually become shallower. A pond that may have been 15 feet deep when it was constructed may only be 10 feet deep after several years. Average depth should be re-calculated every five years to account for the gradual filling in of the pond. Soil disturbances in the watershed or excessive accumulation of decomposing vegetation in the pond will require more frequent measurement of the water depth.
Some pond management activities involve the treatment of only a portion of the water impoundment. In these situations, the same formulas are used but the treatment area dimensions are much smaller.
Example: A pond owner desires to treat a 50' x 100' swimming area for algae, using a rate of 2.7 pounds (equivalent to 1 part per million) of copper sulfate per acre-foot (Figure D).
50 X 100 Surface area to be treated = ________ = 0.11478 acres 43,560 1 + 2 + 3 + 5 + 2 + 3 + 4 Average depth of swimming area = _________________________ = 2.8571 feet 7 Acre-feet in the swimming area = 0.11478 X 2.8571 = 0.32794 acre-feet Amount of cooper sulfate to use = 0.32794 acre-feet X 2.7 lbs per acre-foot = 0.88542 lbs of copper sulfate in swimming area = 0.9 lbs
This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this publication may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-6181