A white clothes line 200 feet long, marked at 10-foot intervals 

 with India ink and provided with floats 20 feet apart, and a 7-foot 

 pole marked in feet and tenths of a foot, are useful items for 

 depth measurements. The clothes line is stretched across the pond 

 at regular intervals, and depths are obtained with the pole by 

 sounding at 10-foot or 20-foot intervals, depending on the evenness 

 of the bottom and the size of the body of water. Average depth is 

 equal to the total of the cross soundings divided by the number of 

 soundings , 



Surface area of an irregular pond is easily determined after 

 an accurate map is prepared. Maps may be prepared by using a plane 

 table or by the stadia method. The stadia method is illustrated 

 in Figure 1. 



This method requires a transit equipped with stadia cross- 

 hairs and a levelling rod. The transit is set-up, if possible, 

 at a point where the entire shoreline is visible. Two or more 

 stations may be used where the pond is very irregular. The angles 

 and distances to several points on the pond-edge are measured by 

 sighting on the rod. A reading is necessary at each point where 

 the pond-edge changes direction. The field data are then plotted 

 on grid paper (one hundred squares to the inch is easy to work 

 with) to a scale of one inch equals one hundred feet. After all 

 points have been plotted, they are connected by smooth lines to 

 form the line representing the pond-edge. 



Determination of the surface area is now simply a matter of 

 counting the squares and multiplying by their area (the one-tenth 

 inch squares in Figure 1 are each equal to .00229 acres) . The 

 number of squares in the pond area of Figure 1 was found to be 1898. 



1898 X .00229 =4.35 acres 



When available a compensating polar planimeter is an excellent 

 instrument for determining area of irregular ponds . This device 

 can be used on maps of any scale, is fast, and gives accuracy more 

 than adequate for this purpose. Current aerial photographs are 

 available in County Agricultural Stabilization and Conservation or 

 Soil Conservation Service offices from which surface areas of ponds 

 may be obtained with reasonable accuracy with this instrument. 



USEFUL UNITS OF MEASUREMENT 



One acre = 43,560 square feet; One acre foot = 43,560 cubic feet 



Acre feet = Area in acres x average depth in feet 



One acre foot = 2,718,144 pounds; One part per million (p. p.m.) = 



2.7 pounds 

 One cubic foot =7.5 gallons = 28.32 liters = 62,42 pounds of water 



