Question: how to work out the volume of a dam?
Answer: Surface area. The surface area of a dam is calculated by multiplying the length by the width. ... 
Volume. With the surface area depth calculated, the volume can then be determined: volume (m3) = surface area (m2) × max depth (m) × 0.4. ... 
Gully dams. You can estimate the capacity of small gully storages using this formula: ... 
Depth.