I am trying to measure a concrete structure to compute the surface area. I have included a sketch of the structure with the dimensions that I have measured. This is part of a drainage canal bank where two canals intersect. The banks along both canals are paved with concrete. I tried to just average the slant dimensions and average the lengths of the top and bottom arcs. Then, I simply multiplied them together to get an area. I feel this is inaccurate. I then tried to stretch it out into a trapezoid, but I feel this is even less accurate. Any help?