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~I .C I I. I I I I I I I. I I I I I I I. I I ,,- - ' -,~",,,..,,--....--~ Annual tl~od lQ~~e~ a~~ ~al~~lated by using the mathematical expec- tAt10n of flood loa~ whi~h is the aTea under the damage-frequency curve. F~r computation purposes: N-1 Average Annusl flood Loss ~ :2: :1."'1 [ Di +2Di + 1] (Pi +1 - Pi) where, D1 ~ damage froID ith flood. Pi E prObAbility of ith flood being exceeded. N E the number of flood magnitudes used in the computation. Referring to the historiesl depth-damage curve, one will notice a defieiency in this method of snsly~ing damages. Can the damage that oecurred in 1936 be compared with that which occurred in 1936? Being only A few YeArs after th~ Great Depres~ion, probably little development was occurring. But the general case is that besides adjusting for inflation fActors, Adjustment also must be made for additional construction to obtain currently valid relationships. The mOTe common methods used to correct for additional development in the flood plain are based on aerial photography anAlya1s. In a 1956 st~dy (White, et alJ which assessed changes in flood plAin occupance, a technique was used to assess changing use of the flood plAin, which can be augmented by the use of aerial photography. To assess change the study defined "structural unit" for the different occupancy cla.ses As follows; Reilidential A, B. C. A single or double-family dwelling. A multi-family dwelling for 3-6 familie~, A multi-family dwelling for 7 or more families, Industrial Buildinc. A separate building, exclusive of small auxiliary buildings, 11