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stores, industrial manufacturing, office buildings or large apartment complexes did not appear in the floodplain, This fact eliminated categori~s such as loss of sales tax revenue, loss of salary, inventory damage, ete, from the analysis. Published relationships are not available for street cleaning, irri(Jation ditch repair or the block <lnd s]ilb construction encountered in the school district's shops, By naking conser- vatively high estimates of costs per day and production per day of the clear.-up and repdlr crews, costs were predictc<! of $2.75 per lineal foot to clean inundated streets of mud and debris and $2,000,00 lump sum repair costs for each canal breech, Using these unit costs, clean-up contributes relatively little to the total damages. The low velocities greatly redueethe magnitude of damages due to washouts and erosion, The peak 100 year flow generally caused velocities of less than four feet per second across open land. In discussing grass-lined channels, Ven Te Chow reproduced a Soil Conservation service table recommending a permissible velocity over alfalfa cover of 3,5 fps!6l Velocities causing erosion over most grasses or grass mixtures are generally higher thnn this. Therefore nO crosion losses were anticipated. The low velocities and relatively short peak durations also pose little threat to street embankments, The one instance ~n Which washouts were retained as a damage category was at the various irrigation ditch cros~ings. Vi.D. Depth-Damage Relationships The cinder block and concrete maintenance buildings near Poudre High SchOOL presented the situation of sustaining little damage to structural finishes or contents while still producing the indirect damages of clean-up, inconvenience and missed work. The options available to estimate damage in this situation were to either prepare a complete content and finish inventory and estimat~ it~miz~d indire~t damages or to make what amounts to an educated guess. In determining the procedure to be used to esti~te d~m~ges, two facts Were considered. First, the flood flows diverge in this area; thus there may be some variations in water surface (see \lydrclulics sPCtion). Second, the low development density and structure vnl~e througho~t the floodplain creates a negative net benefit for all proposed alternative drainagc improvemcnts (soe Economic jl,nillysis section), In the absence of clear economic superiority the intangible and secondary benefits of the alternatives will carry relatively more weight in the deCision making process and the damage estimates relatively less weight. In light of these facts, tho extra accuracy which may be qained from a damage inventory WilS not deemed worth the .:>tfort. Therefore ,1 total damage cstimat_e of two percent of structural value was subjectively chosen for zero to one foot of inundation, Depths over one foot were not encountered in either shop building. As Table 5 indicates, the retained d;;lInage categories are stU)0t clean-up costs, irrigation ditch repair and clean-up, structural and content damage to residences, mobile homes, churches, dnd school district maintenance buildings. Activities completed in this step include procurement of published relationships, development of relationships where no published data exist and structun, ilnd content valuation. Tilt' F<,<l<,1:dl InSUrall"''''' A<lmlnistr..tion h"s prcpJ.red dco:th-d;:::r,:J.gc tables for s<,veral types of residential construction. These tables apply to the single family residences, duplexes and mobile homes fou~d in the b~sin. At the low depths encountered in the floodplain ~ost str~cturnl dan~ge eo~sists of damage to the finishes a~d not the load bearing components or foundations, Damages to the two churches in the floodplain, '~'hich are finished similarlv to residences, were also estirr.'lted from these rIA tables, , -54- -55-