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111-2 Section. No attempt would be made under thi's alternate to structurally reduce flooding to existing structures, roads, bridges, sewer plants, or IrrIgation ditches, The resulting damages are in an annual cost form by studyIng the resulting flood plain of three or four different flood frequences, With this altemate, the effort is primarily aimed at adoptIng appropriate regulations. In addi tlon to flood damages, there are certain maintenance requirements associated with erosion and channel cleaning for IrrigatIon flows. 2. Flood Plain Zonln with Minimal Struqural I.!nprovements - (Seml-Non- Structural Alternative This altern,ste Is based on the IOO-year flood plain under projected future developmE,nt as It would be 'lIhen culvert, brIdge and related Improvements are made: a, Where for economic and/or sociologic re"SOns it is prudent to reduce the flood plaIn width. b. Where for reasons of economics and of meeting street overtopping requl rements, it Is necessary to raise E,mbankments and to COn- struct bridges or culverts, even though the flood plain width I s no t reduced. The economI c criterion for the above (and for subsequent a I ter- nates) Is that the resulting annu;;lI cost of construction and reduced level of maintenance Is less than the annual darn<.ges and maintenance If the Improvements were not made. H"retofore, few reliable attempts have been made at estimating benefits for the sociological, recrea- tional, and road criteria, Selectlve.ly, rOeld, sociological and recreational criteria may prevail in some areas even though economic criteria may show an alternate to be economically less desirable. Because of the traffic and other urban requi rements related to the criteria of the Drainage CrIteria Manual" the bridges and street crossings On Big Dry Creek wi I I bE' replaced, or expanded, and most of the flooding adjacent to roads wi I I be reduced in the normai course of urban development. What remains, then, Is the damage to specifIc existing structures, bridges, embankml".,ts, end other flood-susceptible appurtenances and property. For this al ternate, the design approach Is essentially non- structural. Channel work is primarily that "ssociated with bridge and hIghway work, which would be done '1Ilth Or without a flood hazard problem to solve. 3. Lined Open Channel. In many already urbanized ar'eas, lined op."., channels, especially grass-lIned and European-type, have become a desIrable means of achieving multi-USE' greenbelts. However, arti- ficial open channels are usually justl fled only when the natural channel no longer exists.