of artificial barriers that prevent the inflow of water 

 originating outside of the area. 



Agricultural flood damage reduction. The adjust- 

 ment in land use and the structural and nonstruc- 

 tural measures designed to reduce hazard from 

 floodwater, erosion, and/or sediment. Reduction of 

 sediment on agricultural land will normally serve the 

 single purpose of flood damage reduction. Reduc- 

 tion of sediment in channels or reservoirs may 

 serve other purposes as well (i.e., navigation, water 

 supply, power) and should be identified accordingly. 

 To differentiate flood damage reduction from agri- 

 cultural and rural drainage of flatlands, flood 

 damage reduction is defined as any measure un- 

 dertaken to reduce or prevent damages from sur- 

 face water caused by abnormally high direct pre- 

 cipitation, stream overflow, or floods caused or ag- 

 gravated by wind or tidal effects. 



Flood. A general and temporary condition of par- 

 tial or complete inundation of normally dry land 

 from the overflow of inland or tidal waters, or the 

 unusual and rapid accumulation or runoff of surface 

 waters from any source. 



Nonstructural measure. A modification in public 

 policy, an alteration in management practice, a reg- 

 ulatory change, or a modification in pricing policy 

 that provides a complete or partial alternative for 

 addressing water resources problems and opportu- 

 nities. 



Separable feature. A project element that can be 

 implemented or constructed independently of other 

 features and that does not depend on other fea- 

 tures for its structural (or other) viability. 



Urban drainage. (1) The adjustment in land use 

 and storm sewer systems designed to collect runoff 

 from rainfall or snowmelt in an urban area and 

 convey it to natural water courses or to previously 

 modified natural waterways. Storm sewer systems 

 include storm drains, inlets, manholes, pipes, cul- 

 verts, conduits, sewers and sewer appurtenances, 

 onsite storage and detention basins, curbs and gut- 

 ters, and other small drainageways that remove or 

 help to manage runoff in urban areas. 



(2) Storm sewer systems are designed to solve 

 urban storm drainage problems, which are typified 

 by excessive accumulations of runoff in depres- 

 sions, overland sheet flow resulting from rapid 

 snowmelt or rainfall, and excessive accumulation of 

 water in one or more components of a storm sewer 

 system. 



Urban flood damage reduction. The adjustment in 

 land use and the structural and nonstructural meas- 

 ures designed to reduce flood damages in urban 

 areas from overflow or backwater due to major 

 storms and snowmelt. The measures include struc- 

 tural and other engineering modifications to natural 



streams or to previously modified natural water- 

 ways. Urban flood damage reduction is accom- 

 plished by modifying temporary conditions of inun- 

 dation of normally dry land from the overflow of 

 rivers and streams or from abnormally high coastal 

 waters due to severe storms. 



Water supply. The water that becomes available 

 for consumptive and nonconsumptive uses either 

 through increases in quantity or improvements in 

 quality of existing supplies. 



Section II— NED Benefit Evaluation 

 Procedures— Municipal and Industrial 

 (M&l) Water Supply 



2.2.1 Introduction. 



This section provides procedures for the evalua- 

 tion of NED benefits of municipal and industrial 

 (M&l) water supply features of water resource 

 plans. The procedures presented apply to both 

 structural and nonstructual elements of such plans. 



2.2.2 Conceptual basis. 



(a) The conceptual basis for evaluating the bene- 

 fits from municipal and industrial water supply is so- 

 ciety's willingness to pay for the increase in the 

 value of goods and services attributable to the 

 water supply. Where the price of water reflects its 

 marginal cost, use that price to calculate willing- 

 ness to pay for additonal water supply. In the ab- 

 sence of such direct measures of marginal willing- 

 ness to pay, the benefits from a water supply plan 

 are measured instead by the resource cost of the 

 alternative most likely to be implemented in the ab- 

 sence of that plan. 



(b) The benefits from nonstructural measures are 

 also computed by using the cost of the most likely 

 alternative. However, the net benefits of certain 

 nonstructural measures that alter water use cannot 

 be measured effectively by the alternative cost pro- 

 cedure for the following reasons: (1) Structural 

 measures and many nonstructural measures 

 (except those that alter use) result in similar plan 

 outputs, whereas use-altering measures (e.g., re- 

 vised rate structures) may change levels of output; 

 and (2) use-altering measures may have fewer 

 direct resource costs than measures based on 

 higher levels of output. Because of this lack of 

 comparability, the benefit from such use-altering 

 nonstructural measures should not be based on the 

 cost of the most likely alternative. Attempts to 

 measure the benefits of use-altenng nonstructural 

 measures on the basis of willingness to pay are en- 



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