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tl:l. N w C> ':~ I I.., ,'''''' J , . i ',.1" ".:..,' costs, service facilities, engineering and investigative ancl administrative expenses. Fencing, special diversion and cross drainage and safety structures are includecl in the coefficient, K3' In a main irrigation c1elivery system, the c1ischarge of the network c1eclines along its length due to continuous withdrawal for irrigation and less acreage serviced per unit length. Small ditches including field head ditches and laterals have basically the same cost-effectiveness characteristics as larger scale linings. However, two c1ifferences should be noted. First, the small capacities generally c10 not warrant expensive fencing, diversion, sncl safety structures and therefore K3 in Equation 20 will be much smaller, ancl for head ditches it can be considerecl negligible. For laterals, K3 is primarily related to inexpensive flow measure- ment structures which should be provided at each farmer's turnouts. The second diUerence is that the operation of smaller conveyance channels is distinctly different front larger systems. O"Wnership is often privateancl .sharing of flow 'is often rotated. Consequently, the discharge capacity gener- ally 'does not c1iminish significantly along the channel length. Forthese . conditionS, Equation 1 reduces to: C c K2 = 1':1Q", S~ KZ (1+K2) (21) 1'he coefUcients include costa for earthwork, relocation ancl. lining costs as well as investigations, flow measurement, diversions ancl road crossing struc- tures, etc. They do not inclucle fencing or other 'special safety structures since these are not necessary on small canals. It. is worth noting that using the large canal valuasof Kl' 1(2' ancl K1 coefficients for small c1itches may introduce significant cost overestimati6n errors. Small ditches often have larger slopes and thereby carry a higher flow rate in a smsller cross-section. However, the largest source of error is that the construction specifications do not have to be as stringent, thereby reducing the costs. Low cost plastic pipelines can also be usecl to replace the small open ditches where feasible. For January 1980, values of .~ = 48.5, K2 = 0.56, K3 = $2.35/m appear to give representative values for lateral and small ditch concrete linings in the UCRE. Defining the coefficients in Equation 21 can be accomplished by using typical values of 1980 contractor prices for Agricultural Stabilization and Conservation Service (ASeS) cost-sharing programs of slip-form concrete small ditch and lateral lining costs in the western Unitecl States, approximately 5- 8 em thickness, uaing the sulfate resistant specifications of the U.S. Depart- ment of Agric!tlture, Soil Conservation Service. These costs are currently , about $7.50/m inclu1ing all base preparation. Total lining costs for ditches carrying up to 0.4 m Isec range from 121m to $25/m. Thus, for a specifiecl .lope, the perimeter Can becalculatecl, multipliecl times the length and unit cost for an estimate of SCS lining costs. Administrative, investigative, engineering costs by the supervising agency, and other inclirect costs can be estimatecl (usually 25 to 33 percent of construction costs), ancl the salinity related cost-effectiveness function is then determinecl directly. For purposes 53 ".'... , ~ , e. .. ,,,,.' .., ..