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<br />C00170 <br /> <br />. <br /> <br />are not being used extensively at this time. Operation of the water <br /> <br /> <br />conveyance and storage systems, however, can be operated with the concept <br /> <br /> <br />in mind that large, relatively shallow open water areas are susceptible <br /> <br /> <br />to relatively large evaporation losses, particularly during the warmer <br /> <br /> <br />seasons. <br /> <br />. <br /> <br />Transpiration <br /> <br /> <br />Transpiration is defined as the process whereby the water absorbed <br /> <br /> <br />by the root system of plants is discharged to the atmosphere as a vapor <br /> <br /> <br />from the plant leaves and other surfaces. Most of the water absorbed <br /> <br /> <br />through the roots is discharged from the plants in this process. Only <br /> <br />about one percent of the absorbed moisture is retained in the plant tissue. <br /> <br /> <br />The annual transpiration rate for a given vegetative type is expressed <br /> <br /> <br />in depth of water for the given area of a specific vegetative cover. The <br /> <br /> <br />transpiration rate varies directly with the density of plant growth, the <br /> <br /> <br />amount of sunshine, plant vigor and available moisture supply. Transpira- <br /> <br />tion is essentially nonexistent below 40 degrees Fahrenheit. <br /> <br /> <br />Where there is sufficient soil moisture, growth and transpiration <br /> <br /> <br />are determined mainly by temperature. Trees and other vegetation along <br /> <br /> <br />canals and around reservoirs are generally blessed with adequate soil <br /> <br /> <br />moisture during the growing season. The water used by plants in the trans- <br /> <br />piration process may be supplied directly from open bodies of water in <br /> <br /> <br />reservoirs or canals (in the case of aquatic plants) or from water that <br /> <br /> <br />has seeped from these facilities. The latter use can increase the seepage <br /> <br />rate by increasing the hydraulic gradient. <br /> <br />Seepage <br /> <br />. <br /> <br />Seepage is defined as the slow movement, or percolation, of water <br /> <br /> <br />through the pore structure and interstices of the soil around the wetted <br /> <br /> <br />perimeter of a canal or reservoir, The seepage rate may be expressed as <br /> <br /> <br />a flow volume per unit of time, and/or as a percentage of the flow rate <br /> <br /> <br />occurring at a particular canal cross section. The rate of seepage from <br /> <br /> <br />unlined canals and reservoirs is affected chiefly by the depth of water, <br /> <br /> <br />permeability of the confining soil and the location of the ground-water <br /> <br /> <br />table. Low seepage rates are generally associated with soils having fine <br /> <br /> <br />particle size such as clay, loams and silts, Higher seepage rates occur <br /> <br />-13- <br />