Abstract :
Irrigated area namu sira-sira in Langkat district including rice fields with an area of 6500 Ha. Source of irrigation water in the area Namu Sira-Sira derived from Namu Sira-sira weir, designed to cover the service area of approximately 6500 hectares as a whole, which divided into two channels that is right of primary channels with 4097.5 ha and left channel with 2402.5 Ha
To evaluate large water availability and use of water in irrigation D.I. Namu sira-sira by the cropping pattern is applied, the necessary hydrological data, climatology, topography which will then be analyzed to obtain effective precipitation, eva transport, irrigation needs, debit mainstay, and debit distributed on rice plots as required , Field measurements were also conducted to determine the water needs based on conditions that actually occur in the field. From the calculation of debit mainstay Bingei river with statistical methods namely the frequency analysis using the normal distribution, the obtained value of the maximum discharge flagship Q80 = 11.59m^3/det which occurred in February.
From the results of theoretical calculations, found that the greater availability of water in the dam is by 2.82 1 / s / ha, while based on the results of field measurements obtained large water demand by 2.14 1 / s / ha. At the theoretical level of rice fields, water demand is obtained 1.49 1 / s / ha, and based on field measurements obtained 0.95 1 / s / ha