Water balance study of the north zone of the Magat River Irrigation System, Isabela

Date

1976

Abstract

Study of the North of the Magat River Irrigation System, Isabela. Major Professor: Dr. Wilfredo P. David. The performance of the irrigation system and water requirements for lowland rice of the North zone of the Magat River Irrigation System ((MARIS) at Isabela were evaluated using the water balance approach. A-three-thousand-six-hundred-two (3,602) hectare area of the North zone was selected for this study during the dry season. Water inflows (applied irrigation plus rainfall) and outflows were monitored daily while the deep percolation loss rate and the change in surface storage were determined analytically using the known parameters of the water balance equation including water table depths. The relative rate of percolation loss by location was determined using water table recession rate as monitored through the observation wells. Groundwater storage requirement was calculated from superimposition of groundwater contour maps at 10, 20, 30, and 45 days following irrigation irrigation suspension and a prediction equation was determined. Relationship between daily water inflow and water table depth was also made. Farm irrigation efficiency as a whole was low (50 percent). Abundance and continuous supply of irrigation water results in farmers not concerned in proper control at the source. The lack of appropriate farm irrigation distribution facilities has resulted in uneven water distribution. The long-time lag between the start of water delivery until the arrival of water in the farthest fields had led to over-irrigation in some fields and a shortage of water in others. Water table recession rate was affected by the permeability of the soil and the level of water table with respect to the drainage outlet. Deep percolation loss rate was variable; relatively high on northern portion (facing Magat river) and relatively low on the southern side of the North zone. The average percolation/ rate was relatively high (11.8 mm/day). Water table depth was not influenced by the daily changes in irrigation inflow under continuous submergence method of irrigation. The changes were rather influenced by the uneven distribution of water in the farm brought by non-uniform schedule of planting among farmers, distance of farms from canal or creeks and the water levels from these supply sources. The equation for groundwater storage requirement as a function of the duration of irrigation suspension was best fitted with the second degree parabola (Correlation coefficient, r= 0.95). The results from this study seem to suggest innovation of the present practices through diversification of crops. Intermittent or rotational irrigation may help minimize surface runoff and deep percolation losses.

Document Type

Master Thesis

Language

Englsih

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 995 1977 A2 G36

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