Irrigation & Drainage Systems Engineering

Drainage problem in Beles Sugar Project is becoming severe during rainfall season that the effective rainfall was greater than the sugarcane water requirement and higher area coverage of vertisols. To remove this excess rainfall through installations of surface drainage system, this study was conducted to estimate design rainfall in magnitude and recurrence interval based on the recorded maximum rainfall. The independent, homogeneity, and outliers of the recorded data were tested accordingly. Probability of exceedence and return periods for daily maximum rainfall was determined using Kimball’s method. Gumbels method was used to compute design rainfall of different desired return period. The relation between observed and computed data was undertaken using regression function. Thus, recorded rainfall data was independent and homogenous at 5% signifance level. Also there was no value greater than the high outliers (151.3 mm) and no value less than the low outliers (41.0 mm).The lowest maximum rainfall (48.6 mm) had a probability of 96 .9% which likely to occur every one year. The highest maximum rainfall (150.1 mm) had a probability of 3 .1% which likely to occur three times in every 100 years period. Within the same 10 years return period, the computed design rainfall (114.7 mm) was deviate by 0.04 with the observed rainfall (110.3 mm).The average deviation of observed and computed rainfall data from its trend line function were 0.004 and 0.002 respectively. The correlation between observed and computed rainfall of trend line function was 0.98, thus it was highly correlated and the perfect reality. Design rainfall for 10 years return period (110.3 mm) was suggested for estimation of Beles Sugarcane open earth drainage channels. Thus, the Project Engineers and Hydrologists has to considered this study pre-requisite for planning, design and management of hydrological, hydraulic, drainage structures, barrages, dams, spillways, bridges, culverts and so on that have been executed in the Project.

The development of crop coefficients (KC), the ratio of crop evapotranspiration (ETc) to reference evapotranspiration (ETo) is important for estimating irrigationwater requirements in relation to specific crop phenological development. This research was conducted to determine growth-stage-specific Kc and crop water use for onion at Werer Agricultural Research Center, Middle Awash Valley Ethiopia during the main season (July–October) and during cool cropping seasons (March–June) from 2012-2015. Three non weighing lysimeters of 1.6 m x 1.6 m in surface area and 2 m deep were used to measure crop water use and local weather data were used to determine the reference evapotranspiration (ETo).The results showed that the obtained Kc values for main cropping season planted onion during initial, crop development, mid season and late-season stages were 0.57, 0.78, 1.03 and 0.77 respectively. Meanwhile, the corresponding Kc values for cool cropping season planted onion were 0.49, 0.90, 1.01, and 0.79in the respective growth stages. The seasonal crop evapotranspiration was 525.83mm and 465.57mm during main and cool cropping season respectively. The measured Kc values were significantly different from the FAO-56 reported values. Therefore, local calibration of crop coefficients is an essential for efficient irrigation water management and precise water applications.

Field experiment was conducted at Werer Agricultural Research center to evaluate the effects of drip and furrow irrigation under different irrigation levels on maize yield and water use efficiency. The experiment was laid out in split plot design where drip and furrow irrigations assigned as main plot and irrigation levels (100, 85, 70 and 55% of ETc) assigned in the sub plot arrangement with three blocks. The highest seasonal water requirement of maize was 701.7 mm at 100% ETc under conventional furrow irrigation which is considered as control while the lowest was 192.9 mm at 55% ETc under alternative furrow irrigation. The analysis of variance revealed that there was significant (p<0.05) difference in yield among treatments and the interaction effect of irrigation system and irrigation levels show highly significant (p<0.01) difference among treatments. The highest yield (16.7t/ha) was obtained from drip irrigation with 100% of ETc application and while the lowest (4.04 t/ha) was obtained from plots treated with alternative furrow irrigation 55% ETc treatment.

Deficit irrigation is one of agricultural water management practice in arid area in which the irrigation water management has to be improved so that water supply to the crop can be reduced while still achieving high yield. The main objective of this study was to improve agricultural water use efficiency (WUE) of onion under different deficit irrigation levels. Randomized complete block design (RCBD) with eleven treatments and three replications was used. The treatments were: full irrigation (0% deficit as a control), and 25% and 50% of crop water requirement (CWR) deficit throughout growing season, and one period deficit treatments (25% and 50% of CWR deficit at initial, development, bulb formation and maturity stages). Treatment 10 (50% of CWR deficit at bulb formation stage) showed the minimum harvest index (0.68) and 25% of CWR deficit at initial and maturity stages respectively showed the maximum harvest index. Yield response factor (ky) indicated that onion was sensitive (yield reduced) for water deficit at development and bulb formation stages. The maximum water use efficiency (4.98 kg/m³) was observed at 50% of CWR deficit throughout growing season and the minimum (3.22 kg/m³) was observed at 50% of CWR deficit at bulb formation stage. Water deficit at initial and maturity growth periods had insignificant impact on WUE of onion. Generally, this result indicated that water deficit at bulb formation growth period of onion reduce more water use efficiency than water deficit on other growth periods.