Remote Sensing and Hydrological Measurements for Irrigation Performance Assessments in a Water User Association in the Lower Amu Darya River Basin

Abstract

Irrigation water management in Central Asia is notorious for its inefficiency. We assessed the operational performance of the irrigation scheme in one Water Users Association (WUA), Shomakhulum, in Khorezm district, Uzbekistan, in 2007 to provide recommendations for strategic water management planning. Relative evapotranspiration (RET), delivery performance ratio (DPR), drainage ratio (DR), depleted fraction (DF), overall consumed ratio (OCR), field application ratio (FAR) and conveyance ratio (CR) were used as performance indicators. The components of the water balance were obtained through remote sensing techniques and hydrological field measurements. The surface energy balance algorithm for land (SEBAL) was applied to MODIS satellite data to derive actual and potential evapotranspiration. Inflows and outflows were quantified with field measurements in the irrigation and drainage network using discharge rating curves. Ponding experiments allowed determining canal seepage losses. Water balances at field level were established for application efficiency estimations. The indicator values were then compared to efficiency target values taken from the literature in order to assess the operational capabilities of the irrigation scheme. The general performance of the irrigation scheme is very poor. DPRs exceeding 1.0 indicate that more water is delivered to the system than is demanded. The seasonal DF of 0.4 is lower than the target value of 0.6. Losses during the field application averaged at 57%, which is 24% above target values. Seasonal DR, OCR, CR and RET are 0.55, 0.51, 0.76 and 0.82 against the target values of 0.1, 0.54, 0.84 and 0.75, respectively. We conclude that the distribution mechanism can be considerably improved. Besides improving water distribution (timing and equity) in the network, another recommended intervention would be to increase the DF, particularly by interventions at field level that raise the FAR, which in turn will improve DR and OCR. This can be achieved by introducing modern water management approaches such as laser leveling, doublesided irrigation, and control of inflow through flow-measuring devices installed at farm gates, and adequate water pricing.

Assessment of Irrigation Performance in Large River Basins under Data Scarce Environment—A Case of Kabul River Basin, Afghanistan

“…For the diagnosis of irrigation system performance, researchers use different indicators including overall consumed ratio [19], crop water deficit [20], relative water supply [21], relative evapotranspiration [14,15], delivery performance ratio, drainage ratio and depleted fraction [15], and equity and reliability [8,14], etc. For this study, equity, adequacy, and reliability were used as the primary criteria for the assessment of irrigation performance at administratively important spatial units (sub-basin and provincial) and strategically viable time steps (annual, monthly, and seasonal).…”

“…Usually RET ≥ 0.75 is acceptable for irrigated agriculture, although it is constantly over time [26,27], while RET between 0.75 and 1.0 shows adequate water supply [15]. The value of RET = 0.65 is considered to be the critical value [28] and below that level (RET < 0.65) is considered to be poor performance of the irrigation system, and eventually leads to a loss to the crop yield and biomass.…”

“…However, the irrigation system of KRB is supply-based rather than demand-based. The supply-based irrigation system provides a thin layer of an equal amount of water to different sub units regardless of the cropping pattern [15]. Therefore, the limited and equitable water amounts to all sub units restricting the farmers to grow similar crops.…”

“…Equity, reliability, and adequacy are the main challenges in water distribution at the system level for water managers, and not only in the KRB but also in other large irrigation schemes around the world [14,15]. In the current study, we assessed the equity, reliability, and adequacy of KRB at the system level (e.g., provinces and sub-basin scale).…”

“…We used metrics that require only remote sensing data and have been documented well in other studies. For example, RET was used to assess the adequacy of water distribution at the water user's association level by using satellite remote sensing [13,15]. Similarly, Ahmad, Bastiaanssen and Usman, et al [9] used the CV of actual evapotranspiration (ET a ) for assessing equity, which is the seasonal evaporative fraction for assessing the adequacy and temporal CV of the evaporative fraction for describing reliability.…”