Assessment of spatial and temporal seepage losses in large canal systems under current and future water-saving conditions: A case study in the Hetao Irrigation District, China.

Accurate estimation of seepage losses in large-scale canal systems and identification of their impact factors are important for improving water conveyance efficiency in agricultural districts. However, seepage losses can vary widely across different regions and periods, making it difficult to obtain a complete understanding of the variation process based solely on local scale studies. In addition, although there are currently some complex numerical models available for large-canal systems in agricultural districts, they are rarely used in practice due to their complexity. This study evaluated the regional-scale spatio-temporal seepage processes of the Zaohuo canal, a 55 km's sub-main earthen canal located in the Hetao Irrigation District, China, under current and future water-saving conditions using MODFLOW-SWR. In addition, a pre-processing tool was developed to process spatial geographic data and spatial topology between different canals. Furthermore, the sensitivity of different influencing factors, such as the permeability of canal bed sediments, surface and groundwater level, and local lining, was also investigated. The optimal relationship between lining areas when partial lining is used and seepage losses was also investigated. The calculated water conveyance efficiency coefficient is 0.7871, which fits well with the reported results and proves the reliability of the simulation. In addition, it was found that seepage losses are most sensitive to the surface water level of the canal, followed by the permeability of canal bed sediments and then the groundwater level. Moreover, new hybrid lining can reduce the seepage losses by about 92.02%, but ongoing maintenance is vital. When lining the key portion of the canal, the seepage losses will be significantly reduced with the increase of lining area. The seepage losses reduction factor increases by 5.8% for every 1 × 105 m2 increase in lining area when the lining area is below 1 × 106 m2, while the effect is not significant when that limitation is exceeded. This study can support decision-making for water-saving projects in large water conveyance canals in regional-scale agriculture districts. • The regional-scale spatio-temporal seepage losses in large canal have been evaluated. • Seepage losses were calculated based on surface-subsurface model MODFLOW-SWR. • Seepage losses are more sensitive to surface water levels than groundwater levels. • Lining can reduce seepage losses substantially, but ongoing maintenance is vital. • The optimal relationship between lining areas and seepage losses is investigated. [ABSTRACT FROM AUTHOR]