Characterization and control of irrigation canal seepage losses: A review and perspective focused on field data

Canals compose the arterial structure of irrigated agriculture, transporting free-surface flows to the vast majority of the world’s most productive farmland. Here we present a critical review and perspective of studies that describe the widespread and serious issue of seepage losses that occur as flows move through this critical network of watercourses. Such losses impact the hydrologic setting and pose challenges to water conservation, agricultural productivity, and water quality. With an aim to better understand the characterization and control of irrigation canal seepage in actual field settings, studies employing the most common field methods (inflow-outflow, ponding, and point measurements) in canals with different perimeter types (earthen, or treated with hard-surface, flexible membrane, compacted earth, and polymer sealants) are considered. Information from 44 peer-reviewed journal articles (impact factor > 1.5) is summarized, synthesized, and evaluated. Statistics of measured seepage categorized by different units, methods of measurement, and type of canal treatment indicate significant variation within and across categories. Given the variation in site-specific conditions, reported seepage rates also vary markedly, with seepage from earthen canals ranging on the order of 0.1–1 m3/day per m2 of canal perimeter area. We find that much of the canal treatment literature lacks consistent and comparable reporting, with only a few studies providing both pre-and-post-treatment seepage values for a specific treatment method to assess effectiveness. Nevertheless, field data point to achievable levels of seepage reduction ranging from about 50–95% across treatment methods. Given the current state of knowledge and availability of refined measurement devices and protocols, we recommend the inflow-outflow method as the standard field technique for canal seepage characterization. Recognizing cost and the need for flexibility to allow groundwater recharge as key deciding factors for canal treatments, while acknowledging the need for further investigation, we recommend further consideration be given to the use of polymer sealants as a broadly promising means of canal seepage control.