Canal Seepage Research Articles

Potential and net recharge assessment in paddy dominated Hirakud irrigation command of eastern India using water balance and geospatial approaches

Spatially distributed potential and net recharge rates were assessed in the paddy dominated Hirakud command area (Eastern India) at 100 m grid resolution using surface water balance and Water Table Fluctuation (WTF) methods, respectively, for the period 2001–05. Net recharge estimated using the WTF method corresponding to observation well locations was further interpolated using kriging technique available in the ArcGIS software. Net recharge to potential recharge ratios (%) were also assessed spatially. Water balance components (i) runoff was estimated using the Natural Resources Conservation Service-Curve Number (NRCS-CN) method (ii) reference evapotranspiration by (Hargreaves and Samani, Applied Engineering Agriculture ASABE 1:96–99, 1985)), crop evapotranspiration by (Allen et al., Crop evapotranspiration: Guidelines for computing crop water requirements, FAO Irrigation and Drainage, Food and Agriculture Organization, Rome, Italy, 1998) and evaporation from uncultivated lands by Ritchie (1972) approaches, and (iii) canal seepage using simple canal flow model. Annual groundwater draft during Kharif and Rabi was found to be 144.41 and 112.49 ha-m, respectively. Nearly, 90% of the study area contributed runoff in the range of 200–400 mm during the years 2002–03, 2003–04, and 2004–05. The estimated seepage losses vary between 5 and 15% of irrigation depth for all distributaries. Potential groundwater recharge during wet, normal, and dry years ranges between 650 and 1033 mm, and equivalent to 67%, 78%, and 60% of annual rainfall, respectively. Net recharge ranges between 8 and 11% of the annual rainfall. Mean ratio between net recharge to potential recharge is nearly 30%, indicating that nearly 70% of potential recharge is accounted as outflow from the study area. Parmanpur distributary canal located at the centre of the study area that exhibited higher potential recharge can be scheduled at the end to avoid water logging problem. Further, extraction of groundwater during non-monsoon period for irrigation purpose not only helps in controlling waterlogging but also helps in maintaining stable groundwater level. Overall, spatio-temporal distribution of recharge in the command area indicated that the irrigation demands during non-monsoon season can be met through sustainable management of underexploited groundwater resources. Such an integrated management of surface and groundwater can help in improving water use efficiencies as well as agricultural productivity.

Enabling improved water and environmental management in an irrigated river basin using multi-agent optimization of reservoir operations

In Colorado's Lower Arkansas River Basin (LARB), inefficient irrigation and canal seepage contribute to salinization and waterlogging of irrigated lands and to stream-aquifer pollution. The geographic information system (GIS)-based river basin management model River GeoDSS is applied to further explore best management practices (BMPs) earlier determined to remedy these agro-environmental impacts. Unfortunately, BMP benefits are offset by altered irrigation return flows which change historical downstream river flows, threatening compliance with water rights and the Arkansas River Compact. Compensation is possible through optimal sizing and operation of a dedicated reservoir storage account. Multi-agent optimization combines a metaheuristic mutation linear particle swarm optimization (MLPSO) with a fuzzy rule-based system to produce generalized operational policies along with optimal storage sizing, to enable BMPs while satisfying legal constraints. A storage account making up less than 5% of available reservoir capacity can be operated with rules that enable implementation of even the most aggressive BMPs.

An Experimental Study on Concrete and Geomembrane Lining Effects on Canal Seepage in Arid Agricultural Areas

Canal lining is commonly used to reduce seepage loss and increase water use efficiency. However, few studies have quantitatively estimated the seepage control effects of different lining materials under different service times. Ponding tests were conducted on the same canal section with four different lining statuses to investigate the canal lining effect on seepage control and its impact factors in arid areas. The cracks and holes in different lining materials were surveyed, and the canal seepage rates under the four test treatments were calculated by monitoring the water level change in the canal. The results show that the cracks in the joints of the two precast concrete slabs and holes in the geomembrane, which are located 0.25 m above the canal bottom on two sides of the canal, are responsible for the increased seepage loss. The new concrete and geomembrane lining combination reduces seepage by 86% compared with no lining, while seepage can be reduced by 68% using the concrete and geomembrane lining combination after three service years, and the amount decreases to 11% by using geomembrane lining with a three year service time. Based on the experiment and literature, a statistical relationship between the seepage reduction and lining service time was established, which provided a possible and easy way to estimate seepage losses from lined canals and improve the estimation accuracy using an empirical formula. Without considering the service time lining effect, the seepage loss is underestimated by 58%, and the canal water use efficiency is overestimated.

Assessment of Surface Water -Groundwater Relationship in the Area Between Borg El Arab and West El Hammam, North West Coastal Zone, Egypt

The study area, between Borg El Arab and El Hammam, is recently subjected to intensive land reclamation projects aiming to cultivate about 57000 feddans. It is supplied by two main sources of irrigation, i.e. the surface water as a main source (Bahig canal and El Hammam canal), and the groundwater from more than 600 shallow wells tapping the Ralat aquifer (calcareous sandstone) of Plio-Pleistocene age as a supplement source. During the last three decades (1985 – 2014), conjunctive use of surface water together with groundwater has resulted in serious hydrologic problems e.g. water losses, canal seepage and water logging, where the depth to water level has risen up from about 20 m (1985) to less than 5.0 m (2014). Meanwhile, the groundwater salinity decreased during this period from more than 5000 ppm to less than 2000 ppm, indicating a dilution effect by seeped water. The water seepage from the dissecting canals is estimated in the present work by 65.18 x 106 m3/year replenishing the groundwater system in the down gradient areas. Might as well, the irrigation return flow through permeable soil in the study area is estimated by 4.125 x 106 m3/year due to the applied flood irrigation technique. In other words, 95% of the total groundwater replenishment is from the canal seepage, while only 5% from direct percolation. The investigation of wells tapping the Ralat aquifer in the study area has indicated that water levels are ranging from 21.0 m to 1.0 m above mean sea level. More than 57.6 x 106 m3/year (average 84% of the natural groundwater discharge) are pumping from such wells to get water of about 2000 ppm salinity, indicating a significant hydraulic connection between the surface water canals and the underlying aquifer. The calculated water balance of the Ralat aquifer has resulted in an amount of annual surplus water of the order of 11.705 x 106 m3/year as groundwater storage.

Assessing causes and identifying solutions for high groundwater levels in a highly managed irrigated region

High groundwater levels in urban and irrigated areas around the world can lead to infrastructure damage, land degradation, and crop yield reduction. Causes can include groundwater flooding due to fluvial processes, excess rainfall and irrigation, inadequate subsurface drainage, and additional sources such as injection and seepage from earthen canals and recharge ponds. The principal causes of shallow water tables, however, are difficult to quantify due to the inter-connectedness of all possible causes. This paper presents a method to analyze and quantify the cause of high groundwater levels in highly managed, irrigated stream-aquifer systems, using a combination of numerical groundwater flow modeling and global sensitivity analysis (GSA) tools. A tested MODFLOW groundwater model and Sobol GSA methods are used to simulate and then quantify the influence of all major groundwater stresses on water table elevation for a region in northern Colorado, USA experiencing high groundwater levels, with results showing that recharge from surface water irrigation, canal seepage, and groundwater pumping have the strongest influence on water table elevation, whereas precipitation recharge and recharge from groundwater irrigation have small influences. Time series sensitivity plots quantify the seasonality of these influences over a decadal period, and spatial sensitivity plots indicate regions that are strongly influenced by individual stresses. Results from best management practice (BMP) implementation indicate that limiting canal seepage and transitioning >50 % of cultivated fields from surface water irrigation to groundwater irrigation can decrease water table elevation by 1.5 m–3 m over a 5-year period, leading to beneficial conditions for crop growth in the root zone and dewatering of subsurface infrastructure. These methods can be applied to any waterlogged region worldwide. However, proposed management practices to lower water table may be constrained by local, state, or national water law.

Development in canal lining technology in China

AbstractCanal seepage control is important not only to reduce the canal seepage loss rate, but also to prevent erosion, deposition and collapse of canals and control the surrounding groundwater level, which is taken seriously by the governments. This study reviews the history of canal seepage control in China, introduces the canal lining technologies, concludes the canal lining construction problems and points out the further study fields of seepage control in canals. With the enhancement of environmental protection consciousness, seepage control engineering is confronted with new opportunities and challenges, especially the ecological canals, of which the relative technologies need to be deeply studied.

Stability analysis of unsaturated soil slope under rainfall and seepage conditions

Rainfall infiltration and canal seepage are the main causes of slope instability, the paper considered the factors such as soil type, soil-water characteristic curve and rainfall duration, and analysed the stability of unsaturated soil slope. The calculation results show that rainfall has a significant impact on the stability of the slope, as the matric suction in the unsaturated soil makes the slope safer. However, it reduced during rainfall, so the safety factor is greatly reduced when the continuous rainfall occurred. Moreover, when rainfall infiltration and canal seepage coupled, it is worse than just taking one factor into account, and the slope safety factor decreases from stable to unstable.

An assessment of groundwater recharge estimation techniques for sustainable resource management

Groundwater resources are limited and they are declining in quality and quantity due to contamination and climate change impacts. Under the environment of the increasing water demand for domestic, agricultural, and industrial uses and dwindling resources, the management of groundwater resources is a challenging task worldwide. Precise evaluation of groundwater recharge is vital for its sustainable management and efficient use for various sectors of the economy. An overview of different groundwater recharge estimation techniques is presented in this paper. The techniques covered in this study include numerical approach, tracer method, hydrologic budget method, and multiple methods. The norms of recharge estimation through rainfall, canal seepage, and field percolation are also covered in this study. The literature analysis revealed that the tracer techniques are extensively used in water-scarce areas for estimating groundwater recharge. And the use of watertable fluctuations is a valuable means for shaping the size of both long and short-term alterations in recharge. The analysis also revealed that groundwater recharge can be estimated by using the numerical models. Because each approach is associated with some limitations, the use of multiple approaches was recommended to estimate the groundwater recharge. In many cases, diverse approaches balance every other and aid improve the conceptual model of recharge processes. This literature analysis provides the basis for the selection of an appropriate recharge estimation technique under a specific set of conditions.

Enhancing the capability of hydrological models to simulate the regional agro-hydrological processes in watersheds with shallow groundwater: Based on the SWAT framework

This article introduces the SWAT-AG (a modified SWAT for agro-hydrological modeling) as an enhanced hydrological model for simulating the hydrological processes in agricultural watershed with shallow water tables. The model is developed based on the framework of the SWAT with significant improvements on describing the interactions of the vadose zone water, groundwater, salt and plant growth. The main features of the SWAT-AG include that it can simulate the close interactions of soil water and shallow groundwater with considering the capillary rise effects; it provides functions to simulate the soil salt movement and salt-stress on plant growth; and it incorporates a balance-based module on a sub-basin scale for shallow aquifer with involving canal seepage and ditch drainage calculation. Model testing and application were conducted in Jiyuan Irrigation System located in the Hetao of upper Yellow River basin, northwest China. The comparison between simulated and observed data showed that the SWAT-AG performed well and obviously better than the original SWAT in simulating the soil water and salt dynamics, groundwater depth fluctuations, and plant growth and water consumption. The results showed that the NSE averagely increased from −17.57 to 0.57 and from 0.71 to 0.79 for soil water storage and leaf area index, respectively, in typical croplands and natural patches. In addition, the effects of shallow groundwater in sustaining the agro-ecosystems were reasonably revealed with the spatial analysis of evapotranspiration, capillary rise and salt accumulation. The test case proved that the proposed SWAT-AG could efficiently enhance the functionality and practicality of hydrological models for agricultural watersheds with shallow groundwater.

Hydrological complexities in irrigated agro-ecosystems with fragmented land cover types and shallow groundwater: Insights from a distributed hydrological modeling method

Hydrological effects caused by fragmented land cover types in human-dominated agro-ecosystems are poorly understood. In this study, based on visual interpreted high-resolution land cover map, an agro-hydrological model (HYDRUS-dualKc) was used in a distributed manner to investigate the hydrological complexities caused by fragmented land cover types and shallow groundwater. An irrigation system located in the upper Yellow River basin was chosen as a case study area, where field observations were conducted in 2012 and 2013. Combined effects of vegetation, soil, irrigation and groundwater were considered. Simulations of soil moisture and soil salinity fitted well with field observations; evapotranspiration (ETa) was also comparable with remote sensing data. Results showed that the growing season ETa varied from 162 to 567 mm among the different vegetation covers with the values for crop fields usually higher than those for natural lands. The soil evaporation was obviously larger in natural land and the natural vegetation growth was seriously stressed. Through lateral groundwater exchange, the cropland functioned as a stable groundwater recharge zone while the natural land functioned as a discharge zone during the growing season. As a result, 21% of the total water diverted to Jiyuan migrated to natural lands through groundwater due to field percolation and canal seepage, along with 50–75% of the total salt introduced. The fragmented land covers and complex hydrological processes bring many challenges to remote sensing and model simulation. Future land planning and water resources management should consider the hydrological effects caused by the fragmented land cover types and the associated management strategies.

Design approach for interceptor tile drains using hydrus

Abstract Seepage from irrigation canals can be controlled by interceptor pipe drains located down slope of the canal embankment and parallel to the canal. HYDRUS (2D/3D) is a software that simulates water flow in two-dimensional variably-saturated porous media. This software is used to determine the average water contents of the upper layers, direction of flow and the seepage rate to the pipe drain for different values of evaporation rates, pipe diameters, and horizontal and vertical pipe offsets from the conveyance canal. The results showed that increasing the vertical offset (drain depth) increases the drain discharge. Moreover, increasing the horizontal offset reduces the canal seepage and lower the phreatic surface. The proposed approach can determine drain size and location to cut off canal seepage, ensuring no contribution to the water body under the irrigated lands beyond the drain. The approach accounts for realistic soil formations and considers both saturated and capillary flows.

3-D numerical modelling of groundwater flow for scenario-based analysis and management

In recent years, extensive competition for groundwater use among different consumers has exploited major freshwater aquifers in Pakistan. There is an urgent need for appraisal of this precious resource followed by some mitigation strategies. This modelling study was conducted in the mixed cropping zone of the Punjab, Pakistan. Both remote sensing and secondary data were utilized to achieve objectives of this study. The data related to piezometric water levels, canal gauges, well logs, meteorological and lithological information were collected from Punjab Irrigation Department (PID), Water and Power Development Authority (WAPDA). Groundwater flow models for both steady and transient conditions were set-up using FEFLOW-3D. Water balance components and recharge were estimated using empirical relations and inverse modelling approaches. Both manual and automated approaches were utilized to calibrate the models. Moreover, sensitivity analysis was performed to see the response of model output against different model input parameters. Followed by calibration and validation, the model was run for different management scenarios, including lining of canal sections, minimization of field percolation, and change of groundwater abstraction. The study results show a drop in groundwater levels for almost all scenarios. The highest negative change was observed for the 4th scenario (i.e. 25% increase in groundwater pumping over a 10-year period), with a value of 3.73 m, by ignoring very wet summer and winter seasons. For normal weather conditions, the highest negative change was observed for the 4th scenario with a value of 2.91 m followed by 2.68 m for the 3rd scenario (i.e. 50% reduction in canal seepage and field percolation over a 10-year period). For very wet summer and winter seasons, only one positive change was observed, for the 5th scenario (i.e. 25% decrease in groundwater pumping during 10 years period), with a value of 1.17 m. The changes for all other scenarios were negative. The mitigation strategy may include less groundwater pumping, by supporting cultivation of low delta crops and adjusting cropping patterns considering canal water supplies. It is further suggested to support current modelling results by incorporating more detailed information on cropping and by exploring the effect of climate change.

Tracing groundwater recharge sources in the northwestern Indian alluvial aquifer using water isotopes (δ18O, δ2H and 3H)

Rapid groundwater depletion from the northwestern Indian aquifer system in the western Indo-Gangetic basin has raised serious concerns over the sustainability of groundwater and the livelihoods that depend on it. Sustainable management of this aquifer system requires that we understand the sources and rates of groundwater recharge, however, both these parameters are poorly constrained in this region. Here we analyse the isotopic (δ18O, δ2H and tritium) compositions of groundwater, precipitation, river and canal water to identify the recharge sources, zones of recharge, and groundwater flow in the Ghaggar River basin, which lies between the Himalayan-fed Yamuna and Sutlej River systems in northwestern India. Our results reveal that local precipitation is the main source of groundwater recharge. However, depleted δ18O and δ2H signatures at some sites indicate recharge from canal seepage and irrigation return flow. The spatial variability of δ18O, δ2H, d-excess, and tritium reflects limited lateral connectivity due to the heterogeneous and anisotropic nature of the aquifer system in the study area. The variation of tritium concentration with depth suggests that groundwater above c. 80 mbgl is generally modern water. In contrast, water from below c. 80 mbgl is a mixture of modern and old waters, and indicates longer residence time in comparison to groundwater above c. 80 mbgl. Isotopic signatures of δ18O, δ2H and tritium suggest significant vertical recharge down to a depth of 320 mbgl. The spatial and vertical variations of isotopic signature of groundwater reveal two distinct flow patterns in the aquifer system: (i) local flow (above c. 80 mbgl) throughout the study area, and (ii) intermediate and regional flow (below c. 80 mbgl), where water recharges aquifers through large-scale lateral flow as well as vertical infiltration. The understanding of spatial and vertical recharge processes of groundwater in the study area provides important base-line knowledge for developing a sustainable groundwater management plan for the northwestern Indian aquifer system.

Modeling the impact of aquifer recharge, in-stream water savings, and canal lining on water resources in the Walla Walla Basin

The Walla Walla Basin in Eastern Oregon and Washington, USA, faces challenges in sustaining agricultural water supplies and endangered fisheries in the Walla Walla River (WWR). 11.1 Mm3/year of managed aquifer recharge (MAR) is currently used in the basin to supplement groundwater with the goal of maximizing instream flow during dry summer months. A numerical groundwater–surface water model was calibrated to observed hydrological conditions and applied to predict future conditions under current management practices (baseline model) and for four alternative water management scenarios. These scenarios were developed to predict how lining canals to eliminate seepage losses and concurrently reducing irrigation diversions from the WWR will impact stream flows and groundwater storage with varying levels of MAR. Model results predict that seasonal low flows in the WWR at the downstream reference location will increase an average of 0.13 m3/s relative to baseline conditions due to instream water savings with conversion of unlined canals to pipelines (Current MAR-Piped). With MAR increased to 18.0 and 29.9 Mm3/year and an additional 58 km piping (Increased MAR-Piped and Maximum MAR-Piped scenarios), the predicted flow increases in the WWR-averaged 0.16 and 0.26 m3/s, respectively. Without MAR (No MAR-Piped), flow is predicted to decrease for the months of August and September relative to baseline conditions. The “No MAR-Piped” and “Current MAR-Piped” scenarios are predicted to reduce groundwater storage relative to the baseline model due to reduced canal seepage. The “Maximum MAR-Piped” scenario is predicted to yield groundwater storage that is greater than baseline conditions, while groundwater storage is predicted to be similar to baseline conditions in the “Increased MAR-Piped” scenario. Model results indicate that canal piping in combination with increased MAR can allow for increased summer flows in the WWR while stabilizing groundwater storage levels for agricultural use and ecological benefits; whereas lining canals without MAR would be detrimental to environmental flows in the WWR and its tributaries.

Estimation of Seepage Loss in Irrigation Canals of Tendaho Sugar Estate, Ethiopia

Open canals are the common method used to convey water for irrigation in Ethiopian sugar estate, however, little or no attention is given to the evaluation of conveyance systems. Consequently, many of the existing conveyance systems are deteriorating in their physical structures, operation and management. Due to this the current study was conducted to quantify the amount of seepage loss through lined and unlined irrigation canals of Tendaho sugar estate. Seepage losses were determined by inflow-out flow method for primary, secondary, and tertiary canals, while water velocity was determined using a current-meter. The average seepage losses were resulted in 0.55% per 100 m (0.0126 lit/s/m2) and 0.84% per 100 m (0.0180 lit/s/m2) for lined and unlined primary canals whereas, 3.65% per 100 m (0.0391 lit/s/m2) and 4.27% per 100 m (0.0248 lit/s/m2) were obtained for secondary and tertiary canals, respectively. In the result, primary canal seepage loss was higher in unlined than in lined by 0.0054 lit/s/m2 of wetted area of the canal. The result reveals that high seepage loss for both lined and unlined canals may be attributed through damage of geomembrane lining and poor maintenance of earthen canals. To minimize excess seepage and improve the conveyance system, overall maintenance and repair of canals should be done in the Estate.

Managed aquifer recharge through off‐season irrigation in agricultural regions

AbstractOptions for increasing reservoir storage in developed regions are limited and prohibitively expensive. Projected increases in demand call for new long‐term water storage to help sustain agriculture, municipalities, industry, and ecological services. Managed aquifer recharge (MAR) is becoming an integral component of water resources around the world. However, MAR faces challenges, including infrastructure costs, difficulty in enhancing recharge, water quality issues, and lack of available water supplies. Here we examine, through simulation modeling of a hypothetical agricultural subbasin in the western U.S., the potential of agricultural managed aquifer recharge (Ag‐MAR) via canal seepage and off‐season field irrigation. Weather phenomenon in many regions around the world exhibit decadal and other multiyear cycles of extreme precipitation. An ongoing challenge is to develop approaches to store greater amounts of water during these events. Simulations presented herein incorporate Ag‐MAR programs and demonstrate that there is potential to enhance regional recharge by 7–13%, increase crop consumptive use by 9–12%, and increase natural vegetation consumption by 20–30%, where larger relative increases occur for lower aquifer hydraulic conductivity and higher specific yield values. Annual increases in groundwater levels were 7 m, and sustained levels following several years of drought were greater than 2 m. Results demonstrate that Ag‐MAR has great potential to enhance long‐term sustainability of water resources in agricultural basins.

Modeling sulfur cycling and sulfate reactive transport in an agricultural groundwater system

Many irrigated agricultural areas worldwide suffer from salinization of soil, groundwater, and nearby river systems. Increasing salinity concentrations are due principally to a high water table that results from excessive irrigation, canal seepage, and a lack of efficient drainage systems, and lead to decreased crop yield. High groundwater salinity loading to nearby river systems also impacts downstream areas, where saline river water is diverted for application on irrigated fields. This paper presents a physically-based, spatially-distributed groundwater reactive transport model that simulates the fate and transport of sulfate, the principal salt ion in many salt-affected watersheds, in an agricultural groundwater system. The model, developed from the UZF-RT3D model that simulates chemical species transport in variably-saturated subsurface systems, accounts for sulfur cycling (crop uptake, organic matter decomposition, mineralization/immobilization) in the soil-plant system, oxidation-reduction reactions, including the oxidation of residual Sulfur in marine shale, and also the effect of dissolved oxygen and nitrate on sulfate chemical reduction. The model is tested at the small scale (i.e. soil profile) and at the regional scale (500km2) in the Lower Arkansas River Valley (LARV) in southeastern Colorado, an area acutely affected by salinization in the past few decades. Results demonstrate that although the major sulfate reactive transport processes are accounted for, the model consistently under-predicts measured soil and groundwater sulfate concentrations, pointing to the need for a comprehensive salinity module that accounts not only for advection, dispersion, sulfur cycling, and oxidation-reduction, but also salt ion equilibrium chemistry that includes the dissolution and precipitation of salt minerals in the soil-aquifer system. However, the model can be a useful tool to assess sulfate fate and transport in areas that are not dominated by salt mineral precipitation and dissolution.

Tracer an effective tool in detecting canal seepage: case studies from Northern India

Canal irrigation is well developed in several provinces of India since independence. With the increase in demand and irregular rainfall, several areas are covered using canal network to suffice agricultural and drinking water needs. Besides its utility and functioning, several problems are associated with canal irrigation, such as seepage losses and water logging. Apart from geophysical and geological methods, tracer is a tool which can be used to study canal seepage. It facilitates in identifying maximum seepage zones and expected seepage path qualitatively and quantitatively without interrupting normal activity of the canal. In this paper, identification of canal seepage in detail with two case studies namely Indira Gandhi Main Canal (IGMC), Rajasthan, and canals in Kakrapar network, Gujarat, from Indian subcontinent is reported. Tracer studies revealed the vulnerable zone, i.e., fractures or cracks in the canal lining with excessive seepage in both the cases. Tracer technique is a definite, reliable and cost effective tool, which provides unique insight into canal seepage investigation.

Investigation of Irrigation Canal Seepage Losses through Use of Four Different Methods in Hetao Irrigation District, China

Canal seepage is an important cause of irrigation water losses. Specific seepage losses of Gongan lateral and Zuosi field canals, which are located in the Hetao Irrigation District of Inner Mongolia in China, are calculated in this study. Specifically, canal seepage losses are calculated by field experiments, empirical formulas, the Kostiakov formula, and numerical simulations. The ponding method is rarely utilized in large irrigation canals and canals with many branches or high slopes. The results of the field experiment are utilized to compare and analyze the calculation results of three other methods. When the empirical formulas are employed to calculate canal seepage losses, more related factors are considered; hence, more-accurate calculation results are obtained. The first empirical formula is mostly used for canals that do not adopt seepage control measures or apply simple forms for seepage control. The second empirical formula is suitable for the case wherein the entire flow section of a canal has been paved with a soil impermeable layer and canal seepage is in a free state. When the Kostiakov formula is employed to calculate canal seepage losses, the parameter values may differ significantly from the actual conditions. Thus, a large difference exists between the calculation results of the Kostiakov formula and those of the field experiment. The Kostiakov formula is widely utilized in the planning and design of canals, as well as being applied to seepage loss estimation during canal water conveyance and distribution under normal canal operating conditions. The numerical method is utilized to calculate canal seepage losses by simulating the actual situation in the site. Except for the result of seepage loss for the lined Gongan lateral canal, the simulation results of seepage losses for the unlined Gongan lateral and Zuosi field canals and the lined Zuosi field canal are relatively reasonable. If sufficient data of the study area can be obtained and finite-element software can meet the computing requirements, the numerical method can be applied to any channel.

Evaluating a Water Conservation Response to Climate Change in the Lower Boise River Basin

Aquifers created or sustained by seepage losses from Bureau of Reclamation (Reclamation) Projects extend over vast areas of western states. Yet agricultural water conservation measures such as canal lining top the list of State and Federal policies for mitigating the effect of water shortages brought about by climate change. Cost benefit analysis (CBA) of new Reclamation water conservation infrastructure such as canal lining or piping is too often Project-specific, and detached from basin hydrology. The value of canal seepage as a positive externality is thus ignored in CBA. A basin-wide approach to hydro-economic modeling that accounts for the externalized costs and benefits of both canal seepage and new canal lining conservation insures that incidental aquifer recharge is recognized in CBA of Federally financed irrigation water conservation measures. Integrated hydrologic and partial equilibrium models are employed in the Lower Boise River basin to calculate the foregone benefit to non-project groundwater and drain water irrigation of a hypothetical Boise Project canal lining response to projected climate change water shortages. Basin-wide hydrologic response data is used to compute shifts in non-project groundwater supply functions and drain water supply constraints, and a base-case water supply scenario is compared to six climate change scenarios in which projected water shortages are offset by lining of project canals. The foregone net benefit to non-project groundwater and drain water irrigation resulting from elimination of the canal seepage externality (US$[Formula: see text]4.4–22.6[Formula: see text]million depending on the scenario) outweighs the increase in net benefit to Boise Project irrigation by canal lining (US$[Formula: see text]1.4–19.3[Formula: see text]million). On average, foregone groundwater and drain water irrigation benefit exceeds restored canal irrigation benefit by about 38%. Canal lining conservation is unable to restore total basin-wide irrigation net benefit to the base-case level in any of the climate change scenarios; rather it shifts the foregone benefit of climate change shortages from project canal irrigation to non-project groundwater and drain water irrigation. The canal lining CPA is not a complete accounting of either costs or benefits of canal lining conservation. On the cost side, only the foregone benefits of eliminating the positive canal seepage externality are calculated; construction and maintenance costs of canal lining are omitted. On the benefit side, Arrowrock canal irrigators are assumed to be the sole beneficiary of reduced seepage losses.