Simulating system‐wide effects of reducing irrigation withdrawals in a disputed river basin

Stakeholders in river systems often target larger upstream water consumers as an intuitive solution for increasing flows for downstream ecological needs. Within regulated river systems, simplistic panaceas may have unexpected and unintended results at a watershed level. The Apalachicola–Chattahoochee–Flint River Basin is a large watershed in the south‐eastern United States whose management has been the source of conflict for several decades. This paper tests the hypothesis of whether a reduction in consumptive losses to Flint River flows through the large‐scale implementation of water‐saving agricultural irrigation technologies and practices will have a positive effect on downstream ecosystem water requirements in the Apalachicola River. An existing integrated reservoir/reach model was used to explore multiple irrigation water use scenarios. Because of current federal reservoir operating rules in the Chattahoochee River, irrigation decreases in the Flint River do not always directly translate to elevated flows downstream in the Apalachicola River. In drought years, a large percentage of the Flint River water savings is captured as greater storage volume at upstream Chattahoochee reservoirs because of a requirement to supplement downstream flows to a prescribed minimum level. In nondrought years, the majority of irrigation decreases translate to increased flow in the Apalachicola River. Given these simulation results, public policy decisions need to be formulated with regard to what portion of the Flint River water savings from changing irrigation practices in drought years should be allocated to the upstream Chattahoochee storage reservoirs and what portion to supporting downstream environmental and social needs in the Apalachicola watershed.     

Multi- Objective Optimal Design of on- Demand Pressurized Irrigation Networks

In the context of water as an economic good, from the use of water, one can derive a value, which can be affected by the reliability of supply. On-demand irrigation systems provide valuable water to skilled farmers who have the capacity to maximize economic value of water. In this study, simultaneous optimization of on-demand irrigation network layout and pipe sizes is considered taking into account both investment and annual energy costs. The optimization problem is formulated as a problem of searching for the upstream head value, which minimizes the total cost (investment and energy costs) of the system. The investment and annual energy costs are obtained in two separate phases. Max–Min ant system (MMAS) algorithm is used to obtain the minimum cost design considering layout and pipe diameters of the network simultaneously. Clement methodology is used to determine flow rates of pipelines at the peak period of irrigation requirements. The applicability of the proposed method is showed by re-designing a real world example from literature.     

Simplified Monthly Hydrology and Irrigation Water Use Model to Explore Sustainable Water Management Options in the Murray-Darling Basin

We aimed to provide whole-of-basin simulations of flows and diversions in the Murray-Darling Basin for economic and policy analysis. We describe a model based on a subdivision of the basin into 58 catchments. In each catchment, the monthly runoff, river flow and irrigation demand are modelled as lumped processes. This is the first single model of the whole of the Murray-Darling Basin. The model was calibrated using monthly flow and annual diversion records, both by trial and error and using an automated method. We use the model to examine the impact on the flow and diversions in the Murray-Darling Basin of proposed diversion reductions and climate change. The diversion reductions return water to the environment, increasing river flows below the main irrigation areas. However, a middle-of-the-range climate change projection may result in a 13 % decrease in total flows in 2030, which offsets the enhancement to flows gained by diversion reductions.     

Changes in Irrigation Planning and Development Parameters Due to Climate Change

Considering changes in irrigation planning and development due to climate change is necessary to avoid system failure. This study demonstrated that changes in dependable flow and diversion water requirements in the future due to climate change will reduce potential irrigable areas. Climate change were based on the published projected climate in the study area. The dependable flow derived from successfully calibrated and validated Soil and Water Assessment Tool (SWAT) model streamflow simulations and the diversion water requirements based on the CROPWAT estimations of irrigation scheme were used to assess the potential irrigable areas. Substantial reductions in potential rice production areas (-4% to – 39%) were largely due to dwindled dependable flow (-1% to -25%) and an increase in diversion water requirement (+?7% to?+?26%). Reduction in potential irrigable area was projected during dry and normal years and may worsen towards the late twenty-first century under the worst-case climate scenario. Swelling of rivers during wet years will increase stream flows and potential irrigable areas but may also pose a danger of flooding. The development of water storage structures is necessary to reduce the adverse impacts of too much water during the wet years. Crop calendars should also be retrofitted to optimize the use of available rainfall during dry and normal years and climate-proof future irrigation systems. The results showed that it is necessary to incorporate climate change in irrigation planning and development. The methodologies described here could be used to climate-proof future irrigation systems in other areas in the Philippines and other countries.

     

Relating Crop Water Consumption to Irrigation Water Supply by Remote Sensing

A new set of irrigation performance indicators based on remote-sensing estimates of evapotranspiration is introduced. These evapotranspiration indicators are the relative evapotranspiration or crop stress and the water efficiency as well as their uniformity. With a remote-sensing evapotranspiration algorithm (SEBAL) maps of actual crop water consumption are derived. These maps are one of the inputs in the evapotranspiration indicators, together with GIS data (digitized irrigation unit boundaries) and field data (irrigation delivery schedule and water flow). This approach is applied on the Rio Tunuyan irrigation scheme, Mendoza, Argentina, which is served by surface water and privately owned ground water pumps. A homogeneous pattern of actual crop water consumption is detected from the highest irrigation level till the lowest (farm) level (coefficient of variance from 8.6% to 6.1% and 14.0% of secondary, tertiary and pixel level, respectively). Considering that a rotational irrigation schedule at tertiary and farm level is present, the results indicate that ground water supply through extraction and capillary rise equalize the spatial patterns in crop water consumption. The latter is proved by a comparison between (i) the areal water consumption from remote-sensing measurements, (ii) the areal water supply and (iii) additional field information on ground water extraction and capillary rise.     

黄河自净需水量研究

自净需水量是环境水量的重要组成部分，是河流接纳合理污染物量所对应的、河流必须蓄存的满足良好水质要求的最小水量及水量过程。本文通过建立黄河自净需水量模型，分别对黄河花园口以上河段以及利津断面的自净需水量进行计算。计算结果表明，在现状入黄城镇点源超标排放、入黄支流污染严重的情况下，实现黄河水质目标所需的稀释水量较大，黄河现状水资源无法满足要求；在入黄城镇点源达标排放、入黄支流实现入黄水功能区水质目标的前提下，黄河自净需水量随季节年内变化整体不大，枯水低温期所需自净需水量稍高，其中90％保证率最枯月平均流量能够基本满足黄河自净需水量，但青铜峡、石嘴山、潼关等污染严重河段所需自净需水量仍然较大，对应最枯月平均流量保证率介于8.5%～87%之间。     

Two-step dynamic programming approach for optimal irrigation water allocation

A two-step (deterministic and stochastic) dynamic programming approach has been introduced in this study to solve the complex problem of optimal water allocation in a run-of-the-river-type irrigation project. The complexity of a real-world situation is represented by incorporating in the optimization model the stochasticity of water supply and the nonlinearity of crop production functions. A nonlinear, dated, and multiplicative production function is transformed into a sequentially additive type to replace the usual method of creating an additional state of the plant variable which only increases the dimension of the problem. As compared to the explicit stochastic dynamic programming which necessitates, along with its use, an enormous computational complexity due to the so-called curse of dimensionality, the present model can approximate the theoretical global optimum, at least for the present case study, with a dramatic reduction in computer processing time. It also eliminates the rigidity of the policy derived by the explicit approach, since it provides irrigation planners with alternative decision policies which incorporate intangibles and other nonengineering factors. The traditional method of fixing the cropping pattern based on deterministic estimates of a dependable water supply can likewise be evaluated by the use of the present model. The results of the model's application appear to be practically acceptable.     

Modifiers and Amplifiers of High and low Flows on the Ping River in Northern Thailand (1921–2009): The Roles of Climatic Events and Anthropogenic Activity

We analyse an 89-year streamflow record (1921?C2009) from the Upper Ping River in northern Thailand to determine if anomalous flows have increased over time (Trenberth, Clim Res 47:123?C138, 1999; Trenberth, Clim Chang 42:327?C339, 2011). We also relate the temporal behavior of high and low flows to climatic phenomena and anthropogenic activities. Peak flows have not increased significantly since 1921. However, minimum flows showed a very significant downward trend over the study period (???=?0.01). Annual and wet season discharge show significant downward trends (???=?0.05). All flow variables appear to be more variable now than 90?years ago especially annual peak flows. Both annual peak and minimum flows are correlated with annual and wet season rainfall totals. Minimum flow is also sensitive to the length of the monsoon season and number of rainy days in the previous monsoon season. Peak flow activity is driven predominantly by climate phenomena, such as tropical storm activity and monsoon anomalies, but the relationship between peak flows and ENSO phenomena is unclear. In general, annual discharge variables did not correspond unequivocally with El Nin? or La Nin? events. Minimum flows show a major decline from the mid-1950s in line with major anthropogenic changes in the catchment. The plausible intensification of the hydrological cycle that may accompany global warming is of concern because of the potential to affect tropical storm activity and monsoon anomalies, phenomena that are linked with very high flows in this river system. The obvious effect of human activities such as reservoir management on low flows calls for careful management to prevent droughts in the future.     

Integrated irrigation development planning by multi‐objective optimization

A multi‐objective linear‐programming‐based planning model for irrigation development, incorporating the integrated use of surface and groundwater resources, is presented. Applicability of the model is illustrated by a case study of the Bagmati River Basin, Nepal. Alternative plans for irrigation development are identified by analysing trade‐offs between the specified objectives of maximizing total net economic benefits from agriculture (economic efficiency) and total irrigated cropped area (balanced regional development). Evaluation of the alternatives by compromise programming is carried out in order to indicate the optimal scale of development, cropping plans, system design capacities and water allocation policies.     

Application of ANN-Based Streamflow Forecasting Model for Agricultural Water Management in the Awash River Basin,Ethiopia

This paper presents the application of a long-term streamflow forecasting model developed using artificial neural networks at a stream gauging station in the Awash River Basin, Ethiopia. The gauging station is located above the headworks of a large irrigation scheme called the Middle Awash Agricultural Development Enterprise (MAADE). Based on the forecasted streamflow time series and water requirements for irrigation and environmental purposes, appropriate agricultural water management strategies have been proposed for the irrigation scheme (MAADE). The water management strategies which were evaluated in this study are based on different scenarios of abstraction demands. These demands were formulated based on a range of options for agricultural development and change in MAADE. The scenarios evaluated were based on such factors as the existing planting patterns, changing planting dates, changing crop varieties and reducing the area under cultivation. An appropriate scenario of agricultural development was decided on the basis of the modified flows in the river vis-à-vis the trigger/threshold value established at the Melka Sedi stream gauging station. Considering all the scenarios, it is suggested that a 1–24% reduction in the area currently irrigated in the scheme will ensure a reliable supply of water to the scheme throughout the growing season and will provide sustainable environmental flow in the river.