Regional Frequency Distribution Type of Low Flow in North of Iran by L-moments

A regional low flow frequency analysis in the north of Iran using L-moments was carried out. Low flow events have been represented by the 7-day annual minimum series and the L-moments approach was used to assign these data into homogenous regions. According to the homogeneity measure and climatic properties, two subdivisions were found – one in the west of the study area having a homogenous assemblage of sites, and one in the east in which the sites were found to be heterogeneous. The regional low flow frequency distribution was derived for the western division using L-moments and goodness of fit tests were used to evaluate which of a number of possible distributions best represented this. The evaluation suggested that the Generalized Logistic distribution gives the best overall result. For heterogeneous subdivision, the performance of the 2-parameter distribution such as 2-parameter Log Normal, Normal and Gamma distributions gave the best result for the majority of sites. Regional and at-site frequency curves were also compared for the western division, which showed that the quantile estimates could be very different in the upper and lower tails of the distribution. The influence on flow regime and watershed properties on the type of the best fit distribution was investigated which showed that the 2 and 3 parameter distributions do not have a clear relationship with climatic and physiographic characteristics of the watersheds except the watershed area. This may result in simple scaling laws of low flows.     

Flood Intensification due to Changes in Land Use

The non-stationarity in runoff regime may be attributed to various causes such as climate change, land use change, and man-made runoff control structures. Degradation of land use can induce significant impact on infiltration and surface roughness leading to higher flood discharges. This study aims at quantifying possible effects of land use changes and identifying flood source areas for future flood control planning in the Golestan watershed located northeast of Iran. A preliminary trend analysis on the annual maximum flood record of three stations inside the watershed showed that two stations were subject to anthropogenic change. This is while no trend could be detected in the annual maximum rainfall records in the region. Using a calibrated event-based rainfall-runoff model, flood hydrographs corresponding to land use conditions in 1967 and 1996 were simulated and relative changes in the peak flow of the two subsequent conditions were determined for different return periods. The results showed that the impact of land use changes on the flood peak discharge is considerably greater in some subwatersheds. Two limiting land use scenarios were also considered to investigate the envelope of future flood peaks in the watershed. By successively eliminating subwatersheds from the simulation process in a method titled "unit flood response”, the contribution of each subwatershed to the outlet flood peak was quantified. Contribution, per unit area, to the outlet flood peak was the basis to rank the subwatersheds in terms of their flood potential.     

Optimizing Hydropower Reservoir Operation Using Hybrid Genetic Algorithm and Chaos

Genetic algorithms (GA) have been widely applied to solve water resources system optimization. With the increase of the complexity and the larger problem scale of water resources system, GAs are most frequently faced with the problems of premature convergence, slow iterations to reach the global optimal solution and getting stuck at a local optimum. A novel chaos genetic algorithm (CGA) based on the chaos optimization algorithm (COA) and genetic algorithm (GA), which makes use of the ergodicity and internal randomness of chaos iterations, is presented to overcome premature local optimum and increase the convergence speed of genetic algorithm. CGA integrates powerful global searching capability of the GA with that of powerful local searching capability of the COA. Two measures are adopted in order to improve the performance of the GA. The first one is the adoption of chaos optimization of the initialization to improve species quality and to maintain the population diversity. The second is the utilization of annealing chaotic mutation operation to replace standard mutation operator in order to avoid the search being trapped in local optimum. The Rosenbrock function and Schaffer function, which are complex and global optimum functions and often used as benchmarks for contemporary optimization algorithms for GAs and Evolutionary computation, are first employed to examine the performance of the GA and CGA. The test results indicate that CGA can improve convergence speed and solution accuracy. Furthermore, the developed model is applied for the monthly operation of a hydropower reservoir with a series of monthly inflow of 38 years. The results show that the long term average annual energy based CGA is the best and its convergent speed not only is faster than dynamic programming largely, but also overpasses the standard GA. Thus, the proposed approach is feasible and effective in optimal operations of complex reservoir systems.     

Fuzzy AHP Assessment of Water Management Plans

There are two mainstreams when using the analytic hierarchy process (AHP). One is the standard applications of crisp distributive and ideal mode versions. The other is characterised by fuzzification of the AHP methodology and by attempts to better tackle inherently uncertain and imprecise decision processes with quantitative and qualitative data. The latter is characterised by different approaches to fuzzificating the decision problem; the way of conducting judgment and evaluating process; and finally, in synthesising the results and manipulating fuzzy numbers to devise priorities for the decision alternatives. This paper presents a fuzzy methodology for solving fully structured decision problems with criteria, sub-criteria and alternatives. It follows the logic of AHP in a simple and straightforward manner, efficiently aggregates criteria and sub-criteria into unique hierarchical level and applies a total integral method for comparing decision alternatives. The proposed methodology has been used for the assessment of water management plans in part of the Paraguacu River Basin in Brazil.     

Estimating the Potential Impacts of Irrigation Water Pricing Using Multicriteria Decision Making Modelling. An Application to Northern Greece

A great challenge of the current European water policy is the implementation of volumetric water pricing in the agricultural sector, especially of Mediterranean countries, where irrigation is a necessary precondition of agricultural production and farmers’ income, but also the major consumer of water. The overall aim of the present work is to develop a methodology that will be suitable for the estimation of the potential environmental, economic and social impacts of irrigation water pricing. For this purpose, Multi-Attribute Utility Theory is implemented in order to simulate agricultural decision making at various water pricing scenarios. Water demand functions are then elicited, by means of the best crop and water allocation (farmers’ decisions) in each scenario. The European Water Framework Directive recommends that any issue concerning water resources management (including water pricing policies) should be developed at the river basin level. In this framework, a cluster analysis is performed to partition the river basin area (namely, Loudias River Basin, located in Northern Greece) into a small number of homogeneous sub-regions. The differential impact of water pricing in each region is then analyzed, and finally, an average water demand function is formulated for the whole river basin.     

Study of Drawdown–Drain Discharge Relationship and its Application in Design of Cost Effective Subsurface Drainage System in Mugogo Swamp, Busogo, Rwanda

Mostly the swamps in Rwanda are surrounded by volcanic hills with small streams flowing to discharge runoff and seepage water. Mugogo swamp is located in Busogo sector, Musanze district, North province. Total area of the swamp is approximately 50 ha. The swamp is surrounded by hills and elevated volcanic rocky terrains. Potato is the main crop cultivated in the swamp. The average production rate of potato is 7 MT/ha which is very low compared to 12 MT/ha in well drained areas. During rainy season seepage water and runoff water from the surrounding hills cause the waterlogged condition of the swamp and affecting the potato cultivation and land productivity. The remedial measure for this swamp is to divert separately the runoff and seepage water from surrounding catchment area and then remove the recharge water by pumping through a system of subsurface drains. Hydraulic head–drain discharge relationship can be fitted with quadratic equation. Equivalent drainable porosity and equivalent hydraulic conductivity are determined as 0.105 m/day and 0.34% respectively for drain depth of 40 cm from soil surface. Effective hydraulic conductivity in the soil profile shows that its average value in the top 15 cm of soil layer is 0.17 m/day and that in the remaining depth up to impermeable layer is 0.015 m/day. Third degree polynomial expressions are made for Head–hydraulic conductivity and head–drainable porosity relationships. The nonlinear relation of hydraulic conductivity and drainable porosity with drawdown shows that the proximity of Kinoni stream does not affect drainage parameters of the area because of less seepage from the stream. The study also reveals that adoption of 7 m drain spacing is very less if crop parameter is not considered and will result higher drain cost. Drainage coefficient of 5 mm/day is arrived considering the rainfall distribution, infiltration rate of soil, allowable water logging tolerance of potato crop. Required drain spacings are calculated for different drainage coefficients of 1, 2, 3, 4 and 5 mm/day under different drawdown conditions to plot subsurface drainage characteristic curves of the swamp. These curves are useful to directly read the drain spacing and drain depth for the required drainage coefficient without going for tedious calculations. Cost analysis shows that the ratio of drain spacing to drain depth can be a decisive factor to select best combination of drain depth and drain spacing. For drainage coefficient of 5 mm/day, optimum drain spacing-depth ratio is found as 7.2 with a cost of 0.689 million Frw/ha. For different drainage coefficients in the swamp, the drain depth of 1.5 m is crucial and optimum cost occurs at this depth. It is also found that any increase in drawdown beyond the drawdown at critical drain depth will not reduce the cost significantly.     

Water Right Institution and Strategies of the Yellow River Valley

With the rapid economic and social development in China, pressure on water resources in the Yellow River is becoming more and more prominent. For the sustainable social, economic and agricultural development in the Yellow River valley, it is imperative to create the perfect water right institution, which plays a key role in improving the efficiency, equity and sustainability of water use. This article analyzes the problems with the water right institution of the Yellow River valley, which includes unclear definition of water right, ineffective allocation mechanism, low water price, and water pollution. Correspondingly, some measures need taking in order to address these challenges. First of all, the water right, especially tradable water right should be well defined. In the article, water right is defined as a series of water management capabilities and use requirements. Then, water right allocation system should be built up, including examining and approving water usufruct, the paid transfer, and the paid utilization of water right. In the end, based on the well defined tradable water right and the well developed water right allocation system, water right market should be developed, which will promote the transfer to the highest valued water uses. When the water right trade happens, the water right price should be fixed in certain situation. On one hand, the water right price should be raised; on the other hand, the water right price should be determined according to a two-part water price system. Of course, market should not be the only role in the water right institution. The authorities should also be necessarily responsible for water right organizations, which make proper water right law, policy and regulations that assist the smooth going of water right market. There are some other measures for the yellow river, such as a water booklet should be recorded for mastering the detailed situation of water resources in the Valley; the South-to-North Water Diversion Project should be accelerated in order to alleviate the water scarcity. All the above measures will do good to resolve the problems of water resources of the Yellow River valley when they are correctly taken.     

An Inexact Two-stage Fuzzy-stochastic Programming Model for Water Resources Management

An inexact two-stage fuzzy-stochastic programming (ITFSP) method is developed for water resources management under uncertainty. Fuzzy sets theory is introduced to represent various punishment policies under different water availability conditions. As an extension of conventional two-stage stochastic programming (TSP) method, two special characteristics of the proposed approach make it unique compared with existing approaches. One is it could handle flexible penalty rates, which are much reasonable for both of the authorities and users, and have seldom been considered in the TSP framework. The other is uncertain information expressed as discrete intervals and probability distribution functions can be effectively reflected in the optimization processes and solutions. After formulating the model, a hypothetical case is employed for demonstrating its applicability under two scenarios, where the inflow is divided into four and eight intervals, respectively. The results indicate that reasonable solutions have been obtained. They provide desired allocation patterns with maximized system benefit under two feasibility levels. The solutions present as stable intervals with different risk levels in violating the water demands, and can be used for generating decision alternatives. Comparisons of the solution from the ITFSP with that from the ITSP (inexact two-stage stochastic programming) and TSP approach are also undertaken. It shows that the ITFSP could produce more system benefit than existing methods and deal with flexible penalty policies for better water management and utilization.     

Use of L-Moments Approach for Regional Flood Frequency Analysis in Sicily, Italy

Extremely great floods are among environmental events with the most disastrous consequences for the entire world. Estimates of their return periods and design values are of great importance in hydrologic modeling, engineering practice for water resources and reservoirs design and management, planning for weather-related emergencies, etc. Regional flood frequency analysis resolves the problem of estimating the extreme flood events for catchments having short data records or ungauged catchments. This paper analyzes annual maximum peak flood discharge data recorded from more than 50 stream flow gauging sites in Sicily, Italy, in order to derive regional flood frequency curves. First these data are analyzed to point out some problems concerning the homogeneity of the single time series. On the basis of the L-moments and using cluster analysis techniques, the entire region is subdivided in five subregions whose homogeneity is tested using the L-moments based heterogeneity measure. Comparative regional flood frequency analysis studies are carried out employing the L-moments based commonly used frequency distributions. Based on the L-moment ratio diagram and other statistic criteria, generalized extreme value (GEV) distribution is identified as the robust distribution for the study area. Regional flood frequency relationships are developed to estimate floods at various return periods for gauged and ungauged catchments in different subregions of the Sicily. These relationships have been implemented using the L-moment based GEV distribution and a regional relation between mean annual peak flood and some geomorphologic and climatic parameters of catchments.     

Optimal allocation of water resources in large river basins: II. Application to Yellow River Basin

In this paper, the theoretical approach presented in Part I is demonstrated by means of case study on the optimal allocation water resources for Yellow River Basin of China. The object of the case study was to find the optimization of water allocation among subregions and trunk streams of the basin in order to achieve the maximum national economic benefits and the optimal reservoir storage required to maintain the long-term balance of water resources.The optimal allocation of water resources pattern caters for irrigation, hydropower generation, navigation, water supply and other sectors, depending to a large extent on the objective economic benefits obtained from the whole valley and on the objective of reservoir storage. Other factors incapable of being expressed in terms of the two objectives considered in the section concerning constrained conditions. This research is applicable widely and suitable for the solution of complicated, multi-objective large-system problems involving non-linearity, numerous variables and various constrained conditions. Finally, the results of optimal allocation of water resources for Yellow River Basin (OAWRYRB) have been selected on an optimum basis in accordance with the multi-objective method.The application of our optimization techniques to the Yellow River basic showed that the total water of the Yellow River over a year can be allocated by optimization. The maximum national economic benefits and the optimal reservoir storage required to maintain the long-term balance of water resources can also be obtained by the optimal techniques.