Irrigation
M.H. Naderi; N. Arab; O. Jahandideh; Meysam Salarijazi; A. Aarb
Abstract
Introduction: Hydrological variability is of great importance for water resources management. Analyzing the instream environmental flow demand by coupling the hydrological cycle and the hydrodynamic process with aquatic ecological processes at a watershed scale remains one of the most important yet most ...
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Introduction: Hydrological variability is of great importance for water resources management. Analyzing the instream environmental flow demand by coupling the hydrological cycle and the hydrodynamic process with aquatic ecological processes at a watershed scale remains one of the most important yet most difficult issues. Ecological water demand (environmental flow) refers to the typical—intra-annual and inter-annual natural flow regime variability—which describes the quality, quantity, and timing of flow discharge required to preserve the ecosystem and sustain essential services upon which human livelihoods and well-being depend. Therefore, ecological water demand (EWD) should be considered as a constraint in water resource planning and management.
Materials and Methods: Numerous methods and frameworks have been developed for establishing ecological water demand at regulated rivers. Hydrologically-based ecological water demand methods, because of their simplicity, data availability, and other economic and social aspects, remain the most applied ones. A suitable range of discharges environmental flow Dinavar River was estimated using advocate statistical analysis of hydrological methods Tennant, Annual Distribution Method, and Texas, coupled with habitat suitability model using the program River2D to natural flow variability need. River2D is a two-dimensional, depth-averaged hydrodynamic and fish habitat model widely used in environmental flow assessment studies. A detailed digital model of the river channel and its surrounding area was developed, including all the morphological characteristics of the river channel and its various sandy islets. Data collection was performed through GIS/GPS mapping surveys, hydro-morphological measurements (water depth, flow, substratum type, etc.), and electrofishing samplings at a microhabitat scale under different discharge conditions. Several different steady-state hydraulic simulations were conducted under typical low flow conditions, producing water depth and water velocity (direction and magnitude) maps for each discharge scenario, while results were verified with the use of field measurements. In the next step, River2D was used for the fish habitat modeling of the study area, with the application of fish preference curves developed specifically for the study area. Finally, the fish habitat modeling was conducted for the Capoeta trutta (Heckel, 1843) species, divided into two life groups, forced under the flow conditions. Also, the suitable level of ecological water demand and crucial values with different flow frequencies were analyzed, including water level, water surface width, and Weighted Usable Area.
Results and Discussion: Results show that high environmental flow releases did not necessarily provide the highest habitat availability and suitability at all seasons and fish life-stages. The adult life stage resulted in being more vulnerable to water diversion, particularly during the spring season. Shallow-water hydromorphological units suffered the highest habitat loss. Some of the environmental flow methods demonstrated inconsistent results over seasons and fish life-stages by either allowing for higher environmental flow releases. Also, the Weighted Usable Area -Discharge curve was calculated with the suitability index in medium flow conditions. From the result, the Weighted Usable Area is changed according to flowrate. In the flowrate- Weighted Usable Area/A graph, ecological flow can be determined at 1.38 m3/s for Capoeta trutta (Heckel, 1843) species. Ecological flows were calculated in the range 0.17–3.71 m3/s as the required discharge, which assures the welfare and sustainability of protected fish species populations. It was also noticed that low flow months (June to November) required more proportions of mean monthly flow than high flow months (December to May). When compared with flow-duration analysis, it is demonstrative that simulation results fitted EWD considering the quantity of available habitat for fish species. Also, the results of the study indicated that monthly EWD had an increasing trend during the flood season and a decreasing trend during the non-flood season in three sections at different suitable levels. With the increase of suitable levels, the range of EWD in the three sections also increased. The EWD and crucial values were the lowest in April with the smallest range and were the highest from June to October.
Conclusion: The major finding of this research is that the estimated Suitable Range of Discharges could better address environmental water requirements, rather than simply allocating single value minimum ecological flows. Results reveal that the ecohydraulic modeling of river basins should be considered as an indispensable component in sustainable water resources.
Mohammad Hasan Naderi; M. Zakerinia; Meysam Salarijazi
Abstract
Introduction: The field of ecohydraulics is rapidly growing as the society requires a better understanding of the interrelations amongst the dynamics of the physical processes pertaining to aquatic ecosystems and the modifications observed in their habitat as well as the biological responses of the organisms. ...
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Introduction: The field of ecohydraulics is rapidly growing as the society requires a better understanding of the interrelations amongst the dynamics of the physical processes pertaining to aquatic ecosystems and the modifications observed in their habitat as well as the biological responses of the organisms. Environmental flow science is a common tool for assessing the consequences of changing the flow regime of aquatic ecosystems and providing a minimum flow of aquatic species protection. Environmental Flows assessment is a global challenge involving a number of tangible and intangible segments of hydrology, hydraulics, biology, ecology, environment, socio-economics, and several other branches of engineering including water resources management. River impoundment (dams, weirs), water diversions and consequent modifications to flow regimes have highly destructive effects on aquatic species and ecosystems.
Materials and Methods: In this research, two most common hydrologic methods Tennant and FDC Shifting were compared with a habitat simulation method i.e. PHABSIM. Tennant method is the most popular hydrological method in rivers and is based on the historic flow data. Investigation of the relationship between hydrologic approaches and physical habitat simulation approach and presentation of new recommendations based on the ecological and hydrological data can be very useful for estimating environmental flow in planning phase of river projects. We used river habitat simulation program to model the depth and velocities around boulder clusters to evaluate the habitat for Capoeta habitat in Zarrin-Gol River. The Zarrin-Gol River is one of the rivers in Golestan province in northern Iran. The statistics required for hydrologic calculations were also collected from Zarrin-Gol hydrometry station during the 42-year statistical period (1353-1395). In this regard, after the field studies and the development of the habitat suitability model for the target species, the Habitat simulation of the flow was carried out and eventually the ecological flow regime was extracted. In order to identify the important habitat variables and assess their impact, the life pattern of fish species was divided into juvenile and adult life stages.
Results and Discussion: Based on ecological assessment, the environmental water requirement of Gharahsoo river is 30% of mean annual flow for spring and summer and 10% of mean annual flow for autumn and winter seasons. It was found that application of Tennant and FDC Shifting methods led to dramatically low discharges as fixed minimum environmental flows, while habitat simulation method gave an acceptable estimation of ecological regime. However, habitat simulation technique assesses the allowable value of extraction from river flow dynamically, considering the ecological condition and average intermediate values. River conditions including flow velocity, water depth and river bed substrate are combined to form unique habitats facilitating the survival and growth of fish species populations. Habitat forms are observed in a wide range of rivers depending on the diet and the river type such as Pool, Riffle and Run. The destruction of the Riffle substrate causes disruption and impacts the biological integrity of the current. According to the Q-WUA curve of the Riffle habitat in high waters and flood conditions, the area available for juveniles of the target species decreases because of the flood, morphology and habitat of the river, so large and continuous floods inhibit the opportunity to rebuild habitats from the river and endanger the lives of fish. One of the factors limiting the desirability of the habitat and thus reducing the available habitat in low river flows is the low flow velocity, as well as high stream flow flows. The maximum and minimum flow regime, required to maintain the Zarrin-Gol river ecosystem according to ecological needs, was 2.49 and 0.58 m3/s in April and November, respectively, with an average value of 1.25 m3/s (59 % of natural stream of the river). In the next step, habitat suitability distribution along the stream was investigated. This was performed for the full range of discharges. Habitat suitability distribution along the stream at different discharges indicated that the upstream part of the stream had the poorest habitat condition and moving towards the downstream parts, the habitat suitability condition was improved.
Conclusion: Application of the Tennant method based on a hydrological system can be an inappropriate choice for determining the minimum flow to maintain the ecological environment of the river. According to the results, the PHABSIM model can simulate flow, habitat suitability of target species and the habitats dynamics accurately, which is highly required to protect the proper habitat of fish in river ecosystems.
S. Mostafavi; M. Yasi
Abstract
Introduction Development of water resources projects are accompanied by several environmental impacts, among them, the changes in the natural flow regime and the reduction of downstream water flows. With respect to the water shortages and non-uniform distribution of rainfall, sustainable management of ...
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Introduction Development of water resources projects are accompanied by several environmental impacts, among them, the changes in the natural flow regime and the reduction of downstream water flows. With respect to the water shortages and non-uniform distribution of rainfall, sustainable management of water resources would be inevitable. In order to prevent negative effects on long-term river ecosystems, it is necessary to preserve the ecological requirements of the river systems. The assessment of environmental flow requirements in a river ecosystem is a challenging practice all over the world, and in particular, in developing countries such as Iran. Environmental requirements of rivers are often defined as a suite of flow discharges of certain magnitude, timing, frequency and duration. These flows ensure a flow regime capable of sustaining a complex set of aquatic habitats and ecosystem processes and are referred to as "environmental flows". There are several methods for determining environmental flows. The majority of these methods can be grouped into four reasonably distinct categories, namely as: hydrological, hydraulic rating, habitat simulation (or rating), and holistic methodologies. However, the current knowledge of river ecology and existing data on the needs of aquatic habitats for water quantity and quality is very limited. It is considered that there is no unique and universal method to adapt to different rivers and/or different reaches in a river. The main aim of the present study was to provide with a framework to determine environmental flow requirements of a typical perennial river using eco-hydrological methods. The Barandozchi River was selected as an important water body in the Urmia Lake Basin, Iran. The preservation of the river lives, the restoration of the internationally recognized Urmia Lake, and the elimination of negative impact from the construction of the Barandoz dam on this river were the main concerns in this study.
Materials and Methods: With lack of ecological data, the environmental requirements of the Barandozchi River were investigated using five eco-hydrological methods (1- Tennant, 2- Tessman, 3- Flow Duration Indices, 4- FDC shifting, 5- DRM). Some of these methods are too simplistic and do not take into account the direct hydro-ecological interactions (e.g. Tennant method), and some have been developed for a specific country/region (e.g., DRM), and need to be adapted to a different physiographic environment before they can be reliably applied. Two ecological friendly models GEFC, and DRM were tested to estimate the environmental flow of this river. The results were compared with corresponding flows allocated for the release from the Barandoz Dam (currently under construction).
Results and Discussion: The prediction of the mean annual environmental flows from five eco-hydrological methods are presented and compared with the corresponding value reported in the downstream dam’s documents. The ultimate decision making based on the potential flows in the river, the environmental class of the river management, and engineering judgment is also recommended for the flows in the river towards the Urmia Lake. The results indicated that the flow allocation for the river environment (4% of mean annual flows) is not sufficient to meet the minimum flow requirements for any of the targeting species in the river ecosystem. In order to maintain the Barandozchi River at minimum acceptable environmental status (i.e. Class C of environmental management), an average annual flow of 1.9 m3/s (26% MAR) are to be provided. The distribution of monthly flow rates in the river is also recommended for sustaining the Barandozchi River life.
Conclusion: The provision for the minimum ecological flows was investigated in the Barandozchi River ecosystem. The results indicated that, in order to maintain the Barandozchi River at minimum acceptable environmental status (i.e. Class C), an average annual flow of 1.9 m3/s (26% MAR) are to be provided along the river towards the internationally recognized Urmia Lake, in Iran. Considering the construction of the Barandoz dam on this river, the pre-determined environmental flow releases from the dam are to be revised in order to increase the order of flows from 4% to 26% or more. Further investigation is necessary to take into account for the targeting riverine species and for the saving of the Urmia lake ecosystem. It is noted that minimum flow requirements are to be allocated in critical months of the year or during drought period of the river basin. Water leasing from agricultural users is an option or a necessary action whenever long-term environmental damages to the river ecosystem must be avoided.
