Non-irrigation Season Research Articles

Assessing irrigation impact on water quality conditions: A case study in the River Noguera Ribagorçana (NE Spain)

The need to feed an increasing population while limiting the environmental impact of agriculture is currently one of the greatest challenges relating to the food chain. One of the key factors involved in doing this is irrigation, which has a downstream impact that can be minimised if nutrient and water management are efficiently undertaken. The objective of this study was to determine which irrigation management improvements can be done at field scale in modern irrigated areas to reduce its irrigation return flow impact. The study was conducted in the Noguera Ribagorçana River basin, in NE Spain, where almost 6000 ha of land were brought into irrigation from 2000 to 2009. We based our study on a water quality dataset, measured in four different sites along a 29 km2 stretch of the river over a period of 20 years. Our results show an increase in nitrate (from 1.7 mg·L−1 to 10.5 mg·L−1) and salt concentrations (electrical conductivity from 297 to 675 µS·m−1) in the downstream course of the river compared to the most upstream monitoring site. That was exclusively associated with the irrigation return flows from the newly irrigated area. The highest nitrate and salt concentrations are found during the non-irrigation season which corresponds to the local rainy season. To reduce this impact, better irrigation management is required. Autumn leaching could be lowered by reducing irrigation volume applied during the final weeks of crop cycles in order to allow the soil to retain the volume of water received from rainfall. To deal with this issue, we propose a methodology based on soil moisture to determine the end of the irrigation season. In this way, the impact on ecosystems located further downstream would be reduced while crop yields and productivity in the area could be maintained.

Effects of Surface Water on Artificial Recharge of Coastal Aquifers by GIS Zoning Maps: A Case Study in Ghaemshahr, Iran

Background: The study aimed to assess surface water resources for potential use during non-irrigation seasons to boost groundwater aquifers. This method also helps reduce aquifer depletion, mitigate land subsidence, and enhance groundwater quality. Methods: In this study, artificial feeding methods were used to determine the appropriate location for the Ghaemshahr plain. Water resources were tested in terms of quantity and quality through field and laboratory studies. Based on the findings, geographic information system (GIS) mapping was utilized to create maps and select the best location and feeding method. Results: The most important source of nutrition for recharging the aquifer in terms of quantity and quality was the Talar River. The study area’s conditions like aquifer thickness, permeability, topographic slope, and land use were analyzed using GIS and thematic maps. The results indicated that by using these methods, it is possible to store 5 million cubic meters of surface water in the aquifer for 6 months. Conclusion: This study demonstrated the feasibility of using surface waters in the area for artificial feeding, employing the pond method1. Additionally, it is recommended to dig measuring wells to monitor the water level rise at the bottom of the pond 1. It also suggests the use of simulation software like PMVIN, Mod flow, and GMS to optimize the artificial replenishment process and select the most suitable approach from the defined scenarios before taking any actions.

Migration characteristics of soil salinity in saline-sodic cotton field with different reclamation time in non-irrigation season

Cultivation after converting saline and alkaline wasteland to agricultural land is usually accompanied by accelerated soil salinization. There is general agreement that freezing-thawing process plays a crucial role in soil salinization in mostly cold-arid agricultural areas, which leads to the impoverishment of soil productivity. To investigate the migration characteristics of soil salinity in saline-sodic cotton field with different reclamation time in non-irrigation season, we examined the soil bulk, total porosity, and spatial and temporal migration of soil salinity in winter in an oasis agroecosystem of northern Xinjiang, China. Experimental plots include a saline-alkali wasteland as control and cotton fields under four age categories (cultivation start years were 1998, 2006, 2008, and 2012, respectively). The results showed that converting saline-alkali wasteland to cotton land significantly decreased soil bulk density but increased total soil porosity, especially at 0–40 cm. Conversion significantly decreased soil salinity at 0–200 cm soil depths, with a greater decrease in cotton land after relatively longer time of cultivation. After freezing-thawing process, soil bulk density decreased 4.87% on average, and total porosity increased 5.98%. Soil salt dynamics showed that there were two stages in salt accumulation. Firstly, soil salt storage increased at 0–100 cm depth but decreased at 100–200 cm depth during freezing period; Secondly, rapid increase of salt storage appeared at late thawing period. In addition, salt accumulation positively correlated to initial salt content and bulk density, but negatively correlated to total porosity. At springtime, cotton land with short-term cultivation was desalination comparing with pre-freezing, but salt accumulation occurred after long-term cultivation. These results highlighted that long-term cultivation with mulched drip irrigation decreased soil salinity in the 0–200 cm soil profiles, but freezing-thawing process induced soil salinization which poses a potential risk to agricultural sustainability.

Irrigation-Intensive Groundwater Modeling of Complex Aquifer Systems Through Integration of Big Geological Data

This study identifies hydrogeologic characteristics of complex aquifers based on constructing stratigraphic structure with large, non-uniform well log data. The approach was validated through a modeling study of the irrigation-intensive Chicot aquifer system, which is an important Pleistocene-Holocene aquifer of the Coastal Lowlands aquifer system in the southwestern Louisiana. Various well log types were unified into the same data structure, prioritized based on data sources, and interpolated to generate a detailed stratigraphic structure. More than 29,000 well logs were integrated to construct a stratigraphy model of 56 model layers for the Chicot aquifer system. The stratigraphy model revealed interconnections of various sands in the system, where 90% of the model domain is covered by fine-grained sediments. Although the groundwater model estimated a slight groundwater storage gain during 2005–2014 for the entire region, groundwater storage in the agricultural area was depleted. Nevertheless, the quick groundwater storage recovery during the non-irrigation seasons suggests that the Chicot aquifer system is a prolific aquifer system. The groundwater modeling result shows that the gulfward groundwater flow direction prior to pumping has been reversed toward inland pumping areas. The large upward vertical flow from the deeper sands indicates potential saltwater migration from the base of the Chicot aquifer system.

Combining Uranium, Boron, and Strontium Isotope Ratios (234U/238U, δ11B, 87Sr/86Sr) to Trace and Quantify Salinity Contributions to Rio Grande River in Southwestern United States

In semi-arid to arid regions, both anthropogenic sources (urban and agriculture) and deeper Critical Zone (groundwater with long flow paths and water residence times) may play an important role in controlling chemical exports to rivers. Here, we combined two anthropogenic isotope tracers: uranium isotope ratios (234U/238U) and boron isotope ratios (δ11B), with the 87Sr/86Sr ratios to identify and quantify multiple solute (salinity) sources in the Rio Grande river in southern New Mexico and western Texas. The Rio Grande river is a major source of freshwater for irrigation and municipal uses in southwestern United States. There has been a large disagreement about the dominant salinity sources to the Rio Grande and particularly significant sources are of anthropogenic (agriculture practices and shallow groundwater flows, groundwater pumping, and urban developments) and/or geological (natural groundwater upwelling) origins. Between 2014 and 2016, we collected monthly river samples at 15 locations along a 200-km stretch of the Rio Grande river from Elephant Butte Reservoir, New Mexico to El Paso, Texas, as well as water samples from agricultural canals and drains, urban effluents and drains, and groundwater wells. Our study shows that due to the presence of localized and multiple salinity inputs, total dissolved solids (TDS) and isotope ratios of U, B, and Sr in the Rio Grande river show high spatial and temporal variability. Several agricultural, urban, and geological sources of salinity in the Rio Grande watershed have characteristic and distinguishable U, Sr, and B isotope signatures. However, due to the common issue of overlapping signatures as identified by previous tracer studies (such as δ18O, δD, δ34S), no single isotope tracer of U, Sr, or B isotopes was powerful enough to distinguish multiple salinity sources. Here, combining the multiple U, Sr, and B isotope and elemental signatures, we applied a multi-tracer mass balance approach to quantify the relative contributions of water mass from the identified various salinity end members along the 200-km stretch of the Rio Grande during different river flow seasons. Our results show that during irrigation (high river flow) seasons, the Rio Grande had uniform chemical and isotopic compositions, similar to the Elephant Butte reservoir where water is stored and well-mixed, reflecting the dominant contribution from shallow Critical Zone in headwater regions in temperate southern Colorado and northern New Mexico. In non-irrigation (low flow) seasons when the river water is stored at Elephant Butte reservoir, the Rio Grande river at many downstream locations showed heterogeneous chemical and isotopic compositions, reflecting variable inputs from upwelling of groundwater (deeper CZ), displacement of shallow groundwater, agricultural return flows, and urban effluents. Our study highlights the needs of using multi-tracer approach to investigate multiple solutes and salinity sources in rivers with complex geology and human impacts.

The role of coated fertilizer used in paddy fields as a source of microplastics in the marine environment

Fixed-point and multi-point field survey was conducted to determine the actual contamination of the Japanese coast by microcapsules derived from coated fertilizers. The results indicated that the amount of microcapsules increased during the irrigation season (9423–74,869 pieces/m2) and decreased in the non-irrigation season (77–1471 pieces/m2). Microcapsules accounted for 90% of all microplastics sampled during the irrigation season. The lack of correlation between the area of agricultural land in the watershed and the microcapsule density on the coast suggested that the density of microcapsules on the coast was not only dependent on the total load to the ocean, but also on topographic and meteorological conditions. More than 90% of the microcapsules collected from the shoreline were made of polyethylene. Scanning electron microscopic observation of the surface of the microcapsules revealed that portions of the microcapsules were removed as secondary microplastics in the process of migration to the ocean.

Relationship Between Spatial Pattern of Farmland Management and Frog Habitats during Non-Irrigation Season

Relationship Between Spatial Pattern of Farmland Management and Frog Habitats during Non-Irrigation Season

Impacts of groundwater extraction on groundwater flow and arsenic distribution in the western Hetao Basin, Inner Mongolia, China

Temporal variations in water levels are crucial for understanding As behaviour in groundwater systems. Groundwater levels were recorded in irrigation wells in non-irrigation and irrigation seasons. Groundwater samples were collected yearly in irrigation wells from 2014 to 2016 and in a multilevel well from 2015 to 2016 for analysing geochemical parameters. Results showed that groundwater flow direction was reversed due to groundwater pumping. The change of groundwater flow led to the surface water, as a new groundwater recharge source, which flushed the near-surface sediments enriched in soluble components and increased groundwater TDS. The labile organic matter introduced by the surface water recharge fueled dissimilatory reduction of Fe(III) oxides and further increased groundwater As concentration.

Conservation of aquatic animals inhabiting low-lying plains and mountainous regions in Japanese rural areas

The purpose of this study was to consider the present status and challenges of aquatic animals inhabiting low-lying plains and mountainous regions in Japanese rural areas and to propose future conservation measures. My conclusions are as follows. On low-lying plains where modernizing agriculture such as farmland consolidation is developed, the development project is pointed out the problems from the viewpoint of the conservation of aquatic animals. My preference is for the irrigation water system to be pipelined and the drainage water system to be open channel. As for the drainage network, year-round water flow and the use of natural materials for canal beds are very important. Mountainous regions have suffered from depopulation, and maintaining terrace paddy fields has been difficult. To use agriculture to fulfill multiple functions, I propose zoning into agricultural land management areas, grass and forest management areas, and native forest areas. Appropriate adaptive management is required both on low-lying plains and mountainous regions. Additionally, it is significant to conserve aquatic animals in the watershed. The components of the watershed include farm ponds, dam reservoirs, lakes, flood control basins, paddy fields, rice terraces, rivers, irrigation canals, and drainage canals. It is also important to ensure water flow in the artificial systems around the paddy fields throughout the year. Using springs and groundwater during non-irrigation seasons is effective and efficient both on low-lying plains and in mountainous regions.

Hydrologic impacts of drought-adaptive agricultural water management in a semi-arid river basin: Case of Rincon Valley, New Mexico

This paper examines the coupled effects of weather condition, crop coverage change, and regional water management (i.e., releases from Caballo Reservoir) on hydrologic characteristics of Rincon Valley (2466 km2), a semi-arid agricultural area in New Mexico, U.S.A., using Soil and Water Assessment Tool (SWAT). The model simulates the vertical water budget and horizontal water transfers during the period 1994–2013, incorporating irrigation of fourteen crops in normal (2008) and dry (2011) years to evaluate the hydrologic impacts of cropping change as a drought-adaptive water management strategy. It was calibrated (2000–2002) and validated (2003–2005) using daily-observed streamflow data. Furthermore, evapotranspiration, diversion and irrigation water volume were verified for the period of 2000–2005 using monthly crop irrigation requirement data and canal discharge data. Results demonstrate the significant role of surface water infiltration, providing approximately 18% of the average annual groundwater recharge during the irrigation season. Watershed scale evapotranspiration (ET) and return flows for the irrigation season were estimated to be 23% and 1% higher than those for the non-irrigation season, respectively. For irrigation units, the ratio of ET to combined precipitation and irrigation water for the dry year was 5% higher than the normal year whereas surface runoff, soil water storage, and groundwater recharge were 7%, 17%, and 39% lower than the normal year, respectively. High groundwater recharge occurs in the hydrologic response units (HRU) where corn and cotton are planted on silty clay loam soil. The Alfalfa acreage (i.e., the largest water user) was reduced by 15% while the cotton acreage was increased by 13% in order to adapt to lower water availability during the dry year. Quantitative understanding of the hydrologic fluxes in the Rincon Valley’s irrigated agricultural area illuminates adaptive land and water management to buffer the adverse impacts of prolonged droughts.

The Niobrara Formation as a challenge to water quality in the Arkansas River, Colorado, USA

Study regionArkansas River, east of the Rocky Mountains. Study focusCretaceous sedimentary rocks in the western United States generally pose challenges to water quality, often through mobilization of salts and trace metals by irrigation. However, in the Arkansas River Basin of Colorado, patchy exposure of multiple Cretaceous formations has made it difficult to identify which formations are most problematic. This paper examines water quality in surface-water inflows along a 26-km reach of the Arkansas River relative to the presence or absence of the Cretaceous Niobrara Formation within the watershed. New hydrological insights for the regionPrincipal component analysis (PCA) shows Niobrara-influenced inflows have distinctive geochemistry, particularly with respect to Na, Mg, SO42−, and Se. Uranium concentrations are also greater in Niobrara-influenced inflows. During the irrigation season, median dissolved solids, Se, and U concentrations in Niobrara-influenced inflows were 83%, 646%, and 55%, respectively, greater than medians where Niobrara Formation surface exposures were absent. During the non-irrigation season, which better reflects geologic influence, the differences were more striking. Median dissolved solids, Se, and U concentrations in Niobrara-influenced inflows were 288%, 863%, and 155%, respectively, greater than median concentrations where the Niobrara Formation was absent. Identification of the Niobrara Formation as a disproportionate source for dissolved solids, Se, and U will allow for more targeted studies and management, particularly where exposures underlie irrigated agriculture.

Seasonal and depth variation of soil chemical and biological properties in alfalfa crops irrigated with treated wastewater and saline groundwater

In areas with limited water resources, treated wastewater can be used for irrigation. This is the case in many places on the Mediterranean coast where groundwater is affected by seawater intrusion. A study was conducted under real agricultural conditions and during irrigation and non-irrigation seasons in order to evaluate changes in soil chemical and biological properties in crops of alfalfa (Medicago sativa L.) irrigated with secondary-treated municipal wastewater and saline groundwater for >20years. Depth distribution and the effect of soil type were also investigated. The soil parameters studied were: salinity, content of N-NO3−, N-NH4+ and water-extractable organic carbon (WEOC), microbial biomass C (MB) and the enzymatic activities of dehydrogenase (DH), β-glucosidase (GL), alkaline phosphatase (AP), arylsulphatase (AS), BAA-protease (PR) and urease (UR). The results demonstrate the positive effect of treated wastewater on soil GL, AS and UR activities during the irrigation season in comparison to irrigation with saline groundwater. Salinity and N-NO3 also increased during the irrigation season although these parameters decreased considerably after the rains in soils irrigated with both types of water. Soil salinity, WEOC and extracellular enzymatic activities differed significantly between soil types; these were higher in the soils of finer texture and higher soil organic carbon content. Traditional non-tillage crop management (between 5 and 7years without ploughing) produced a clear depth distribution of most soil chemical and biological parameters in five-year-old alfalfa crops. The results indicate that treated wastewater is a suitable alternative to saline groundwater and allows the maintenance of traditional irrigation of alfalfa crops.

An economic analysis of photovoltaic water pumping irrigation systems

ABSTRACTIrrigation using the photovoltaic water pumping (PVWP) systems represents a sustainable and attractive solution, which can combat Chinese grassland desertification and promote a sustainable development of the agricultural sector. This paper investigates the economics of PVWP systems taking into consideration the effects of the key components on the initial capital cost (ICC), life cycle cost (LCC), and revenues. Sensitivity analyses are conducted regarding the crop yield and price, cost of photovoltaic modules, and system components included in the ICC. Results show that the cost of the PVWP system is the most sensitive parameter affecting the ICC under the assumptions made, especially the cost of the PV modules; whereas, the crop production and price affect the net present value (NPV) and payback period (PBP) clearly. The PVWP has surplus power output when the crop water demand is low or it is non-irrigation season. The potential benefit from selling the surplus electricity is also discussed. In addition, the indirect benefits of carbon sequestration and CO2 emission reduction by applying PVWP systems are addressed in this paper.

Effects of wetland restoration on nitrate removal in an irrigated agricultural area: The role of in-stream and off-stream wetlands

Eleven in-stream and five off-stream wetlands were restored in the southern portion of the Flumen River basin, an intensively irrigated agricultural area located in NE Spain, to evaluate their efficiency for nitrate removal and to assess the factors affecting their performance. Samples were taken during different periods of the year during 2011–2014 to evaluate the influence of agricultural activities during the two years following their completion. Nitrate concentration was significantly higher in the in-stream wetlands, showing a clear dilution effect caused by the inputs of the irrigation return flows. The patterns followed by the first-order nitrate removal rate constant were different for in-stream and off-stream wetlands and during irrigation and non-irrigation seasons. During non-irrigation seasons, the nitrate outflowing concentration was found to be negatively correlated (p<0.01) to the first-order nitrate removal rate constant for in-stream wetlands, indicating that high nitrate inputs may restrict the effectiveness of the wetlands. Temperature and dissolved oxygen were also found to significantly influence the performance of off-stream wetlands during non-irrigation seasons, but only dissolved oxygen promoted the nitrate removal during the irrigation period, indicating the influence of the seasonal factor on nitrate and wetlands dynamics. The results of this study showed that although a longer time is required to achieve optimal wetland development, wetlands can be used as buffer zones that effectively remove nitrates. This study emphasizes the influence of the agricultural seasonality of the factors affecting nitrate removal in wetlands, expanding the information provided by similar studies and validating a model that is applicable to a wide range of agricultural, hydrological and seasonal conditions.

Origin of particulate organic matter in a river with remarkable water pollution in Shikoku Island, Japan

This study on the origin of particulate organic matter (POM) in a river under efficient water use for irrigation in a basin was carried out on the Shin River in Kagawa Prefecture, Japan. The organic pollution in the basin where water resources are scarce was studied. The level of POM in the Shin River was significantly influenced by the natural and artificial hydrological environment in the river basin. The degree of organic pollution in the Shin River was high, and most of the organic matter was algae. The δ18O of water of the middle and lower reaches of the Shin River was high, and water subjected to evaporation for a lengthy time period in the basin flows into the river. The concentration of organic matter in the Shin increases along with the increase in δ18O. Algae also increases in the stay waters in the basin of the middle–lower reaches and flows into the Shin. It was thought that the irrigation ponds in the basin were the main sources of water and organic matter for the river. This tendency was notable during the nonirrigation season in that the volume of water in the basin decreased. On the other hand, the proportion of algae in organic matter in the river decreased when there was considerable precipitation.

Soil salinization as a threat to the sustainability of deficit irrigation under present and expected climate change scenarios

Deficit irrigation (DI) strategies using moderately saline waters save water, but may enhance soil salinization. Based on data gathered during years 2007–2012 in three drip-irrigated grapevine, peach, and nectarine crops subjected to several irrigation and soil-mulching treatments, we assessed trends in root-zone soil salinity [saturation extract electrical conductivity (ECe)], related the changes in soil salinity (ΔECe) to field-wide leaching fraction (LF), evaluated management strategies for soil salinity control, and examined the sustainability of DI strategies under present and expected climate change (CC) scenarios in the Middle Ebro River Basin (ERB, Spain). ECe increased in 82 % of the irrigation seasons and decreased in 75 % of the non-irrigation seasons examined. Soil salinization trends were not apparent during the study years due to these annual salt accumulation–salt leaching cycles. ECe increases were higher in the more severe DI treatments and in the geotextile-mulched soil and lower in the full and less severe irrigation treatments and in the organic-mulched soil. As expected, ΔECe and LF were linearly and negatively correlated (P < 0.01), indicating that soil salinization increased with decreasing LF. These linear relationships provided a way to evaluate best management strategies (increased irrigation, rainfall harvesting, and soil mulching) for soil salinity control. These strategies decreased soil salinization, but did not guarantee the sustainability of severe DIs in the study area. The application of these relationships to the CC precipitation and crop evapotranspiration projections in the ERB shows that the examined DI strategies will be unsustainable due to soil salinization.

Acidification of floodplains due to river level decline during drought

A severe drought from 2007 to 2010 resulted in the lowest river levels (1.75m decline from average) in over 90years of records at the end of the Murray–Darling Basin in South Australia. Due to the low river level and inability to apply irrigation, the groundwater depth on the adjacent agricultural flood plain also declined substantially (1–1.5m) and the alluvial clay subsoils dried and cracked. Sulfidic material (pH>4, predominantly in the form of pyrite, FeS2) in these subsoils oxidised to form sulfuric material (pH<4) over an estimated 3300ha on 13 floodplains. Much of the acidity in the deeply cracked contaminated soil layers was in available form (in pore water and on cation exchange sites), with some layers having retained acidity (iron oxyhydroxysulfate mineral jarosite). Post drought, the rapid raising of surface and ground water levels mobilised acidity in acid sulfate soil profiles to the floodplain drainage channels and this was transported back to the river via pumping. The drainage water exhibited low pH (2–5) with high soluble metal (Al, Co, Mn, Fe, Mn, Ni, and Zn) concentrations, in exceedance of guidelines for ecosystem protection. Irrigation increased the short-term transport of acidity, however loads were generally greater in the non-irrigation (winter) season when rainfall is highest (0.0026tonnesacidity/ha/day) than in the irrigation (spring–summer) season (0.0013tonnesacidity/ha/day). Measured reductions in groundwater acidity and increases in pH have been observed over time but severe acidification persisted in floodplain sediments and waters for over two years post-drought. Results from 2-dimensional modelling of the river-floodplain hydrological processes were consistent with field measurements during the drying phase and illustrated how the declining river levels led to floodplain acidification. A modelled management scenario demonstrated how river level stabilisation and limited irrigation could have prevented, or greatly lessened the severity of the acidification.

Regulated deficit irrigation, soil salinization and soil sodification in a table grape vineyard drip-irrigated with moderately saline waters

Irrigation with moderately saline waters may provoke soil salinization and sodification. The objectives of this three-year study were (1) to quantify these processes in two seedless table grapevines (Vitis vinifera cvs. Autumn Royal and Crimson) subject to a full irrigation and two regulated deficit irrigations (RDI, irrigated at 80% and 60% of net irrigation requirements from post-veraison till harvest) with 1.7dSm−1 electrical conductivity irrigation waters, and (2) to assess the impact of soil salinization on grapevine's response. Soil samples were taken three times along each irrigation season and soil solution samples were extracted weekly by suction cups. Soil saturation extract electrical conductivity (ECe) and sodium adsorption ratio (SARe) were high in Autumn Royal (4.4dSm−1 and 6.1 (mmoll−1)0.5) and very high in Crimson (7.0dSm−1 and 8.6 (mmoll−1)0.5) due to relatively low leaching fractions (LF) (0.20 in Autumn Royal and 0.13 in Crimson). Soil solution salinity and sodicity were generally higher in the more severe RDI than in the full irrigation treatment. Soil salinity and sodicity generally increased along the irrigation seasons and decreased along the non-irrigation seasons. Salt accumulation or leaching and LF were significantly correlated, so that LF estimates could anticipate the required irrigation depths for soil salinity control. Grapevine yield declined with increases in soil salinity. Leaf Na concentrations were very low (<0.1%), but leaf Cl concentrations were higher and the maximum value of 0.61% measured in the more severe Crimson RDI treatment was within the interval reported as toxic in grapevine. Despite the water saving benefits of drip irrigation in combination with deficit irrigation strategies, its implementation in low-precipitation semiarid areas must be cautiously assessed and monitored because soil salinization and sodification may threaten the sustainability and profitability of these grapevine orchards irrigated with moderately saline waters.

둑높이기 농업용저수지의 운영기준에 따른 환경용수 방류패턴 분석

The importance of environmental water has been risen in terms of river ecosystem soundness with preventing stream flow depletion in rural area, while enlarging agricultural reservoir project is conducted under the 4 main river restoration project for supplying more water to 4 main rivers. The aim of this study was to estimate the amount of environmental water release and analyze the release pattern during non-irrigation season in enlarged agricultural reservoirs. The 4 reservoirs (Dansan, Samga, Geumbong, Changpyeong) located on the upper region of Nakdong river were simulated applying the operation rule which was determined by release criteria curves. The simulated results indicated that the more environmental water could be released than the spillway release and continuous release was achieved with smaller range of fluctuation. In case of Changpyeong reservoir, average 506.0 thousand <TEX>$m^3$</TEX> environmental water could be released on Feb., and it was about twice as much as the spillway release before the enlargement, and also, the 18 thousand <TEX>$m^3$</TEX>/day environmental water could be supplied to a stream consistently after enlargement. From the results, it was expected that the additional environmental water release will improve stream water flow during dry season in terms of quantity and quality of water.

The impact of improving irrigation efficiency on wetland distribution in an agricultural landscape in the upper reaches of the Yellow River in China

Wetlands in irrigated agricultural areas have great environmental benefits as agricultural pollution sinks; but agricultural development and water resources redistribution have caused these wetlands to diminish rapidly worldwide. This is the case in the YinNan Irrigation District (YNID) in the upper reaches of the Yellow River in China, where wetlands once flourished as the result of large amount of irrigation diversion and low irrigation efficiency. In this paper, we presented an analytical study on the impact of irrigation water saving practices on wetland distribution in YNID; we also discussed the effect of considering wetland water consumption as beneficial or efficient use on the overall water use efficiency. The study area has a maximal wetland to farmland areal ratio of 10.5% during the irrigation season due to recharges from canal seepage and field percolation; and 45% of the wetland area remains as the permanent pool area during the non-irrigation season. The observed maximum water table rise in the irrigation season is 1.5m. The current irrigation system efficiency in YNID is 0.30, which is a product of the field level efficiency of 0.68 and the conveyance efficiency of 0.44. Our analysis presented in this paper shows that improving the application efficiency to 0.90 at the field level will reduce the maximum water table rise by 0.53m, causing the wetland area to shrink by 17% and the subsequent wetland water consumption to decrease by 11%; further improving conveyance efficiency to 0.60 will reduce the maximum water table rise by 0.95m, causing the wetland area to shrink by 30% and the subsequent wetland water consumption to decrease by 19%. These results indicate that water saving at the conveyance level will have greater impact on wetland water use than that at the field level. If wetland water consumption is considered as efficient use, this fraction of the irrigation water loss becomes efficient use, which will increase the system efficiency proportionally by the percentage of wetland water consumption. The amount of wetlands, and thus additional beneficial wetland water use, is directly dependent on the amount of traditional water losses, such as wetland consumption here. The key question then becomes: where lies the optimum level or the acceptable balance between increasing efficiencies at irrigation scheme level while providing optimal beneficial use for wetlands.