The influence of seepage from canals and paddy fields on the groundwater level of neighboring rotation cropping fields: a case study from the lower Ili River Basin,Kazakhstan

In the large-scale irrigation schemes of the lower Ili River Basin of Kazakhstan, crop rotation combines paddy rice and non-rice crops. Continuous irrigation is practiced in paddy fields, whereas other crops are sustained from groundwater after only limited early irrigation. The water table in non-rice crops is raised by seepage from canals and the flooded paddy fields. We investigated the areal extent to which the groundwater level of non-irrigated fields is influenced by seepage from canals and paddy fields by examining the relationship between distance (from canal and paddy field) and groundwater level in upland fields. The groundwater level was influenced for up to 300 and 400 m from the canals and paddy fields, respectively. Geographic information system analysis of crop and canal patterns in the 11 selected years showed that if the zone of influence is 300 and 400 m from the canals and paddy fields, respectively, the groundwater level of most of the area of upland fields was raised by seepage. We conclude that the water supply to cropping fields by seepage from irrigation canals and paddy fields is adequate, but the spatial distribution of the paddy fields may be an important factor that needs more attention to help improve water use efficiency in this irrigation district.     

Modelling of groundwater recharge potential from irrigated paddy field under changing climate

Groundwater recharge from irrigated paddy field under various projected climate change scenarios was assessed using HYDRUS-1D model. Recharge flux, root water uptake, evaporation and surface runoff were simulated on daily time step for the growing period of paddy. Crop evapotranspiration and effective rainfall during the simulation period were estimated to be 301.9 and 269.4 mm, respectively. Cumulative bottom flux, root water uptake, evaporation and surface runoff were 69.2, 23.2, 30.8 and 0.0 cm for sandy loam and 37.2, 23.0, 30.8 and 0.7 cm for clay loam soils, respectively. Simulation results showed that the groundwater recharge potentials in sandy loam and clay loam soils with paddy crop are 69.2 and 37.2 cm, respectively. Cumulative recharge under various climate change scenarios from paddy field varied from 63.9 to 74.4 cm, 33.7 to 39.8 cm, 29.3 to 35.4 cm and 27.1 to 34.3 cm from land units A1 (sandy loam), B1 (clay loam with slight salinity), C1 (clay loam with moderate saline and slight sodic) and D1 (clay loam with strong saline and sodic), respectively. Cumulative recharge flux under the scenarios in which increase in relative humidity along with decrease in duration of sunshine hours was associated with rise in average temperature and wind speed, groundwater recharge would increase by 7.4 %. Cumulative recharge flux under the scenarios which were based on rise in temperature along with the increase in rainfall, groundwater recharge would increase by 0.2–3.9 %. Simulation results also showed that cumulative recharge would decrease under all those scenarios, which were based on rise in temperature only.     

The role of paddy rice in recharging urban groundwater in the Shira River Basin

Agricultural fields in the middle Shira River basin play an important role as a source of groundwater recharge; however, the water balance between the agricultural water and river water is unclear. This study was conducted to investigate the water balance in the fields by measuring the stream flow of agricultural water channels, which draw water from the Shira River. The flow rate of water channels was found to increase in the beginning of May, which corresponded to the cultivation of paddy rice fields. During summer, the total agricultural intake was comparable to the river flow observed in the middle Shira River Basin. Determination of the water budget for the targeted area revealed that most of the recharged water was dependent on agricultural irrigation from the river. The annual recharge of the overall target area was estimated to be as high as 15,300 mm. In addition, the infiltration rate was as high as 170 mm/day in the paddy fields during summer, and as high as 30 mm/day in the upland fields during winter. In order to recover the groundwater recharge in this region, it is necessary to extend the submerged period to include periods in which the stream water in the Shira River is not subject to heavy rainfall as well.     

Long-term evaluation of the groundwater recharge function of paddy fields accompanying urbanization in the Nobi Plain, Japan

The groundwater recharge function, one example of the multifunctionality of agriculture, is closely related to hydrogeological phenomena and socioeconomic factors such as pumpage and land use. A long-term evaluation of the groundwater recharge function is necessary to understand its role among the multiple functions of agriculture. The Nobi Plain, one of the largest coastal plains in Japan, was selected as the study area because it has experienced typical socioeconomic changes. We conducted a long-term evaluation of the groundwater recharge function based on simple water-balance equations using long-term data on groundwater levels and river flows. Leakage recharge from paddy fields in 1975 was about 2.8×10⁸ m³/year, decreased to 0.6×10⁸ m³/year in 1984, and ceased in 1985. Its monetary value of the function in 1975 was estimated by the replacement cost method, was about $56 million for 20 ha×10³ ha of paddy fields. The value per unit area of paddy fields was calculated as $2820/ha and that in Japan was calculated as $400/ha. Paddy fields in suburbs of big cities have a higher value than the average paddy field in Japan. However, this recharge value is no longer produced because no leakage recharge occurs at present owing to socioeconomic changes.     

Modeling Pumped Water Salinity and Salt Water Upconing

SUMMARY

The farmers of the South-West Punjab, India, lift fresh groundwater for irrigation from the upper layers of the aquifers through interconnected, shallow, and low discharge tube wells. The groundwater of higher salinity usually present at deeper depths remains untouched. Besides permitting irrigation, some control over the water table rise is also achieved during the process. The SUTRA model was used to study the influence of vertical permeability, recharge, pumping rate, and pumping schedule on quality of the pumped water of a well. The results show that vertical permeability, recharge, and pumping rate have significant influence on quality of the pumped water. The influence of pumping schedule is less straightforward. It appears that daily pumping schedules are of limited influence. Seasonal changes in the pumping schedule, however, have significant impact on pumped water quality.     

Quantification of the effect of rice paddy area changes on recharging groundwater

This study quantifies the effects of paddy irrigation water on groundwater recharge. A numerical model of groundwater flow was conducted using MODFLOW in a 600 ha study site in an alluvial plain along the Chikugo River, located in southwestern Japan. To specify the surface boundary condition, data on the land use condition stored in the GIS database were transferred into a numerical model of groundwater flow. The simulated results were consistent with the observed yearly changes of groundwater level. Thus, it was appropriate to use the model to simulate the effects of paddy irrigation on groundwater. To quantify these effects, the groundwater level was simulated during the irrigation period when all farmlands in the study site were ponded. In this situation, the groundwater level was 0.5 to 1.0 m higher, the ground water storage 20% larger, and the return flow of the groundwater to the river 50% larger than in the present land use condition.     

Systematic assessment of flood mitigation in a tank irrigated paddy fields area

Flood mitigation in irrigation tanks and paddy fields is their favorable aspect though its practical effect is not known very well. A dynamic and systematic approach is presented to assess flood mitigation in a tank irrigated paddy fields area in the worst case where no static buffer function is expected. Based on the linear control theory, transfer function models for runoff process in catchments are identified. Hydraulic models are developed to represent flood dynamics in irrigation tanks, paddy fields, and drainage channels. These models are integrated as an ordinary differential equations system. Then, using the perturbed linear system, flood mitigation in each component of the system is examined in terms of frequency response. An application example demonstrates that a tank irrigated paddy fields area has a significant flood mitigation effect as a low-pass filter. This method has the advantage of assessing flood mitigation even in the case of an increase in the total runoff ratio.     

Determination of the magnitudes and values for groundwater recharge from Taiwan's paddy field

Flooded paddy fields have many functions, including not only rice production, and ecological and environmental conservation. This work estimates the extent of paddy field infiltration in Taiwan by adopting a one-dimensional Darcy-based soil/water balance model SAWAH (Simulation Algorithm for Water Flow in Aquatic Habitats). A 10 cm thick plow sole layer with a hydraulic conductivity of 0.03 cm/day, coupled with the soil texture and irrigation data obtained from 15 irrigation associations, is used to estimate the volumetric amount of annual infiltration in Taiwan. Simulation results from SAWAH indicate that the plow sole layer controls the movement of infiltrated water, with a rate about 1.8 billion cubic meters annually. The estimated infiltration rate of 1.8 billion m³/yr comprises more than 40% of the annual infiltration recharge to ground water in Taiwan. Additionally, the amount of infiltration recharge to groundwater is equivalent to 20 billion Taiwan dollars NT$ (or 0.65 billion US$) while the yearly rice crop production is 35 billion NT$ (or 1.13 billion US$). It is evident that the infiltration from rice paddy is of great importance to the economy, environment, and water resources conservation in Taiwan.     

Numerical assessments of the impacts of climate change on regional groundwater systems in a paddy-dominated alluvial fan

Quantitative assessment of the impacts of climate change on groundwater levels is important for sustainable groundwater use. This study examined the Tedori River alluvial fan in Ishikawa Prefecture, Japan, where paddy fields occupy 45 % of the total area. A regional groundwater flow model simulated future groundwater levels in response to 38 climate change projections generated for each of three GCMs, using three GHG emission scenarios with the ELPIS-JP datasets. The numerical groundwater flow model consisted of a 1-D unsaturated water flow model (HYDRUS-1D) for estimating groundwater recharge and a 3-D groundwater flow model (MODFLOW). Variable parameters consisted of daily air temperature, precipitation, humidity, solar radiation, and wind speed, which influence groundwater through infiltration, evapotranspiration, snowfall, and snowmelt. Groundwater levels had both decreasing and increasing trends, depending on climate change. There were more decreasing than increasing trends, and the maximum groundwater drawdown during 2010–2090 was ~1 m. Groundwater level was most sensitive to change in rate of precipitation during the non-irrigation period. Variations of relatively low-intensity precipitation days, when daily precipitation was <10 mm, had an effect on groundwater level. These results contribute to development of adaptive and sustainable groundwater managements (e.g. land use management and pumping strategies) in the future.     

Assessment of rice hydraulic loading impacts on groundwater and salinity levels

This paper describes the impact of rice hydraulic loading (percentage area under rice crop) on groundwater levels and salinity in the Murrumbidgee irrigation area (MIA), Australia using a MODFLOW-based modelling approach. The model simulations show that the groundwater levels will be in equilibrium after a fall of approximately 1 m under most of the areas, however, the groundwater salinity levels will rise by more than 1,000 μs/cm in most parts of irrigation area. If the rice growing area is reduced by 50 and 75%, there can be a net decline in groundwater levels during the first 2 years and then a new quasi-equilibrium will be established. To downscale these results at the farm level, SWAGMAN Farm model in conjunction with groundwater outflow rates obtained from a three-dimensional MODFLOW model was applied for determining net recharge rates under rice for different areas within the MIA. The highest net recharge during 2005–2006 season was 0.84 ML/ha (84 mm) in parts of the irrigation system, whereas the average net recharge due to rice hydraulic loading for the whole MIA during 2005–2006 season was estimated as 0.34 ML/ha (34 mm).     

Application of machine-learning models for diagnosing health hazard of nitrate toxicity in shallow aquifers

There is a growing concern about health hazards linked to nitrate (NO₃) toxicity in groundwater due to overuse of nitrogen fertilizers in rice production systems of northern Iran. Simple-cost-effective methods for quick and reliable prediction of NO₃ contamination in groundwater of such agricultural systems can ensure sustainable rural development. Using 10-year time series data, the capability of adaptive neuro-fuzzy inference system (ANFIS) and support vector machine (SVM) models as well as six geostatistical models was assessed for predicting NO₃ concentration in groundwater and its noncarcinogenic health risk. The dataset comprised 9360 water samples representing 26 different wells monitored for 10 years. The best predictions were found by SVM models which decreased prediction errors by 42–73 % compared with other models. However, using well locations and sampling date as input parameters led to the best performance of SVM model for predicting NO₃ with RMSE = 4.75–8.19 mg l^?1 and MBE = 3.3–5.2 mg l^?1. ANFIS models ranked next with RMSE = 8.19–25.1 mg l^?1 and MBE = 5.2–13.2 mg l^?1 while geostatistical models led to the worst results. The created raster maps with SVM models showed that NO₃ concentration in 38–97 % of the study area usually exceeded the human-affected limit of 13 mg l^?1 during different seasons. Generally, risk probability went beyond 90 % except for winter when groundwater quality was safe from nitrate viewpoint. Noncarcinogenic risk exceeded the unity in about 1.13 and 6.82 % of the study area in spring and summer, respectively, indicating that long-term use of groundwater poses a significant health risk to local resident. Based on the results, SVM models were suitable tools to identify nitrate-polluted regions in the study area. Also, paddy fields were the principal source of nitrate contamination of groundwater mainly due to unmanaged agricultural activities emphasizing the importance of proper management of paddy fields since a considerable land in the world is devoted to rice cultivation.     

A refined hydro-environmental watershed model with field-plot-scale resolution

A distributed hydro-environmental model is developed that achieves detailed analysis of the movement of water at a field-plot-scale resolution in a mesoscale watershed including lowland areas where, especially for agricultures, it is an essential need to get rid of redundant groundwater by drainage facilities such as rivers, canals and/or underdrains. For this, the problem geometry is meshed with unstructured cells of triangular shape. Profile of a column cell is zoned into two: surface zone and groundwater zone in which water movement is represented by combined tank and soil moisture sub-models, and well-defined two-dimensional unconfined shallow groundwater flow sub-model, respectively. The top-two sub-models serve to evaluate evapotranspiration, infiltration, soil water content, lateral surface water flow, and vertical percolation. The vertical percolation so evaluated is given as longitudinal recharge to the bottom sub-model for computing groundwater flow. Surface water–groundwater interactions through beds and stream-banks of perennial and ephemeral canals are considered by treating the canal courses as internal boundaries in the groundwater flow model. The finite volume method (FVM) that allows of unstructured mesh and produces conservative solutions is employed for groundwater flow computation. The model developed is applied to an actual watershed which includes a low-lying paddy area to quantify the hydrological impact of land-use management practices over a period of 29 years in which the farmland consolidation project was implemented and part of the paddy fields were converted to upland crop fields and housing lands. From the results obtained, it is concluded that the model presently developed lends itself to water—as well as land-use management practices.     

Effect of N-fertilizer application on return flow water quality from a terraced paddy field in Northern Taiwan

Intensive use of chemical fertilizer for crops may be responsible for nitrogen and phosphate accumulation in both groundwater and surface waters. The return flow polluted by nutrients not only results in the limitation of water reuse goals but also creates many environmental problems, including algal blooms and eutrophication in neighboring water bodies, posing potential hazards to human health. This study is to evaluate the N-fertilizer application of terraced paddy fields impacting return flow water quality. Water quality monitoring continued for two crop-periods around subject to different water bodies, including the irrigation water, drainage water at the outlet of experimental terraced paddy field, and shallow groundwater were conducted in an experimental paddy field located at Hsin-chu County, Northern Taiwan. The analyzed results indicate that obviously increasing of ammonium-N (NH₄ ⁺-N) and nitrate-N (NO₃ ^?-N) concentrations in the surface drainage water and ground water just occurred during the stage of basal fertilizer application, and then reduced to relatively low concentrations (<0.1 mg/l and <3 mg/l, respectively) in the remaining period of cultivation. The experimental results demonstrate the potential pollution load of nitrogen can be reduced by proper drainage water control and fertilizer application practices.     

Evaluation of irrigation water requirements and crop yields with different irrigation schedules for paddy fields in ChiaNan irrigated area,Taiwan

Recent water shortages in reservoirs have caused such problems as insufficient water and fallow rice fields in Southern Taiwan; therefore, comparing irrigation water requirements and crop production of paddy fields using a technique that differs from the conventional flood irrigation method is important. Field experiments for the second paddy field with four irrigation schedules and two repeated treatments were conducted at the HsuehChia Experiment Station, ChiaNan Irrigation Association, Taiwan. Experimental results demonstrate that irrigation water requirements for the comparison method, and 7-, 10- and 15-day irrigation schedules were 1248, 993, 848, and 718 mm, respectively. Compared to the conventional method of flooding fields at a 7-day interval, the 10- and 15-day irrigation schedules reduced water requirements by 14.6 and 27.3 %, respectively; however, crop yields decreased by 7 and 15 %, respectively. Based on the results, it was recommended that the ChaiNan Irrigation Association could adopt 10 days irrigation schedule and plant drought-enduring paddy to save irrigation water requirements for the water resource scarcity in southern Taiwan. The CROPWAT model was utilized to simulate the on-farm water balance with a 10-day irrigation schedule for the second paddy field. A comparison of net irrigation water requirements with the 10-day irrigation schedule from model and field experiment were 818 and 848 mm, respectively, and the error was 3.54 %.     

Evaluation of water intake rate using the diffusive tank model in the low-lying paddy area

The subject of this study is water management in low-lying paddy fields. The objective of this study is to quantify the water requirement, and estimate an appropriate volume and facilitate management of irrigation water in areas where it is difficult to estimate the flow rate continuously. A field observation was conducted at a 14-ha study site located in the Kuwabara area, Fukuoka City, southwest of Japan, to evaluate water management conditions in the command area of the reservoir. This site near the reservoir was selected, because it was impossible to understand the water supply situation in the entire command area. The farmers in this region have been unable to retain sufficient irrigation water. The observation results indicate that the water depth fluctuates widely in every irrigation canal. The canals are frequently empty because rotational irrigation is conducted by water managers; this makes quantifying the flow rate in the irrigation canal very difficult. To quantify the water requirement, an improved tank model was introduced. The accuracy of the model was examined by comparing the observed and calculated ponding depths at a paddy field. The simulation results agreed with the observed data. Using this model, water management for the reduction of water managers’ labor was simulated. Simulation results indicated that rotational irrigation effectively reduces labor and saves irrigation water.     

Effects of tillage and irrigation on the occurrence and establishment of native wetland plant species in fallow paddy fields

Traditional weed management, such as tillage and irrigation, has led to an enhanced maintenance of wetland plant species in fallow paddy fields. Recent herbicide usage and improvements in irrigation and drainage systems however have caused habitat loss of these species, especially in fields on open lowlands. We conducted experiments in three fallow paddy fields situated on the alluvial Echigo Plain in central Japan with an aim to restore the habitat of native wetland plant species. The three experimental fields were managed under different irrigation regimes, (1) perennially flooded with water, (2) intermittent irrigation, and (3) temporary irrigation. Half the area of each experimental field was tilled before irrigation. Detrended correspondence analysis revealed obvious floristic differences between experimental and control fields with no irrigation. The proportion of wetland plant species in the experimental fields increased corresponding to the irrigation period, ranging 60–86%, and was relatively greater than that in control fields. In the experimental fields, differences in both tillage and irrigation affected the occurrence of plant species. Tillage restricted the occurrence of many non-wetland plant species, and had a positive effect on the establishment of several annual wetland plant species. In addition, a longer duration of irrigation is not necessarily suitable for the occurrence of all wetland plant species. We concluded that fallow paddy fields provide a possible habitat for the restoration of native wetland plant species through appropriate tillage and irrigation.     

Analysis of water balance in the Tedori river alluvial fan areas of Japan: focused on quantitative analysis of groundwater recharge from river and ground surface, especially paddy fields

Water balance in the Tedori River alluvial fan areas was analyzed for all components of the hydrological cycle based on exchange of the channel/soil surface and aquifer horizon fractions with river water. The results were summarized on an annual basis, as well as for the irrigation and non-irrigation periods. The study area received 6.28 mm/day of precipitation and had an outflow of 2.32 mm/day as direct runoff, resulting in 3.96 mm/day of water being supplied to the soil surface. The channel/soil horizon fraction received this 3.96 mm/day, as well as 9.12 mm/day intake water from the head works. Conversely, 2.74 and 2.85 mm/day were lost by evapotranspiration and percolation, respectively. Thus, surface runoff of 7.49 mm/day flowed from the study area to the Sea of Japan or drainage canals near the river mouth. In the aquifer horizon fraction, 2.85 mm/day of water was supplied from the channel/soil horizon fraction and 2.15 mm/day was supplied from the Tedori River, while 1.73 mm/day was extracted by groundwater. Thus, 3.27 mm/day of groundwater flowed out to the Sea of Japan or into downstream drainage canals. An outline of the water balance of the irrigation and non-irrigation period is also shown. Because various hydrological components are closely related to each other, planning and management of water resources for individual goals are not adequate, but require the integrated aspect of water balance for sustainable water use.     

Equivalent cropping area and whole farm water balance approaches to reduce net recharge to shallow saline groundwater from rice based cropping systems

Sustainability of irrigated agriculture in the semi-arid regions such as the rice growing regions of the southern Australia could be under serious threat due to recharge to saline groundwater leading to secondary salinisation. This paper presents two approaches to reduce net recharge to shallow saline groundwater from ponded rice cropping systems using a soil, water and groundwater management model–SWAGMAN model. First approach applies the concept of growing deep-rooted crop (crop consuming water from soil and shallow water table) over an area equivalent to recharge from a unit area of rice crop to maintain the total water balance. The second approach involves achieving whole farm water balance for average and wet climatic conditions to find out optimum cropping pattern to minimise recharge from rice based system. Results of both approaches are sensitive to water table depth and regional groundwater outflow rates. The first approach was applied to determine an optimal mix of rice/lucerne crop to keep water tables and average soil salinity changes less than 0 m/year and 0.015 dS/m, respectively. The area of lucerne required to match the net groundwater rise caused by 1 ha of rice is 1.27, 2.45 and 3.55 ha for 1, 0.5 and 0.2 ML/ha regional groundwater outflow capacity. Results from second approach revealed that it is possible to control net recharge under above average rainfall using a suitable whole farm cropping mix e.g. 50 ha rice–wheat rotation, 19 ha rice, 25 ha of lucerne and 136 ha of fallow.     

Potential rainwater storage capacity of irrigation ponds

From antiquity to the present, Japan has irrigated many paddy fields from irrigation ponds. There are some 64,000 such irrigation ponds with a benefit area of over 2 ha each. These irrigation ponds not only function as a water-source for the stable production of food, but also are thought to reduce flooding in lower regions through temporary storage of rainwater and catchment runoff because they are located upstream of paddy fields, upland fields and residential land. Centering our research on Kagawa and Osaka Prefectures, we assessed the potential of rainwater storage capacity created by free space in irrigation ponds resulting from irrigation at a macro level as an indicator of flood mitigation. In these prefectures, potential rainwater storage capacity of irrigation ponds in early September was 2.1 and 1.4 times that of the potential storage capacity of associated paddy fields in an ordinary year.     

Effect of water management on soil respiration and <Emphasis Type="Italic">NEE</Emphasis> of paddy fields in Southeast China

Water management is an important factor in regulating soil respiration and the net ecosystem exchange of CO₂ (NEE) between croplands and atmosphere. However, how water management affects soil respiration and the NEE of paddy fields remains unexplored. Thus, a 2-year field experiment was carried out to study the effects of controlled irrigation (CI) during the rice season on the variation of soil respiration and NEE, with flooding irrigation (FI) as the control. A decrease of irrigation water input by 46.39% did not significantly affect rice yield but significantly increased irrigation water use efficiency by 0.99 kg m^?3. The soil respiration rate of CI paddy fields was larger than that of FI paddy fields except during the ripening stage. Natural drying management during the ripening stage resulted in a significant increase of the soil respiration rate of the FI paddy fields. Variations of NEE with different water managements were opposite to soil respiration rates during the whole rice growth stages. Total CO₂ emission of CI paddy fields through soil respiration (total R _soil) increased by 11.66% compared with FI paddy fields. The increase of total R _soil resulted in the significant decrease of total net CO₂ absorption of CI paddy fields by 11.57% compared with FI paddy fields (p < 0.05). There were inter-annual differences of soil respiration and the NEE of paddy fields. Frequent alternate wetting and drying processes in the CI paddy fields were the main factors influencing soil respiration and NEE. CI management slightly enhanced the rice dry matter amount but accelerated the consumption and decomposition of soil organic carbon and significantly increased soil respiration, which led to the decrease of net CO₂ absorption. CI management and organic carbon input technologies should be combined in applications to achieve sustainable use of water and soil resources in paddy fields.