Analysis of water balance by surface–groundwater interaction using the SWAT model for the Han River basin,South Korea

The water balance and groundwater dynamics due to surface–groundwater interactions for watershed health assessment were investigated for the Han River basin (34,148 km²) of South Korea using the Soil and Water Assessment Tool (SWAT). The model was established considering 4 multipurpose dams and 3 multifunction weirs. The SWAT was spatially calibrated and validated using daily observed inflows for the dam (2005–2014) and weir (2012–2014) as well as evapotranspiration, soil moisture, and groundwater level data (2009–2013). The simulation results revealed the impact of surface–groundwater exchange fluxes on the water balance and baseflow by evaluating the vertical water budget and horizontal water transfer. Evapotranspiration in the surface and return flows from the shallow aquifer for the dry season was estimated to be 29 and 10% higher than for the wet season, respectively. Percolation’s role was also significant, providing approximately 24% of the annual groundwater recharge to shallow aquifers in the rainy season. On average, the February to August period (A) was characterized by a net flux of infiltration into the groundwater. For the September to January period (B), the proportion of groundwater flow into the river of the basin was nearly balanced by a slight increase in surface water infiltration. During period A of average surface water infiltration into the groundwater, the net groundwater recharge was positive and up to 20% of the infiltration during this period resulted from groundwater recharge. These results showed that groundwater recharge is strongly affected by the surface water and groundwater interactions.     

Influence of paddy rice terraces on soil erosion of a small watershed in a hilly area of Northern Vietnam

Soil erosion is the main cause of soil degradation in northern Vietnam. In this study, soil erosion was measured in 2 m² field plots, a 19.1-ha sub-watershed, and a 248.9-ha main watershed in Tam Quan commune, Tam Duong district, northern Vietnam during 2 years, i.e., 2004–2005. The main watershed includes lowland paddy fields, and is representative for watersheds in the northern Vietnamese landscape. Soil erosion was measured for eight events, at all the three scales to increase our understanding of erosional processes and to assess the effects of paddy fields within the main watershed. The results show that total discharge and sediment yield in both sub-watershed and main watershed were much lower than those in the field plots. Total discharge per unit area in the main watershed was higher than in the sub-watershed, because during the growing season, the paddies are filled with water and any rainfall on them therefore becomes runoff. Sediment yield in the main watershed fluctuated, depending on the soil erosion contribution from many sub-watersheds. Annual rainfalls in 2004 and 2005 were 1,172 and 1,560 mm, respectively, resulting in corresponding total discharges of 54 and 332 mm and total soil losses of 163 and 1,722 kg ha^?1 year^?1. High runoff volumes occurred in July, August, and September, but April, June, the last 10 days of September and October, were the susceptible periods for soil erosion in the study area because of low plant cover and many agricultural activities during these periods.     

Hydrologic impact of climate change with adaptation of vegetation community in a forest-dominant watershed

This study evaluated the impact on watershed hydrology by predicting future forest community change under a climate change scenario. The Soil and Water Assessment Tool (SWAT) was selected and applied to Chungju dam watershed (6,642 km²) of South Korea. The SWAT was calibrated and validated for 6 years (1998–2003) using the daily streamflow data from three locations. For the future evaluation of forest community and hydrology, the MIROC3.2 HiRes monthly climate data were adopted. The future data were corrected using 30 years (1977–2006, baseline period) of measured weather data, and they were daily downscaled by the Long Ashton Research Station-Weather Generator statistical method. To predict the future forest vegetation cover, the baseline forest community was modeled by a multinomial LOGIT model using variables of baseline precipitation, temperature, elevation, degree of base saturation, and soil organic matter, and the future forest community was predicted using the future precipitation and temperature scenario. The future temperature increase of 4.8 °C by 2080s (2070–2099) led to prediction of 30.8 % decrease of mixed forest and 75.8 % increase of coniferous forest compared to the baseline forest community. For the baseline evapotranspiration (ET) of 491.5 mm/year, the 2080s ET under the forest community change was 591.1 mm/year, whereas it was 551.8 mm/year with the remaining forest community stationary. The different ET results considering the future forest community clearly affected the groundwater recharge and streamflow in sequence.     

SWAT modeling of best management practices for Chungju dam watershed in South Korea under future climate change scenarios

Suitable and practicable best management practices (BMPs) need to be developed due to steadily increasing agricultural land development, intensified fertilization practices, and increased soil erosion and pollutant loads from cultivated areas. The soil and water assessment tool model was used to evaluate the present and future proper BMP scenarios for Chungju dam watershed (6,642 km²) of South Korea, which includes rice paddy and upland crop areas. The present (1981–2010) and future (2040s and 2080s) BMPs of streambank stabilization, building recharge structures, conservation tillage, and terrace and contour farming were examined individually in terms of reducing nonpoint source pollution loads by applying MIROC3.2 HiRes A1B and B1 scenarios. Streambank stabilization achieved the highest reductions in sediment and T-N, and slope terracing was a highly effective BMP for sediment and T-P removal in both present and future climate conditions.     

Evaluation of MODIS NDVI and LST for indicating soil moisture of forest areas based on SWAT modeling

This study examined the capability of remotely sensed information gained using the terra moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and land surface temperature (LST) to explain forest soil moisture. The soil and water assessment tool (SWAT) was used for the analysis. Nine years (2000–2008) of monthly MODIS NDVI and LST data from a 2,694.4 km² watershed consisting of forest-dominant areas in South Korea were compared with SWAT simulated soil moisture. Before the analysis, the SWAT model was calibrated and verified using 9 years of daily streamflow at three gauging stations and 6 years (2003–2008) of daily measured soil moisture at three locations within the watershed. The average Nash–Sutcliffe model efficiency during the streamflow calibration and validation was 0.72 and 0.70, respectively. The SWAT soil moisture showed a higher correlation with MODIS LST during the forest leaf growing period (March–June) and with MODIS NDVI during the leaf falling period (September–December). Low correlation was observed in the year of frequent rains, regardless of the leaf periods.     

Modification of SWAT auto-calibration for accurate flow estimation at all flow regimes

To secure accuracy in the Soil and Water Assessment Tool (SWAT) simulation for various hydrology and water quality studies, calibration and validation should be performed. When calibrating and validating the SWAT model with measured data, the Nash–Sutcliffe efficiency (NSE) is widely used, and is also used as a goal function of auto-calibration in the current SWAT model (SWAT ver. 2009). However, the NSE value has been known to be influenced by high values within a given dataset, at the cost of the accuracy in estimated lower flow values. Furthermore, the NSE is unable to consider direct runoff and baseflow separately. In this study, the existing SWAT auto-calibration was modified with direct runoff separation and flow clustering calibration, and current and modified SWAT auto-calibration were applied to the Soyanggang-dam watershed in South Korea. As a result, the NSE values for total streamflow, high flow, and low flow groups in direct runoff, and baseflow estimated through modified SWAT auto-calibration were 0.84, 0.34, 0.09, and 0.90, respectively. The NSE values of current SWAT auto-calibration were 0.83, 0.47, ?0.14, and 0.90, respectively. As shown in this study, the modified SWAT auto-calibration shows better calibration results than current SWAT auto-calibration. With these capabilities, the SWAT-estimated flow matched the measured flow data well for the entire flow regime. The modified SWAT auto-calibration module developed in this study will provide a very efficient tool for the accurate simulation of hydrology, sediment transport, and water quality with no additional input datasets.     

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.     

Evaluation of soil erosion risk for watershed management in Shenmu watershed,central Taiwan using USLE model parameters

This study compiles the latest regional topographic data from field investigation and remote-sensing images to recalculate parameters of the universal soil loss equation (USLE) model of the Shenmu watershed; also to compensate for reduced accuracy of this model on small-scale slopes, this study incorporates soil erosion pin data which were collected periodically to measure the extent of soil erosion. Firstly, this study utilized the USLE model and soil erosion pin data to compare the soil erosion potential of the Chushui and Aiyuzi subwatersheds and concluded that soil erosion drastically increased if accumulated rainfall exceeded 200 mm; also, erosion depths were greater in the Aiyuzi subwatershed while estimated total erosion volume was higher in the Chushui subwatershed; this was attributed to the larger area of Chushui subwatershed and based on field measurements which supported the results of the USLE model. Secondly, this study utilized modified USLE model to compare the extreme event erosion resulting from typhoon Morakot which revealed that high rainfall intensity and long-duration rainfall events can generate large volume non-point sources of sediment that is estimated to far exceed 7–10 times of the annual soil erosion. Thirdly, this study related the C parameter of the USLE model to the existing land use in the Shenmu watershed using current, real data. Finally, this study established a post-typhoon Morakot soil erosion risk map composed of five categories of risk which was compared with post-event land cover to suggest high-erosion risk zones that may require further monitoring, remediation, and engineering measures to limit soil loss.     

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.     

Evaluation of land use change and groundwater use impact on stream drying phenomena using a grid-based continuous hydrologic model

The effect of land use change on drying streams was evaluated using a grid-based continuous hydrological model (PGA-CC). For a drying stream-progressed watershed (398.8 km²), the model was calibrated and validated using 7 years (2005–2011) of streamflow data at the watershed outlet with an average Nash–Sutcliffe model efficiency of 0.71. Based on the model simulation results for 36 years (1976 to 2011), both land use change and climate change decreased the 10-day minimum flow by 0.16 m³/s and increased the day counts below the annual average by 40.6 days/year. These changes resulted from the 8.7 % increase in urban area, 1.43-fold increase in groundwater use, and 1.1 °C temperature increase during the 36-year period. From the distributed results of the model, we identified the drying stream location and progression. The spring and winter seasons were relatively strongly affected, and drying streams were identified in more urbanized areas with greater groundwater use.     

Comparative effectiveness of different infiltration models in estimation of watershed flood hydrograph

The present study aims to evaluate performance of different infiltration models, namely initial and constant rate, soil conservation service (SCS) curve number and Green–Ampt in simulation of flood hydrographs for the small-sized Amameh Watershed, Iran. To achieve the study purpose, the infiltration rates were measured using rainfall simulator in work units acquired through overlaying topography, land use, drainage network and soil hydrologic group maps. All parameters of the study infiltration models were determined with the help of the Infilt. software package. The performances of the models in simulation of the observed output hydrographs from the entire watershed were ultimately evaluated for 28 rainfall–runoff events in the HEC-HMS environment. The different components of the observed and estimated hydrographs including time to peak, runoff volume, peak discharge, discharge values and peak time deviation were compared using relative error (RE), coefficient of determination (R²), peak-weighted root mean square error (PWRMSE) and Nash–Sutcliffe (NS) criteria. The general performance of estimations was also qualitatively assessed using scatter plot and distribution of study variables around standard lines of 1:1 slope. The results revealed that the SCS infiltration model with PWRMSE = 0.61 m³ s^?1 and NS = 0.53 performed better than initial and constant rate model with PWRMSE = 1.1 m³ s^?1 and NS = 0.54, and Green Ampt model with PWRMSE = 1.35 m³ s^?1 and NS = 0.29 in estimation of flood hydrograph for the Amameh Watershed.     

Effect evaluation of shotcrete vegetation mulching technique applied to steep concrete-face slopes on a highway of Taiwan

The Shotcrete Vegetation Mulching Technique (SVMT) was introduced to revegetate existing steep concrete-face slopes. By mixing cement and greening additives with hydraulic mulching materials in a particular proportion and directly spraying the mixture on steep concrete-face slopes, SVMT was proven to be superior to several traditional methods. SVMT can make a slope surface resistant to erosion within a short time (the uniaxial compressive strength of the slope was higher than 294.3 kN/m² on the 14th day), create an environment suitable for plant growth (the vegetation coverage rate on the 90th day was higher than 90%) and foster a plant community capable of natural succession (competition and succession among Bermudagrass, turf-type tall fescue, hairy beggarticks, chamber bitter, oriental false hawksbeard, American burnweed, Pacific Island silvergrass, and inchplant were observed), effectively improving wildlife habitat and increasing biodiversity (small arthropods were found on the site, including spiders, grasshoppers, ants, ladybirds, etc.). Furthermore, the ecological engineering effects of SVMT on the experiment site were evaluated according to Mitsch and Jørgensen’s 19 Ecological Design Principles. It was found that the site treated with SVMT conformed to principles 2, 3, 8, 10, 11, and 16.     

A distributed hydro-environmental watershed model with three-zoned cell profiling

A cell-based distributed watershed model is developed which enables us to simulate the hydrological and hydraulic aspects of the watershed in a refined fashion. With three-zoned cell profiling, the model is composed of three sub-models; tank model for a surface water zone, soil moisture model for a surface soil zone, and unconfined shallow groundwater flow model for a subsurface zone. Inclusion of the soil moisture sub-model modified to reroute the infiltration, routed from the tank sub-model, into the return flow and the groundwater recharge features the model. The groundwater flow sub-model, numerically approximated by use of the finite volume method and the implicit time-marching scheme, considers a network of on-farm drainage canals as internal boundaries, which is an essential need for modeling the watershed including farmlands. Cascade-linking of the three sub-models in a cell and assembling of all the cells over the entire watershed domain provides the global equations system to be solved. Applicability of the model is demonstrated with its practical application to a real watershed in that paddy and upland crop fields take great part of the land-use practice. It is then indicated in a quantified manner that rice farming significantly contribute as a major groundwater recharger in an irrigation period to fostering and conservation of regional water resources. Along with appropriately profiling a cell, the model is so versatile and tough that it can be applied without difficulty to a watershed of diverse terrains and land-uses and the computations can stably be carried out. It is thus concluded that the model presently developed could be a powerful “watershed simulator” to investigate and assess the time-varying hydro-environmental properties of a watershed while separating and integrating the hydrological and hydraulic components of particular importance.     

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.     

覆盖作物对坡耕地的减流减沙效应及玉米产量的影响

在2020-2021年进行两年田间径流试验场玉米大田试验，在玉米进入拔节期时播种覆盖作物，共设置3个播期处理，拔节期播种覆盖作物(T1)、播种覆盖作物延后10 d(T2)、播种覆盖作物延后20 d(T3)，不覆盖作物处理作为对照(CK)，研究不同覆盖作物播期对径流量、侵蚀量及玉米产量和构成因素的影响，分析不同覆盖作物处理对坡耕地的减流减沙效应，为吉林省东部种植玉米的坡耕地区提供覆盖作物的最适播期，结果表明，黑麦草和红三叶能够有效减少水土流失，T1处理的地表径流量较其他两组覆盖处理至少下降18.8%、土壤侵蚀量下降8.8%。覆盖作物处理在中强度降雨下的保水保土作用更为显著，黑麦草和红三叶覆盖对玉米有明显的增产作用，其中T1效果最好。播种覆盖作物对于坡耕地的减流减沙作用、玉米生长发育和玉米增产最为显著。     

Mulching potatoes: Aspects of mulch management systems and soil erosion

Intensive potato production occupies much of the sloping arable land of Prince Edward Island, Canada, and is at the center of soil erosion concerns in this province. Corrective considerations have turned recent attention to mulching, but there is limited knowledge of its workability or effectiveness in potato systems. This study looks at the effect of mulching on soil loss from potatoes grown on standard erosion plots, and examines a relatively simple approach to assessing soil-surface splash detachment (splash erosion) under mulch-management systems with potatoes. Three sizes of splash cup (25, 50, and 100 mm in diameter) were used under simulated rainfall at 150 mm·h^?1 for 10 minutes to measure splash erosion on potato plots under mulch-management systems which, respectively, left surface coverage of ～ 5%, ～ 15%, and ～20%. The lowest straw coverage gave up to 56% more erosion than either of the two higher coverages. The 25-mm splash cup yielded 14% more sediment splash than the 100-mm splash cup on the basis of unit surface area of soil in the splash cup (unit area). Regression modeling of unit-area splash against straw cover showed an exponential decay in splash detachment with increasing straw cover. On the erosion plots, soil loss with mulching was half of what it was without mulching; and soil water retention was 5% greater with mulching.     

Guidelines for soil conservation towards integrated basin management for sustainable development: A new approach based on the assessment of soil loss risk using remote sensing and GIS

Soil suspension in the Cidanau River of western Java, Indonesia, has increased recently, perhaps because of rapid environmental change in this watershed region. The objectives of this research are to assess soil loss risk using remote sensing and GIS and to develop effective guidelines for soil conservation in this watershed. To assess soil loss risk, a new soil loss model based on Universal Soil Loss Equation (USLE) was applied, in which C factor (crop management factor) was estimated using the perpendicular vegetation index (PVI); this was computed with satellite remote sensing data and used to simulate soil loss risk. The simulation showed that areas with highest risk of soil loss are on northern- and southern-facing hillsides with poor vegetation. Guidelines for soil conservation in the watershed were proposed: under these guidelines soil-loss risk is managed by evaluating the effectiveness of contour farming, belt farming, and mulch farming. Some recommended measures for soil conservation are as follows: (1) Green vegetation cover should be preserved as much as possible. (2) Vegetation coverage must be increased by forestation in steep sloped areas. (3) Belt farming and contour farming are recommended in areas with slopes under 100%, and mulch farming (more than 50% ground cover mulching is recommended) is desirable in areas with slopes over 100% and without green cover.     

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.     

Estimating time of concentration in large watersheds

For hydrologists, time of concentration (TC) is one of the most important parameters to be able to predict the response of a watershed to a given rain event and plays a key role in rainfall-runoff simulation. There are several methods to calculate the TC. The time of concentration is defined as the time from the hydraulically furthermost point to watershed outlet. In this study, we integrated 22 formulas from various references for calculating time of concentration and selected seven formulas by considering the specific conditions and limitations that are suitable for Shafaroud watershed with an area of 345.4 km², located in the western Guilan province of northern Iran. They included Ventura, Passini, Bransby-Williams, Carter, Johnstone-Cross, Izzard and Papadakis-Kazan. The TC values obtained from the mentioned methods were applied in HEC-HMS software for the four rainfall events of June 5, 2003; October 20, 2005; December 2, 2007; and June 19, 2008. The results indicated that peak flow values obtained by the Bransby-Williams method are most consistent with the observed peak data values and better presents the hydrologic condition of the watershed.     

Relationship between increment of groundwater level at the beginning of irrigation period and paddy filed area in the Tedori River Alluvial Fan Area, Japan

There are many paddy fields and large amounts of groundwater in the Tedori River Alluvial Fan in Ishikawa Prefecture, Japan. Water infiltration from paddy fields during irrigation may significantly contribute to groundwater recharge. Groundwater recharge is known to be one outcome of paddy farming, and in general is usually related to land use. However, a decreased area of paddy fields because of socioeconomic factors such as urbanization and increasing area of fallow fields has possibly affected the groundwater environment. Evaluation of the quantitative effect of paddy fields on groundwater is necessary for groundwater conservation. This study examined the relationship between differences in the depth of groundwater from just before the irrigation period to just after the first irrigation of paddy fields (increments of groundwater levels) in observation wells and the area of paddy fields around each well. The paddy areas within circular buffer zones, which were delineated at 0.2 km intervals between 0.2 and 2.0 km centered on each observation well, were calculated. A positive relationship was found between the rise in groundwater and the area of paddy field within different buffer zones at most wells. In addition, in the middle or upper part of the fan, the effect of changes in the area of paddy fields surrounding the well on the groundwater level rise was greater than that on the lower part of the fan.