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1.
Although a variety of rainfall-runoff models are available, selection of a suitable rainfall-runoff model for a given watershed
is essential to ensure efficient planning and management of watersheds. Such studies are relatively limited in developing
nations, including India. In this study, rainfall-runoff modeling was carried out using HEC-HMS and WEPP hydrologic models,
and remote sensing and GIS (geographical information system) techniques in the Upper Baitarani River basin of Eastern India
using daily monsoon season (June–October) rainfall and the corresponding streamflow data of 6 years (1999–2005). Other input
data such as soil map, land use/land cover map, and slope map were prepared using remote sensing and GIS techniques. The modeling
results revealed that both the models under predict streamflow for 1999, 2002, 2004, and 2005 and over predict for 2001 and
2003, whereas HEC-HMS under predicts and WEPP over predicts streamflow for the year 2000. The percent deviation of total runoff
volume simulated by HEC-HMS ranges between −2.55 and 31%, while it varies from −13.96 to 13.05% for the WEPP model which suggests
that the WEPP model simulates annual flow volumes more accurately than the HEC-HMS model for most years. However, the lower
values of root mean square error (RMSE) and RMSE-observation standard deviation ratio coupled with the higher values of Nash–Sutcliffe
efficiency, percent deviation and coefficient of determination for HEC-HMS during calibration and validation periods indicated
that the streamflow simulated by HEC-HMS is more reliable than that simulated by WEPP. Overall, it is concluded that the HEC-HMS
model is superior to the WEPP model for simulating daily streamflow in the Baitarani River basin of Eastern India. 相似文献
2.
Evaluation of MODIS NDVI and LST for indicating soil moisture of forest areas based on SWAT modeling
Park Jong-Yoon Ahn So-Ra Hwang Soon-Jin Jang Cheol-Hee Park Geun-Ae Kim Seong-Joon 《Paddy and Water Environment》2014,12(1):77-88
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. 相似文献
3.
海南岛典型农业土壤产流与面源污染特征分析 总被引:1,自引:0,他引:1
采用径流场结合人工模拟降雨方式,研究各种降雨条件下海南岛不同土地类型产流产沙的规律与面源污染特征。结果表明:土壤(泥沙)产流系数与平均流失速率表现为暴雨>大雨>中雨,且暴雨时的泥沙平均流失速率为中雨时的416%、大雨时的261%,在中雨、大雨和暴雨强度下,平均径流系数分别为24.49%、33.97%和53.40%;雨强对土壤营养物质流失速率的影响达到显著水平,COD、有机质和氮素以径流流失为主,磷素以泥沙流失为主;土壤径流和泥沙中的COD、有机质、氮素和磷素流失速率随雨强的增大而增大,坡度也可明显影响面源污染物的流失;海南岛农业土壤平均流失量为3.79 t/(hm2·a),中雨强度条件时为1.92 t/(hm2·a),大雨强度条件时为2.57 t/(hm2·a),暴雨强度条件时为6.87 t/(hm2·a)。海南岛农业土壤的水土流失强度较高,海南农业土壤的水土流失与农田污染物输出状况不容乐观。 相似文献
4.
The Total Maximum Daily Load (TMDL) program is an integrated process of watershed assessment and management to address surface
water quality impairment. The management of organic contaminants and nutrients is a primary concern in conserving surface
water bodies. Watershed-scale pollutant loads simulation can assist stakeholders and watershed planners in making decisions
on immediate and long-term land use schemes to improve water quality. However, the behavior of contaminants in a watershed
needs to be characterized prior to such model applications. The objectives of this study were to characterize point and nonpoint
pollutants runoff at a watershed scale and to develop a Pollutant Load Calculation Model (PLCM), which facilitates the estimation
of pollutant delivery to a watershed outlet. The developed model was applied for the six sub-watersheds of the Saemangeum
estuarine watershed in Korea, where a large tidal reclamation project has been underway. Two years stream flow and water quality
data were used for the model calibration, while 1 year data were utilized for the model validation. The model calibration
resulted in the R
2 values of 0.58, 0.53, and 0.35 for BOD, TN, and TP, respectively. Overall performance for the validation period was similar
with that for the calibration period although the R
2 values were slightly decreased. The PLCM tends to substantially under or overestimate delivery pollutants loads during the
summer rainy seasons when most rainfall events occur. This is probably because once-a-month-measured water quality data, which
might not represent appropriately monthly water quality, particularly, for rainy seasons, were used for the loads calculation.
Thus, more frequently monitored water quality data should be used for the delivery loads estimation at least for a rainy season
in order to improve the PLCM performance. Nevertheless, the developed model took the pollutant reduction process into account,
which is not allowed with the conventional unit loading method, and furthermore temporal variations of pollutant loads based
on stream flows were also incorporated into the pollutant loads estimation. The developed PLCM can be a useful tool to assess
pollutants delivery loads at a watershed scale and thus assist decision makers in developing watershed pollution management
schemes. 相似文献
5.
Le Van Chinh Haruka Iseri Kazuaki Hiramatsu Masayoshi Harada Makito Mori 《Paddy and Water Environment》2013,11(1-4):97-112
In watershed management, the determination of peak and total runoff due to rainfall and prediction of pollutant load are very important. Measurement of rainfall runoff and pollutant load is always the best approach but is not always possible at the desired time and location. In practice, diffuse pollution has a complex natural dependence on various land-use activities such as agriculture, livestock breeding, and forestry. Estimation of pollutant load is therefore essential for watershed management and water pollution control. In this study, a model of rainfall runoff and pollutant load, which uses a geographical information system (GIS) database, is a convenient and powerful tool for resolving the abovementioned complexities. This technology was applied in order to simulate the runoff discharge and the pollutant load of total nitrogen (TN) and total phosphorus (TP) in the Chikugo River basin of Kyushu Island, Japan. First, a hydrologic modeling system (HEC-HMS) and GIS software extension tool were used for simulations of elevation, drainage line definition, watershed delineation, drainage feature characterization, and geometric network generation. The spatial distributions of land cover, soil classes, rainfall, and evaporation were then analyzed in order to simulate the daily runoff discharge at the Chikugo Barrage from April 2005 to December 2007. An important point in this approach is that a new development for data input processing with HEC-HMS was introduced for optimizing parameters of the model. Next, the water quality indicators TN and TP were examined, and an efficient approach was investigated for estimating monthly pollutant loads directly from unit load and ground-observed hydrological data. Both nonpoint and point sources of pollutants were considered, including different land-cover categories, sewers, factories, and livestock farms. The observed and simulated results for the runoff discharges and pollutant loads were in good agreement and totally consistent, indicating that the proposed model is applicable to simulation of rainfall runoff and pollutant load in the Chikugo River basin. Further, this model will be able to provide managers with a useful tool for optimizing the water surface management of this river basin. 相似文献
6.
A study was undertaken to estimate the sediment yield of the Karso watershed of Hazaribagh, Jharkhand State, India using modified
universal soil loss equation (MUSLE), remote sensing (RS) and geographic information system (GIS) techniques. The runoff factor
of MUSLE was computed using the measured values of runoff and peak rate of runoff at outlet of the watershed. The topographic
factor (LS) was determined using GIS while crop management factor (C) was determined from land use/land cover data, obtained from RS and field survey. The conservation practice factor (P) was obtained from the literature. Sediment yield at the outlet of the study watershed was simulated for 345 rainfall events
spread over a period of 1996–2001 and validated with the measured values. Nash–Sutcliffe simulation model efficiency of 0.8
and high value of coefficient of determination (0.83) indicated that MUSLE model estimated sediment yield satisfactorily. 相似文献
7.
High streamflow variability is a potential risk factor in river management in Korea because the use of water resources in Korea depends primarily on surface water. In this regard, analysis of streamflow variability is critical for efficient water resources management. Because streamflow variability is mainly influenced by the contributions of direct runoff and baseflow, the relationship between baseflow and streamflow is an important hydrological indicator that reflects river characteristics. Accordingly, this study was conducted to estimate the effect of baseflow on streamflow variability. For this purpose, a number of streamflow variability indices (SVIs), such as the Richard–Baker flashiness index, the coefficient of variation, the ratio of high flow to low flow (Q5:Q95), and the coefficient of flow regime, were calculated for Korea’s major river systems to determine which SVI best reflects the characteristics of Korean rivers. In addition, baseflow separation was performed to calculate the relationship between SVIs and the baseflow index. The results of this study show that the baseflow index is inversely proportional to streamflow variability. In particular, the impact of baseflow on streamflow variability was highest in the Yeongsan–Sumjin River system. These results are valuable information expected to be used in river management to better secure water resources. 相似文献
8.
Efficacy of foliar applied fungicides following simulated rainfall for the control of dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) was assessed in a two-year field study on creeping bentgrass (Agrostis stolonifera L.) turf maintained as a golf course fairway. The study was conducted as a randomized complete block design with a factorial arrangement. Fluazinam (0.8 kg a.i. ha−1), chlorothalonil (3.79 kg a.i. ha−1) or iprodione (1.5 kg a.i. ha−1) were applied, then subjected to simulated rainfall (2.54-mm) at intervals of 15-, 30-, 60-min post-application, or no simulated rain. In most cases, simulated rainfall occurring ≤60 min post-application had greater disease than no rain plots; however, few differences occurred among rainfall intervals ≤60 min. Fluazinam provided the greatest dollar spot reduction regardless of simulated rainfall interval throughout the study. Chlorothalonil was most susceptible to losses in efficacy due to simulated rainfall, resulting in the greatest disease incidence of those fungicides evaluated. Iprodione was comparable to chlorothalonil during high disease pressure, although during moderate disease pressure it controlled dollar spot for approximately 7 days before disease increased in plots receiving simulated rain compared to those without simulated rain. These data demonstrate that efficacy of fungicides applied for dollar spot control are affected by rain, and differ in their ability to control disease following post-application rain events. Fluazinam, a recently introduced contact fungicide for use on turfgrass, can provide improved control compared to chlorothalonil or iprodione when rain is eminent. 相似文献
9.
Junichiro Takeuchi Toshihiko Kawachi Chie Imagawa Natsuki Buma Koichi Unami Shigeya Maeda 《Paddy and Water Environment》2010,8(2):145-156
A sophisticated modeling approach for simulating-coupled surface and subsurface flows in a watershed is presented. The watershed
model developed is a spatially distributed physically based model of composite dimension, consisting of 3-D variably saturated
groundwater flow submodel, 2-D overland flow submodel and 1-D river flow submodel. The 3-D subsurface flow is represented
by the complete Richards equation, while the 2-D and 1-D surface flows by the diffusive approximations of their complete dynamic
equations. For piecewise integration of these equations, the finite volume method (FVM) is employed assuming unknown variables
such as the water depth and the pressure head to be volume-averaged state ones. Problem plane geometry is meshed with the
unstructured cells of triangular shape which conforms to external as well as internal irregular boundaries such as those between
1-D and 2-D flows. A cell size controlling scheme, referred to as quasi-adaptive meshing scheme, is introduced to keep the
local discretization errors caused by topographic elevation gradient even over the entire-meshed geometry. Performance of
the model is tested through its practical application to a rugged intermountain watershed. Tuning the values of the three
key parameters ensures successful calibration of the model. Once the model is so calibrated, it could reproduce satisfactory
runoff response to any rainfall event. Expansion and shrinkage of the contributing area importantly affecting the direct runoff,
caused by the vicissitude of rainfall during its total duration, are well reproduced, like what the commonly accepted runoff
theory argues. It is thus concluded that the model developed could serve as a powerful watershed simulator usable for investigating
and assessing the hydrological aspect of a watershed. 相似文献
10.
Hyunwoo Kang Jongpil Moon Yongchul Shin Jichul Ryu Dong Hyuk Kum Chunhwa Jang Joongdae Choi Dong Soo Kong Kyoung Jae Lim 《Paddy and Water Environment》2016,14(4):499-508
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. 相似文献
11.
In-Kyun Jung Jong-Yoon Park Geun-Ae Park Mi-Seon Lee Seong-Joon Kim 《Paddy and Water Environment》2011,9(3):275-290
A grid-based, KIneMatic wave STOrm Runoff Model (KIMSTORM) is described. The model adopts the single flow-path algorithm and
routes the water balance during the storm period. Manning’s roughness coefficient adjustment function of the paddy cell was
applied to simulate the flood mitigation effect of the paddy fields for the grid-based, distributed rainfall-runoff modeling.
The model was tested in 2296 km2 dam watershed in South Korea using six typhoon storm events occurring between 2000 and 2007 with 500 m spatial resolution,
and the results were tested through the automatic model evaluation functions in the model. The average values of the Nash–Sutcliffe
model efficiency (ME), the volume conservation index (VCI), the relative error of peak runoff rate (EQp), and the absolute error of peak runoff (ETp) were 0.974, 1.016, 0.019, and 0.45 h for calibrated storm events and 0.975, 0.951, 0.029, and 0.50 h for verified storm
events, respectively. In the simulation of the flood mitigation effect of the paddy fields, the average values of the percentage
changes for peak runoff, total runoff volume, and time to peak runoff were only −1.95, −0.93, and 0.19%, respectively. 相似文献
12.
Naoki Kabeya Akira Shimizu Tatsuhiko Nobuhiro Koji Tamai 《Paddy and Water Environment》2008,6(1):25-35
To elucidate the water cycle in lowland forests of the Mekong River basin, our research group established four experimental
watersheds in the Stung Chinit River basin in Kampong Thom Province, Cambodia. The drainage areas of these experimental watersheds
ranged from small (4 km2) to mesoscale (3,659 km2). Here, we present the first preliminary results of our rainfall-discharge observations and analyses of temporal variations
of stable isotope ratios in rainfall, stream water, and groundwater. This paper focuses on the following three main topics:
annual rainfall, discharge, and water balance; stormflow generation and dominant flow pathways; and flow regimes and stream
water residence times. All stream water residence times (τ = 1.7–7.5 months) for the four experimental watersheds were shorter than the residence time of the groundwater (τ = 9.4 months) through the soil and regolith layers, implying that the stream waters consisted of not only the groundwater-flow
component, but also younger-aged flow components such as saturation-excess overland flow. The smallest (4 km2; O Toek Loork) watershed had longer residence time (τ = 7.5 months) than the three larger watersheds (126–3,659 km2; τ = 1.7–3.9 months). This may suggest differing contributions of the groundwater and younger-aged flow components in the stream
water in each watershed. Our approach of multi-scale watershed observation might better contribute to the needs of physically
based models and aid in predictions for ungauged basins. 相似文献
13.
E. Taghvaye Salimi A. Nohegar A. Malekian M. Hoseini A. Holisaz 《Paddy and Water Environment》2017,15(1):123-132
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. 相似文献
14.
Terraced paddy field rainfall-runoff mechanism and simulation using a revised tank model 总被引:1,自引:0,他引:1
Terraced paddy fields play important roles in water and soil conservation because their water storage effect reduces and delays
flood peaks. This study applies the terraced paddy field rainfall-runoff mechanism to the tank model. Though the traditional
four-section tank model can easily simulate rainfall-runoff in a terraced paddy field, it has many parameters that are difficult
to calibrate. To address the shortcomings of the traditional four-section tank model, this study develops a revised tank model
to simulate rainfall-runoff. This study selects a terraced paddy field located in Hsuing-Pu village in Hsiuing-Chu County
as the experimental field. The field under investigation was equipped with automatic monitoring stations, water-stage, and
rain gauges. These stations collected data on rainfall and water flow to simulate the rainfall-runoff model in that region.
To simulate the runoff behavior of the experimental terraced paddy field, two rainfall events were selected from the gathered
data and five normal evaluation indexes based on static and hydrological theory were applied to calculate the results of simulation
simultaneously. The revised tank model performed better than expected, and precisely predicted the variations and trends in
flow charge. Comparison with representation indexes proved that the revised tank model is an appropriate and valuable tool
for rainfall-runoff simulation. 相似文献
15.
Tasuku Kato 《Paddy and Water Environment》2005,3(1):21-27
Water quality in the watershed mainly used for agriculture is degraded by nutrients from fertilizers and animal wastes. These diffuse (non-point) sources have accumulated in soils and been released into the river system for the long-term. In this paper, a water quality tank model classified by land use is modified for the accumulation, and total nitrogen (T-N) is simulated over 40 years in the Yamada River basin within the Lake Kasumigaura watershed, Japan. For considering the nitrogen balance, the model has a database comprising statistical data such as population, land use, rain, fertilizer, and animal waste; it calculates cumulative load in soils and dissolved load separately. The model simulated the measured data with relative error of 15% for runoff and 7% for T-N. Five scenarios for the reduction of cumulative load were developed as a countermeasure plan: soil washing, slow-release fertilizer, fertilizer application reduction, cover crop, and animal waste reduction. The results show that T-N first decreases and then increases after 30 years in the case of the slow-release fertilizer scenario and that T-N is reduced by 30% after 40 years in the case of the 100% animal waste reduction scenario. 相似文献
16.
Simulation of water quality with the application of system dynamics model for population and land-use changes 总被引:1,自引:0,他引:1
Tasuku Kato 《Paddy and Water Environment》2005,3(2):103-109
Water quality is degraded due to urbanization because it causes population growth and land-use changes in a watershed. These
changes are usually simulated using a linear equation; however, in reality, population and land use are very closely related.
A watershed system dynamics model (WSD model) was developed in the simulation of the relation among population, land use (paddy
fields, upland fields, forest, and household), and runoff. The model comprised of three sectors: the agricultural sector,
nature sector, and urban sector. The elements in the WSD model were selected based on interviews with local government officers
and references. The WSD model simulated population, land use, and runoff with an average relative error of about 5%. Total
nitrogen (T-N) and total phosphorus (T-P) were simulated using the results of the WSD model and unit effluent loads. Field
surveys were conducted to determine the rate of mitigation in paddy fields. In addition, correction equations for runoff and
phosphate-containing detergent were introduced. The model simulated T-N with an average relative error of 9%, and T-P with
27%; a sensitivity analysis for the principal elements in the WSD model showed reasonable results. 相似文献
17.
Sang-Jin Lee Seung-Jin Maeng Hyung-San Kim Sang-Il Na 《Paddy and Water Environment》2012,10(4):265-280
This study begins to address the need for a runoff model that is able to simulate runoffs at control points in a dam’s upper and lower stream during the seasons of high and low water levels. We need to establish a synthetic management plan on water resources considering the runoff at the upper and lower streams to effectively manage the limited water resources in Korea. For this reason, we classified the Han River Basin into 24 sub-basins and arranged a great amount of rainfall data using 151 rainfall observation stations so as to prepare for the spatial distribution of precipitation. We chose several dams as subjects for this study, which includes the Chungju Regulating Reservoir, Soyang, Chungju, Hoengseong, Hwacheon, Chuncheon, Euiam, Cheongpyeong, and Paldang Dams as main controlling points. Also, we made up input data of this model, selecting the Streamflow Synthesis and Reservoir Regulation (SSARR) model as a runoff model in the Han River Basin. We performed a sensitivity analysis of parameters using hydrological data from the year 2002. And as a result, the findings of this study showed that, among many parameters related to the basin runoff, the following have revealed greater sensitivity than any other parameters: soil moisture index-runoff percent, baseflow infiltration index-baseflow percent, and surface-subsurface separation. On the basis of the above sensitivity analysis, we have used hydrological data between 2001 and 2002 when drafts and floods broke out in Korea to verify and calibrate the parameters of the SSARR model. Furthermore, we verified and calibrated the 2000 data using corrected parameters and performed an analysis of annual water balance in the Han River Basin from 1996 to 2005 considering agricultural water. 相似文献
18.
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. 相似文献
19.
Kwang-Wook Jung Sang-Woo Lee Ha-Sun Hwang Jae-Ho Jang 《Paddy and Water Environment》2008,6(3):275-284
Researchers generally accept that land use types within a watershed closely relate with the water quality characteristics
of streams. Despite numerous studies investigating the relationships between water quality and land use, there are increasing
concerns about the geographical variation and lack of spatial integration in previous studies. We investigated the relationships
between land use and water quality characteristics including biological oxygen demand (BOD5), total nitrogen (TN), total phosphorus (TP), and Escherichia coli in the Wha-Ong estuarine reservoir watershed in Korea, which has spatially integrated land uses. Residential and paddy areas
appear to be positively and negatively correlated, respectively, with degraded water quality. The spatial variations of these
relationships were also examined using zonal analysis. Some results contrasted with those of previous studies that were conducted
mostly in developed Western countries and may reflect the different land use intensities and agricultural practices in Korea.
Relationships across zones, distinguished by distances from streams, were inconsistent and erratic, suggesting that the relationships
between remote land uses and water quality may be affected more significantly by sub-basin characteristics than by the land
use itself. The geographical differences and spatial variations found in this study indicate that caution must be taken in
generalizing the relationship between land use and water quality. 相似文献
20.
Van Trinh Mai Herman van Keulen Rudi Hessel Coen Ritsema Reimund Roetter Thai Phien 《Paddy and Water Environment》2013,11(1-4):285-298
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. 相似文献