Sediment yield modelling of an agricultural watershed using MUSLE, remote sensing and GIS

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.     

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.     

Application of USLE for the prediction of nutrient losses in soil erosion processes

Soil erosion in agricultural fields affects not only land productivity but also water environment down stream. Many investigations have been made for the prediction of soil erosion processes. The Universal Soil Loss Equation (USLE) has been applied broadly for the prediction of average annual soil loss from upland fields. However, there are few reports concerning the prediction of nutrient (N, P) losses based on the USLE. Thus, the objective of this study is to propose the prediction equation of nitrogen and phosphorus losses during soil erosion processes on the basis of the USLE. In order to predict total nitrogen and phosphorus losses, the coefficients for total nitrogen or phosphorus transfer are derived on the basis of results from experimental field plots. Three bare-cover USLE plots with different amounts of granular chemical fertilizer were installed in an experimental upland field. There was a tendency for the coefficient of total nitrogen or phosphorus transfer to increase with the average concentration of total nitrogen or phosphorus in the soils. It follows that the more granular chemical fertilizer applied caused a higher coefficient of total nitrogen or phosphorus transfer in the calculations. Moreover, the coefficients in heavily fertilized plots were higher than 1.0. Through this investigation, it became clear that the nutrient losses during soil erosion could be predicted on the basis of the coefficient of total nitrogen or phosphorus transfer along with other soil erosion parameters.     

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.     

Assessing the effect of watershed slopes on recharge/baseflow and soil erosion

Aquatic ecosystems are threatened by increasing variability in the hydrologic responses. In particular, the health of river ecosystems in steeply sloping watersheds is aggravated due to soil erosion and stream depletion during dry periods. This study suggested and assessed a method to improve the adaptation ability of a river system in a steep watershed. For this, this study calibrated soil and water assessment tool (SWAT) for runoff and sediment, and quantified the changes in hydrologic responses such as groundwater recharge rate soil erosion and baseflow according to two scenarios for adjustment of the watershed slope (steep to mild). Here, one scenario was set by three measured slopes, and the other was set by fixing the entire watershed slopes with 5 %. Moreover, SWAT and web-based hydrograph analysis tool (WHAT) models were applied to estimate groundwater recharge, soil erosion, and baseflow in the Haean-myeon watershed in South Korea. The results show that the reduction of watershed slope increased groundwater recharge and baseflow, and decreased sediment. Specifically, groundwater recharge rate was increased from 257.10 to 364.60 mm, baseflow was increased from 0.86 to 1.19 m³/s, and sediment was decreased from 194.6 to 58.1 kg/km². Based on these results, the suggested method will positively contribute to aquatic ecosystems and farming environments in a steeply sloping watershed due to improvements in the quantity and quality of river water.     

Impacts of soil erosion in the upper Manupali watershed on irrigated lowlands in the Philippines

With concerns about possible environmental degradation associated with agricultural production, the impacts of soil erosion in the upper Manupali watershed and the consequent sedimentation in the plains on the productivity of the Manupali River Irrigation System's (ManRIS) service area of 4,422 ha were assessed. Land-use changes in the watershed for the past 2 decades caused soil erosion and the consequent increasing trend of canal siltation at ManRIS. This resulted in a significant decline in the productivity and income of the farmers. Rice yields in farms that were heavily affected by siltation had decreased by 27% from 1990 to 1995. Furthermore, in addition to the regular Operation and Maintenance (O and M) costs, the ManRIS management incurred desilting costs in its operation. To cope with the siltation problem, the ManRIS management and farmers made adjustments in the water delivery schedule, cropping pattern and land allocation to various crops. However, it is expected that the siltation in the ManRIS canal network and the consequent decline in crop yield and income will continue in the coming years. Drastic measures are needed to remedy the soil erosion problem in the upper Manupali watershed. Electronic Publication     

Evaluation of HEC-HMS and WEPP for simulating watershed runoff using remote sensing and geographical information system

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.     

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.     

Experimental study on soil erosion characteristics in flooded terraced paddy fields

This experimental study assesses the effects of event rainfall on soil erosion characteristics in terraced rice paddy fields. A 0.75-ha terraced paddy field located in Northern Taiwan was used to investigate the soil erosion under the regular cultivation of rice during two crop seasons. The environmental changes were investigated in the neighboring areas in which terraced paddy fields have been converted to other land usages. The annual rate of soil erosion calculated from the observed rainfall runoff and suspended solid contained was 0.77 ton/ha, which is significantly less than the erosion rate associated with upland crop cultivation reported by other research conducted in Taiwan. Experimental results also showed that the terraced paddy field retained the highest percentages of clay, silt, and organic matter's content, as compared to those of other upland crops, indicating that the topsoil was less susceptible to rainfall erosion under flooded conditions of rice-cultivation. The results of this study show that the rice-planted terraced paddy offers the highest level of soil conservation. The function of soil and water conservation in terraced paddy fields could be further increased by effective maintenance of embankment and to raise the height of the bund. Poor management, abandoned cultivation, and converse to other upland crops of terraced paddy fields are regarded as major contributors to increased soil erosion in mountainous areas. The government in Taiwan should formulate effective measures and maintain sustainable rice cultivation in the terraced paddies.     

海南岛典型农业土壤产流与面源污染特征分析

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。     

Reduction of runoff and soil loss over steep slopes by using vetiver hedgerow systems

Vetiver hedgerow system has potential for reducing runoff and soil loss especially on steep slope areas, but the dynamics of these reductions are not fully understood. This research was conducted to determine reduction in runoff and soil loss by vetiver hedgerow system. Vetiver hedgerow systems with three vertical intervals of hedgerow were tested on three land slopes and compared with the case without hedgerow for six simulated rainfall amounts. The vetiver hedgerows reduce runoff volume and soil loss by 31–69 and 62–86 %, respectively compared to the case without vetiver hedgerow. Runoff volume increases with rainfall amount, and hence increases soil loss. Therefore soil loss increases with land slope, runoff volume, rainfall amount, and vertical hedge interval. Two final equations for estimating soil loss are presented in this study. The first equation contains parameters of runoff volume, land slope, and vertical hedge interval, while the second equation contains rainfall amount instead of runoff volume. The correlation coefficients between estimated soil losses and the experimental data in this study and in the literatures were found to be 0.94 and 0.90 for the first and second equations, respectively.     

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.     

Biological Practices and Soil Conservation in Southern China

Summary

Southern China has abundant natural resources and is a major region of agricultural production. However, soil erosion is increasingly threatening the agricultural productivity of this region. Increases in soil erosion are caused by improper land use practices with soils of high rainfall erosivity. Much of the area prone to accelerated erosion was previously forested and subsequently logged four times since the 1920s. This paper discusses the effects of biological control practices on soil erosion according to erosion types, soil properties, and terrain.     

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.     

Estimation of pollutant loads in an estuarine reservoir considering pollution source characteristics and seasonal variation

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.     

Simulation of rainfall runoff and pollutant load for Chikugo River basin in Japan using a GIS-based distributed parameter model

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.     

Surface drainage nitrate loading estimate from agriculture fields and its relationship with landscape metrics in Tajan watershed

Pasture, forest, and farmland are the dominant land covers in the Tajan River watershed and this landscape status has a direct connection with nitrate pollution. Understanding the correlations between landscape variables and nitrate pollutant is a priority in order to assess pollutants loading and predicting the impact on surface water quality. The soil and water assessment tool was used to simulate nitrate loads in different land cover types in different years. The landscape pattern was calculated by FRAGSTATS. The contributing share of each land use/land cover shows nitrate pollutant produced by grassland (5.7%) and forest (29%) are less than those produced by agricultural land (64.2%). Agricultural land was identified as the main source of nitrate pollution. Paddy fields and orchards had the most intensive soluble nitrate loss especially in spring and summer. Statistical analysis indicated that nitrate was positively associated with patch density, edge density, patch number, total edge, effective mesh size, largest patch index, and landscape shape index (p ≤ 0.01). We then analyzed how nitrate was related to landscape attributes in six different sites. Also the regression analysis results suggested that landscape metrics could account for more than 94% of the variance of nitrate in the whole catchment. The regression models confirmed the great importance of the agriculture metrics and forest metric in predicting nitrate in watershed. Defining the generation and extent of pollution in this particular watershed which discharges into the Caspian Sea can constitute an important step toward protecting this ecosystem.     

Assessment and mapping of soil erosion risk by water in Tunisia using time series MODIS data

Soil erosion by water is a common environmental problem which can affect the sustainable development and the agriculture of developing countries especially. Therefore, several countries, threatened by this phenomenon, adopt different measures to preserve and protect their natural resources. The main purpose of this study was to identify vulnerable areas to establish a soil erosion risk map in Tunisia. In order to do so, an approach based on a combination of the Revised Universal Soil Loss Equation (RUSLE) as an erosion model, Geographic Information System (GIS) and Remote Sensing was applied. RUSLE, which is a model to predict soil loss, is composed of five factors. Erosivity factor (R factor), erodibility factor (K factor), topography factor (LS factor), crop management factor (C factor), and supporting practices factor (P factor). Furthermore, in order to get the most accurate C factor for each land use, times series Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation index (MODIS-EVI) were used. MODIS-EVI time series was helpful for distinguishing vegetation dynamics with taking into account phenological variation of the crops. The results indicated that Tunisia has a serious risk of soil erosion. Indeed, about 24.57% of our study area had a soil loss rate more than 30 t/ha. In these areas, suitable and urgent measures and treatments should be required. Finally, this approach which is based on remote sensing techniques, GIS and erosion model can be useful for planning appropriate environmental decision-making policy in a global scale.     

A study of rationality of slopeland use in view of land preservation

In recent years, frequent attacks of heavy rain and typhoon have severely devastated the vulnerable mountains of Taiwan; slopelands are artificially disturbed by improper development and utilization. People are getting more aware of the importance of slopeland preservation as well as disaster prevention and mitigation. The government, realizing the criticality of gradually worsened land safety issues, has also set forth the “Draft of National Land Planning Act” and the “Draft of Regulations on Land Preservation Act” in the purposes of rehabilitating the excessively explored ecosystems and diminishing the development extent of environmentally susceptible areas, so as to effectively preserve soil, water, and organism resources and to achieve perpetual development of national lands. “Classification of Slopeland Utilization Limitations” is a critical link to national land preservation. The classification is based on four factors, namely average slope, effective soil depth, soil erosion, and parent rock, with different utilization zones defined as bases of landuse planning. However, current classification results of the environmentally susceptible and disaster-prone mountain lands are mostly defined as suitable for forestry or husbandry. Scattered allocation of these lands results in critical issues such as segmented landuse and impaired landscape and ecotype. It is necessary to re-adjust land resources planning and usage management. Therefore a review of the current standards for classifying slopeland utilization limitations is proposed to facilitate rational allocation of slopeland use. Jhuoshuei River is selected as the scope of the case study, with data of debris flows induced by the typhoon Toraji in 2001 as the training data. Eight susceptibility factors, which include form factor of watershed, integral hypsometric, slope of main stream, density of stream network, density of road network, area ratio of historical landslide, and area ratio of triggered landslide, together with the total rainfall of the storm event as the triggering factor, are selected for creating the debris flow susceptibility model by employing the logistic regression within the multivariate geostatistics analysis. This model interprets the curve of success ratio of debris flows triggered by typhoon Toraji, of which the area under the curve is as high as 74.3%. The debris flow susceptibility model created in the study takes the Feng-Chiu section of Sinyi Township, Nantou County, Taiwan within the Jhuoshuei River as the scope of research. GIS technology has been applied in the feasibility study of classification standards. New concepts have been further proposed in view of national land preservation addressing the medium and high elevation disaster-prone areas that are not suitable for agricultural use, for standard revision reference.     

A physically based FVM watershed model fully coupling surface and subsurface water flows

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.