Simulating Water and Pollution Exports from Soil to Stream during the Thawing Period at the Small River Basin Scale

A physical model was developed to describe the soil-to-stream export processes of water and pollutants in a small river basin during the soil thawing period. The hydrological and pollution transport and transformation behaviors in paddy- and corn-dominated catchments were numerically simulated; the impacts of the pollution concentrations, interactions between the migrated water and pollutants in the soil, and pollutant transformations during the pollution export were coupled. Experimental field data from the Heidingzi river basin during the soil thawing period were used to calibrate the model parameters and evaluate the performance. The mass of the dissolved pollutants from soil particles in the migrated soil pore water was the key factor affecting the pollution export into the streams; the water content directly affected the pollution export. The concentration of the pollutants peaked when the initial exported water was high. The pollutant transport processes influenced the pollution export more significantly after the soil water was significantly reduced. The N-S efficiency coefficients between the simulated and monitored flow rates and the pollution concentrations at the outlets of the paddy- and corn-dominated catchments were >0.60 and >0.54, respectively. The system deviations between the simulated and monitored flow rates and the pollution concentrations were <10% and <15%, respectively. The proposed model effectively described the water flow, pollution transport and transformation processes.

CHANGE OF RADIATION PARAMETERS ALONG A LANDSCAPE PROFILE IN THE MAJDAN RIVER POOL OF THE ULLYANOVSK REGION

The article presents the results of assessing the contribution of technogenic and terrigenic radionuclides to the formation of the dose rate of gamma radiation for geosystems of the small river basin.

Hydro-meteorological preconditions and geomorphological consequences of extreme flood in the small river basin in the wet subtropical zone (the Tsanyk River case study, Sochi region)

The overall increase in precipitation and the frequency of extreme rainfall is confirmed by several meteorological observations both on the Black Sea coast of the Caucasus. In this context, research on the drivers of an extreme meteorological event becoming a severe flood and an extreme geomorphological (erosion) event becomes especially important. The article analyses the factors contributing to the development of a flash flood on the watershed of the river Tsanyk (Great Sochi area) and estimates its geomorphological impact. Analysis of hydrologic-meteorological situation during the Tsanyk flood on 7-9 September 2018 and in the previous period showed that the event is unique for the investigated watershed from the hydrologic perspective. After a prolonged period without precipitation, the rainfall on 7-8 September resulted in a flash flood with a rapid water level rise (117 cm in 40 min). We determined the rates and volumes of channel erosion based on a repeated survey of the channel section, estimation of the speed and length of the banks being flushed out, composed of loose sediments and bedrock using the pin method. The amount of erosion on the banks composed of loosened sediments is on average 2-3 times higher than on the flysch banks. At the same time, the material export for one erosion event in September 2018 is comparable (or even exceeds) the total amount of bank erosion for the year, previously identified based on stationary observations.

Research on the non-point source pollution characteristics and water environmental capacity within small river basin of agricultural areas a case study of the small watershed near Gan village, Tanxia town

A small watershed of a tributary of the Gantang River was chosen as the study object. The water environment capacity and the amount of non-point source pollutants entering the river were calculated by combining field measurements and survey data. The results reveal that the water quality in the basin exceeds the standard severely, with 23.12t of TN, 1.64t of TP, 58t of CODMn, and 12.05t of NH3-N exceed during the plentiful period; The watershed exceeded the TN standard by 14.3t, TP by 1.64t with 17.489t of CODMn remaining in water environmental capacity and 0.71t of NH3-N exceed during the drought period. Finally, suggestions for the prevention and control of the water environment in the watershed were proposed in response to the pollution characteristics, which are of great significance for improving the water environment of the agricultural area.

A Consideration of the Estimation of the Design Flood for Small Basin in Gangwon Yeongdong Region

Due to the recent increase in heavy localized rain caused by climate change, the risk of flooding in mountainous areas and small streams is growing daily. To prevent damage to human life and property, it is necessary to accurately estimate the amount of design flood in the small river basin. Recently, the Standard Guidelines for Flood Estimation (Ministry of Environment, 2019) have been proposed to reduce uncertainties such as the subjective interpretations of engineers, which differ in the flood dischargeestimation, and to ensure a certain level of uniformity. However, in the case of Gangwon region,where the watershed area is small and the channel slope is steep, it is necessary to carefully approach the application of Clark’s watershed tracking method, suggested in the standard guidelines. As Gangwon-Yeongdong region is expected to be more sensitive to localized heavy rainfall due to the influence of the Taebaek Mountains andhas a relatively steeper watershed mean slope and euro slope than other regions, this study compares and analyzes the results of Clark’s basin tracking method and the “rational method”, to derive a more reasonable flood calculation method. Additionally, it suggests an appropriate flood discharge estimation method for the small river in Gangwon-Yeongdong region. Consequently, the flood amount can reasonably be calculated by applying a rational formula rather than Clark’sbasin tracking method, in which the flood volume is underestimated, when calculating the flood volume of a small river in Yeongdong, Gangwon Province, which has a low flow effect of less than 5 km².

Geomorphologic Analysis of Small River Basin within the Framework of Fractal Tree

This paper presents the modified framework of geomorphologic analysis based on the concept of fractal tree. Especially, it is intended to provide hydrologic practitioners with the information on the fractal property of small river basins. To this end, the complete drainage path network is applied to a growth process of a fractal tree for the basin of interest by connecting a channel network to overland drainage pathways. The growth process of a fractal tree would occur only within the limited region possessing channel flow properties in a natural river basin. The exponent of the intra basin type of Hack’s law could show a variable trend in small river basins mainly due to anisotropic property of the catchment planform. The bifurcation process of a drainage path network might be more sensitive to the growth step of the fractal tree than the meandering process of drainage path segment. The fractal dimension from the sinuosity of a channel segment is relatively stable compared to the one from the bifurcation process of the network, so that the geomorphologic features of a small river basin can be characterized by the anisotropic property of catchment planform as well as the bifurcation property of drainage path network with the growth of the fractal tree.

The Effects of Hydraulic Jumps Instability on a Natural River Confluence: The Case Study of the Chiaravagna River (Italy)

The occurrence and the effects of hydraulic jump instabilities on a natural river confluence in a small river basin in Liguria (Italy) is here investigated. Hydraulic jump instability has been extensively studied in controlled and simplified laboratory rectangular flumes. In the present study, a scaled physical model of the Chiaravagna River and Ruscarolo Creek confluence has been used, retaining the realistic geometry of the reaches. This reach has been subject to frequent floods in the last twenty years and the entire area of the confluence has been redesigned to decrease the flood risk. A series of experiments has been performed varying the discharge on the two reaches and the geometrical configurations. Free surface levels and two dimensional horizontal velocities have been measured in several positions along the physical model. The analysis of the water levels and velocities reveals that oscillations characterised by large amplitude and low frequency occur under particular hydraulic conditions. These oscillations have been found to be triggered by the hydraulic jump toe instability of the smallest reach of the confluence. Aiming at reducing the amplitude of the oscillations, which can be of the order of the flow depth, possible constructive solutions have been tested to control or damp the oscillations. Indeed, the insertion of a longitudinal dyke at the confluence has proven to be an effective solution to limit the amplitude of the transversal oscillations.

VARIATION OF NDVI VEGETATION INDEX IN LANDSCAPE CHANGE OF AMBON CITY, MALUKU PROVINCE

The development of Ambon City has always been linear with urbanization and land use, where an increasing number of people have urged forest lands to be converted to open lands, such as settlements, businesses, and other infrastructure in the form of built-up land. On a larger scale, the process of land-use change results in land cover changes that affect changes in the Ambon City landscape and microclimate conditions. The biogeophysical characteristic cs of Ambon City as a small island region have a large and small river basin and hilly topography makes it risky when city development pays little attention to the balance of ecological landscape aspects. Therefore this study aims to analyze the variation of the vegetation index NDVI (Normalized Difference Vegetation Index) on changes in the Ambon City, Maluku Province. The results showed that during the last 25 years (1993 to 2018) there was an increase in class area from Very Rare Forest to Rare Forest by 874.04 ha, an increase in the class area of ​​Medium Forest by 567.42 ha, an increase in class area from Dense Forest to Very Dense by 2,861.80 ha and a decrease in class area from Dense Forest to Very Dense Forest by 4,176.07 ha. If the reduction in the classes size of Dense Forest and Very Dense Forest is combined into groups of class increase of Very Rare Forest and Rare Forest, then the total increase in the land landscape area with a reduced or lost vegetation value was 5,050.11 ha.