GIS&Remote Sensing Based Morphometric Parameters and Topographic Changes of the Lower Orashi River in Niger Delta Desmond

In watershed hydrology,the morphometric features of a river basin are vital to examine the lower Orashi River basin morphological and hydrological aspects,as well as its flood potential,based on their morphometric characteristics using remotely sensed SRTM data that was analyzed with ArcGIS software.The areal,linear,and relief aspects of the Orashi River basin were examined as morphometric parameters.The lower Orashi river basin,according to the findings,has a total size of 625.61 km2 and a perimeter of 307.98 km,with a 5th order river network based on Strahler categorization and a dendritic drainage pattern.Because of low drainage density,the drainage texture is very fine,the relief is low,and the slope is very low.Bifurcation ratio,circularity ratio,drainage density aspect ratio,form factor,and stream frequency values indicate that the basin is less elongated and would produce surface runoff for a longer period,while topographic changes show that the river is decreasing with depth in the land area at about the same elevation as a result of sand deposited due to lack of maintenance by dredging,which implies that the basin is morphometrically elevated and sensitive to erosion and flooding.To understand geo-hydrological features and to plan and manage watersheds,morphometric analysis based on geographic information systems and remote sensing techniques is beneficial.

Analysis on Suspended Sediment Deposition Rate for Muddy Coast of Reclaimed Land

A new expression for calculating suspended fine-sediment deposition rate is developed based on theoretic analysis and experiments. The resulting equation is applied to simulation of fine sediment deposition in the reclaimed land in the Hangzhou Bay, China. The hydrodynamic environment in this area is solved by use of a long wave model, which gives the 2D-velocity field and considers bathymetric changes due to fine sediment deposition. The expression is proved convenient to use in engineering practice, and the predicted deposition rate agrees with the annual data available from field measurements from the first year to the third year after the construction of the long groin as a reclaiming method.

Impacts of oak deforestation and rainfed cultivation on soil redistribution processes across hillslopes using ^(137)Cs techniques

Background:As one of the main components of land-use change,deforestation is considered the greatest threat to global environmental diversity with possible irreversible environmental consequences.Specifically,one example could be the impacts of land-use changes from oak forests into agricultural ecosystems,which may have detrimental impacts on soil mobilization across hillslopes.However,to date,scarce studies are assessing these impacts at different slope positions and soil depths,shedding light on key geomorphological processes.Methods:In this research,the Caesium-137(^(137)Cs)technique was applied to evaluate soil redistribution and soil erosion rates due to the effects of these above-mentioned land-use changes.To achieve this goal,we select a representative area in the Lordegan district,central Iran.^(137)Cs depth distribution profiles were established in four different hillslope positions after converting natural oak forests to rainfed farming.In each hillslope,soil samples from three depths(0–10,10–20,and 20–50 cm)and in four different slope positions(summit,shoulder,backslope,and footslope)were taken in three transects of about 20m away from each other.The activity of ^(137)Cs was determined in all the soil samples(72 soil samples)by a gamma spectrometer.In addition,some physicochemical properties and the magnetic susceptibility(MS)of soil samples were measured.Results:Erosion rates reached 51.1 t·ha^(−1)·yr^(−1) in rainfed farming,whereas in the natural forest,the erosion rate was 9.3 t·ha^(−1)·yr^(−1).Magnetic susceptibility was considerably lower in the cultivated land(χhf=43.5×10^(−8)m^(3)·kg^(−1))than in the natural forest(χhf=55.1×10^(−8)m^(3)·kg^(−1)).The lower soil erosion rate in the natural forest land indicated significantly higher MS in all landform positions except at the summit one,compared to that in the rainfed farming land.The shoulder and summit positions were the most erodible hillslope positions in the natural forest and rainfed farming,respectively.Conclusions:We concluded that land-use change and hillslope positions played a key role in eroding the surface soils in this area.Moreover,land management can influence soil erosion intensity and may both mitigate and amplify soil loss.

持续强降雨影响下黄土高原地形变化分布特征——以延安市顾屯流域为例

As China's Loess Plateau has lately witnessed increasingly extreme precipitation events,it is important to analyze the impact of extreme precipitation and identify the conditions for the occurrence of geological disasters.Field surveys can provide detailed geological information in this regard but are time consuming and labor intensive.In this paper,we provide a case study on the Gutun catchment of Yan'an,which was affected by prolonged heavy rainfall in July 2013.We used Digital Elevation Model(DEM)data obtained by processing ZY-03 stereo-pair images before and after the rainy season,including the period of prolonged heavy rainfall mentioned above,to analyze the topographical changes triggered by the rainfall.The results showed the following:(1)The rainy season reduced the elevation of the catchment by about 1.7 cm.The major change in its elevation ranged from-0.5 to 0 m,accounting for 38.41%of the overall area of change and dominating above 70 m of slope height.(2)The rainy season increased the average inclination of the slopes in the area from 28.81°to 28.95°,while the range of their peak inclination was mainly distributed in the range of 24°-36°.(3)Sunny and half-sunny slopes exhibited a greater loss in elevation,while shady and half-shady slopes exhibited an increase in elevation.More drastic topographical changes were observed in the shady and half-shady slopes.(4)The morphology of the area that had undergone a reduction in elevation was characterized by concave slopes,while convex slopes abounded in the area with increased elevation.(5)The sunny or shady properties of the slope aspect constituted the key factor influencing the topographical changes,followed by the height,inclination,and shape of the slopes.The work here can provide guidance for measures related to disaster prevention and mitigation.