Assessment of soil erosion in a tropical mountain river basin of the southern Western Ghats,India using RUSLE and GIS

Revised Universal Soil Loss Equation(RUSLE) model coupled with transport limited sediment delivery(TLSD) function was used to predict the longtime average annual soil loss, and to identify the critical erosion-/deposition-prone areas in a tropical mountain river basin, viz., Muthirapuzha River Basin(MRB; area=271.75 km~2), in the southern Western Ghats, India. Mean gross soil erosion in MRB is 14.36 t ha~(-1) yr~(-1), whereas mean net soil erosion(i.e., gross erosion-deposition) is only 3.60 t ha~(-1) yr~(-1)(i.e., roughly 25% of the gross erosion). Majority of the basin area(~86%) experiences only slight erosion(5 t ha~(-1) yr~(-1)), and nearly 3% of the area functions as depositional environment for the eroded sediments(e.g., the terraces of stream reaches, the gentle plains as well as the foot slopes of the plateau scarps and the terrain with concordant summits). Although mean gross soil erosion rates in the natural vegetation belts are relatively higher, compared to agriculture, settlement/built-up areas and tea plantation, the sediment transport efficiency in agricultural areas and tea plantation is significantly high,reflecting the role of human activities on accelerated soil erosion. In MRB, on a mean basis, 0.42 t of soil organic carbon(SOC) content is being eroded per hectare annually, and SOC loss from the 4th order subbasins shows considerable differences, mainly due to the spatial variability in the gross soil erosion rates among the sub-basins. The quantitative results, on soil erosion and deposition, modelled using RUSLE and TLSD, are expected to be beneficial while formulating comprehensive land management strategies for reducing the extent of soil degradation in tropical mountain river basins.     

Assessment of soil erosion in a monsoon-dominated mountain river basin in India using RUSLE-SDR and AHP

The long-term average annual soil loss (A) and sediment yield (SY) in a tropical monsoon-dominated river basin in the southern Western Ghats, India (Muthirapuzha River Basin, MRB; area: 271.75 km²), were predicted by coupling the Revised Universal Soil Loss Equation (RUSLE) and sediment delivery ratio (SDR) models. Moreover, the study also delineated soil erosion risk zones based on the soil erosion potential index (SEPI) using the analytic hierarchy process (AHP) technique. Mean A of the basin is 14.36 t ha^?1 year^?1, while mean SY is only 3.65 t ha^?1 year^?1. Although the land use/land cover types with human interference show relatively lower A compared to natural vegetation, their higher SDR values reflect the significance of anthropogenic activities in accelerated soil erosion. The soil erosion risk in the MRB is strongly controlled by slope, land use/land cover and relative relief, compared to geomorphology, drainage density, stream frequency and lineament frequency.     

Distribution and seasonal abundance of large cetaceans in the Durban whaling grounds off KwaZulu-Natal,South Africa, 1972–1975

Daily charts of the aerial search effort (432 206 nautical miles) of the Union Whaling Company and 1 099 sightings of 10 497 whales were available from 628 flights off Durban between 1972 and 1975. Densities of whales were analysed by month and water depth distribution over the four-year period. Low observed densities of blue Balaenoptera musculus, right Eubalaena australis, sei B. borealis and humpback Megaptera novaeangliae whales most likely resulted from earlier whaling pressure. Seasonality of blue, sei and humpback whales was bimodal, indicative of winter migrations to the north of the Durban whaling grounds, whereas the unimodal seasonality of fin whales B. physalus and minke whales B. bonaerensis or B. acutorostrata suggest the offshore region as the northern terminus of their migrations. Sperm whales Physeter macrocephalus migrate northwards offshore of the KwaZulu-Natal coast in autumn/early winter and southwards in late winter/spring, with larger males migrating later than the smaller males and females. Killer whale Orcinus orca presence was coincident with that of offshore minke whales and the southward migrations of other baleen whales, whereas densities of animals deemed as bottlenose whale Hyperoodon planifrons suggest strong early and late summer seasonal abundance in the offshore region. Such extensive surveys offshore of the KwaZulu-Natal coast are unlikely to be repeated; hence, data-extraction of whaling records provides a valuable source of seasonal and distributional information for marine management.     

Forest type mapping and volume stratification of man-made forests with aerial photographs

The use of panchromatic (black & white) aerial photographs on 1:15,000 scale for forest type mapping and evolving a suitable basis of volume stratification for man-made forests of Haldwani Division of U.P. is discussed. Forest types by species, height and density were identified and ground survey data collected in 0.1 hectare circular plots were used to evolve the basis of volume stratification by statistical analysis. The methodology used for pilot studies before regional surveys are undertaken is presented.     

http://www.sciencedirect.com/science/article/pii/S1674987114000036

The paper evaluates sensitivity of various spaceborne digital elevation models （DEMs）, viz., Advanced Spaceborne Thermal Emission and Reflection Radiometer （ASTER）, Shuttle Radar Topography Mapping Mission （SRTM） and Global Multi-resolution Terrain Elevation Data 2010 （GMTED）, in comparison with the DEM （TOPO） derived from contour data of 20 m interval of Survey of India topographic sheets of 1 ： 50,000 scale. Several topographic attributes, such as elevation （above mean sea level）, relative relief, slope, aspect, curvature, slope-length and -steepness （LS） factor, terrain ruggedness index （TRI）, topo- graphic wetness index （TWI）, hypsometric integral （lhyp） and drainage network attributes （stream number and stream length） of two tropical mountain river basins, viz. Muthirapuzha River Basin and Pambar River Basin are compared to evaluate the variations. Though the basins are comparable in extent, they differ in respect of terrain characteristics and climate. The result.,; suggest that ASTER and SRTM provide equally reliable representation of topography portrayed by TOP（） and the topographic attributes extracted from the spaceborne DEMs are in agreement with those derived from TOPO. Despite the coarser resolution, SRTM shows relatively higher vertical accuracy （RMSE -- 23 and 20 m respectively in MRB and PRB） compared to ASTER （RMSE - 33 and 24 m） and GMTED （RMSE - 59 and 48 m）. Vertical accuracy of all the spaceborne DEMs is influenced by relief of the terrain as well as type of vegetation. Further, GMTED shows significant deviation for most of the attributes, indicating its inability for mountain-river-basin-scale studies.     

Seasonal variation in major ion chemistry of a tropical mountain river,the southern Western Ghats,Kerala, India

A comprehensive and systematic study to understand various geochemical processes as well as process drivers controlling the water quality and patterns of the hydrochemical composition of river water in Muthirapuzha River Basin, MRB (a major tributary of Periyar, the longest river in Kerala, India), was carried out during various seasons, such as monsoon, post-monsoon and pre-monsoon of 2007–2008, based on the data collected at 15 monitoring stations (i.e., 15 × 3 = 45 samples). Ca²⁺ and Mg²⁺ dominate the cations, while Cl^? followed by HCO₃ ^? dominates the anions. In general, major ion chemistry of MRB is jointly controlled by weathering of silicate and carbonate rocks, which is confirmed by relatively larger Ca²⁺ + Mg²⁺/Na⁺ + K⁺ ratios as well as Ca²⁺/Na⁺ vs. Mg²⁺/Na⁺ and Ca²⁺/Na⁺ vs. HCO₃ ^?/Na⁺ scatter plots. The relationship between Cl^? and Na⁺ implies stronger contributions of anthropogenic activities modifying the hydrochemical composition, irrespective of seasons. The water types emerged from this study are transitional waters or waters that changed their chemical character by mixing with waters of geochemically different ionic signatures. However, various ionic ratios, hydrochemical plots and graphical diagrams suggest seasonality over the hydrochemical composition, which is solely controlled by the rainfall pattern. Relatively higher pCO₂ indicates the disequilibrium existing in natural waterbodies vis-à-vis the atmosphere, which is an outcome of both the contribution of groundwater to stream discharge and anthropogenic activities. Hence, continuous monitoring of hydrochemical composition of mountain rivers is essential in the context of climate change, which has serious implications on tropical mountain fluvial-hydro systems.     

Morphometrical analysis of two tropical mountain river basins of contrasting environmental settings, the southern Western Ghats, India

The morphometric analysis of river basins represents a simple procedure to describe hydrologic and geomorphic processes operating on a basin scale. A morphometric analysis was carried out to evaluate the drainage characteristics of two adjoining, mountain river basins of the southern Western Ghats, India, Muthirapuzha River Basin (MRB) in the western slopes and Pambar River Basin (PRB) in the eastern slopes. The basins, forming a part of the Proterozoic, high-grade, Southern Granulite Terrain of the Peninsular India, are carved out of a terrain dominantly made of granite- and hornblende-biotite gneisses. The Western Ghats, forming the basin divide, significantly influences the regional climate (i.e., humid climate in MRB, while semi-arid in PRB). The Survey of India topographic maps (1:50,000) and Shuttle Radar Topographic Mission digital elevation data were used as the base for delineation and analysis. Both river basins are of 6th order and comparable in basin geometry. The drainage patterns and linear alignment of the drainage networks suggest the influence of structural elements. The Rb of either basins failed to highlight the structural controls on drainage organization, which might be a result of the elongated basin shape. The irregular trends in Rb between various stream orders suggest the influence of geology and relief on drainage branching. The Dd values designate the basins as moderate- to well-drained with lower infiltration rates. The overall increasing trend of Rl between successive stream orders suggests a geomorphic maturity of either basins and confirmed by the characteristic I _hyp values. The Re values imply an elongate shape for both MRB and PRB and subsequently lower vulnerability to flash floods and hence, easier flood management. The relatively higher Rr of PRB is an indicative of comparatively steeply sloping terrain and consequently higher intensity of erosion processes. Further, the derivatives of digital elevation data (slope, aspect, topographic wetness index, and stream power index), showing significant differences between MRB and PRB, are useful in soil conservation plans. The study highlighted the variation in morphometric parameters with respect to the dissimilarities in topography and climate.     

Morpho-hypsometric evolution of the Karuvannur River Basin,a tropical river in central Kerala,southwestern peninsular India

An integrated morphometric and hypsometric analysis coupled with asymmetric factor used as a proxy for the landscape evolution of the catchment of Karuvannur River. The present study area is a sixth order tropical river in the central Kerala which supplies water and sediments to the Vembanad-Kol Ramsar site. The Karuvannur River Basin (KRB) has been divided into six sub-watersheds (SW). Morphometric parameters (areal, linear, and relief) and hypsometric and asymmetric factors are measured for the delineation of morphotectonic evolution of the area. High values of drainage density, texture, ruggedness number, and hypsometric integral with relatively high volume of leftover rocks in the basin in SW-II and SW-III compared to the entire basin of KRB imply that these two sub-watersheds have been influenced by the tectonic activities. Further, detailed asymmetric data indicated that these two watersheds are tilted in opposite direction. It may be the result of reactivation of Precambrian fault/lineament in recent past. This has been supported by recent tremors and neotectonic studies in Kerala. Moreover, detailed field evidence along with google imagery revealed that the entire basin is a part of regional anticline associated with PCSZ. Geomorphic response to disturbance will produce a sensible, recognizable response; it can be well studied in rivers through detailed study of their sensitivity or behavioral changes. Rivers have an enormous capacity to absorb perturbation and these types of studies are essential for identifying/measuring tectonic activities, sediment diffusion, surface runoff in a drainage basin, and as an important tool for target oriented micro watershed management.     

Seismic performance of precast shear wall-slab connection under cyclic loading: experimental test vs. numerical analysis

The structural behaviour of precast shear wall-diaphragm connection was compared with the monolithic connection under seismic loading. The monolithic connection was made by using U-bars connecting shear wall and slab, and the precast connection was made by using dowel bars in two steps. Firstly, U-shaped dowel bars from the precast shear wall lower panel and precast slab were connected by the longitudinal reinforcement, and screed concreting was done above the precast slab. Secondly, the shear wall upper panel was connected using the dowel bar protruding from the shear wall lower panel. The gap between the dowel bars and the duct was filled with non-shrink grout. The specimens were subjected to reverse cyclic loading at the ends of the slab. This study also aimed to develop a 3-D numerical model using ABAQUS software. The non-linear properties of concrete were defined by using the concrete damaged plasticity(CDP) model to analyse the response of the structure. The precast dowel connection between the shear wall and slab showed superior performance concerning ductility, strength, stiffness and energy dissipation. The developed finite element model exactly predicted the behaviour of connections as similar to that of experimental testing in the laboratory. The average difference between the results from finite element analysis and experimental testing was less than 20%. The results point to the conclusion that the shear resistance is provided by the dowel bars and the stiffness of the precast specimen is due to the diaphragm action of the precast slab. The damage parameter and the interaction between structural members play a crucial role in the modelling of precast connections.     

Geospatial and MCDM tool mix for identification of potential groundwater prospects in a tropical river basin,Kerala

The efficiency of GIS, RS and multi-criteria tools in isolating potential groundwater (GW) zones in the Kuttiyadi River basin (KRB), Kerala, has been robustly demonstrated by analysis of relevant data. To infer geohydrological makeup and consequent behavior of the KRB in respect of GW potential, firstly, various thematic layers viz. geomorphology, geology, slope, soil, lineament density and drainage density, were created. Secondly, thematic layers and their features were assigned suitable weights on the Saaty’s scale according to their relative significance for the presence and potential of GW. The assigned weights of the layers and their features were normalized using analytic network process method, and then the selected thematic maps were integrated in GIS using weighted overlay method to create the final groundwater prospect zone map. From the outcomes, the groundwater prospect zones of the KRB basin was found to be very good (166.21 km²), good (92.01 km²), moderate (180.33 km²), poor (237.25 km²), which constitute 24, 15, 26 and 35% of the study area, respectively. The GW prospect zone map was finally validated using geohydrology of area and GW level data from 43 phreatic wells in the study area. This study showed that groundwater prospect zone demarcation along with multi-criteria decision making is a powerful tool for proper utilization, planning and management of the precious groundwater resource.