Hypsometric Integral Values Research Articles

Evaluation of morphometric parameters derived from Cartosat-1 DEM using remote sensing and GIS techniques for Budigere Amanikere watershed, Dakshina Pinakini Basin, Karnataka, India

The quantitative analysis of drainage system is an important aspect of characterization of watersheds. Using watershed as a basin unit in morphometric analysis is the most logical choice because all hydrological and geomorphic processes occur within the watershed. The Budigere Amanikere watershed a tributary of Dakshina Pinakini River has been selected for case illustration. Geoinformatics module consisting of ArcGIS 10.3v and Cartosat-1 Digital Elevation Model (DEM) version 1 of resolution 1 arc Sec (~32 m) data obtained from Bhuvan is effectively used. Sheet and gully erosion are identified in parts of the study area. Slope in the watershed indicating moderate to least runoff and negligible soil loss condition. Third and fourth-order sub-watershed analysis is carried out. Mean bifurcation ratio (Rb) 3.6 specify there is no dominant influence of geology and structures, low drainage density (Dd) 1.12 and low stream frequency (Fs) 1.17 implies highly infiltration subsoil material and low runoff, infiltration number (If)1.3 implies higher infiltration capacity, coarse drainage texture (T) 3.40 shows high permeable subsoil, length of overland flow (Lg) 0.45 indicates under very less structural disturbances, less runoff conditions, constant of channel maintenance (C) 0.9 indicates higher permeability of subsoil, elongation ratio (Re) 0.58, circularity ratio (Rc) 0.75 and form factor (Rf) 0.26 signifies sub-circular to more elongated basin with high infiltration with low runoff. It was observed from the hypsometric curves and hypsometric integral values of the watershed along with their sub basins that the drainage system is attaining a mature stage of geomorphic development. Additionally, Hypsometric curve and hypsometric integral value proves that the infiltration capacity is high as well as runoff is low in the watershed. Thus, these mormometric analyses can be used as an estimator of erosion status of watersheds leading to prioritization for taking up soil and water conservation measures.

Morphometric Assessment of Wadi Wala Watershed, Southern Jordan Using ASTER (DEM) and GIS

Morphometric analysis is of vital concern to understand hydromophological processes in a given watershed, and thus, it is a priority for assessing water resources in drainage basins. A morphometric analysis was conducted to identify the drainage properties of Wadi Wala and the 23 fourth-order sub-basins. ASTER DEM data was employed to compile slope, elevation, and aspect maps. Arc GIS software was used to measure and calculate basic, derived and shape morphometric parameters. W. Wala is found to be a sixth-order drainage basin, and the drainage pattern is trellis to sub-trellis in the central and lower part of the catchment, whereas it is dendritic to sub-dendritic pattern in the southern and northern parts. The slopes of the catchment vary from 0° - 5° to >35° in slope categories. Tectonic uplifting and tilting, lithology, structure and rejuvenation are the major factors controlling morphological variation over the watershed. The recognized fault systems are chiefly controlling the drainage pattern, and the elongated shape of the sub-basins is attributed to dense lineaments in the central and eastern parts of the watershed. The Rb values for the entire catchment and the sub-catchments range from 2 to 7, with a mean of 4.55, which indicates the distortion of drainage pattern by geological structure. Hypsometric integral values are high for the W. Wala watershed and the sub-basins, where it ranges from 70% to 89%. High HI values indicate that drainage basins are at the youth-age stage of geomorphic development, and they are affected by tectonic uplifting, tilting, and the dominance of hillslope process. Variation in HI values is apparent between sub-basins located at the western part, or, the rejuvenated belt where HI values range from 85% to 89%. Whereas the HI values of the sub-basins located at the eastern part of the watershed, vary from 70% to 84%. Regression analysis reveals that R2 values, which represent the degree of control of driving parameters on HI are reasonably high for the height of local base level (m) and the mean height of sub-basins (m). Both parameters contribute 0.42 and 0.39 respectively (where the F-value is significant at 0.1% and 0.5% levels). Such results imply that the height of local base level (m), and the mean height (m) are the only morphometric driving parameters which have significant control on HI values in the W. Wala watershed. High annual soil loss and sediment load estimated recently, denote that the catchment is highly susceptible to surface erosion at present. Hence, the present study, and the resultant information would help to plan for efficient soil and water conservation measures to reduce soil erosion rates, conserve water, and to control sediment into W. Wala dam.

Hypsometric integral for the identification of neotectonic and lithology differences in low tectonically active area (Utica-Mateur region, north-eastern Tunisia)

The present work tests the use of hypsometric integral (HI) in identifying neotectonic and lithology signals in the Utica-Mateur basin (north-eastern Tunisia), a region recognised by low deformation rates. We computed HI values using three digital elevation models (DEMs) of 10, 30 and 90 m pixel resolution. We extracted maximum, minimum and mean elevations from each DEM. The obtained results reveal that the HI spatial distributions did not demonstrate clear spatial patterns and did not correlate with geological substrates. We also find that the distribution of HI is independent of the DEM resolution, but are influenced by the size of the moving window. By applying the hot spot analysis (-statistics) on extracted HI data, we find two main clusters with high (hot spots) and low (cold spots) HI values. These hot spots correspond mainly to active faults and coincide with shallow earthquake clusters in the study area.

Hypsometric Analysis Using Geographical Information System of Gour River Watershed, Jabalpur, Madhya Pradesh, India

Hypsometric analysis of drainage basins reveals the geological stage of watershed and is a measure of its maturity, indicating the susceptibility of the watershed to erosion. In the present study sub watersheds of Khurji Nala and Dala Nala watersheds which are tributaries of GourRiver located in Jabalpur district of Madhya Pradesh was considered as the case study area. The watersheds were delineated into sub watersheds and hypsometric analysis was carried out for all of them using the digital contour map, which was generated using Arc GIS. The hypsometric integral values of Khurji Nala and Dala Nala sub watersheds reveals that sub watershed 2 of Khurji Nala and sub watershed 7 of Dala Nala watershed should be given top priority for soil and water conservation.

Geomorphic and lithologic control on bedrock channels in drainage basins of the Western Arabian Peninsula

Hypsometric curves, their integrals and channel profiles have long been used as effective indicators of stages in topographic evolution. This work presents the geomorphic and lithologic aspects of the drainage basins in the Western Arabian Peninsula by analysing basin hypsometry and channel longitudinal profile steepness and concavity indices in order to understand the erosion regimes. A total of 36 drainage basins in the region were analysed in a geographic information system (GIS) environment with a 30-m ASTER Global Digital Elevation Model. Hypsometric curves display shapes resembling from S-shaped to concave curves. Hypsometric integral (HI) shows generally low values in the study area and varies between 0.13 and 0.5, with a mean of 0.27. From the main set of 36 drainage basins defined, three sets of sub-basins were derived for each Strahler order ranging from 4 to 6. Their HI varied between 0.08 and 0.66 with an average HI of 0.33. Then, the HI for each basin order was plotted against the distance from the central location of each basin from south to north. Results reveal that basin hypsometry is independent of spatial variation and spatial scale. Also no clear relations were found between HI and basin area and shape. Further, HI and hypsometric curves were analysed in terms of lithological control on landforms. Results indicate that basin hypsometry is sensitive to lithological variation in the study area. At the largest scale, the HI values can be divided into two populations. More evenly distributed erosion in crystalline rocks and relatively uneven erosion in volcanic rocks are suggested from the results. Channel longitudinal profile steepness and concavity indices provide the distribution of anomalously steep channels and also reflect variations in the locus and rate of differential erosion. High steepness and low concavity in a basin underlain by volcanic rocks and a reverse trend in crystalline rocks confirm the observation from the results of basin hypsometric analysis.

Hypsometric Analysis of Wadi Mujib-Wala Watershed (Southern Jordan) Using Remote Sensing and GIS Techniques

Hypsometric analysis is considered an effective tool for understanding the stages of geomorphic evolution and geological development of river catchment, and for the delineation of erosional proneness of watershed. In the present study, twenty eight fourth order sub-basins of W. Mujib-Wala (Southern Jordan) were selected, and hypsometric analysis was carried out using 30 m ASTER DEM. Elevation-relief ratio method was employed to calculate the hypsometric integral values within GIS environment. The hypsometric integral values range from 0.71 to 0.88, whereas, the hypsometric curves exhibit remarkably upward convex shapes which indicate that all sub-basins and the W. Mujib-Wala watershed are at the youth-age stage of geomorphic development. Thus, they are of high susceptibility to erosion, incised channel erosion and mass movement activity. Marginal differences exist in mass removal from the watershed and the 28 sub-basins are attributed to variation in tectonic effect, lithology and rejuvenation processes. The relation between basin area and hypsometric integral was examined using regression analysis. Results reveal that negative and weak relationships dominate, where r2 ranges from 0.05 to 0.478 which confirm with other results reported elsewhere. Indirect assessment of erosion status based on hypsometric integral values was validated using estimated sediment yield information related to wadi Mujib and wadi Wala watersheds separately. The recorded sediment yields were in affirmation with high hypsometric integrals values, where higher values of hypsometric integrals and sediment yields occurred in the western part of the W. Mujib-Wala watershed. These findings would help in the construction of appropriate soil and water conservation measures across the watershed and its sub-basins to control soil erosion, to conserve water, and to reduce sediment discharge into the W. Mujib and W. Wala reservoirs.

Sensitivity of the hypsometric integral (HI) and its connections with lithology and neotectonics in the Rodna Mountains, Romanian Carpathians

This study investigates the sensitivity of the hypsometric integral (HI) and its connections with lithology and neotectonics from northern Romanian Carpathians, Rodna Mountains. Two types of DEM was used in analysis (a 30m DEM resolution with specific grid size and a non-gridded 30m DEM resolution). Several methods have been applied in order to calculate HI as: the CalHypso GIS extension was used to automatically extract multiple hypsometric curves from digital elevation model (DEM) and to calculate the main statistics related to the HI by applying polynomial fits; local indices of spatial autocorrelation were applied using Anselin Local Moran’s I and Getis-Ord Gi* in order to see if HI distribution has spatial patterns values and selection of valid squares (500m 2 grid using 30m DEM using ArcMap 10.1) for the lithological analysis. The values of the hypsometric kurtosis density, kurtosis, skew and density skew are increasing eastwards. Values of hypsometric skewness for the northern slope are in range between 0.290 – 0.816 and sowthern part between 0.414 – 0.507. The results show that HI values are higher than 0.5 in the areas with recent tectonic influences especially in northern part near Dragos Voda fault system. The formations with a Oligocene, Miocene, Pleistocene and Holocene age have low values ( 0.5). Comparing HI values from these two analysis (500m grid size DEM and the DEM without grid size) of the DEM we find some slightly differences in HI values specially in the northern part of the range on Repedea, Negoiescu Mare, Fântâna and Lala basins

Hypsometric Properties of South Zagros Fold-Thrust Belt Basins: A Case Study in Namdan Basin in SW Iran

Study area is located in Southwest Iran with relatively flat topography. Outcropped lithological units in the region belong from Triassic and Jurassic till recent era. The study area of the Namdan basin is related to the tectonic zone of the high Zagros region and the compressional-extensional regime. Geomorphic indices of active tectonics are useful tools to analyze the influence of activity. One of them is hypsometric integral which has generally been used to reveal the stages of geomorphic development. It is estimated by the graphical plot of the measured contour elevation and encompassed area by using empirical formulae. In constructing the hypsometric integral curve, a Digital Elevation Model (DEM) with 30 m spatial resolution has been used. This index is calculated in the study area. Then, based on index of its values, the hypsometric properties of drainage basins are analyzed in Namdan basin. Three different approaches were used for estimation of hypsometric integrals. The hypsometric integral values (HI) range between 0.18 and 0.31 for all the basins of study basin. In the study area, one stage of erosion cycle development, namely old stage is distinguished. Our results indicate that there is anomaly in Hi value which is located on faulted area. The results indicate the Northwest of Namdan basin and a small part of its Southeast are more active than other ones.

Morphometric analysis of the River Thamirabarani sub-basin in Kanyakumari District, South west coast of Tamil Nadu, India, using remote sensing and GIS

The quantitative analysis of the drainage morphometric system is vital to understand the hydrological and environmental interaction and its processes of an area. The present study deals with quantitative characteristics of morphometry of steep slope and short length sub-basin of R. Thamirabarani in Kanyakumari District, Tamilnadu, India, using geospatial technology. In this study, the digital elevation model data product (ASTER DEM), Landsat ETM+ image and Survey of India topographical map were used to delineate slope, relief and drainage system structures such as drainage pattern, stream order, stream network and stream length of the sub-basin using ArcGIS 9.3 software. The morphometric analysis deals with hydrologic processes such as stream frequency, bifurcation ratio, circulatory ratio and length of overland flow of the sub-basin area and their influences on the local morphologic landforms. The quantitative measurement of these characteristics is used to explore the basin’s contribution to the hydrological cycle and the shape, size and formation of the local landscapes in the region. Moreover, the hypsometric analysis and denudation rate were estimated for understanding the quantitative geomorphological characteristics of the sub-basin. The relationship of the morphometric parameters reveals that the drainage network is strongly controlled by geological and geomorphological structures of the area. The geometry of streams exhibits dendritic drainage pattern associated with coarse drainage texture in primary order of streams present on hilly terrain surface and semi-dendritic pattern in higher stream order flow on less elevated surface with gentle slope. The drainage density of the study area ranges from 0.1 to 1.89 km/km2, and the maximum density value was found along the higher stream order. The mean bifurcation ratio of this area is 4.21 and the high ratio was measured between the third and fourth order of stream segments. The morphometry of this area is depicted by the length of the stream segment, drainage pattern and stream flow direction, which are influenced by relief, steep slope and local geological structure. Furthermore, the sub-basin is found to be strongly elongated in shape with a length of 42.78 km, and the circularity ratio of this area is measured as 0.33 and elongation ratio as 0.57. The textural dissection of the landforms shows low drainage density in the high elevated hilly terrain in the north and high level in the plain areas in the southern part. The values of the circulatory ratio, length of overland flow and elongation ratio are relatively close to one another and the relationship among them shows their influences on the process of surface runoff and sediment deposition along the estuary landforms in the study area. Moreover, it is observed that the hypsometric curve of this study area is characterized by convex-up shape in nature and represents the youth stage (inequilibrium) of landscapes. Consequently, the hypsometric integral value 0.49 reflects the distribution of a major volume of the landmass (435.32 km2) at relatively low elevations (<180 m). The morphometric parameters-induced denudation rate of this study area is 65.14 t/km2/year and indicates the occurrence of a wide range of denudation intensities throughout the sub-basin, which is relatively proportional to the suspended sediment yield that is transported in the suspension per unit area. Based on the realistic output, it is proved that remote sensing and GIS are effective tools for morphometric studies of the drainage basin.

Hypsometric analysis of Shakkar river catchment through geographical information system

Hypsometric analysis of watershed (area-elevation analysis) has generally been used to reveal the stages of geomorphic development (stabilized, mature and young). The geologic stages of development and proneness of the watersheds for erosion are quantified by hypsometric integral. The estimation of hypsometric integral is carried out from the graphical plot of the measured contour elevation and encompassed area by using empirical formulae. In this study, efforts were made to estimate the hypsometric integral values of Shakkar river watershed which is a tributary of Narmada river located in Madhya Pradesh. The watershed was delineated into eight sub-watersheds and hypsometric analysis was carried out for all of them using digital contour maps, which was generated using Arc/Info GIS. The hypsometric integral values for all the sub-watersheds of Shakkar river ranges between 0.47 and 0.51. In the study area, only mature stage of erosion cycle is identified.

Recent tectonic activity of the Gafsa fault through morphometric analysis: Southern Atlas of Tunisia

This article focuses on the neotectonics of the southern Atlas of Tunisia based on morphometric analyses. Five major relevant morphometric parameters were processed and analyzed: residual topography, hypsometric index, drainage anomalies, maximum vertical curvature, and terrain roughness, and compared to the structural and tectonics of the study area. These are relevant to describe the topographic changes, and therefore suggest possible neotectonic activity.The analysis of these morphometric indices reveals that two structures in the study area (Jebels Ben Younes and Bou Ramli) are distinguished by a specific morphometric footprint: high residual topography, high hypsometric integral value of some watersheds (HI > 0.6), high frequency of drainage anomalies, high maximum vertical curvature, and high roughness index. The correlation of these geomorphic indices with the structural pattern of the study area confirms the neotectonic reactivation (dating from the Quaternary) and the dextral strike-slip component of the Gafsa fault (the major tectonic feature in the southern Atlas of Tunisia). Thus, the morphometric analysis of the Digital Elevation Model and the drainage network provide a more accurate insight into the morphodynamics of the study area.

Appraisal of active tectonics using DEM-based hypsometric integral and trend surface analysis in Emilia-Romagna Apennines, northern Italy

The hypsometric integral (HI) has generally been used to explain the stages of landscape evolution and erosional processes. It is an important tool to investigate tectonics and lithologic and climatic effects on topographic change. We analyzed the significance of the HI to investigate active tectonics in the Emilia-Romagna Apennines of northern Italy. We used a digital elevation model of 5-m spatial resolution to calculate grid-based HI values. The HI distribution does not show clear spatial patterns of high and low HI values. However, when statistical methods of local indices of spatial autocorrelation were applied, it was possible to identify clear clusters of high and low HI values. Trend surface analysis (TSA) was carried out to distinguish areas with anomalously high and low elevations, and to observe their spatial correlation with the HI and regional geological structures. The results indicate that the high HI values and TSA anomalies are positively correlated with the areas of high tectonic activity and along the regional tectonic structures.

GIS-based morpho-tectonic studies of Alaknanda river basin: a precursor for hazard zonation

Alaknanda river basin is considered to be tectonically active where damaging earthquakes and landslides have occurred. The whole basin was divided into 8 sub-basins to carry out morphometric analyses, hypsometric integral (HI) analysis and valley floor width to valley height ratio (V f) factor. The sub-basins 2 and 3 show that they are highly active, because of the higher values of bifurcation ratio, stream frequency asymmetric factor, and lower values of form factor, elongation ratio and circulatory ratio. In these areas, HI values are very low indicating that the landscape is highly eroded, deeply dissected and tectonically active. The result obtained from V f was similar which classified both these basins as highly active. Morphometric analysis, HI and V f analyses along with structural map of study area are used to prepare morpho-tectonic map classifying the whole area into very high, high, moderate and low zones of tectonic activity. This map clearly indicates that the areas near MCT II (Munsiari Thrust), MCT III (Ramgarh Thrust) and North Almora Thrust are tectonically very active which fall in sub-basins 2, 3, 4 and parts of 5. Various locations such as Chamoli, Birahi, Pipalkoti, Rudraprayag, etc. are situated in these zones where many earthquakes and landslides occur every year. Moreover, the data plotted for earthquakes and landslides occurrences are consistent with morpho-tectonic map and can be used as a precursor for demarcation of natural hazard vulnerable zones.

Scale independence of basin hypsometry and steady state topography

Basin hypsometry has long been used as an indicator of stages in landscape evolution. It has also served as a tool for detecting tectonically active regions. Whether hypsometric curve and its integral are independent of differences in basin size and relief has been discussed in many recent studies. The Taiwan Mountain Range, the result of an oblique collision between the Phillipine Sea Plate and the Eurasian Plate, provides an excellent opportunity to study landscape evolution in relation to steady state conditions. Taking advantage of the space-for-time substitution concerning the building process of Taiwanese mountains, this study sampled major drainage basins for hypsometric analysis, from the southern tip of the island to the northern end. This study found that the area previously known as steady state topography is characterized by 1) the hypsometric integral (HI) close to 0.5, 2) S-shaped hypsometric curves, and 3) normally distributed elevations. The response time required for a drainage basin of various Strahler orders to evolve from exposure of sub-aerial erosion to steady state topography ranges from 0.5 to 2.0My, and is longer for basins of a higher Strahler order. The HI value of 0.5 for a drainage basin seems critical in terms of landscape evolution. The scale dependence of basin hypsometry is manifested mainly by the fact that HI of basins increases as basin order and/or basin size decreases. This study also found that basin hypsometry is scale independent where topography is in a steady state; scale dependence occurs only when drainage basins are in a non-steady state. The basin hypsometry may therefore be useful to probe into the nature of steady-state topography.

Hypsometric analysis of Kali River Basin, Karnataka, India, using geographic information system

Hypsometric analysis is useful for understanding the geomorphic stages of a river basin. Hypsometric parameters have been evaluated and curves are prepared forall the 20 sub-basins of Kali River. Thirteen sub-basins are found to be under younger geomorphic stages with high hypsometric integral (Ea) values and subjected to recent tectonic activities. The remaining seven sub-basins are approaching mature stage and subjected to more erosion and less impacted by recent tectonic activities. Six sub-basins with lower hypsometric head values (<0.56) indicate least effect of diffusive processes and another six sub-basins with medium hypsometric head values (0.60–0.68) depict moderate diffusive erosion. The remaining eight sub-basins with higher hypsometric head values (>0.75) indicate highest diffusive processes at their upper reaches. Lower (<0.28) and higher (>0.44) hypsometric toe values indicate minimum and maximum mass accumulation respectively at the sub-catchment mouth.

Analyzing Spatial Autocorrelation for the Hypsometric Integral to Discriminate Neotectonics and Lithologies Using DEMs and GIS

This investigation documents the sensitivity of the hypsometric integral (HI) and its relationship to neotectonics and lithology. We used digital elevation models (DEMs) of 30 and 90 m spatial resolution from the Shuttle Radar Topographic Mission (SRTM) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to calculate HI values in the Hindu Kush and its vicinity (Northwest Pakistan and Northeast Afghanistan). We used an analysis grid of regular squares of different sizes to calculate maximum, minimum, and mean elevations. The spatial distributions of HI do not show clear spatial patterns and correlation with mean elevation or relief amplitude. We applied spatial pattern analysis using Local Indices of Spatial Autocorrelation (LISA) to measure the degree to which our HI distribution was clustered, dispersed, or randomized. LISA analysis shows that the data are autocorrelated because of high positive z-scores. Hot spots (clusters with high HI values) are consistent with tectonic uplift and show a strong correlation with the different structural domains in the region. Cold spots represent recent sedimentation close to faults and coincide with shallow earthquake clusters in the region. The HI values do not show any correlation with relative topographic position or lithology. Analysis of HI distribution shows that they are robust and independent of digital elevation model (DEM) resolution but are strongly scale dependent. The LISA technique allows the extraction of clusters of the HI that reveal recent tectonic processes; otherwise it is difficult to interpret the high variability of HI values. The scale dependency of the HI may reflect the varying importance of drainage network and hillslope processes.

Seismic hazard assessment in the Jia Bhareli river catchment in eastern Himalaya from SRTM-derived basin parameters, India

SRTM (Shuttle Radar Topographic Mission), Landsat ETM+ satellite image analysis along with earthquake data in the Jia Bhareli river catchment, an eastern Himalayan tributary of the Brahmaputra indicates neotectonic activities in the region. We have envisaged from the study that the western part of the river catchment (western tectonic domain) is highly tectonically active as indicated by earthquake data, and SRTM DEM-derived longitudinal profiles, valley profiles, valley asymmetry, hypsometric integral values. On the other hand, the eastern part of the catchment has no sign of such active tectonics (eastern tectonic domain) except the south convex fan-shaped zone further east with linear ridges paralleling the convex shape deforming the Miocene–Pleistocene Siwalik sediments and the Quaternary piedmont deposits in the Himalayan foothills. The catchment seems tilting to the east due to the ongoing tectonic activities propagating the deformational activities, generating folded structures, to the east and yielding earthquakes due to rigid deformation in the western part of the catchment. From the study, seismic risk in the south–central part of eastern Himalayas around Bomdila in the state of Arunachal Pradesh appears to be high.

Hypsometric Integral Estimation Methods and its Relevance on Erosion Status of North-Western Lesser Himalayan Watersheds

Assessment of erosion status of a watershed is an essential prerequisite of integrated watershed management. This not only assists in chalking out suitable soil and water conservation measures to arrest erosion and conserve water but also helps in devising best management practices to enhance biomass production in watersheds. The geologic stages of development and erosion proneness of the watersheds are quantified by hypsometric integral. The estimation of hypsometric integral is carried out from the graphical plot of the measured contour elevation and encompassed area and by using empirical formulae. In this study, efforts were made to estimate the hypsometric integral values of the Sainj and Tirthan watersheds and their sub watersheds in the Lesser Himalayas using four different techniques, and to compare the procedural techniques of its estimation and relevance on erosion status. It was revealed that the hypsometric integral calculated by elevation–relief ratio method was accurate, less cumbersome and easy to calculate within GIS environment. Also comparison of these hypsometric integral values revealed that the Sainj watershed (0.51) was more prone to erosion than the Tirthan watershed (0.41). Further, the validation of these results with the recorded sediment yield data of 24 years (1981–2004) corroborated that the average annual sediment yield during this period for Sainj watershed (0.53 Mt) was more than that of the Tirthan watershed (0.3 Mt). Thus, the hypsometric integral value can be used as an estimator of erosion status of watersheds leading to watershed prioritization for taking up soil and water conservation measures in watershed systems.

Réponse des bassins versants à l'activité tectonique : l'exemple de la terminaison orientale de la chaîne pyrénéenne. Approche morphotectonique / Drainage basins response to active tectonics: example from Eastern Pyrenees. Morphotectonic approach

Extended Abstract The aim of this paper is to demonstrate the validity of morphométrie analysis in an area of low seismo-tectonic activity. There, drainage divide responds to uplift modifying their morphologic and sedimentologic parameters, such as drainage density, drainage divide size, hypsometric integral value. Tectonic and geomorphic investigations are focused on the relationship between Plio-Pleistocene deformation and landform ruptures using quantitative geomorphology. Morphométrie and geomorphic analysis of drainage basins can be correlated with tectonic input. Correlation research between channel network parameters (such as slope, channel length and drainage density), or basin parameters (area, relief and hypsometry) and uplift is tested. This method is applied to the Tet drainage basin (1500 km2), a Mediterranean coastal river, (eastern Pyrenees, South France). This river was developed during the Neogene time along a major regional fault, NE-SW direction, the Têt fault. This fault is still active (Souriau and Pauchet, 1998). Numerous drainage anomalies, such as antecedence, dissymetry and avulsion, lead us to expect drainage responses to active tectonics. First, Horton's laws are tested. Confluence and length ratio are homogenous in the Tet drainage divide. They reflect the organisation of the drainage network at the regional scale and are not related to local tectonic variations, as previously shown by Kirschner (1993). First order drainage frequency, defined as the number of first order streams per square km, reveals a North - South drainage basin structural asymmetry. The southern part of the drainage basin is excessively dissected. This opposition is confirmed by basin parameter analysis. The sizes of the third and fourth order basins show antagonistic responses at the periphery of the Tet basin. In the southern portion of the basin, the median size of the. third and fourth order basins is 50% greater than their northern counterparts. The same observation can be made about the hypsometric curve. Moreover, this parameter points out the presence of an est - west gradient. On the southern margin of the Têt basin, hypsometric integrals decrease from 0,36 to 0,63. These values are highly correlated with tectonic uplift as deduced from scarp fault morphology, using height, slope and complicity ratios of the vounger spure generation. Morphometric results are compared with field data. The calculation of deformation rates by two different methods shows a linkage between them. During the Pliocene, uplift rates varied from 0.2 mm/year in the eastern part of the fault to 1 mm/year in the western part. The morphostructural organisation of the eastern part of the Pyrenees shows evidence of strike-slip faulting, related to a meridian compressional stress regime. It induced left-lateral faulting on the Tet fault and a propagation of deformation. As a result, the inversion of stress regime in the Pliocene, previously pointed out by other studies (Grellet et al., 1993), is confirmed by a geomorphological approach.

La estructura de las láminas inferiores del Complejo de Cabo Ortegal y su autóctono relativo (Galicia, NW de España)

The High Basin of the Nalon River show fluvial valleys with a graded longitudinal profile under 750-650 m and deposits resulting from three terrace levels (T1, 30 m; T2, 10 m; T3, 3-4 m) and the present aluvial plain. The fluvial network, with a 6th order, fits to the theoretical Horton principles; there is not a correspondance between the relief parameters and the hypsometric integral value (39%), due to methodological restrictions; the geometrical parameters suggest a quick rainfall response; the low value of the drainage density (2.62 km/km2) is according to the physical basin features. The fluvial morphology is conditioned by the lithological variety of the Palaeozoic bedrock; by the Hercynian and Alpine Tectonics influence and by the Quaternary evolution of the area, which still shows a lackness of regional data.