Large Drainage Basins Research Articles

Application of a new river classification scheme to Australia's tropical rivers

A revised typology of Australian tropical rivers was applied to the complete channel network (named and major rivers) shown on 1:250 000 topographic maps for three large drainage basins in northern Australia (Daly River, NT; Fitzroy River, WA; Flinders River, Qld). Reach mapping and classification were conducted using the revised typology. The 12 major river types proposed were: (1) bedrock rivers; (2) bedrock‐confined and ‐constrained rivers; (3) low sinuosity (straight) rivers; (4) meandering rivers; (5) wandering rivers; (6) anabranching rivers; (7) chains of ponds; (8) gullies; (9) floodouts; (10) lakes, swamps, billabongs and wetlands; (11) non‐channelized valley floors; and (12) estuarine rivers. The 12 major river types were developed based on river reach mapping for more than 264 000 km2 of tropical Australian catchments. At scales larger than 1:250 000, subdivision of each major river type is recommended. In the Daly and Fitzroy catchments, confined and constrained rivers dominate, whereas in the Flinders and Fitzroy catchments, anabranching rivers dominate. The dominant river types need benchmarking with adequate numbers of control reaches so that channel changes induced by human and natural impacts can be measured by reference to the stability of these controls. Wandering rivers, floodouts and non‐channelized valley floors were rare for the 1:250 000 channel network in northern Australia but need inclusion in national parks.

Signal to noise ratio in water balance maps with different resolution

What is the best resolution of annual water balance maps for a correct balance between the basic spatial signal in the observations of precipitation, actual evapotranspiration and runoff across a larger drainage basin and the error in estimates for grid cells in the map to avoid giving a false impression of accuracy? To answer this question an approach based a signal to noise ratio is proposed, which allows finding the optimal resolution maximizing the signal in the map. The approach is demonstrated on gauge data in the Huai River Basin, China. Stochastic interpolation methods were applied to create grid maps of long-term mean values, as well as for estimating variances of the three water balance components in a range of scales from 5×5km to 200×200km2 grid cells. Interpolation algorithms using covariances of long-term means of data with different spatial support were developed. The identified optimal resolutions by the signal to noise ratio appeared to be very different – 10×10, 50×50, and 30×30km2 for precipitation, actual evapotranspiration, and runoff, respectively. These values are directly linked to the observation network densities. The magnitude of the signal to noise ratio shows similar strong differences with values 34, 3.7, and 5.4, respectively. It gives a direct indication of the reliability of the map, which can be considered as satisfactory only for precipitation for the data available for the present study. The critical factors for this magnitude are parameters characterising the spatial covariance in data and the network density.

Physical characteristics and discharges of suspended particulate matter at the continent-ocean interface in an estuary located in a semiarid region in northeastern Brazil

This study reports the hydrodynamics of the transport of suspended particulate matter (SPM) in the Jaguaribe River estuary, which receives the runoff from the largest drainage basin in the state of Ceará, Brazil. The estuary is located in the semiarid region of Brazil, where rainfall occurs primarily between January and May and results in water flow rates exceeding 3000 m3s−1. The drainage basin contains more than 4000 dams, which, during the dry season, block most of the flow of freshwater and sediment. The net balance and transport of sediments were calculated for the wet and dry seasons considering a tidal cycle of 13 h at the interfaces between the upper and middle estuary and between the middle and lower estuary. The Jaguaribe River estuary is classified as partially mixed with weak vertical stratification and a tendency toward being well mixed. The SPM transported during the rainy season originates in the drainage basin due to high river inflow, whereas during the dry season, resuspension and hydraulic fills generated by tides causes the accumulation of SPM in the middle estuary, forming a zone of maximum turbidity. The transport of salt in the estuary was predominantly caused by gravity flow and tidal propagation.

A new perspective on West African hydroclimate during the last deglaciation

Widespread drought characterized the Heinrich 1 and Younger Dryas cold periods of the last deglaciation throughout much of Africa, causing large increases in dust emissions from the Sahara and Sahel. At the same time, increases in wind strength may have also contributed to dust flux, making it difficult to interpret dust records alone as reflecting changes in rainfall over the region. The Niger River has the third largest drainage basin in Africa and drains most of the Sahara and Sahel and thus preserves and propagates climatic signals. Here, we present new reconstructions of Niger Delta sea surface salinity and Niger River discharge for the last 20,000 years in order to more accurately reconstruct the onset of the Western African Monsoon system. Based on calculated δ18OSEAWATER (δ18OSW) and measured Ba/Ca ratios in planktonic foraminifera, these new records reflect changes in sub-Saharan precipitation across the Niger River Basin in West Africa and reveal that the West African Monsoon system began to intensify several thousand years after the equatorial Monsoon system in Central Africa. We also present new records of primary productivity in the Niger Delta that are related to wind-driven upwelling and show that productivity is decoupled from changes in Niger River discharge. Our results suggest that wind strength, rather than changes in monsoon moisture, was the primary driver of dust emissions from the Sahara and Sahel across the last deglaciation.

Post-glacial acidification of two alpine lakes (Sudetes Mts., SW Poland), as inferred from diatom analyses

Abstract Past environmental changes in mountain lakes can be reconstructed with the use of subfossil diatoms from post-glacial sediments. This study applied such an analysis to two mountain lakes in the Sudetes Mts. in Poland: Mały Staw (MS) and Wielki Staw (WS). Cores 882 cm long (MS) and 1100 cm long (WS) taken from the centre of each lake in 1982 were used to study the long-term acidification history of these lakes. Changes in vegetation indicate that the initial phase of MS started at the end of the Pleistocene. WS sediments began to accumulate shortly after that, at the beginning of the Holocene. The majority of the diatom assemblages are typical of oligotrophic acidic lakes located in alpine and arctic regions. A pH reconstruction based on diatoms (DI-pH) showed long-term acidification dating to almost the beginning of the lakes’ existence. Natural acidification began after the deglaciation, and the most intensive acidification continued to the end of the mid-Holocene. Through the whole period studied, pH decreased by 1.4 in MS and 0.9 in WS. After a period of relatively stable lake water pH, it decreased rapidly during the last few decades of the 20th century, due to anthropogenic pollution: pH declined by 0.7 in MS and 0.3 in WS. Mały Staw, being shallower, smaller, and with a larger drainage basin than Wielki Staw, is more sensitive to acid deposition; this accounts for the difference in pH.

Active tectonic deformation along rejuvenated faults in tropical Borneo: Inferences obtained from tectono-geomorphic evaluation

The island of Borneo is enveloped by tropical rainforests and hostile terrain characterized by high denudation rates. Owing to such conditions, studies pertaining to neotectonics and consequent geomorphic expressions with regard to surface processes and landscape evolution are inadequately constrained. Here we demonstrate the first systematic tectono-geomorphic evaluation of north Borneo through quantitative and qualitative morphotectonic analysis at sub-catchment scale, for two large drainage basins located in Sarawak: the Rajang and Baram basins. The extraction of morphometric parameters utilizing digital elevation models arranged within a GIS environment focuses on hypsometric curve analysis, distribution of hypsometric integrals through spatial autocorrelation statistics, relative uplift values, the asymmetry factor and the normalized channel steepness index. Hypsometric analysis suggests a young topography adjusting to changes in tectonic boundary conditions. Autocorrelation statistics show clusters of high values of hypsometric integrals as prominent hotspots that are associated with less eroded, young topography situated in the fold and thrust belts of the Interior Highlands of Borneo. High channel steepness and gradients (>200m0.9) are observed in zones corresponding to the hotspots. Relative uplift values reveal the presence of tectonically uplifted blocks together with relatively subsided or lesser uplifted zones along known faults. Sub-catchments of both basins display asymmetry indicating tectonic tilting. Stream longitudinal profiles demonstrate the presence of anomalies in the form of knickzones without apparent lithological controls along their channel reaches. Surfaces represented by cold spots of low HI values and low channel gradients observed in the high elevation headwaters of both basins are linked to isolated erosional planation surfaces that could be remnants of piracy processes. The implication of our results is that Borneo experiences active folding of the Rajang Group fold–thrust belt to present and these events reactivated old major faults and minor related dislocations. From geomorphic analysis associated with sedimentary record, we posit that the terrain could have undergone high uplift rates since 5Ma or multi-phased uplift with periodic intermittent pulses of high and low uplift rates.

Past ice-sheet behaviour: retreat scenarios and changing controls in the Ross Sea, Antarctica

Abstract. Studying the history of ice-sheet behaviour in the Ross Sea, Antarctica's largest drainage basin can improve our understanding of patterns and controls on marine-based ice-sheet dynamics and provide constraints for numerical ice-sheet models. Newly collected high-resolution multibeam bathymetry data, combined with two decades of legacy multibeam and seismic data, are used to map glacial landforms and reconstruct palaeo ice-sheet drainage. During the Last Glacial Maximum, grounded ice reached the continental shelf edge in the eastern but not western Ross Sea. Recessional geomorphic features in the western Ross Sea indicate virtually continuous back-stepping of the ice-sheet grounding line. In the eastern Ross Sea, well-preserved linear features and a lack of small-scale recessional landforms signify rapid lift-off of grounded ice from the bed. Physiography exerted a first-order control on regional ice behaviour, while sea floor geology played an important subsidiary role. Previously published deglacial scenarios for Ross Sea are based on low-spatial-resolution marine data or terrestrial observations; however, this study uses high-resolution basin-wide geomorphology to constrain grounding-line retreat on the continental shelf. Our analysis of retreat patterns suggests that (1) retreat from the western Ross Sea was complex due to strong physiographic controls on ice-sheet drainage; (2) retreat was asynchronous across the Ross Sea and between troughs; (3) the eastern Ross Sea largely deglaciated prior to the western Ross Sea following the formation of a large grounding-line embayment over Whales Deep; and (4) our glacial geomorphic reconstruction converges with recent numerical models that call for significant and complex East Antarctic ice sheet and West Antarctic ice sheet contributions to the ice flow in the Ross Sea.

Drainage basin and topographic analysis of a tropical landscape: Insights into surface and tectonic processes in northern Borneo

We investigated the recent landscape development of Borneo through geomorphic analysis of two large drainage basins (Rajang and Baram basins). The extraction of morphometric parameters utilizing digital terrain data in a GIS environment, focusing on hydrography (stream length–gradient index, ratio of valley floor width to valley height, and transverse topographic symmetry factor) and topography (local relief and relief anomaly), was carried out in order to elucidate processes governing drainage and landscape evolution. Anomalously high and low values of stream length–gradient indices of main tributary streams associated with faults and multiple knick-points along the channel profiles are linked to deformation events. The development of deeply incised V-shaped valleys show enhanced incision capability of streams in response to steepening of hillslope gradients following tectonic inputs. Deflection of streams and probable dynamic reorganization of the drainage system through stream capture processes as feedbacks to tectonic uplift and orographic effect are observed. Local relief and relief anomaly maps highlight the presence of preserved elevation-accordant relict portions of landscapes characterized by low amplitude relief, nested between ridgelines in regions of complex folding. Our results reveal dynamic geomorphic adjustment of the landscape due to perturbations in tectonic and climatic boundary conditions. The implication is that the landscape of north Borneo experienced a tectonic phase of rapid uplift after 5Ma and undergoes active folding of the Rajang Group thrust belts in the present-day. Active shortening combined with high rates of denudation in Sarawak, demonstrates transience emphasized by the drainage system attempting to adjust to tectonic and climatic forcing.

Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River

AbstractReconstructing the evolving geometry of large river catchments over geological time scales is crucial to constraining yields to sedimentary basins. In the case of Africa, it should further help deciphering the response of large cratonic sediment routing systems to Cenozoic growth of the basin‐and‐swell topography of the continent. Mapping of dated and regionally correlated lateritic paleolandscape remnants complemented by onshore sedimentological archives allows the reconstruction of two physiographic configurations of West Africa in the Paleogene. Those reconstructions show that the geometry of the drainage is stabilized by the late early Oligocene (29 Ma) and probably by the end of the Eocene (34 Ma), allowing to effectively link the inland morphoclimatic record to offshore sedimentation since that time, particularly in the case of the Niger catchment—delta system. Mid‐Eocene paleogeography reveals the antiquity of the Senegambia catchment back to at least 45 Ma and suggests that a marginal upwarp forming a continental divide preexisted early Oligocene connection of the Niger and Volta catchments to the Equatorial Atlantic Ocean. Such a drainage rearrangement was primarily enhanced by the topographic growth of the Hoggar hot spot swell and caused a stratigraphic turnover along the Equatorial margin of West Africa.

Phylogeography, historical demography and habitat suitability modelling of freshwater fishes inhabiting seasonally fluctuating Mediterranean river systems: a case study using the Iberian cyprinid Squalius valentinus.

The Mediterranean freshwater fish fauna has evolved under constraints imposed by the seasonal weather/hydrological patterns that define the Mediterranean climate. These conditions have influenced the genetic and demographic structure of aquatic communities since their origins in the Mid-Pliocene. Freshwater species in Mediterranean-type climates will likely constitute genetically well-differentiated populations, to varying extents depending on basin size, as a consequence of fragmentation resulting from drought/flood cycles. We developed an integrative framework to study the spatial patterns in genetic diversity, demographic trends, habitat suitability modelling and landscape genetics, to evaluate the evolutionary response of Mediterranean-type freshwater fish to seasonal fluctuations in weather. To test this evolutionary response, the model species used was Squalius valentinus, an endemic cyprinid of the Spanish Levantine area, where seasonal weather fluctuations are extreme, although our findings may be extrapolated to other Mediterranean-type species. Our results underscore the significant role of the Mediterranean climate, along with Pleistocene glaciations, in diversification of S.valentinus. We found higher nuclear diversity in larger drainage basins, but higher mitochondrial diversity correlated to habitat suitability rather than basin size. We also found strong correlation between genetic structure and climatic factors associated with Mediterranean seasonality. Demographic and migration analyses suggested population expansion during glacial periods that also contributed to the current genetic structure of S.valentinus populations. The inferred models support the significant contribution of precipitation and temperature to S.valentinus habitat suitability and allow recognizing areas of habitat stability. We highlight the importance of stable habitat conditions, fostered by typical karstic springs found on the Mediterranean littoral coasts, for the preservation of freshwater species inhabiting seasonally fluctuating river systems.

Neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (Burkina Faso, West Africa)

The regionally correlated and dated regolith–paleolandform sequence of Sub-Saharan West Africa offers a unique opportunity to constrain continental-scale regolith dynamics as the key part of the sediment routing system. In this study, a regolith mapping protocol is developed and applied at the scale of Southwestern Burkina Faso. Mapping combines field survey and remote sensing data to reconstruct the topography of the last pediplain that formed over West Africa in the Early and Mid-Miocene (24–11Ma). The nature and preservation pattern of the pediplain are controlled by the spatial variation of bedrock lithology and are partitioned among large drainage basins. Quantification of pediplain dissection and drainage growth allows definition of a cratonic background denudation rate of 2m/My and a minimum characteristic timescale of 20Ma for shield resurfacing. These results may be used to simulate minimum export fluxes of drainage basins of constrained size over geological timescales. Background cratonic denudation results in a clastic export flux of ~4t/km2/year, which is limited by low denudation efficiency of slope processes and correlatively high regolith storage capacity of tropical shields. These salient characteristics of shields' surface dynamics would tend to smooth the riverine export fluxes of shields through geological time.

10Be-derived denudation rates from the Burdekin catchment: The largest contributor of sediment to the Great Barrier Reef

Terrestrial cosmogenic nuclides (TCNs) such as Beryllium-10 (10Be) are now routinely used to reconstruct erosional rates over tens of thousands of years at increasingly large basin scales (>100,000km2). In Australia, however, the approach and its assumptions have not been systematically tested within a single, large drainage basin. This study measures 10Be concentrations in river sediments from the Burdekin catchment, one of Australia's largest coastal catchments, to determine long-term (>10,000years), time-integrated rates of sediment generation and denudation. A nested-sampling design was used to test for effects of increasing catchment scale on nuclide concentrations with upstream catchment areas ranging from 4 to 130,000km2. Beryllium-10 concentrations in sediment samples collected from the upstream headwater tributaries and mid-stream locations range from 1.8 to 2.89×105atomsg−1 and data confirm that nuclide concentrations are well and rapidly mixed downstream. Sediment from the same tributaries consistently yielded 10Be concentrations in the range of their upstream samples. Overall, no decrease in 10Be concentrations can be observed at the range of catchment scales measured here. The mean denudation rate for all river sediment samples throughout the Fanning subcatchment (1100km2) is 18.47mMa−1, which compares with the estimate at the end of the Burdekin catchment (130,000km2) of 16.22mMa−1. Nuclide concentrations in the lower gradient western and southern catchments show a higher degree of variability, and several complications emerged as a result of the contrasting geomorphic processes and settings. This study confirms the ability of TCNs to determine long-term denudation rates in Australia and highlights some important considerations in the model assumptions that may affect the accuracy of limited sampling in large, low-gradient catchments with long storage times.

Prioritization of Sub Watershed Based on Morphometric Characteristics Using Fuzzy Analytical Hierarchy Process and Geographical Information System – A Study of Kallar Watershed, Tamil Nadu

Watershed prioritization has gained importance in natural resources management, especially in the context of watershed management. Delineation of watersheds within a large drainage basin and their prioritization is required for proper planning and management of natural resources for sustainable development. Delineation of potential zones for implementation of conservation measures above the entire watershed at similar occurrence is inaccessible as well as uneconomical; therefore it is a prerequisite to apply viable technique for prioritization of sub watersheds (SW). The present research attempted to study various morphological characteristics and to implement Geographical Information System (GIS) and Multi Criteria Decision Making (MCDM) through Fuzzy Analytical Hierarchy Process (FAHP) techniques for identification of critical sub watersheds situated in transaction zone between mountainous and water scarcity region of kallar watershed, Tamil Nadu. The morphometric characterization was obtained through the measurement of three distinct linear, areal and relief aspects over the eleven sub-watersheds. The morphometric characterization showed vital role in distinguishing the topographical and hydrological behavior of the watershed. Each morphometric parameters were ranked with respect to the value and weightings obtained by deriving the relationships between the morphometric parameters obtained through classification of the SW by associating the strength of Fuzzy Analytical Hierarchy Processes (FAHP). Based on FAHP approach, sub watersheds were evaluated and divided into five prioritization zones: very less, less, medium, high and very high classes. The FAHP techniques is a practical approach for identification of the sensitive priority zones and is useful for better management practices such as implementation of land and water resource management, conservation and sustainable agricultural development.

Sub-basin prioritization using remote sensing and geographical information system techniques

Land resource development programmes are applied generally on a watershed basis. Delineation of watersheds or subbasins within a large drainage basin and their prioritization is required for proper planning and management of natural resources for sustainable crop production. Morphometric analysis is commonly applied to prioritization of watersheds or sub-basins. The present study attempts to prioritize sub-basins based on morphometric analysis using remote sensing and geographical information system (GIS) techniques in Jharol river basin of Udaipur district, Rajasthan, India. Various morphometric parameters, namely linear and shape have been determined for each subbasins and assigned ranks on the basis of value/relationship, so as to arrive at a compound parameter values for a final ranking of the sub-basins and prioritization rating of five sub-basin of Jharol river basin is carried out. The sub-basin with the lowest compound parameter value is given the highest priority. The prioritization results revealed that subbasin 4 ranked highest, which compound parameter value was lowest as 2.375 and were considered as high priority for conservation measures by planners and decision makers; hence, it should be provided with immediate soil and water conservation measures.

Soil denitrification fluxes from three northeastern North American forests across a range of nitrogen deposition.

In northern forests, large amounts of missing N that dominate N balances at scales ranging from small watersheds to large regional drainage basins may be related to N-gas production by soil microbes. We measured denitrification rates in forest soils in northeastern North America along a N deposition gradient to determine whether N-gas fluxes were a significant fate for atmospheric N inputs and whether denitrification rates were correlated with N availability, soil O2 status, or forest type. We quantified N2 and N2O fluxes in the laboratory with an intact-core method and monitored soil O2, temperature and moisture in three forests differing in natural and anthropogenic N enrichment: Turkey Lakes Watershed, Ontario; Hubbard Brook Experimental Forest, New Hampshire; and Bear Brook Watershed, Maine (fertilized and reference plots in hardwood and softwood stands). Total N-gas flux estimates ranged from <1 in fertilized hardwood uplands at Bear Brook to >100 kg N ha(-1) year(-1) in hardwood wetlands at Turkey Lakes. N-gas flux increased systematically with natural N enrichment from soils with high nitrification rates (Bear Brook < Hubbard Brook < Turkey Lakes) but did not increase in the site where N fertilizer has been added since 1989 (Bear Brook). Our results show that denitrification is an important and underestimated term (1-24% of atmospheric N inputs) in N budgets of upland forests in northeastern North America, but it does not appear to be an important sink for elevated anthropogenic atmospheric N deposition in this region.

Long‐term water budget imbalances and error sources for cold region drainage basins

AbstractThis study assessed the long‐term (1979–2008) water budget closures for 19 large cold region drainage basins in Canada using recently developed datasets for precipitation (P), land surface evapotranspiration and water surface evaporation, and observed streamflow. Total water storage (TWS) trends from the GRACE satellite observations were also used to assist the assessment. The objectives are to quantify the magnitudes and spatial patterns of the water budget imbalance (ε) and its source of errors for these cold region basins. Results showed that the water budget was closed within 10% of the P on average for all the basins. The ε showed a general pattern of positive values in the south and negative values in the north and mountainous regions over the country. Basins with large ε values were mostly found in the north. Uncertainties in the water budget variables, particularly P, were found to play a major role in the ε. Significant trends in TWS were found over 11 basins, which accounted for 31% of their ε on average. Improvements in the observation network, data quality assurance, and spatial models for P are critical for further improving the water budget closure for the cold region drainage basins. © 2014 Her Majesty the Queen in Right of Canada. Hydrological Processes. © John Wiley &amp; Sons, Ltd.

Palaeoenvironment and anthropogenic activity in the southeastern Mediterranean since the mid-Holocene: The case of Tell es-Safi/Gath, Israel

The “younger fill” phenomenon defined by Vita-Finzi, related to sediments that were deposited in many Mediterranean valleys, has been a topic of discussion for several decades. The main challenge regarding this issue is deciphering the origin of the fill: geomorphic processes induced by natural climatic, or by anthropogenic activity. The current research is an attempt to deal with this issue by using a concept in which the environmental records, i.e. climate, hydrology and sedimentology, were examined in conjunction with human history, in the area of the Bronze and Iron Age archaeological site of Tell es-Safi/Gath, in central Israel. The study investigated geomorphic structures of various scales: a single slope, 1st and 2nd order valleys, and larger drainage basins of a few tens to hundreds km2. High-resolution dating of the sediments by OSL and 14C allowed the identification of different sedimentary phases.The sedimentary history of the Tell es-Safi/Gath environs shows that: (a) During the Chalcolithic period and Early Bronze Age (∼4200–3050 BCE), stable conditions prevailed in the small valleys, represented by soil formation; (b) During the Iron Age II and up to the Early Arab period (∼800 BCE–800CE), aggradation took place in the small and the large valleys; (c) During the post-Byzantine/Early Arab periods (after 800 CE), major incision occurred in the large valleys, whereas minor aggradation occurred in the small valleys. Climatic and natural geomorphic processes are the major factors shaping the landscape in the current research area.Anthropogenic activity was expressed at localized sites and for a limited time, in two locations only. One location is the siege trench that surrounds Tell es-Safi/Gath, where sedimentation occurred shortly after the destruction of the site by Hazael, king of Aram Damascus (ca. late 9th century BCE), and in the same locality during the Byzantine period. The other location is the 2nd order valley close to the archaeological site, where enhanced sedimentation rates occurred shortly after site destruction. In addition, these results suggest that the small basin valleys underwent aggradation that continuously recorded the local environmental history, whereas the large drainage basins underwent cut and fill processes related to the regional environmental history in a less continuous record.

Assessment of water budget for sixteen large drainage basins in Canada

Summary This study represents the first attempt to examine the spatial and seasonal variations of the surface water budget by using state-of-the-art datasets for sixteen large Canadian drainage basins with a total area of 3.2 million km2. The datasets used include two precipitation grids produced using measurements and reanalysis models, land surface evapotranspiration and water surface evaporation estimated using the EALCO model, streamflow measured at hydrometric stations, and total water storage change derived from GRACE satellite observations. The monthly water imbalance resulted from these datasets varied from 7.0 mm month−1 to 21 mm month−1 among the studied basins, which was 30% on average of the corresponding monthly precipitation. The accumulated water budget imbalance over the 7 years of 2002–2008 varied from close to zero to ±10 mm month−1. The positive and negative imbalances among the sixteen basins were largely offset and the all-basin imbalance was very close to 0. The uncertainties in precipitation, streamflow, evapotranspiration and total water storage change all contributed to the water budget imbalance and their relative magnitudes were found to vary with basin and season. In most cases, precipitation showed the largest uncertainties, which had similar magnitudes to the water budget imbalances. While improvements are noted in comparison with previous water budget studies over the regions, the water imbalance obtained for some basins is quite large, suggesting that considerable improvements in both the observation networks and models are necessary before the water budget closure can be substantially improved over this region.

Evaluation of Current Approaches to Stream Classification and a Heuristic Guide to Developing Classifications of Integrated Aquatic Networks

Conservation and management of fresh flowing waters involves evaluating and managing effects of cumulative impacts on the aquatic environment from disturbances such as: land use change, point and nonpoint source pollution, the creation of dams and reservoirs, mining, and fishing. To assess effects of these changes on associated biotic communities it is necessary to monitor and report on the status of lotic ecosystems. A variety of stream classification methods are available to assist with these tasks, and such methods attempt to provide a systematic approach to modeling and understanding complex aquatic systems at various spatial and temporal scales. Of the vast number of approaches that exist, it is useful to group them into three main types. The first involves modeling longitudinal species turnover patterns within large drainage basins and relating these patterns to environmental predictors collected at reach and upstream catchment scales; the second uses regionalized hierarchical classification to create multi-scale, spatially homogenous aquatic ecoregions by grouping adjacent catchments together based on environmental similarities; and the third approach groups sites together on the basis of similarities in their environmental conditions both within and between catchments, independent of their geographic location. We review the literature with a focus on more recent classifications to examine the strengths and weaknesses of the different approaches. We identify gaps or problems with the current approaches, and we propose an eight-step heuristic process that may assist with development of more flexible and integrated aquatic classifications based on the current understanding, network thinking, and theoretical underpinnings.

The Nisi Fault as a key structure for understanding the active deformation of the NW Peloponnese, Greece

The previously unknown Nisi Fault in NW Peloponnese was ruptured during the 2008 Movri Mountain earthquake attaining a maximum offset of 25cm. The fault is interpreted as a branch of a flower structure above a blind strike-slip fault. We investigate the Nisi Fault seismotectonic evolution using morphotectonic analysis in order to determine whether the landscape is affected by tectonic forcing and paleoseismology to determine earthquake recurrence interval and fault slip rates. We applied several geomorphic indices, such as the asymmetry factor (AF), the stream length–gradient index (SL), the valley floor width to valley height ratio (Vf), the mountain-front sinuosity (Smf), the drainage basin shape (Bs) and the hypsometric curve (Hc), in four large drainage basins of the study area. The results show that fault-related vertical motions and the associated tilting influenced the drainage geometry and the landscape development. Values of stream-gradient indices (SL) are relatively high close to the fault trace. Mountain-front sinuosity (Smf) mean values along the fault zones range from 1.12 to 1.23. Valley floor width to valley height ratios (Vf) mean values along the studied fault range between 0.21 and 2.50. Drainage basin shape (BS) mean values along the fault range from 1.04 to 3.72. Lateral fault growth was likely achieved by propagation primarily towards north-northwestward. The paleoseismic history of the fault, investigated by a trench and 14C dating of seven samples, indicates two morphogenic earthquakes in the last 1kyr. Therefore, we suggest that the Nisi Fault displays a slip rate on the order of 1mm/yr and a recurrence interval ranging between 300 and 600years. From a seismotectonic point of view, the fault is classified as high activity rate, with abundant but discontinuous geomorphic evidence of its activity. Other similar faults affecting the western Peloponnese can be envisaged with a similar procedure. Additionally, the seismic history and surface expression of the Nisi Fault, resembles other faults of similar length in Greece and Italy. Particularly, a crucial issue in terms of seismic risk management is that neotectonic analysis has to be envisaged carefully on short in length faults, since these faults can be possibly related to strong earthquakes.