Mean Basin Slope Research Articles

Tan DEM‐X Preserves the Relationship Between Hilltop Curvature and Erosion Rate in the Qilian Shan

AbstractHilltop curvature (CHT) can record erosional responses to tectonic forces and/or climate change. Although CHT has a linear relationship with the erosion rate, which is a significant advantage over traditional indicators, it is not widely used, mainly because it requires high‐resolution terrain data. Previous studies show that terrain steepness is strongly correlated with catchment‐wide erosion rates in the Qilian Shan. This relationship enables us to test the potential of CHT based on medium‐resolution terrain data (e.g., Tan DEM‐X with a resolution of ∼12 m) as an indicator of the erosion rate. We selected three typical sites in the Qilian Shan with evenly spaced ridge valleys and a continuous soil cover. At each site, we produced a high‐resolution digital surface model (DSM) using uncrewed aerial vehicles (UAVs), and then compared CHT from the UAV DSM with that from Tan DEM‐X, via LSDTopoTools. The results show that both Tan DEM‐X and the UAV DSM record similar spatial patterns of CHT, although the magnitudes vary between the three selected areas. We then examined the relationship between CHT based on Tan DEM‐X and the catchment‐wide erosion rate in the Qilian Shan. CHT has a linear relationship with the erosion rate in an area of clastic rocks, where the erosion rate is below 400 mm/Kyr. CHT extracted by Tan DEM‐X is superior to the mean basin slope in predicting the erosion rate in this clastic rock landscape. Overall, our results demonstrate the utility of Tan DEM‐X in calculating CHT to indicate the erosion rate.

Global Riverine Export of Dissolved Lignin Constrained by Hydrology, Geomorphology, and Land‐Cover

AbstractThe land‐to‐ocean export of terrestrial dissolved organic matter (tDOM) links the two largest organic carbon (OC) pools on Earth and is changing due to anthropogenic activity and climate change. Lignin phenols are often utilized as diagnostic markers for tDOM in aquatic systems, but information on the global dissolved lignin flux is still uncertain as linkages between future changes in export and global changes are poorly constrained. Thirty‐two new measurements from 15 Chinese rivers and 548 measurements collected from 97 global rivers were combined to analyze its distributions, fluxes, and potential controls. Dissolved lignin concentrations (in μg L−1) varied by more than two orders of magnitude (0.7–138 μg L−1) and were positively correlated with dissolved OC (DOC) concentrations globally, suggesting coupled export of dissolved lignin and DOC. The carbon‐normalized lignin yields (in mg g OC−1) varied by an order of magnitude (<1–30 mg (g OC)−1) and was significantly lower in the Arctic than in temperate and tropical rivers. Correlation analyses indicated that the dissolved lignin flux (FLignin) was mainly affected by water discharge and mean basin slope, while the area‐normalized yield of dissolved lignin as well as discharge‐weighted lignin concentration strongly and positively correlated with forest coverage. We, for the first time, estimated global FLignin ranges from 0.58 to 1.2 Tg yr−1 by using different approaches. Our synthesis reveals that future changes in land‐cover that is driven by climate change as well as other human activities would impose a significant influence on the land‐to‐ocean export of tDOM.

Coupling MCDM-based ensemble and AHP for the sustainable management of erosion risk in a tropical Sub-Saharan basin

Intensified erosion threats are one of the major ecological problems ravaging global basins. To address this problem, it is crucial to identify erosion-prone areas at the sub-watershed level. In this study, a seven multi-criteria decision-making (MCDM) models ensemble was developed to prioritize sub-watersheds in the Anambra Basin based on erosion risk. The integration of the MCDM models with the Analytical Hierarchical Process and Geographic Information System with 23 geomorphometric parameters (specifically 12 linear, 6 shape, and 5 relief parameters), enabled a comprehensive ranking approach. The accuracy of the models was tested using normalised Spearman's rank correlation to compute a uniform sub-watershed ranking. The results revealed that the study area is a 7th order basin with drainage densities between 0.54 km/km2 to 0.62 km/km2, average peak flow between 88 m3/sec to 361 m3/sec, texture ratio between 2.54/km to 11.25/km, and mean basin slope values between 10.9° to 22.2°. Out of the eight sub-watersheds, as indicated by the MCDM models, H returned the highest aggregate rank (1st), making it the top priority for erosion risk mitigation while B ranked the least (8th) suggesting the presence of some environmental conditions that are less erosion prone. The top-ranked MCDM models, MOORA (multi-objective optimisation based on ratio analysis) and COPRAS (complex proportional assessment), show that they are the best options for managing erosion in the Anambra Basin. These findings offer prospects for sustainable erosion risk control at the sub-watershed level and a scientific basis for resource management for basins with similar characteristics around the world.

Coupled influence of precipitation and vegetation on millennial-scale erosion rates derived from 10Be.

Water is one of the main agent of erosion in many environmental settings, but erosion rates derived from beryllium-10 (10Be) suggests that a relationship between precipitation and erosion rate is statistically non-significant on a global scale. This might be because of the strong influence of other variables on erosion rate. In this global 10Be compilation, we examine if mean annual precipitation has a statistically significant secondary control on erosion rate. Our secondary variable assessment suggests a significant secondary influence of precipitation on erosion rate. This is the first time that the influence of precipitation on 10Be-derived erosion rate is recognized on global scale. In fact, in areas where slope is <200m/km (~11°), precipitation influences erosion rate as much as mean basin slope, which has been recognized as the most important variable in previous 10Be compilations. In areas where elevation is <1000m and slope is <11°, the correlation between precipitation and erosion rate improves considerably. These results also suggest that erosion rate responds to change in mean annual precipitation nonlinearly and in three regimes: 1) it increases with an increase in precipitation until ~1000 mm/yr; 2) erosion rate stabilizes at ~1000 mm/yr and decreases slightly with increased precipitation until ~2200 mm/yr; and 3) it increases again with further increases in precipitation. This complex relationship between erosion rate and mean annual precipitation is best explained by the interrelationship between mean annual precipitation and vegetation. Increased vegetation, particularly the presence of trees, is widely recognized to lower erosion rate. Our results suggest that tree cover of 40% or more reduces erosion rate enough to outweigh the direct erosive effects of increased rainfall. Thus, precipitation emerges as a stronger secondary control on erosion rate in hyper-arid areas, as well as in hyper-wet areas. In contrast, the regime between ~1000 and ~2200 mm/yr is dominated by opposing relationships where higher rainfall acts to increase erosion rate, but more water also increases vegetation/tree cover, which slows erosion. These results suggest that when interpreting the sedimentological record, high sediment fluxes are expected to occur when forests transition to grasslands/savannahs; however, aridification of grasslands or savannahs into deserts will result in lower sediment fluxes. This study also implies that anthropogenic deforestation, particularly in regions with high rainfall, can greatly increase erosion.

Developing an overall assessment map for flood hazard on large area watershed using multi-method approach: case study of Wadi Qena watershed, Egypt

Many parts of Upper Egypt as Sinai and Red Sea areas were hit by severe flash floods since 1976. Wadi Qena is considered one of the most watersheds that suffers from floods in Red Sea area. It was recorded by the General Authority for Roads, Bridges & Land Transport (GARBLT) that the flash flood destructive effect always occurs on El-Geesh–Hurghada Road which is located in the southern part of Wadi Qena watershed. The current study investigates the assessment of endangered areas in Wadi Qena watershed based on a suggested concept of multi-method approach which is a combination of morphometric ranking method and El-Shamy approach. The morphometric analysis is applied using set of parameters which are classified into three categories: basin geometry, drainage network and texture, and relief parameters. For basin geometry, the considered parameters are the watershed area (A), elongation ratio (Re), circularity ratio (Rc), form factor (Ff), and compactness coefficient (Cc). For drainage network and texture parameters, stream frequency (F), texture ratio (Rt), length of overland flow (Lo), and drainage density (D) parameters are considered. For relief parameters, the parameters are mean basin slope (Sm), relief ratio (Rr), and ruggedness number (Rn). A filtration process for the above twelve parameters is considered for reducing the number of parameters by omitting the parameters which have inverse effect on the flood severity of the study area. It is concluded that six parameters have a direct effect on sub-basin hazardous including A, D, Lo, Sm, Rr, and Rn. Sensitivity analysis is concerned for ranking the selected parameters by their significant parameters in assessing the most hazard sub-basins. An overall assessment map is constructed showing the hazard degrees of the sub-basins. The constructed map concludes that the sub-basins are divided into moderate and high hazard ones. Moreover, the results show that the high hazard degree sub-basins are concentrated in the middle and east of the watershed with a percentage of 18.5% of the total area. The developed overall assessment map can be used for assessment and mentoring processes of flood mitigation and planning.

Global evaluation of erosion rates in relation to tectonics

Understanding the mechanisms and controlling factors of erosion rates is essential in order to sufficiently comprehend bigger processes such as landscape evolution. For decades, scientists have been researching erosion rates where one of the main objectives was to find the controlling factors. A variety of parameters have been suggested ranging from climate-related, basin morphometry and the tectonic setting of an area. This study focuses on the latter. We use previously published erosion rate data obtained mainly using 10Be and sediment yield and sediment yield data published by the United States Geological Survey. We correlate these data to tectonic-related factors, i.e., distance to tectonic plate boundary, peak ground acceleration (PGA), and fault distribution. We also examine the relationship between erosion rate and mean basin slope and find significant correlations of erosion rates with distance to tectonic plate boundary, PGA, and slope. The data are binned into high, medium, and low values of each of these parameters and grouped in all combinations. We find that groups with a combination of high PGA (> 0.2.86 g) and long distance (> 1118.69 km) or low PGA (< 0.68 g) and short distance (< 94.34 km) are almost inexistent suggesting a strong coupling between PGA and distance to tectonic plate boundary. Groups with low erosion rates include long distance and/or low PGA, and groups with high erosion rates include neither of these. These observations indicate that tectonics plays a major role in determining erosion rates, which is partly ascribable to steeper slopes produced by active crustal movements. However, our results show relatively unclear correlation of slope with erosion rates, pointing to problems with using mean basin-wide slope as a slope indicator because it does not represent the complex slope distribution within a basin.

Tectonic and Climatic Controls on the Spatial Distribution of Denudation Rates in Northern Chile (18°S to 23°S) Determined From Cosmogenic Nuclides

AbstractIn the arid region of northern Chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation. Previous studies of denudation rates from cosmogenic 10Be and 26Al concentrations are limited to single drainages. In this study, we examine catchment‐ to orogen‐scale spatial variation in denudation rates between 18 and 23°S in the Coastal and Western Cordilleras of northern Chile. 10Be and 26Al data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment‐averaged denudation rates. At broader scales, we examine whether denudation rates and orogen topography reflect the 3‐D plate geometry of the region. Cosmogenic nuclide‐derived denudation rates range from 0.4 ± 0.5 to 20.6 ± 1.5 m/Myr in the Coastal Cordillera and from 1.4 ± 0.7 to 168.0 ± 19.8 m/Myr in the Western Cordillera. The controls on the denudation rates are evaluated using a statistical factor analysis of 10 selected catchment parameters. Denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates, drainage area, stream order, mean elevation, mean local relief, mean basin slope, and grain size of the sampled sediments. Moreover, denudation rates are better correlated with tectonic controls at catchment scale than orogen‐scale plate tectonics in the Western and Coastal Cordillera.

Environmental controls on 10Be‐based catchment‐averaged denudation rates along the western margin of the Peruvian Andes

AbstractWe present 10Be‐based basin‐averaged denudation rates for the entire western margin of the Peruvian Andes. Denudation rates range from c. 9 mm ka−1 to 190 mm ka−1 and are related neither to the subduction of the Nazca plate nor to the current seismicity along the Pacific coast and the occurrence of raised Quaternary marine terraces. Therefore, we exclude a tectonic control on denudation on a millennial time‐scale. Instead, we explain &gt;60% of the observed denudation rates with a model where erosion rates increase either with mean basin slope angles or with mean annual water discharge. These relationships suggest a strong environmental control on denudation.

Understanding landscape dynamics of the Sierra de Juarez, southern Mexico: An exploratory approach using inherited luminescence signals

We explore inherited luminescence signals to generate information about different mechanisms involved in mobilization of debris flows in rivers (n = 12) of the Sierra de Juárez (Oaxaca, Mexico), that flow across the Oaxaca and Donaji faults. Sediment samples composed of poly-mineral and poly-grain sizes were optically stimulated using a Pulsed-Photon Stimulated Luminescence unit. In most of the rivers, the luminescence signals intensities fall with increasing distance from their source and the luminescence of different grain size fractions were variable. Our results suggest that mineral grains were transported in the water column without any stratification based on grain sizes, indicating debris flows and/or hyper-concentrated flows. A correlation between the inherited luminescence signals and the mean basin slope provides information about the river basin topography. Our results suggest that mobilization of sediments is related to the steepness of topography produced by the Oaxaca fault formation and inherited luminescence signals has a good potential to unravel the processes involved in the transport of fluvial sediment in mountainous settings of southern Mexico.

Evaluating carbon storage on subalpine lake deltas

AbstractMountainous regions are important contributors to the terrestrial organic carbon (OC) sink that affect global climate through the regulation of carbon‐based greenhouse gases. However, mountain OC dynamics are poorly quantified. We quantified OC storage in subalpine lake deltas in the Washington Central Cascades and Colorado Front Range with the objectives of determining the magnitude of transient carbon storage and understanding the differences in storage between the two ranges. We used field, laboratory, and GIS techniques to determine the magnitude of and controls on the subalpine lake delta OC pool in 26 subalpine lake deltas. Soil moisture, soil texture, mean basin slope, and delta valley confinement are significantly correlated with soil carbon on deltas. Average soil OC concentration on subalpine lake deltas ranges from 3 to 41%, and stocks range from 140 to 1256 Mg C/ha. Surprisingly, the carbon content of subalpine lake deltas is not significantly different between the two regions, despite stark contrasts in their climate, vegetation, and total ecosystem carbon stocks. We present a conceptual model that invokes geomorphic and biogeochemical processes to suggest that carbon is more likely to reach subalpine lake deltas from the upstream basin in the Colorado Front Range compared with the Washington Central Cascades, thus accounting for the similarity in OC storage between the two regions despite differences in total ecosystem carbon stocks and climate. This points to a complex interaction among carbon production, transport, and stability in each region, and supports the idea that geomorphic and biogeochemical processes determine the magnitude of transient OC storage more strongly than primary productivity or climate. Copyright © 2017 John Wiley &amp; Sons, Ltd.

The Map of Kashafrud Catchments Prioritization in terms of Flooding Susceptibility Located in Khorasan Razavi Province Based on ELECTRETRI Algorithm

Flooding is one of the natural disasters which have effects most areas of the country and caused the loss of life and property; therefore, identifying of areas which are susceptible to flooding is one the most important measures in reducing losses. Classification and prioritization of sub-catchments is the first step to counter or mitigate the effects of flooding in the drainage basins. On this basis, the purpose of this study was to classify the flooding potential of sub-catchments of “Kashafrud” catchment in the “Khorasan Razavi” province by the use of ELECTRE-TRI Algorithm based on optimistic procedure and consistency control perspectives. To achieve this, the 1: 250,000 topographic map and waterways map of the target area were studied and area was divided into 10 sub-basins, then 8 morph hydrological parameters affecting the flooding potential including basin’s form factor, elongation ratio, circularity ratio, bifurcation ratio, drainage density, Mean basin slope and area were evaluated. After the evaluation, it was found that “Mashhad” and “Torghabe” subbasins had a high-risk of flooding because of the high value of drainage density and low value of bifurcation ratio in these areas, which both have a higher effect in flooding potential compared to other factors. Toos, Chenaran, Qazqan and sub-basins had a low risk of flooding because of the low values of the factors which increase the flooding potential and high values of the factors which decrease it.

Long-term background denudation rates of southern and southeastern Brazilian watersheds estimated with cosmogenic 10Be

In comparison to humid temperate regions of the Northern Hemisphere, less is known about the long-term (millennial scale) background rates of erosion in Southern Hemisphere tropical watersheds. In order to better understand the rate at which watersheds in southern and southeastern Brazil erode, and the relationship of that erosion to climate and landscape characteristics, we made new measurements of in situ produced 10Be in river sediments and we compiled all extant measurements from this part of the country.New data from 14 watersheds in the states of Santa Catarina (n=7) and Rio de Janeiro (n=7) show that erosion rates vary there from 13 to 90m/My (mean=32m/My; median=23m/My) and that the difference between erosion rates of basins we sampled in the two states is not significant. Sampled basin area ranges between 3 and 14,987km2, mean basin elevation between 235 and 1606m, and mean basin slope between 11 and 29°. Basins sampled in Rio de Janeiro, including three that drain the Serra do Mar escarpment, have an average basin slope of 19°, whereas the average slope for the Santa Catarina basins is 14°. Mean basin slope (R2=0.73) and annual precipitation (R2=0.57) are most strongly correlated with erosion in the basins we studied. At three sites where we sampled river sand and cobbles, the 10Be concentration in river sand was greater than in the cobbles, suggesting that these grain sizes are sourced from different parts of the landscape.Compiling all cosmogenic 10Be-derived erosion rates previously published for southern and southeastern Brazil watersheds to date (n=76) with our 14 sampled basins, we find that regional erosion rates (though low) are higher than those of watersheds also located on other passive margins including Namibia and the southeastern North America. Brazilian basins erode at a pace similar to escarpments in southeastern North America. Erosion rates in southern and southeastern Brazil are directly and positively related to mean basin slope (R2=0.33) and weakly but significantly to mean annual precipitation (R2=0.05). These relationships are weaker when considering all southern and southeastern Brazil samples than they are in our smaller, localized data set. We find that smaller, steeper headwater catchments (many on escarpments) erode faster than the larger, higher-order but lower slope catchments. Erosion in southern and southeastern Brazil appears to be controlled largely by mean basin slope with lesser influence by climate and lithology.

Regional Flood Frequency Analysis in the Volta River Basin, West Africa

In the Volta River Basin, flooding has been one of the most damaging natural hazards during the last few decades. Therefore, flood frequency estimates are important for disaster risk management. This study aims at improving knowledge of flood frequencies in the Volta River Basin using regional frequency analysis based on L-moments. Hence, three homogeneous groups have been identified based on cluster analysis and a homogeneity test. By using L-moment diagrams and goodness of fit tests, the generalized extreme value and the generalized Pareto distributions are found suitable to yield accurate flood quantiles in the Volta River Basin. Finally, regression models of the mean annual flood with the size of the drainage area, mean basin slope and mean annual rainfall are proposed to enable flood frequency estimation of ungauged sites within the study area.

GIS based drainage morphometry and its influence on hydrology in parts of Western Ghats region, Maharashtra, India

Various drainage morphometric parameters in the Upper Bhima river basin and its influence on hydrological processes (e.g. runoff, peak flow, time to peak, infiltration, overland flow, etc.) were discussed using geographical information system (GIS) and remote sensing techniques. Survey of India topographical maps and ASTER digital elevation model was incorporated for thematic database generation and morphometric parameter evaluation in GIS environment. The whole study basin was divided into 8 sub-basins so that the spatial variation of morphological parameters and its influence on hydrology could be analyzed. The interrelationship between morphometric variables were computed (p < 0.05) and presented in a correlation matrix. The study revealed that mean basin slope (), drainage density (), length of overland flow () and basin relief () are closely associated and significantly related with a large number of morphometric variables. Due to close proximity of Western Ghats, sub-basins 1, 2, 4, 5 and 6 are highly influenced by slope, as a result, length of overland flow decreases and water immediately follows channel path. In contrast, sub-basins 3, 7 and 8 are relatively flatter, overland flow is relatively longer and favourable for infiltration. This study emphasizes on qualitative description about the hydrological variables influenced by the morphometric parameters in a mountainous basin in western India. Independent morphometric variables were identified from correlation matrix and used in a multiple criteria analysis (MCA) framework for watershed prioritization. Analytical hierarchical process, a MCA technique, identified the highest (sub-basin 4) and lowest (sub-basin 7) priority sub-basins in the Upper Bhima basin. The outcome of the study may be useful for watershed managers and planners while implementing soil and water conservation measures in the region.

Spatiotemporal patterns of baseflow metrics for basins draining the Oak Ridges Moraine, southern Ontario, Canada

The Oak Ridges Moraine (ORM) is a key hydrogeologic feature in southern Ontario, supplying potable water along with important aquatic ecosystem services. Stream baseflow is a useful indicator of groundwater discharge to streams on the ORM and gives insight into the regional hydrogeologic system. This study examines how climatic and basin attributes explain spatiotemporal patterns in baseflow metrics for streams draining the ORM. Baseflow was separated from streamflow using an automated digital filter, and water-year baseflow and baseflow as a fraction of precipitation and total streamflow (baseflow index, BFI) were determined. Much of the variability in baseflow metrics was explained by such characteristics as water-year precipitation, mean basin slope, spatial extent of outcrops of permeable sands and gravels, and forest and urban cover. Identified thresholds for basins with above- or below-average baseflow and BFI could serve as a screening tool in resource management decisions on the ORM. Precipitation has increased for many basins in the latter part of the twentieth and early part of the twenty-first century, often accompanied by greater baseflow. The rate of baseflow increase was related to the spatial extent of sand and gravel outcrops, implying a nonuniform response of baseflow to rising precipitation for basins across the ORM. Although baseflow from these basins may continue to increase under the wetter climate predicted for southern Ontario in the twenty-first century, such forecasts must consider the role of land-use change (e.g. forest expansion, urban development) in altering the partitioning of precipitation between direct runoff and baseflow contributions to streamflow.La moraine Oak Ridges (ORM) est une caractéristique hydrogéologique importante dans le sud de l’Ontario fournissant en eau potable et délivrant de nombreux services pour l’écosystème aquatique. Le débit de base des cours d’eau est un indicateur important de l’écoulement des eaux souterraines dans l’ORM et donne un aperçu du système hydrogéologique régional. Cette étude examine l’influence des caractéristiques climatiques et les propriétés du bassin versant sur les variations spatio-temporelles des débits de base des cours d’eau drainants l’ORM. Le débit de base a été séparé du débit d’eau à l’aide d’un filtre numérique automatisé alors que le débit de base eau annuel, le débit de base sous forme de précipitation et le débit total (débit de base indice, BFI) ont été déterminés expérimentalement. Une grande partie de la variabilité des mesures de débit de base s’expliquait par les précipitations annuelles, la pente moyenne du bassin, l’étendue spatiale des affleurements de couches perméables de sable et gravier, et du couvert forestier et urbain. Les seuils identifiés pour les bassins avec débit de base supérieur ou inférieur au débit de base moyen et BFI pourraient servir d’outil de dépistage dans les décisions de gestion des ressources pour l’ORM. Au cours des dernières décennies, les précipitations ont augmenté dans de nombreux bassins versants et elles ont souvent été accompagnées par de grands débits de base. Les taux d’augmentation du débit de base étaient associés à l’étendue spatiale des affleurements de sable et de gravier, impliquant une réponse non uniforme du débit de base vers la hausse des précipitations pour les bassins à travers l’ORM. Bien que le débit de base de ces bassins pourrait continuer à augmenter avec un climat plus humide comme prédit pour le sud de l’Ontario au vingt-et-unième siècle, les prévisions de débit de base devraient considérer le rôle du changement d’affectation des terres telle que l’expansion des forêts et le développement urbain, et modifier le cloisonnement des précipitations entre ruissellement direct et contribution du débit de base au débit d’eau.

Erosion rates in and around Shenandoah National Park, Virginia, determined using analysis of cosmogenic 10Be

We use cosmogenic 10Be analysis of fluvial sediments and bedrock to estimate erosion rates (104-105 year timescale) and to infer the distribution of post-orogenic geomorphic processes in the Blue Ridge Province in and around Shenandoah National Park, Virginia. Our sampling plan was designed to investigate relationships between erosion rate and lithology, mean basin slope, basin area, and sediment grain size. Fifty-nine samples were collected from a variety of basin sizes ( Inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3.0 to 21 m/My. The area-weighted mean erosion rate for single-lithology basins in the Park is 12.2 m/My. Single-lithology erosion rate ranges for fluvial samples are: granite, 7.0 to 20 m/My; metabasalt, 3.8 to 21 m/My; quartzite, 3.8 to 15 m/My; and siliciclastic rocks, 5.2 to 15 m/My. Multilithology basins erode at rates between 3.0-16 m/My. The Shenandoah River basin (3305 km2) is eroding at 6.6 m/My. Bedrock erosion rates range from 1.8 to 11 m/My across all lithologies, with a mean of 6.5 ± 4.3 m/My. Grain-size specific 10Be analysis of four samples showed no consistent trend of concentration with grain size. Cosmogenic analysis of bedrock and sediment from the Shenandoah National Park area allows us to speculate about why some parts of the Appalachian Mountains erode more slowly and some more rapidly. Overall, it appears that steep drainage basins erode more rapidly than gently sloped basins. Climate and lithology may also influence basin-scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite- and granite-dominated basins. Data are conflicting in regards to the evolution of relief over time. Analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins (Susquehanna River, Shenandoah National Park region) or at similar rates (Great Smoky Mountains) providing a mechanism for growing relief at the scale of individual ridgelines. However, considering relief on a landscape or physiographic province scale, by comparing erosion rates of the highlands versus the lowlands, suggests that relief of the range as a whole is either steady or very slowly decreasing over multi-millennial timescales. The presence of significant erosion rate/slope relationships negates a broad Hackian view of the landscape because there is not uniform erosion across this landscape. The aspect-erosion rate and slope-erosion rate relationships present in the Shenandoah area suggest that the landscape is not fully adjusted to rock strength.

Erosion rates as a potential bottom-up control of forest structural characteristics in the Sierra Nevada Mountains.

The physical characteristics of landscapes place fundamental constraints on vegetation growth and ecosystem function. In actively eroding landscapes, many of these characteristics are controlled by long-term erosion rates: increased erosion rates generate steeper topography and reduce the depth and extent of weathering, limiting moisture storage capacity and impacting nutrient availability. Despite the potentially important bottom-up control that erosion rates place on substrate characteristics, the relationship between the two is largely unexplored. We investigate spatial variations in aboveground biomass (AGB) across a structurally diverse mixed coniferous/deciduous forest with an order of magnitude erosion-rate gradient in the Northern Californian Sierra Nevada, USA, using high resolution LiDAR data and field plots. Mean basin slope, a proxy for erosion rate, accounts for 32% of variance in AGB within our field area (P < 0.001), considerably outweighing the effects of mean annual precipitation, temperature, and bedrock lithology. This highlights erosion rate as a potentially important, but hitherto unappreciated, control on AGB and forest structure.

A model to predict stream water temperature across the conterminous USA

AbstractStream water temperature (ts) is a critical water quality parameter for aquatic ecosystems. However, ts records are sparse or nonexistent in many river systems. In this work, we present an empirical model to predict ts at the site scale across the USA. The model, derived using data from 171 reference sites selected from the Geospatial Attributes of Gages for Evaluating Streamflow database, describes the linear relationship between monthly mean air temperature (ta) and ts. Multiple linear regression models are used to predict the slope (m) and intercept (b) of the ta–ts linear relation as a function of climatic, hydrologic and land cover characteristics. Model performance to predict ts resulted in a mean Nash–Sutcliffe efficiency coefficient of 0.78 across all sites. Application of the model to predict ts at additional 89 nonreference sites with a higher human alteration yielded a mean Nash–Sutcliffe value of 0.45. We also analysed seasonal thermal sensitivity (m) and found strong hysteresis in the ta–ts relation. Drainage area exerts a strong control on m in all seasons, whereas the cooling effect of groundwater was only evident for the spring and fall seasons. However, groundwater contributions are negatively related to mean ts in all seasons. Finally, we found that elevation and mean basin slope are negatively related to mean ts in all seasons, indicating that steep basins tend to stay cooler because of shorter residence times to gain heat from their surroundings. This model can potentially be used to predict climate change impacts on ts across the USA. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Baseflow recession analysis in the inland Pacific Northwest of the United States

The storage-discharge relationships of 26 watersheds in the inland Pacific Northwest of the United States were analyzed. Four fitting methods were used to obtain the baseflow coefficients: lower envelope, organic correlation, and ordinary and inverse least squares. Several climatic and terrain attributes were evaluated as predictors of baseflow coefficients. Watersheds dominated by basalt and flatter landscapes exhibited the smallest recession time scales (K) (12.5–20.0 days). Greater K values (33.3–66.7 days) were obtained over catchments dominated by metamorphic and sedimentary rocks. Mean basin slope and the aridity index were found to be the best estimators of baseflow coefficients. Baseflow in flat basalt landscapes, located in dry warm climates, decrease rapidly during summer months and are most sensitive to future droughts and warming climates. Groundwater systems feeding streams during the driest months can drop to less than 1 mm of effective storage in these sensitive systems. In contrast, the minimum annual storage in mountainous systems can have greater than 10 mm effective storage. By understanding the main factors controlling baseflow recession characteristics, environmental agencies could prioritize efforts in areas where future droughts and land use changes may affect ecological assemblages and socio-economic activities.

Sediment supply and channel morphology in mountain river systems: 1. Relative importance of lithology, topography, and climate

[1] Quantifying landscape-scale variations in sediment supply to streams and rivers is fundamental to our understanding of both denudational processes and stream channel morpho-dynamics. Previous studies have linked a variety of sediment-supply proxies to climatic, topographic, or geologic factors, but few have connected these directly to the characteristics of fluvial systems draining these landscapes. Here we correlate landscape controls on sediment supply to observed sedimentology and channel patterns through direct measurements of water and sediment fluxes in over 80 drainage basins ranging in area from 1.4 to 35,000 km2 in the northern Rocky Mountains, USA. These data show that the relative sediment supply, defined by the bankfull sediment concentration, is dominated by basin lithology, while exhibiting little correlation to factors such as relief, mean basin slope, and drainage density. Bankfull sediment concentrations (bed load and suspended load) increase as much as 100-fold as basin lithology becomes dominated by softer sedimentary and volcanic rocks, relative to basins with more resistant lithologies. As bed load concentrations increase, stream beds become less armored, and bed load grain size coarsens. At very high sediment concentrations, bed surface, subsurface, and bed load grain sizes converge and a transition from single-thread to to braided channel patterns is commonly observed.