Increasing Drainage Area Research Articles

A physics-based model for fluvial valley width

Abstract. The width of fluvial valley floors is a key parameter to quantifying the morphology of mountain regions. Valley floor width is relevant to diverse fields including sedimentology, fluvial geomorphology, and archaeology. The width of valleys has been argued to depend on climatic and tectonic conditions, on the hydraulics and hydrology of the river channel that forms the valley, and on sediment supply from valley walls. Here, we derive a physically based model that can be used to predict valley width and test it against three different datasets. The model applies to valleys that are carved by a river migrating laterally across the valley floor. We conceptualize river migration as a Poisson process, in which the river changes its direction stochastically at a mean rate determined by hydraulic boundary conditions. This approach yields a characteristic timescale for the river to cross the valley floor from one wall to the other. The valley width can then be determined by integrating the speed of migration over this timescale. For a laterally unconfined river that is not uplifting, the model predicts that the channel-belt width scales with river flow depth. Channel-belt width corresponds to the maximum width of a fluvial valley. We expand the model to include the effects of uplift and lateral sediment supply from valley walls. Both of these effects lead to a decrease in valley width in comparison to the maximum width. We identify a dimensionless number, termed the mobility–uplift number, which is the ratio between the lateral mobility of the river channel and uplift rate. The model predicts two limits: at high values of the mobility–uplift number, the valley evolves to the channel-belt width, whereas it corresponds to the channel width at low values. Between these limits, valley width is linked to the mobility–uplift number by a logarithmic function. As a consequence of the model, valley width increases with increasing drainage area, with a scaling exponent that typically has a value between 0.4 and 0.5, but can also be lower or higher. We compare the model to three independent datasets of valleys in experimental and natural uplifting landscapes and show that it closely predicts the first-order relationship between valley width and the mobility–uplift number.

Steady‐State Bedrock Channel Width

AbstractThe increase in bedrock channel width and the decline in bedrock channel slope with increasing drainage area are fundamental characteristics of mountainous landscapes. Compared with slope, little is known about controls on steady‐state bedrock channel width. We model steady‐state bedrock channel width by iteratively solving models for bed and bank erosion by impacting bedload, using measurable physical parameters, including uplift rate, water discharge, sediment supply, grain size, rock strength, and bank angle. The results indicate that width is largely controlled by sediment flux, rather than water discharge. The commonly used width‐discharge scaling relation is an artifact of the covariance of sediment flux and water discharge. Scaling up from cross‐section to drainage basin scales, our model reproduces the width‐drainage area scaling relation and suggests that the scaling exponent is largely controlled by the downstream change in the fraction of total sediment supply transported as bedload.

Citizen science and land use data provide insight into the invasive riparian plant composition of the Hudson River Valley watershed

AbstractInvasive plants in the riparian zone can negatively affect the characteristics and quality of a watershed. To support the development of a watershed management plan and foster public appreciation of the value of the riparian zone, Mohonk Preserve established a volunteer monitoring program surveying sites for invasive species. Between 2017 and 2019, citizen scientists repeatedly surveyed 20 sites in the Hudson River Valley in New York for 10 invasive plant species: purple loosestrife (Lythrum salicaria L.), common reed [Phragmites australis (Cav.) Trin. ex Steud], multiflora rose (Rosa multiflora Thunb.), garlic mustard [Alliaria petiolata (M. Bieb.) Cavara & Grande], dame’s rocket (Hesperis matronalis L.), Japanese knotweed (Polygonum cuspidatum Siebold & Zucc.), wineberry (Rubus phoenicolasius Maxim.), barberry (Berberis spp.), Japanese stiltgrass [Microstegium vimineum (Trin.) A. Camus], and Asiatic bittersweet (oriental bittersweet, Celastrus orbiculatus Thunb.). We found that the number of target species detected was higher on sites closer to paved roads and with increasing drainage area size, while lower with higher percentages of forested land in the basin. Our analysis results highlight variation in the presence of target invasive species across the Hudson River Valley region, highlighting sites and areas to monitor for future introductions and take action to prevent species’ invasions. Our results highlight differences in the most relevant abiotic factors for hydrophytes and non-hydrophyte species, underscoring the importance of considering species’ life-history traits before the development of management plans for invasive plant species in the riparian zone. Our case study of community-collected data in the Hudson River Valley region using a relatively simple monitoring protocol can provide a road map for other regions fostering volunteer engagement with invasive plants.

Drainage reorganization induces deviations in the scaling between valley width and drainage area

Abstract. The width of valleys and channels affects the hydrology, ecology, and geomorphic functionality of drainage networks. In many studies, the width of valleys and/or channels (W) is estimated as a power-law function of the drainage area (A), W=kcAd. However, in fluvial systems that experience drainage reorganization, abrupt changes in drainage area distribution can result in valley or channel widths that are disproportional to their drainage areas. Such disproportionality may be more distinguished in valleys than in channels due to a longer adjustment timescale for valleys. Therefore, the valley width–area scaling in reorganized drainages is expected to deviate from that of drainages that did not experience reorganization. To explore the effect of reorganization on valley width–drainage area scaling, we studied 12 valley sections in the Negev desert, Israel, categorized into undisturbed, beheaded, and reversed valleys. We found that the values of the drainage area exponents, d, are lower in the beheaded valleys relative to undisturbed valleys but remain positive. Reversed valleys, in contrast, are characterized by negative d exponents, indicating valley narrowing with increasing drainage area. In the reversed category, we also explored the independent effect of channel slope (S) through the equation W=kbAbSc, which yielded negative and overall similar values for b and c. A detailed study in one reversed valley section shows that the valley narrows downstream, whereas the channel widens, suggesting that, as hypothesized, the channel width adjusts faster to post-reorganization drainage area distribution. The adjusted narrow channel dictates the width of formative flows in the reversed valley, which contrasts with the meaningfully wider formative flows of the beheaded valley across the divide. This difference results in a step change in the unit stream power between the reversed and beheaded channels, potentially leading to a “width feedback” that promotes ongoing divide migration and reorganization. Our findings demonstrate that valley width–area scaling is a potential tool for identifying landscapes influenced by drainage reorganization. Accounting for reorganization-specific scaling can improve estimations of erosion rate distributions in reorganized landscapes.

Production Behavior Analysis of Multibranched Horizontal Oil Well considering Reservoir and Well-Type Factors

Multibranched horizontal well is an important means to develop low permeability reservoirs. Fishbone multibranched horizontal well has the advantages of increasing drainage area, reducing drilling number, utilizing existing wells, and saving oilfield development cost, especially for marginal oilfield exploitation. The morphological structure of fishbone multibranched horizontal well is very complex, so the numerical simulation study is of great significance to guide the production of fishbone multibranched horizontal well. In this paper, the numerical model is established for fishbone multibranched horizontal well in the oil reservoir. The finite element method is used to numerically solve the mathematic model. The oil well production can be achieved by using the material balance method. Sensitivity analysis is made on the important reservoir and well-type factors that affect the production behavior and transient pressure distribution of fishbone multibranched horizontal well. It is concluded that the effective reservoir thickness and flowing bottomhole pressure have great influence on the productivity, but the influence of heterogeneity is not obvious. The length of main wellbore has great effect on the productivity in the early stage. Fishbone multibranched horizontal wells should be placed in the middle of the reservoir to increase productivity. Branch length, branch angle, branch number, and branch spacing are important parameters affecting the productivity of fishbone multibranched horizontal well. The variation of these parameters has obvious influence on the stimulation effect in the early stage of production, but the influence degree is different. Under the premise of drilling technology and drilling safety, the comprehensive impact of these four factors on productivity should be considered simultaneously. The presented model and obtained results not only enrich production behavior analysis of fishbone multibranched horizontal well but also have significance on formulation of stimulation measures and efficient low permeability reservoir development.

Linkage of geographically weighted regression with spatial cluster analyses for regionalization of flood peak discharges drivers: Case studies across Iran

Iran has experienced very destructive flooding events with significant socio-economic and environmental consequences over the last years. Identifying and analyzing the driving factors of flood peak discharges (FPDs) with different return periods in the Iran's basins provides a clear picture of the impact degree of different factors on the flood which is crucial for proper management of flood and associated risk mitigation. In this study, the long-term (>30yr) data of 206 continuous-gauging stations across Iran with various hydro-climatic characteristics were selected for the spatial analysis of FPDs drivers with an average recurrence of 2- to 1000-yr. For this aim, the change points, trend analysis, stepwise regressions, global and local Moran's I index, geographically weighted regression (GWR) and two-step cluster analysis were utilized. The results of GWR model demonstrated the drainage area, elevation, heavy precipitation, slope and NDVI are the most FPDs drivers in different frequencies (Q2 to Q1000). The regression coefficients indicated an increase in FPDs with increasing drainage area, heavy precipitation and slope while a decrease in FPDs magnitude obtained with increasing elevation and NDVI for all study basins and different frequencies (Q2 to Q1000). The results also showed that the impact degree of vegetation increases from Q50 to Q1000 and heavy precipitation from Q100 to Q1000. The findings of this study and the proposed methodology provide a replicable research practice that can help the managers and decision-makers to adopt/implement policies for flood risk management.

An Increase in Specific Discharge With Catchment Area Implies That Bedrock Infiltration Feeds Large Rather Than Small Mountain Headwater Streams

AbstractMountains are a source of water for downstream areas; thus, it is important to understand the storage and discharge characteristics of steep mountain catchments. Nested catchment studies have indicated that the relation between catchment area and specific discharge during baseflow can represent mesoscale storage and discharge characteristics, but this is poorly understood. We found that baseflow‐specific discharge increased with catchment size in the headwater of the Arakawa River and identified the processes responsible for this spatial pattern. Synoptic discharge measurements obtained in catchment areas of 0.05 to 93.58 km2 showed that specific discharge increased more than threefold with increasing drainage area. Analyses of the spatial variation in precipitation, hydrographs from three continuous gauging stations, and isotopic tracers implied that in this catchment, considerable amounts of water infiltrated in bedrock on hillslopes and did not discharge into small streams, but instead fed surface flow into a larger downstream catchment. A review of previous nested studies demonstrated three spatial patterns for specific discharge: Specific discharge may increase or decrease with catchment area, or it may be independent of area. An increase in specific discharge with area was observed only in catchments with permeable bedrock, which implies that such an increase is a useful indicator of the importance of the bedrock flow path to mountain watershed storage. The pattern of relationships between catchment area and specific discharge can be used to assess the storage and discharge properties of mesoscale catchments when the processes driving each pattern have been clarified.

Factors characterizing phosphate oxygen isotope ratios in river water: an inter-watershed comparison approach

We compared the oxygen isotope ratio of dissolved phosphate $$\left( {\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }} } \right)$$ in two rivers with different land-cover and geological features (Ado River and Yasu River) within Lake Biwa basin, central Japan, to explore what factor primarily characterizes the $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ . Mean values of $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ in river water were 19.0 ± 2.4‰ (n = 7) in Ado River and 13.1 ± 2.3‰ (n = 15) in Yasu River, which were significantly different. Comparisons of $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ between river water and potential sources of phosphate revealed that in the Ado River, the $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ was similar to that in rocks from the accretionary complex and decreased with increasing sedimentary rock coverage. In the Yasu River, the $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ was low in the upper forested areas, but increased with paddy field coverage. These results demonstrate that river $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ strongly reflects inputs from geological substances, but is also impacted by land-use activities and varies with anthropogenic land coverage in the watershed. Thus, river $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ relates to land or bedrock coverage differentially in each river. Regression analysis showed that residuals of the $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ tended to converge to zero with increasing drainage area, suggesting that river $$\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}$$ more explicitly reflects land-cover and geological features on a larger watershed scale.

Quantifying the Distribution and Diversity of Fish Species Along Elevational Gradients in the Weihe River Basin, Northwest China

In this study, species compositions, distributions, and diversity patterns of fish assemblages were investigated at 50 sampling sites in the Weihe River and its two largest tributaries, the Jinghe River and the Beiluo River, under high- and low-flow conditions in 2017. For every condition tested and in the all rivers tested, Cyprinidae was the richest family, containing 17 of the 39 identified fish species. Carassius auratus was the most common species, accounting for 11.3% of the total individuals. Nonmetric multidimensional scaling (NMDS), analysis of similarities (ANOSIM), and similarity percentage analysis (SIMPER) revealed that fish species composition differed significantly among rivers (p < 0.05), with dissimilar species assemblages found in the different rivers. Variation was influenced by a combined effect of habitat conditions, environmental factors, and human impact. Canonical correspondence analysis (CCA) identified variables explaining the variation in fish species (p < 0.05), and elevation contributed the most under both flow conditions. Alpha diversity decreased with increasing elevation within rivers as a result of changing environmental conditions, especially for wetted width. Alpha and beta diversities of rivers increased with increasing drainage area, which is related to habitat heterogeneity. The decrease in alpha diversity and the increase in beta diversity with increasing elevation can be explained by variations in habitat and geographic features.

Comparison of discharge pulses in temperate and tropical rainforest headwater stream networks

We use sub-daily gage records from montane headwater channels in the Luquillo Experimental Forest of Puerto Rico (tropical rainforest) and the HJ Andrews Experimental Forest of Oregon (temperate rainforest) to characterize differences in discharge pulses (rapid, high-magnitude discharge fluctuations) and determine whether the characteristics of discharge pulses differ with respect to drainage area between these two regions. The study sites have different precipitation regimes and runoff generation mechanisms, and we quantify differences in discharge pulses between sites. The assessment of discharge pulses, which are defined as flows that are higher than one standard deviation above the historical mean flow at each site, represents a novel approach to characterizing flashy discharge events in headwater streams using high temporal resolution datasets. Our analyses indicate a clear difference between regions, with discharge in the Luquillo streams pulsing more frequently, for shorter periods of time, and at higher magnitudes than discharge in the Andrews streams. We also quantify how discharge pulses change with increasing drainage area at each of the sites. Differences in discharge pulse metrics with respect to drainage area include an increase in the number of pulses, an increase in the normalized magnitude of pulses, an increase in the standard deviation in normalized magnitude, and a decrease in kurtosis with increasing drainage area at the Luquillo site. These results indicate that there is no attenuation of discharge pulses with increasing drainage area at Luquillo. In contrast, there is a decrease in the normalized magnitude with increasing drainage area at the Andrews site, indicating some attenuation of discharge pulses with increasing drainage area. The characteristics of these pulsed events have implications for ecological processes by transporting sediment, biota, and organic matter, likely altering stream substrates, biotic communities, and organic matter retention times.

A generic data-driven technique for forecasting of reservoir inflow: Application for hydropower maximization

A generic and scalable scheme is proposed for forecasting reservoir inflow to optimize reservoir operations for hydropower maximization. Short-term weather forecasts and antecedent hydrological variables were inputs to a three-layered hydrologically-relevant Artificial Neural Network (ANN) to forecast inflow for 7-days of lead-time. Application of the scheme was demonstrated over 23 dams in U.S. with varying hydrological characteristics and climate regimes. Probabilistic forecast was also explored by feeding ANN with ensembles of weather forecast fields. Results suggest forecasting skill improves with decreasing coefficient of variation in inflow and increasing drainage area. Forecast-informed operations were simulated using a rolling horizon scheme and assessed against benchmark control rules. Over two years of operations from Pensacola dam (Oklahoma), additional 47,253 MWh of energy could have been harvested without compromising flood risk with optimal operations. This study reinforces the potential of a numerically efficient and skillful reservoir inflow forecasting scheme to address water-energy security challenges.

Application of liver three-dimensional visualization technologies in the treatment planning of hepatic malignant tumor

Objective: To discuss the application of three dimentional(3D)visualization technologies in treatment plan of hepatic malignant tumor. Methods: The clinical data of 300 patients with liver malignant tumor who received treatment from January 2016 to January 2017 in the Third Department of Hepatic Surgery of Eastern Hepatobiliary Surgery Hospital was retrospectively analyzed in this study, including 221 male and 79 female patients aged from 7 to 76 years with median age of 54 years. The median height was 168 cm (115-183 cm), the median weight was 65 kg (20-105 kg) and the median tumor volume was 142 ml (23-2 493 ml). Three-dimensional visualization technology was used in all patients to reconstruct liver three-dimensional graphics. Also, two and three-dimensional methods were taken respectively to evaluate patients and develop treatment strategy. The change of treatment strategy caused by 3D evaluation, actual surgical plan, operation time, time of hepatic vascular occlusion, intraoperative blood loss, volumes of blood transfusion and postoperative complications was observed. Results: After three-dimensional visualization technology was applied, 75(25%) of 300 patients' treatment strategies had been changed. The range of hepatectomy was extended in 25 patients. And 7 of them were due to hepatic venous variation, which resulted in increasing drainage area. In other 4 patients, liver resections were extended due to lack of perfusion of the liver parenchyma after the removal of portal vein. And hepatectomy was expanded in 14 patients in order to increase the surgical margin. The range of hepatectomy was reduced in 8 patients, 4 of which were due to hepatic venous variation, such as hepatic vein of segment 4 or lower right posterior hepatic vein. The remaining 4 cases were because of insufficient residual liver volume.The surgical resection was performed in 278 cases, 257 of which received operation directly. Left hepatectomy was performed in 24 patients and right hepatectomy was performed in 33 patients. Left trisectionectomy was carried out in 12 patients and right trisectionectomy was carried out in 11 patients. Caudate lobectomy was applied in 10 patients. There were 18 cases of left lateral sectionectomy, 7 cases of right anterior sectionectomy, 25 cases of right posterior sectionectomy and 18 cases of mesohepatectomy. Single or multi segment resection was performed in 99 patients. The treatment strategy of thirty-six patients was converted to staged hepatectomy (ALPPS 11 cases and portal vein embolization 25 cases). The median operation time was 130 minutes (90-360 minutes) and the median inflow blood occlusion time was 20 minutes (0-75 minutes). Median blood loss volume was 200 ml (20-1 600 ml). Thirty-seven of 278 patients received transfusions, and the average red blood transfusion volume was (4.4±1.7)units (0-8 units). Median hepatic resection volume was 530 ml(30-2 600 ml). There were 117 cases of pleural effusion after operation, including 3 patients needing invasive therapy. Ascites occurred in 23 patients, 6 of whom needed invasive therapy. Biliary leakage was observed in 30 patients. Eight patients occurred hepatic cutting surface hemorrhage, 6 of whom received blood transfusion, and 4 of whom underwent laparotomy to stop bleeding. Three patients had pulmonary infection after surgery and 3 patients appeared biliary obstruction. Deep vein thrombosis took place in 2 patients and portal vein thrombosis was observed in 4 patients. No postoperative liver failure and death ever happened in our study group. Conclusion: Three-dimensional visualization technique can optimize the treatment strategy of patients with liver malignant tumor, improve surgical safety.

Seasonal and animal farm size influences on in-stream phosphorus transport in an agricultural watershed

Excess phosphorus (P) is generally responsible for the eutrophication of Midwestern surface waters and causes algal blooms, fish kills, and other detrimental ecological effects. In-stream transport of dissolved and particulate P (PP), under both stormflow and baseflow conditions, was studied in an agricultural Wisconsin watershed with diverse sizes of animal farm operations. Trends in P losses were compared both on an individual event and seasonal (spring, summer, fall) basis. In-stream P transport was characterized by high PP losses in the spring during periods of relatively little crop cover and high dissolved P losses in the fall, when surface coverage was still present. The majority of P (64–71%) was transported in the spring season during periods of high flow. Presence of high animal density at lower portions of the watershed resulted in increasing downstream P concentration and load (i.e., concentration dilution effects with increasing drainage area were absent). The baseflow TP concentrations were always above the USEPA eutrophication threshold [Ecoregion VII, level III-53: 0.08 mg L−1; (USEPA in Ambient water quality criteria recommendations. Information supporting the development of state and tribal nutrient criteria. Rivers and stream in nutrient ecoregion VII. EPA 822-B-00-018. https://www.epa.gov/sites/production/files/documents/rivers7.pdf, 2000)]. While upland conservation practices are necessary for non-point source pollution control, it is important to ensure that these practices afford protection during the spring time periods when agricultural fields are most vulnerable for offsite movement of sediments and associated constituents.

Stream Temperature Spatial Variability Reflects Geomorphology, Hydrology, and Microclimate: Navarro River Watershed, California

Stream temperatures are critical to coldwater fish and vary with microclimate, geomorphology, and hydrology, including influx of groundwater. Spatial variability of stream temperatures was examined at reach and watershed scales within the 816 km2 Navarro River watershed in California. Field monitoring and numerical modeling illustrate that stream temperatures were highest at sites with high solar incidence (low shading and wide streams), long travel times, and low discharge. Microclimate helps explain deviation from the general pattern of streams warming with increasing drainage area. Reach-scale field observations of channel width and groundwater influx explain variation in stream temperatures not captured by watershed-scale models.

Variability in isotopic composition of base flow in two headwater streams of the southern Appalachians

AbstractWe investigated the influence of hillslope scale topographic characteristics and the relative position of hillslopes along streams (i.e., internal catchment structure) on the isotopic composition of base flow in first‐order, forested headwater streams at Coweeta Hydrologic Laboratory. The study focused on two adjacent forested catchments with different topographic characteristics. We used stable isotopes (18O and 2H) of water together with stream gauging and geospatial analysis to evaluate relationships between internal catchment structure and the spatiotemporal variability of base flow δ18O. Base flow δ18O was variable in space and time along streams, and the temporal variability of base flow δ18O declined with increasing drainage area. Base flow became enriched in 18O moving along streams from channel heads to catchment outlets but the frequency of enrichment varied between catchments. The spatiotemporal variability in base flow δ18O was high adjacent to large hillslopes with short flow paths, and it was positively correlated with the relative arrangement of hillslopes within the catchment. These results point to influence of unique arrangement of hillslopes on the patterns of downstream enrichment. Spatial variability in base flow δ18O within the streams was relatively low during dry and wet conditions, but it was higher during the transition period between dry and wet conditions. These results suggest that the strength of topographic control on the isotopic composition of base flow can vary with catchment wetness. This study highlights that topographic control on base flow generation and isotopic composition is important even at fine spatial scales.

Paleotopographic controls on loess deposition in the Loess Plateau of China

AbstractThe underlying pre‐existing paleotopography directly influences the loess deposition process and shapes the morphology of current loess landforms. An understanding of the controlling effects of the underlying paleotopography on loess deposition is critical to revealing the mechanism of loess‐landform formation. However, these controlling effects exhibit spatial variation as well as uncertainty, depending on a study's data sources, methodologies and particular research scope. In this study, the geological history of a study area in the Loess Plateau of China that is subject to severe soil erosion is investigated using detailed geological information and digital elevation models (DEMs), and an underlying paleotopographic model of the area is constructed. Based on the models of modern terrain and paleotopography, we introduce a watershed hierarchy method to investigate the spatial variation of the loess‐landform inheritance relationship and reveal the loess deposition process over different scales of drainage. The landform inheritance relationships were characterized using a terrain‐relief change index (TRCI) and a bedrock terrain controllability index (BTCI). The results show that the TRCI appears to have an inverse relationship with increasing research scope, indicating that, compared with the paleotopography of the region, modern terrain has lower topographic relief over the entire area, while it has higher topographic relief in the smaller, local areas. The BTCI strengthens with increasing drainage area, which demonstrates a strong controlling effect over the entire study area, but a weak effect in the smaller, local areas because of the effect of paleotopography on modern terrain. The results provide for an understanding of the spatial variation of loess deposition in relation to paleotopography and contribute to the development of a process‐based loess‐landform evolution model. Copyright © 2015 John Wiley & Sons, Ltd.

Distribution and biophysical processes of beaded streams in Arctic permafrost landscapes

Abstract. Beaded streams are widespread in permafrost regions and are considered a common thermokarst landform. However, little is known about their distribution, how and under what conditions they form, and how their intriguing morphology translates to ecosystem functions and habitat. Here we report on a circum-Arctic survey of beaded streams and a watershed-scale analysis in northern Alaska using remote sensing and field studies. We mapped over 400 channel networks with beaded morphology throughout the continuous permafrost zone of northern Alaska, Canada, and Russia and found the highest abundance associated with medium to high ground-ice content permafrost in moderately sloping terrain. In one Arctic coastal plain watershed, beaded streams accounted for half of the drainage density, occurring primarily as low-order channels initiating from lakes and drained lake basins. Beaded streams predictably transition to alluvial channels with increasing drainage area and decreasing channel slope, although this transition is modified by local controls on water and sediment delivery. The comparisons of one beaded channel using repeat photography between 1948 and 2013 indicate a relatively stable landform, and 14C dating of basal sediments suggest channel formation may be as early as the Pleistocene–Holocene transition. Contemporary processes, such as deep snow accumulation in riparian zones, effectively insulate channel ice and allows for perennial liquid water below most beaded stream pools. Because of this, mean annual temperatures in pool beds are greater than 2 °C, leading to the development of perennial thaw bulbs or taliks underlying these thermokarst features that range from 0.7 to 1.6 m. In the summer, some pools thermally stratify, which reduces permafrost thaw and maintains cold-water habitats. Snowmelt-generated peak flows decrease rapidly by two or more orders of magnitude to summer low flows with slow reach-scale velocity distributions ranging from 0.01 to 0.1 m s−1, yet channel runs still move water rapidly between pools. The repeating spatial pattern associated with beaded stream morphology and hydrological dynamics may provide abundant and optimal foraging habitat for fish. Beaded streams may create important ecosystem functions and habitat in many permafrost landscapes and their distribution and dynamics are only beginning to be recognized in Arctic research.

Effective run‐off flow length over biological soil crusts on silty loam soils in drylands

AbstractSurface hydrological behaviour is important in drylands because it affects the distribution of soil moisture and vegetation and the hydrological functioning of slopes and catchments. Microplot scale run‐off can be relatively easily measured, i.e. by rainfall simulations. However, slope or catchment run‐off cannot be deduced from microplots, requiring long‐time monitoring, because run‐off coefficients decrease with increasing drainage area. Therefore, to determine the slope length covered by run‐off (run‐off length) is crucial to connect scales. Biological soil crusts (BSCs) are good model systems, and their hydrology at slope scale is insufficiently known. This study provides run‐off lengths from BSCs, by field factorial experiments using rainfall simulation, including two BSC types, three rain types, three antecedent soil moistures and four plot lengths. Data were analysed by generalized linear modelling, including vascular plant cover as covariates. Results were the following: (i) the real contributing area is almost always much smaller than the topographical contributing area; (ii) the BSC type is key to controlling run‐off; run‐off length reached 3 m on cyanobacterial crust, but hardly over 1 m on lichen crust; this pattern remained through rain type or soil moisture; (iii) run‐off decreased with BSC development because soil sealing disappears; porosity, biomass and roughness increase and some changes occur in the uppermost soil layer; and (iv) run‐off flow increased with both rain type and soil moisture but run‐off coefficient only with soil moisture (as larger rains increased both run‐off and infiltration); vascular plant cover had a slight effect on run‐off because it was low and random. Copyright © 2014 John Wiley & Sons, Ltd.

Scale dynamics of extensive green roofs: Quantifying the effect of drainage area and rainfall characteristics on observed and modeled green roof hydrologic performance

Green roofs offer many benefits for dense urban environments, one of which is their potential to supplement existing stormwater management infrastructure. The ability of green roof systems to act as a decentralized rainwater retention and detention network has been the topic of many recent studies. While these studies have provided important insight into the hydrologic performance of green roofs, none to date, to the knowledge of the authors, have specifically examined the effect of green roof drainage area on system performance in an urban climate. This research aims to understand how rainfall characteristics and green roof scale impact the peak and cumulative volume of green roof runoff during individual storm events. The performance of three extensive green roofs in New York City, each having the same engineered components and age but different drainage areas, is analyzed. It is found that green roof drainage area has the greatest impact on peak runoff reduction – peak runoff reduction increases with increasing drainage area – whereas rainfall retention and the time to peak runoff are not greatly influenced by drainage area. Data collected from the three green roofs are used to examine the applicability of a one-dimensional infiltration model, HYDRUS-1D, in predicting hydrologic behavior across the different green roof spatial scales. It is found that model performance improves as the green roof drainage area and rainfall volume increases. However, in general, HYDRUS-1D is only partially able to capture the hydrologic behavior of extensive green roofs across the different rooftop scales examined during this study.

The contribution of mountains to global denudation

The hypothesis that mountains infl uence global climate through links among rock uplift, physical and chemical denudation, and the carbon cycle remains vigorously debated. We address the contribution of mountains to global denudation with an empirical model that predicts that >50% of the total denudation and 40% of the chemical denudation occur on the steepest ~10% of Earth’s terrestrial surface. These fi ndings contrast with those from a recent study that suggested global-scale denudation occurs primarily on gently sloping terrain, but did not account for the infl uence of digital elevation model resolution on modeled denudation rates. Comparison of calculated denudation rates against the sum of measured sediment and solute yields from 265 watersheds indicates a positive correlation (R 2 = 0.44) with order-ofmagnitude variability refl ecting, among other things, the effects of dams and agriculture. In addition, ratios of measured river yield to modeled denudation rate decline as catchment area increases due to progressively greater sediment storage with increasing drainage area. Our results support the conclusion that the small mountainous fraction of Earth’s surface dominates global denudation and the fl ux of sediment and solutes to oceans.