Surface Hydrological Connectivity Research Articles

Deciphering the interplay between tectonic and climatic forces on hydrologic connectivity in the evolving landscapes

The intricate interplay between climate and tectonics profoundly shapes landscapes over time frames surpassing 10 million years. Active tectonic processes and climatic shifts unsettle established drainage systems, instigating fragmentation or amalgamation of watersheds. These activities yield substantial transformation in surface hydrologic connectivity, thereby underlining the profound influence of these tectonic and climatic forces on the evolution of both landscape and hydrology. Such transformations within the hydrological landscape have direct implications for the evolution of aquatic species. As connections among aquatic habitats undergo reconfiguration, they incite shifts in species distribution and adaptive responses. These findings underscore the role of tectonics and climate in not only sculpting the physical landscape but also steering the course of biological evolution within these dynamically changing aquatic ecosystems relying on hydrologic connections. Despite the significance of these interactions, scholarly literature seldom examines alterations in hydrologic connectivity over tectonic, or orogen-scale, timescales. This study aims to bridge this gap, exploring changes in hydrologic connectivity over extended periods by simulating a continental rift system akin to the Rio Grande Rift, USA, subject to various tectonoclimatic scenarios. Multiple rift basins hosting large lakes, brought into existence by active tectonic extension, are further molded by tectonic extension and post-rift climatic changes. The study focuses on phenomena such as interbasin river breakthroughs and knickpoint generation, assembling a time-series of connectivity metrics based on stream network characteristics such as flow rate, flow distance, and captured drainage areas. We anticipate that the insights gleaned from this study will enhance our comprehension of the enduring impact of tectonic and climate processes on hydrologic connectivity and the subsequent evolution of aquatic species.

Lithospheric Flexure Controls on Geomorphology, Hydrology, and River Chemistry in the Andean Foreland Basin

AbstractTectonics exerts a strong control over the morphology of Earth's surface that is apparent in active mountain belts. In lowland areas, subtle processes like lithospheric flexure and isostatic rebound can impact Earth surface dynamics, hydrologic connectivity, and topography, suggesting that geomorphic and hydrologic analyses can shed light on underlying lithospheric properties. Here we examine the effect of lithospheric flexure on the geomorphology, hydrology, and river water chemistry of the Rio Bermejo fluvial system in the east Andean foreland basin of northern Argentina. Results show that proximal to the mountain front, foredeep basin subsidence causes sedimentation along a braided channel belt that is superelevated relative to the surrounding flood basin. During floods, water flows from the superelevated channel into the groundwater reservoir, causing a net loss of discharge with distance downstream. Further downstream, forebulge uplift forces channel narrowing, high lateral migration rates, and incision up to 13 m into older river deposits. This incision locally allows groundwater flow into the river, causing a ∼20% increase in river solute load. Groundwater emerges from the forebulge into the backbulge, predominantly as spring‐fed channels. Here, channel migration rates decrease, suggesting a switch from net uplift to subsidence that reduces the depth to the groundwater table. This analysis shows that subtle lithospheric flexure can have significant effects on river channel morphology that determine hydrologic flow paths, and ultimately influence geochemical and ecological patterns. We suggest that these effects may elucidate lithospheric properties that are otherwise inferred from bulk geophysical observations.

Selecting and refining suitable methods of developing digital elevation models to represent geomorphic features and characteristics of smaller wetlands in data-scarce environments

Land surface geomorphology plays an important role in water and sediment dispersal processes in wetlands. For wetland practitioners and researchers to engage with these processes in time and space, they require topographic data in order to derive wetland surface gradient, cross-sectional shape and area, surface and subsurface hydrological connectivity, and hydraulic characteristics. A range of data options, with varying spatial resolutions, are available, ranging from free national and global resources (e.g. contour data and global elevation models) to project-specific high-resolution surveys (e.g. Differential Global Positioning Systems (DGPS), Photogrammetry, Light Detection And Ranging (LiDAR)). Due to the scarcity of high-resolution and high-accuracy data, especially in developing countries, data gathering and processing costs can be significant. This paper presents a commentary on a range of topographic data and processing options for a relatively small (~ 40 ha) floodplain wetland in the Eastern Cape, South Africa. It critically reviews the usefulness and shortfalls of various wetland-related applications ranging from gradient calculations to more detailed hydraulic modelling, and the data resolution required for each application. Free, low-resolution, datasets have a limited representation of geomorphology at this scale due to the relatively low-resolution and large vertical error. Field-based surveys (using survey-grade equipment such as a DGPS) have the benefit of providing accurate terrain results in areas with dense vegetation and surface water, while photogrammetry and LiDAR data are useful to represent the higher resolution morphology across the wetland, despite shortcomings regarding the penetration of dense vegetation and surface water. However, combining DGPS data with LiDAR proves to yield the best model for detailed process modelling for wetlands at the local scale.

Refining the concept of hydrological connectivity for large floodplain systems: Framework and implications for eco-environmental assessments

Recent years, the hydrological connectivity has gained popularity in various research fields, however, its definition and threshold effects at a system scale have not received adequate attention. The current research proposes a promising framework to refine the concept of surface hydrological connectivity by combining hydrodynamic modeling experiments, threshold effects and geostatistical connectivity analysis, exemplified by the flood-pulse-influenced Poyang Lake floodplain system (China). To enhance the inherent linkage between hydrological connectivity and eco-environments, total connectivity (TC), general connectivity (GC), and effective connectivity (EC) were proposed to refine the metrics of hydrological connectivity. The results show that substantial differences between the three connectivity metrics are observed for all target directions, demonstrating that the joint role of water depth and flow velocity may produce more dynamic and complex influences on EC than the other two metrics of TC and GC. Topographically, the connectivity objects/areas within the flood pulse system reveal that the floodplain is a more sensitive area than the lake's main flow channels under different connectivity conditions. The modelling experimental studies show that variations in water depth thresholds are more likely to have a strong effect on connectivity for the dry, rising, and falling limbs, rather than the flooding period, while the flow velocity may exert an opposite threshold effect. The lake-floodplain system is characterized by a dynamic threshold behavior, with seasonally varying water depth and velocity thresholds. This study highlights the importance of redefined connectivity concept for facilitating scientific communication by combining hydrodynamic thresholds and offering recommendations for future connectivity assessments using our proposed metrics of TC, GC, and EC.

Integrating the JRC Monthly Water History Dataset and Geostatistical Analysis Approach to Quantify Surface Hydrological Connectivity Dynamics in an Ungauged Multi-Lake System

Determining the dynamics of surface hydrological connectivity in a landscape of multiple lakes with different sizes and depths is challenging. This is especially the case for ungagged, large areas of multi-lake systems. Integrated use of remote sensing and geostatistical analysis can be a useful approach for developing metrics that can be used to identify the hydrological connectivity and their changes. In this study, we conducted a geostatistical analysis of 18 wet and dry binary state rasters derived from Landsat images over a large ungauged multi-lake system, the Momoge National Nature Reserve in Northeast China. Our goal was to investigate applicability and dynamics of three surface hydrological connectivity metrics, namely, geostatistical connectivity function (GCF), maximum distance of connection (MDC), and surface water extent (SWE) of the top 10 largest connectomes (i.e., seasonally connected water bodies). We found that, during a dry year, the reduction rate of the GCF curve was slower along the west–east (W–E) direction than along the north–south (N–S) direction, which was contrary to the patterns exhibited in a normal or wet year. The minimum values of the MDC in W–E and N–S directions in the dry year were 22.4 km and 6.3 km, respectively, while the maximum values of the MDC along the above two directions in the wet year were 50.7 km and 65.1 km, respectively. The components and spatial distribution of the top 10 largest connectomes changed dramatically in different months of each hydrological year, resulting in a huge change in the monthly SWE of the top 10 largest connectomes. Overall, this study validated the usefulness of combining remote sensing image analysis with geostatistical methods to quantify the surface hydrological connectivity from different perspectives in an ungauged area. The approach may be applicable to studies in other geographical regions, to guide water resources and wetland management practices.

Quantitative assessment of surface hydrological connectivity in Momoge National Nature Reserve, Northeast China

Quantitative assessment of hydrological connectivity is a hot but difficult issue in current research. Using the 30-m resolution global monthly surface water remote sensing dataset released by the EU Joint Research Center and three indicators of geostatistical connectivity, maximum distance of connection (MDC), and surface water extent of connectome (i.e., seasonally connected water bodies), we quantified the hydrological connectivity of surface water in Momoge National Nature Reserve in different months of a normal year (May to October 2016), and in September of different hydrological years (a wet year, namely 1998; a normal year, namely 2016; a drought year, namely 2002), and different directions (west-east and north-south). Our results showed that: 1) the geostatistical connectivity function (GCF) along the west-east direction was better than that along the north-south direction. The GCF in August and July was better than that in other months. The GCF along the west-east direction of each hydrological year was better than that in the drought year, whereas the GCF in the drought year was better than the corresponding value in the normal year. The GCF along the north-south direction in each hydrological year was better than that in the normal year, whereas the GCF in the normal year was better than that in the drought year. The MDC along the west-east direction in June, July, September, and October of the normal year was all concentrated at 25.26 km. MDC was more concentrated along the north-south direction, with 10 km for all months. The MDC in the normal and drought years was relatively close, but both were much smaller than that in the wet year. 2) frequent seasonal connections between the Yuelianghu Reservoir and the Nenjiang River, and between Etoupao and its neighboring lakes occurred in the study area during the normal year, while most of the other lakes remained isolated. The patterns of hydrological connection in the study area differed across different hydrological years: two giant connectomes were formed in the wet year, some lakes are periodically connected in the normal year, and all lakes remain isolated in the drought year. 3) As a drainage area for farmland receding water, the surface water extent of the Etoupao connectome increased visibly during the three water supplement seasons (spring, summer, and autumn). By quantifying the surface hydrological connectivity in Momoge National Nature Reserve with multiple water sources from different perspectives, our results provide a scientific basis for wetland protection and restoration and integrated management of watershed water resources.

New insights on the surface hydrological connectivity of water depth thresholds in a flood-pulse-influenced floodplain system (Poyang Lake, China)

Knowledge of hydrological connectivity and its threshold behaviors plays an important role in sustaining and managing floodplains; however, threshold behaviors at a system scale have not received adequate attention. This study used a geostatistical connectivity method in combination with hydrodynamic modeling experiments to provide new insights on the surface hydrological connectivity of water depth thresholds in a flood-pulse-influenced floodplain system (Poyang Lake, China). The results reveal that hydrological connectivity is more sensitive to changes in water depth during dry, rising, and receding water phases than in the flooding phase under different depth thresholds. Geographically, the connectivity patterns show that large water bodies are mainly distributed in the main lake and floodplain river channels; extensive floodplain areas are dynamically connected to the main lake, indicating that the lake's floodplain is a sensitive area of the flood pulse system. From a systemic perspective, the surface water connectivity exhibits abrupt changes under the depth threshold of around 50 cm, demonstrating a rapid system response to the threshold value. In the floodplains of Poyang Lake, surface topography and flood pulse dynamics play a combined role in affecting hydrological connectivity, especially low and intermediate connectivity. The filling-spilling process generally extends from the lower-lying main lake and floodplain rivers to the upper-lying floodplains of the lake. The current work quantifies the influences of depth thresholds on surface hydrological connectivity to pave the way for performing a joint assessment of hydrological connectivity and ecological responses based on developing comprehensive modellings in threshold-affected floodplains.

Assessment of Surface Hydrological Connectivity in an Ungauged Multi-Lake System with a Combined Approach Using Geostatistics and Spaceborne SAR Observations

Connectivity metrics for surface water are important for predicting floods and droughts, and improving water management for human use and ecological integrity at the landscape scale. The integrated use of synthetic aperture radar (SAR) observations and geostatistics approach can be useful for developing and quantifying these metrics and their changes, including geostatistical connectivity function (GCF), maximum distance of connection (MDC), surface water extent (SWE), and connection frequency. In this study, we conducted a geostatistical analysis based on 52 wet and dry binary state (i.e., water and non-water) rasters derived from Sentinel-1 A/B GRD products acquired from 2015 to 2019 for China’s Momoge National Nature Reserve to investigate applicability and dynamics of the hydrologic connectivity metrics in an ungauged (i.e., data such as flow and water level are scarce) multi-lake system. We found: (1) generally, the change of GCF in North–South and Northeast–Southwest directions was greater than that in the West–East and Northwest–Southeast directions; (2) MDC had a threshold effect, generally at most 25 km along the W–E, NW–SE and NE–SW directions, and at most 45 km along the N–S direction; (3) the flow paths between lakes are diverse, including channelized flow, diffusive overbank flow, over-road flow and “fill-and-merge”; (4) generally, the values of the three surface hydrological connectivity indicators (i.e., the MDC, the SWE, and the conneciton frequency) all increased from May to August, and decreased from August to October; (5) generally, the closer the distance between the lakes, the greater the connection frequency, but it is also affected by the dam and road barrier. The study demonstrates the usefulness of the geostatistical method combining Sentinel-1 SAR image analysis in quantifying surface hydrological connectivity in an ungagged area. This approach should be applicable for other geographical regions, in order help resource managers and policymakers identify changes in surface hydrological connectivity, as well as address potential impacts of these changes on water resources for human use and/or ecological integrity at the landscape level.

Integrated factor analysis of water level variation in geographically isolated ponds.

Small geographically isolated ponds provide a multitude of ecological functions and services, but water table fluctuations alter the magnitude of these services. Understanding temporal and spatial changes of surface water levels in the watershed, and their spatial variability, is critical for restoration and protection of small ponds. A biweight spatial consistency test was employed to quantify the seasonal variability of surface water tables for 50 ponds and hydrological connectivity models, and land use metrics, topographic characteristics, and irrigation needs, for groundwater, were introduced into the model to identify influencing factors. The spatial difference of water level changes in the rice season was greater than the wheat season while water table increased in the wheat season and declined in the rice season. Continuous runoff with complete surface hydrological connectivity of ponds, which was strongly related to precipitation, occurred only one time during the study period. Water level dynamics were largely uncorrelated to surface hydrological connectivity but were linked to watershed and pond size. By evaluating irrigation water requirements, irrigation was a primary human management factor affecting the water table changes in ponds. Groundwater also enriched influence factors that estimated water level variation in ponds, and these results will provide support for improved water resource management and ponds protection purposes.

Estimation of water volume in ungauged, dynamic floodplain lakes

Lakes play a crucial role in retaining water and altering biogeochemical processes on floodplains. Existing strategies and algorithms for estimation of water storage are insufficient for dynamic floodplain lakes due to the scarcity of available observations. Combining a time series of open water area with a fine spatial-temporal resolution by integrating Landsat and MODIS observations of Poyang Lake (China) with digital elevation models, and limited gauge data, generated water storage estimates as a function of surface hydrological connectivity. Despite possessing a relatively small portion of Poyang Lake’s water volume, the floodplain lakes occupy a large part of the surface water area, especially in the low water period. Floodplain lakes, in particular, those distributed in the upper delta contribute to relieving drought conditions in Poyang Lake.

A new approach for measuring surface hydrological connectivity

AbstractThe development of surface hydrological connectivity is a key determinant of flood magnitude in drylands. Thresholds in runoff response may be reached when isolated runoff‐generating areas connect with each other to form continuous links to river channels, enabling these areas to contribute to flood hydrographs. Such threshold behaviour explains observed nonlinearities and scale dependencies of dryland rainfall–runoff relationships and complicates attempts at flood prediction. However, field methods for measuring the propensity of a surface to transmit water downslope are lacking, and conventional techniques of infiltration measurement are often inappropriate for use on non‐agricultural drylands. Here, we argue for a reconceptualization of the dryland surface runoff process, suggesting that the downslope transfer of water should be considered alongside surface infiltration; that is, there is a need for the “aggregated” measurement of infiltration and overland flow hydraulics. Surface application of a set volume of water at a standardized rate generates runoff that travels downslope; the distance it travels downslope is determined by infiltration along the flow, integration of flow paths, and flow resistance. We demonstrate the potential of such a combined measurement system coupled with structure‐from‐motion photogrammetry to identify surface controls on runoff generation and transfer on dryland hillslopes, with vegetation, slope, surface stone cover, and surface roughness all having a significant effect. The measurement system has been used on slopes up to 37° compared with the flat surface typically required for infiltration methods. On average, the field workflow takes ~10–15 min, considerably quicker than rainfall simulation. A wider variety of surfaces can be sampled with relative ease, as the method is not restricted to stone and vegetation‐free land. We argue that this aggregated measurement represents surface connectivity and dryland runoff response better than standard hydrological approaches and can be applied on a much greater variety of dryland surfaces.

Assessment of water storage response to surface hydrological connectivity in a large floodplain system (Poyang Lake, China) using hydrodynamic and geostatistical analysis

Floodplains play a significant role in affecting the transport of water, dissolved matter and sediments during wide-ranging drying and wetting. This study uses a hydrodynamic model and geostatistical method to explore the variations of water storage and its relationship with the surface hydrological connectivity, exemplified by the large Poyang Lake-floodplain system (in China). The simulations show that the floodplain storage exhibits largely similar behavior to that of the total lake water storage, but the water storage in the main lake is distinctly higher than the floodplains. The lake storage is estimated to be from 20 × 108 to 163 × 108 m3 and differs considerably between seasons, and the contribution of the floodplain to the total lake storage varies from 18 to 34%. Geostatistical analysis reveals that the degree of surface hydrological connectivity can be classified as high connectivity in summer, low connectivity in winter, and intermediate connectivity during other seasons. Higher variability of water storage and lower frequency of hydrological connectivity are found in the seasonal floodplains, whereas the lower variability and higher frequency are observed in the main lake, indicating that water storage is inextricably linked to the dynamic behaviors of surface hydrological connectivity. Additionally, the estimated water storage significantly increases from the low and intermediate conditions to the high connectivity condition, mainly due to the key process of the west–east connectivity in controlling lake-floodplain interactions. This study improves understanding of Poyang Lake floodplain behavior and other similar floodplain systems by providing knowledge of water balance, water allocation and water management.

The role of a seasonal lake groups in the complex Poyang Lake-floodplain system (China): Insights into hydrological behaviors

Seasonal lakes that exist in floodplain settings have significant effects on hydrological and ecological processes and are highly susceptible to various changes; however, they are rarely investigated, mainly because of the large extent and remoteness of floodplains. This study uses physically based hydrodynamic modeling in combination with a bathymetry adjustment approach to investigate the coupling effects of 77 seasonal lakes (defined as the seasonal lake group) on hydrological behaviors within the Poyang Lake-floodplain system (China) from a systemic perspective. Elucidation of the role of seasonal lake groups could benefit from hydrodynamic modeling, which enables complex lake-floodplain simulations and comparison analyses of natural (original bathymetry) and hypothetical conditions (adjusted bathymetry). In the present study, the simulation results showed that the temporal influences of the seasonal lake group on water levels, lake outflows, and inundation dynamics were greater during dry seasons than wet seasons for both the dry (2006) and wet years (2010). The spatial effects of the seasonal lake group on the hydrology of the lake’s floodplains were stronger than those of the main lake for both hydrological years. The findings demonstrate that the seasonal lakes are likely to have very limited effects on the main lake and the associated flood levels. On average, the role of the seasonal lake group during the dry seasons was around several times stronger than that during flood seasons in terms of the magnitudes of hydrological responses. Additionally, it is expected that the seasonal lake group may exert an important role in influencing the surface hydrological connectivity and associated dry-wet hydrological shift across lake-floodplains, indicating a dominant role of the floodplain bathymetry changes. Overall, the results of this study will support management and planning of Poyang Lake and other similar floodplain regions with numerous small, shallow, and seasonal lakes by providing more reliable information regarding bathymetry changes, water management and lake-floodplain interactions to decision-makers for improved floodplain protection strategy.

Exploring the contribution of precipitation to water within the active layer during the thawing period in the permafrost regions of central Qinghai-Tibet Plateau by stable isotopic tracing

Stable isotopic tracing has proven to be a useful tool for assessing surface water source dynamics and hydrological connectivity in permafrost regions. This study has investigated the contribution of precipitation to water within the active layer at three long-term observation sites, including Fenghuoshan (FHS), Hoh Xil (KKXL) and Wudaoliang (WDL), by using isotopic tracer technique and two-component mixing model. The results showed that precipitation was the predominant source for water within the active layer, permafrost and ground ice near permafrost table at the three sites. Precipitation in August was the predominant source for water within the active layer at FHS, and precipitation in September was the main source at KKXL and WDL. The variation of isotopic values at different levels indicated that the water sources within the active layer could vary as the depth increases. The evaporation fractionation of water within the active layer at WDL was noticeable at depths of 0–50 cm, and the evaporation intensity decrease gradually from late June to late September. The relationship of isotopic tracing values between precipitation and water within the active layer at depths of 0–50 cm becomes more significant as the amount of the recently-occurring precipitation increases. Moreover, the relatively higher d-excess in precipitation indicates that local recycled moisture has greater contribution to precipitation. The differences of d-excess in most water within the active layer, permafrost and ground ice near permafrost table revealed that there were isotopic fractionation when precipitation supplying to above-mentioned three water bodies. The precipitation event amounted to 8.1 mm at KKXL can exert 49% ± 7.1% and 30.8% ± 3.6% contribution to water within the active layer at depths of 0–10 cm and 10–20 cm, respectively. While the long-period contribution cannot be identified because of the impact of evaporation. The results would provide new insights into the contribution of precipitation to water within the active layer on the QTP, which is also helpful to improve process-based hydrological models in the permafrost regions.

Hydrodynamic investigation of surface hydrological connectivity and its effects on the water quality of seasonal lakes: Insights from a complex floodplain setting (Poyang Lake, China)

Small, seasonal lakes that exist in floodplains are rarely investigated, and yet they play an important role in the protection of biodiversity and are highly susceptible to modification due to human activities. This study presents a first attempt to combine hydrodynamic modeling and statistical methods to investigate hydrological connectivity and its relationship with the water quality of nine seasonal lakes within the floodplains of Poyang Lake (China). The hydrodynamic model reproduced reasonably well the hydrological regime of the lake and surrounding floodplains, based on field measurements and remote sensing data. Floodplain lakes exhibit similar water-level dynamics to the main lake during connected periods of flooding, while they decouple from the main lake during recession periods. Geostatistical results reveal that although the north-south hydrological connectivity extends over a longer pathway than the west-east connectivity, the rapid reduction in the west-east connectivity indicates a more sensitive response. The west-east connectivity tends to play a dominant role in affecting the interactions between the main lake and floodplains, as expected. Statistical methods indicate that surface hydrological connectivity across the floodplain results in an enhanced spatial similarity in the water quality of the floodplain lakes, in terms of a multitude of water quality parameters (TN, TP, NH4+-N, NO3−-N, NO2−-N, PO43−, CODMn, and Chl a), while surface hydrological isolation was observed to increase the water quality differences between the seasonal lakes. Additionally, enhanced hydrological connectivity may lead to improved water quality of the seasonal lakes from low connectivity to high connectivity condition. Hydrological connectivity may be a key factor controlling the dynamics in water quality between seasonal lakes. The findings of this study support the management of both Poyang Lake and the floodplain wetlands by providing important information on both water resource and water quality, and proposals to better manage the impacts of intensive human activities.

Coupling hysteresis analysis with sediment and hydrological connectivity in three agricultural catchments in Navarre, Spain

Rain storm events mobilise large proportions of fine sediments in catchment systems. Sediments from agricultural catchments are often adsorbed by nutrients, heavy metals and other (in)organic pollutants that may impact downstream environments. To mitigate erosion, sediment transport and associated pollutant transport, it is crucial to know the origin of the sediment that is found in the drainage system, and therefore, it is important to understand catchment sediment dynamics throughout the continuity of runoff events. To assess the impact of the state of a catchment on the transport of fine suspended sediment to catchment outlets, an algorithm has been developed which classifies rain storm events into simple (clockwise, counter-clockwise) and compound (figure-of-eight; complex) events. This algorithm is the first tool that uses all available discharge and suspended sediment data and analyses these data automatically. A total of 797 runoff events from three experimental watersheds in Navarre (Spain) were analysed with the help of long-term, high-resolution discharge and sediment data that was collected between 2000 and 2014. Morphological complexity and in-stream vegetation structures acted as disconnecting landscape features which caused storage of sediment along the transport cascade. The occurrence of sediment storage along transport paths was therefore responsible for clockwise hysteresis due to the availability of in-stream sediment which could cause the “first flush” affect. Conversely, the catchment with steeper channel gradients and a lower stream density showed much more counter-clockwise hysteresis due to better downstream and lateral surface hydrological connectivity. In this research, hydrological connectivity is defined as the actual and potential transfer paths in a catchment. The classification of event SSC-Q hysteresis provided a seasonal benchmark value to which catchment managers can compare runoff events in order to understand the origin and locations of suspended sediment in the catchment. A new algorithm uses all available discharge and suspended sediment data to assess catchment sediment dynamics. From these analyses, the catchment connectivity can be assessed which is useful to develop catchment land management.

Efficient Delineation of Nested Depression Hierarchy in Digital Elevation Models for Hydrological Analysis Using Level-Set Methods.

In terrain analysis and hydrological modeling, surface depressions (or sinks) in a digital elevation model (DEM) are commonly treated as artifacts and thus filled and removed to create a depressionless DEM. Various algorithms have been developed to identify and fill depressions in DEMs during the past decades. However, few studies have attempted to delineate and quantify the nested hierarchy of actual depressions, which can provide crucial information for characterizing surface hydrologic connectivity and simulating the fill-merge-spill hydrological process. In this paper, we present an innovative and efficient algorithm for delineating and quantifying nested depressions in DEMs using the level-set method based on graph theory. The proposed level-set method emulates water level decreasing from the spill point along the depression boundary to the lowest point at the bottom of a depression. By tracing the dynamic topological changes (i.e., depression splitting/merging) within a compound depression, the level-set method can construct topological graphs and derive geometric properties of the nested depressions. The experimental results of two fine-resolution Light Detection and Ranging-derived DEMs show that the raster-based level-set algorithm is much more efficient (~150 times faster) than the vector-based contour tree method. The proposed level-set algorithm has great potential for being applied to large-scale ecohydrological analysis and watershed modeling.

Decomposition of 2D polygons and its effect in hydrological models

Abstract 2D non-uniform polygonal meshes allow representation of the impact of landscape elements and small infrastructures on water flows. The initial vectorial mesh, derived from the intersection of several geographical information systems' layers, can have highly non-convex or sliver polygons. These bad-shaped elements compromise accurate numerical flow computation. We propose a flexible divide-and-conquer strategy to decompose polygons into physiographical meaningful parts using shape descriptors to better represent the surface terrain and hydrologic connectivity. We use the convexity index (CI) and the form factor (FF) to consider convex and square like optimum shapes. The strategy was applied to two peri-urban areas whose hydrologic response was simulated using distributed modeling. Good-quality meshes were generated with threshold values of CI≈0.8 and FF≈0.2, and CI≈0.95 and FF≈0.4 for undeveloped and highly urbanized zones, respectively. We concluded that the mesh segmentation facilitates the representation of the spatially distributed processes controlling not only the lumped response of the catchment, but also the spatial variability of water quantity and fluxes within it at medium and small scales.

Landscape metrics as predictors of hydrologic connectivity between Coastal Plain forested wetlands and streams.

Geographically isolated wetlands, those entirely surrounded by uplands, provide numerous landscape‐scale ecological functions, many of which are dependent on the degree to which they are hydrologically connected to nearby waters. There is a growing need for field‐validated, landscape‐scale approaches for classifying wetlands on the basis of their expected degree of hydrologic connectivity with stream networks. This study quantified seasonal variability in surface hydrologic connectivity (SHC) patterns between forested Delmarva bay wetland complexes and perennial/intermittent streams at 23 sites over a full‐water year (2014–2015). Field data were used to develop metrics to predict SHC using hypothesized landscape drivers of connectivity duration and timing. Connection duration was most strongly related to the number and area of wetlands within wetland complexes as well as the channel width of the temporary stream connecting the wetland complex to a perennial/intermittent stream. Timing of SHC onset was related to the topographic wetness index and drainage density within the catchment. Stepwise regression modelling found that landscape metrics could be used to predict SHC duration as a function of wetland complex catchment area, wetland area, wetland number, and soil available water storage (adj‐R 2 = 0.74, p < .0001). Results may be applicable to assessments of forested depressional wetlands elsewhere in the U.S. Mid‐Atlantic and Southeastern Coastal Plain, where climate, landscapes, and hydrological inputs and losses are expected to be similar to the study area.

Using stable isotopes to assess surface water source dynamics and hydrological connectivity in a high-latitude wetland and permafrost influenced landscape

Climate change is expected to alter hydrological and biogeochemical processes in high-latitude inland waters. A critical question for understanding contemporary and future responses to environmental change is how the spatio-temporal dynamics of runoff generation processes will be affected. We sampled stable water isotopes in soils, lakes and rivers on an unprecedented spatio-temporal scale along a 1700 km transect over three years in the Western Siberia Lowlands. Our findings suggest that snowmelt mixes with, and displaces, large volumes of water stored in the organic soils and lakes to generate runoff during the thaw season. Furthermore, we saw a persistent hydrological connection between water bodies and the landscape across permafrost regions. Our findings help to bridge the understanding between small and large scale hydrological studies in high-latitude systems. These isotope data provide a means to conceptualise hydrological connectivity in permafrost and wetland influenced regions, which is needed for an improved understanding of future biogeochemical changes.