Hydraulic Geometry Relationships Research Articles

Development and evaluation of hydraulic geometry relationships for large Brazilian river basins

ABSTRACT River cross-section characteristics are not available for many regions of the world, and they are generally expressed as hydraulic geometry (HG) relationships. These relationships usually represent average characteristics of a region, which can generate biased estimates in smaller basins. Therefore, to improve the representation of river channel geomorphological characteristics, the objective of this study was to use a large database of river cross-section geometries to refine HG relationships for five river basins in Brazil. HG relationships were developed for the entire basins and for hydraulically homogeneous regions, obtained through a geographical convenience method. The relationship between the coefficients of the geometric relationships and morphoclimatic characteristics was assessed, showing a trend between precipitation and slope and the coefficients of the depth relationships. The estimated bankfull width and depth values were also compared to observed data and global datasets, showing an improvement in estimates with the more refined HG relationships.

Monthly hydraulic geometry relationship quantification with environmental LAI by utilizing sentinel data: A case in Jingjiang reach of the Yangtze River

This study presents a novel approach for quantifying the dynamics of monthly hydraulic geometry relationships in the Jingjiang reach of the Yangtze River by integrating leaf area index (LAI) data as an indicator of riparian vegetation. A comprehensive system of ordinary differential equations (ODEs) couples traditional power-law hydraulic geometry equations with LAI, capturing the influence of erosion control on channel morphology. The periodic delayed response theory and automatic differentiation techniques are employed to enhance the modeling framework’s capabilities. Calibration and verification demonstrate the models’ effectiveness in capturing overall trends in discharge, width, and depth dynamics, outperforming traditional constant-parameter approaches. However, model predictive abilities are limited under extreme climate conditions due to training on normal climate data. Key assumptions, including the periodic delayed response theory’s neglect of peak discharges, simplified representation of artificial cut-offs, and reliance on remotely sensed data with limited local validation, introduce uncertainties. The proposed modeling framework shows potential for broader application to other river systems with appropriate adjustments. Future research could incorporate additional environmental factors, integrate models across scales, couple with advanced simulation techniques, and expand stability assessments beyond the riverbed index. By addressing related challenges, this integrated approach lays a foundation for enhancing understanding of river morphodynamics and channel stability.

Hydraulic Geometry and Theory of Equilibrium Water Depth of Branching River

Based on the flow continuity formula, resistance formula, sediment transport capacity formula and width-depth ratio relationship, the hydraulic geometry relationship and theory of equilibrium water depth for a branching river are established and are suitable for arbitrary section shape. The ratio of cross-sectional area of a distributary channel and the main stream is a power function of its bifurcation ratio with an exponent of 6/7. This was applied to a 12.5 m deep-water channel of the Yangtze River (the North Passage, Fujiangsha Waterway and Shiyezhou Waterway). The reliability of the equilibrium water depth was verified and the construction effect of the channel regulation project was predicted. The results show that the regulation project has achieved certain results on the whole, but some waterways still cannot meet the requirement of 12.5 m navigation depth. It is necessary to adjust the layout of the regulation project and focus on increasing the bifurcation ratio and reducing the flow resistance so as to increase the maximum equilibrium water depth.

Historical development of the Regime Geometry Equations, Part-I

The present study intended to review the historical development of the regime geometry equations proposed by many researchers since 1895. Kennedy started the search for the attributes of stable channels on the Upper Bari Doab Canal of Punjab in 1980-1984. The regime concept was presented by Lindley (1919) that later on Lacey (1930) modified to a set of most widely used regime relations. Later on, Blench (1941-1957), and Simons and Albertson (1960) presented their equations. This period is called ‘canal regime period’ because most of the research focused on canal design. The concept of regime was extended to river systems by Leopold and Maddock in 1953. In 1963, Henderson proposed some regime equations that can be applied for predicting canal and river geometry. This period was the transition from canal regime period to river regime period and from an empirical approach to analytical approach and is called as ‘Transitional Period’. Many other researchers written the information based on analytical approach, or a combination between analytical and empirical approaches, and more focused to river regime especially gravel bed river regime. This period is, called ‘River regime period’. Flow discharge, sediment size, and bed-load sediment are the three main factors that influence the geometry of alluvial channels. The hydraulic geometry relationships indicate that sediment size and bed-load sediment strongly influence the channel slope, moderately influence the flow velocity, and slightly influence the channel depth and the channel width. This study also shows that in terms of Shields parameter, the exponents of discharge, sediment size, and sediment transport are dependent on the relative submergence (D/d50).

Achieving Equilibrium as a Semi‐Alluvial Channel: Anthropogenic, Bedrock, and Colluvial Controls on the White Clay Creek, PA, USA

AbstractBased on well‐developed hydraulic geometry relations for width and depth, classic studies initially interpreted the Mid‐Atlantic White Clay Creek (WCC) as a quasi‐equilibrium, alluvial channel. Subsequent studies document the legacy of colonial‐age watershed disturbances and urban development, confounding earlier classifications. To investigate this matter, we contribute new data from reach‐scale geomorphic mapping, and observations and modeling of bed material transport. WCC's longitudinal profile reflects a history of bedrock incision, while hydraulic geometry equations for width and depth indicate quasi‐equilibrium cross‐sectional adjustment. Alluvial landforms such as pools and riffles, bars, and actively forming floodplains occur at all 12 study sites, but exposures of bedrock and colluvium are also common. The ratio of bankfull to threshold Shields stress averages 1.41 (range: 0.41–2.63), suggesting that WCC is an alluvial, threshold, gravel‐bed river. However, a numerical model of WCC bed material transport and grain size, calibrated to bedload tracer data, demonstrates that 22% (range: 8%–73%) of bed material is composed of immobile, locally sourced cobbles and boulders, while the remaining bed material represents mobile, sand to cobble‐sized alluvium; this leads us to classify WCC as a semi‐alluvial river. Additional computations suggest that channel morphology is insensitive to bed material supply. Field observations imply that bankfull Shields stresses do not represent channel adjustments to achieve stable banks; rather, width adjustment likely reflects cohesive bank processes. Despite the numerous and contradictory labels applied to WCC (i.e., quasi‐equilibrium, Anthropocene, bedrock, semi‐alluvial, and gravel‐bed), each term contributes insight that any single conceptual model would be unable to provide alone.

The estimation of bedload in poorly-gauged mountain rivers

Bedload transport is one major driver of gravel-bed river morphodynamics, and its quantification is capital for many environmental issues and river engineering applications, as well as for landscape evolution studies. To this point, bedload transport rates and volumes have been classically computed by means of sediment transport formulae. The most used bedload transport equations compute the bulk bedload mass based on section-averaged hydraulic parameters. However, due to the non-linear behavior of sediment transport, bedload formulae are sensitive to the input parameters. Then, some doubts arise when applying bedload equations on poorly gauged river reaches, i.e. rivers where there are no hydrological records and rating curves. In this paper, we assess the application of bedload equations in the case of poorly gauged river reaches, and we test a workflow to follow in such situations. This workflow consists of three steps: (i) Reconstructing the flow duration curve, based on gauging records from neighboring river basins; (ii) Solving the hydraulic geometry relations of the study-case river-reach, based on a flow friction equation; and finally, (iii) Computing bedload with a sediment transport equation. We tested this approach against the bedload information available in the literature for Idaho streams and we found that it could potentially approximate annual bedload volumes in ungauged reaches under certain conditions. To illustrate the potential of this workflow, we also computed bedload volumes for two ungauged river reaches from the Cantabrian mountains (NW Spain).

Modelling surface water dynamics in an Amazonian sub-basin: impacts of hydraulic geometry refinement

ABSTRACT This study describes the impacts of refinement of hydraulic geometry (HG) relationships in the hydrological MGB model applied to an Amazonian sub-basin (Purus River basin). To this end, HG relationships were developed for the entire basin and for hydrologically homogeneous regions, and their performances were compared with observed data and a global width and depth database. Two simulations were then performed using the MGB model: one using the refined HG relationships and the other using the global width and depth database. The simulated streamflow and water level estimates were compared with observed data. The results showed that HG relationships for the hydrologically homogeneous regions provided better estimates of hydraulic parameters for the basin, with Nash-Sutcliffe efficiency of 0.96 for width and 0.95 for depth, and its use provided an improvement in the performance of the hydrological modelling in some gauge stations, with an increase in the Nash-Sutcliffe efficiency between 18% and 65%.

Equilibrium sediment transport, grade and discharge for suspended-load-dominated flows on Earth, Mars and Titan

Recent surface observations have emphasised the importance of bedload transport by rivers and streams on Mars and Titan. Previous “hydraulic” analysis, however, has also shown that transport as suspended load should be possible, if not more prevalent due to lower critical shear stresses, under reduced gravity conditions compared with Earth; where the dominant mode of sediment flux by rivers is as suspended load. A new suspended-load equilibrium condition (zero net erosion and deposition) constraint is advanced, using a flux-balance model applicable to transport (capacity) limited alluvial channels. The theory unifies Gilbert's relation for slope and flow capacity model with the Shields criterion for incipient motion. Shields-stress analysis shows that sediment transport thresholds on Earth, Mars and Titan are dynamically similar. Thus, despite large differences in dimensional shear stresses, variations in the critical slopes and flow depths required for threshold and equilibrium conditions are comparatively modest. Under reduced gravity conditions, there exists a slightly higher potential for sediment transport as suspended load; except for systems involving high particle-fluid density ratios, as may apply to the transport of organic particles on Titan. Critically we show that graded suspended-load channels should develop gentler slopes under reduced gravity, and not steeper slopes as previously inferred based on generalized hydraulic geometry relationships of terrestrial river and submarine channels. We further argue that the use of submarine channels as analogues for channels formed under reduced gravity is not physically justified. Finally, compared with bedload channels, suspended-load channels should also have markedly higher discharges, with implications for mechanistic-based discharge predictions and precipitation models.

Consistent Theoretical and Empirical Predictions of at‐a‐Station Hydraulic Geometry Exponents in Stream Reaches

AbstractReach‐scale at‐a‐station hydraulic geometry (AHG) relationships are power laws that describe variations of reach‐averaged water depth, wetted width, and current velocity in stream reaches when discharge varies. Modeling AHG exponents is important, because the variations of hydraulics with discharge in stream networks influence physical habitats of aquatic species, biodiversity, water temperature, nutrient fluxes, and sediment transport. Theoretical approaches indicated that AHG exponents should depend on topographic descriptors of cross sections and roughness elements. Empirical approaches suggested that AHG exponents partly depend on hydraulic characteristics measured at a single discharge. We used a unique data set of AHG observed in 812 stream reaches (obtained from measurements at several discharge rates or from hydrodynamic models) to (1) test the consistency of theoretical and empirical predictions of AHG exponents and (2) test the generality of AHG predictions across rivers of different countries with variable landscape settings. We found that observed AHG depended on topographic predictors (describing cross‐section shape and substrate size) as expected from theory. However, AHG exponents were better predicted by empirical hydraulic characteristics of reaches: the ratio of wetted width to bankfull width and the reach Froude number. The effects of hydraulic variables were consistent with those of topographic predictors. In addition, relations between AHG and hydraulic predictors were significant and with similar direction in different data sets. Despite limited explanatory power, our results help identifying general drivers of AHG exponents. Their application still requires measurements at a single discharge rate but open perspectives of generalized AHG prediction by remote sensing.

The roles of flood magnitude and duration in controlling channel width and complexity on the Green River in Canyonlands, Utah, USA

Predictions of river channel adjustment to changes in streamflow regime based on relations between mean channel characteristics and mean flood magnitude can be useful to evaluate average channel response. However, because these relations assume equilibrium sediment transport, their applicability to cases where streamflow and sediment transport are decoupled may be limited. These general relations also lack the specificity that is required to connect specific characteristics of the streamflow and sediment regime with the dynamics of channel morphological change that create channel complexity, which is often of ecological interest. We integrate historical records of channel change, observations of scour and fill during a snowmelt flood, measurements of sediment transport, and predictions from a two-dimensional streamflow model to describe how annual peak flow magnitude and peak-flow duration interact with the upstream sediment supply to control channel form for a 15-km study reach on the regulated Green River in Canyonlands National Park, Utah. Two major decadal-scale episodes of channel narrowing have occurred within the study area. For each of these episodes, the reduction in average channel width was consistent with the change predicted by hydraulic geometry relations as a function of average flood magnitude. However, channel narrowing occurred during periods of exceptionally low annual floods. The most recent episode of channel narrowing occurred between 1988 and 2009, during low-flow cycles when the 5-yr mean peak flow was less than 60% of the long-term (1959–2016) mean peak flow. These findings, together with findings from previous studies, demonstrate that decreases in peak-flow magnitude caused by streamflow regulation, climate change, or a combination of those factors have driven episodes of channel narrowing on the Green River. Observations of streamflow, sediment-transport, and morphologic change coupled with predictions from a two-dimensional streamflow model indicate that peak flow magnitudes of at least 75% of the long-term mean peak flow are required to transport bed-material sand in suspension in all regions of the multi-thread channel and that the ~2-month duration of the snowmelt flood played an important role in creating conditions necessary to maintain channel conveyance. These results indicate that detailed characterizations of channel response such as these are needed to predict how river channels will respond to changes in streamflow regime that affect annual peak flow magnitude and duration.

Reach‐scale bankfull channel types can exist independently of catchment hydrology

AbstractReach‐scale morphological channel classifications are underpinned by the theory that each channel type is related to an assemblage of reach‐ and catchment‐scale hydrologic, topographic, and sediment supply drivers. However, the relative importance of each driver on reach morphology is unclear, as is the possibility that different driver assemblages yield the same reach morphology. Reach‐scale classifications have never needed to be predicated on hydrology, yet hydrology controls discharge and thus sediment transport capacity. The scientific question is: do two or more regions with quantifiable differences in hydrologic setting end up with different reach‐scale channel types, or do channel types transcend hydrologic setting because hydrologic setting is not a dominant control at the reach scale? This study answered this question by isolating hydrologic metrics as potential dominant controls of channel type. Three steps were applied in a large test basin with diverse hydrologic settings (Sacramento River, California) to: (1) create a reach‐scale channel classification based on local site surveys, (2) categorize sites by flood magnitude, dimensionless flood magnitude, and annual hydrologic regime type, and (3) statistically analyze two hydrogeomorphic linkages. Statistical tests assessed the spatial distribution of channel types and the dependence of channel type morphological attributes by hydrologic setting. Results yielded 10 channel types. Nearly all types existed across all hydrologic settings, which is perhaps a surprising development for hydrogeomorphology. Downstream hydraulic geometry relationships were statistically significant. In addition, cobble‐dominated uniform streams showed a consistent inverse relationship between slope and dimensionless flood magnitude, an indication of dynamic equilibrium between transport capacity and sediment supply. However, most morphological attributes showed no sorting by hydrologic setting. This study suggests that median hydraulic geometry relations persist across basins and within channel types, but hydrologic influence on geomorphic variability is likely due to local influences rather than catchment‐scale drivers. © 2020 John Wiley & Sons, Ltd.

Constraining the Assimilation of SWOT Observations With Hydraulic Geometry Relations

AbstractThe Surface Water Ocean Topography (SWOT) satellite mission expected to launch in 2021 will offer a unique opportunity to map river discharge at an unprecedented spatial resolution globally from observations of water surface elevation, width, and slope. Because river discharge will not be directly observed from SWOT, a number of algorithms of varying complexity have been developed to estimate discharge from SWOT observables. Outstanding issues include the lack of accurate prior information and parameter equifinality. We developed a new data assimilation discharge algorithm that aimed to overcome these limitations by integrating a data‐driven approach to estimate priors with a model informed by hydraulic geometry relations. A comprehensive simulated dataset of 18 rivers was used to evaluate the algorithm and four different configurations (rectangular channel, generic channel, and geomorphologically classified channel with and without regularization) to assess the impact of progressively adding hydraulic geometry constraints to the estimation problem. The algorithm with the full set of constraints outperformed the other configurations with median Nash‐Sutcliffe coefficients of 0.77, compared with −0.46, 0.31 and 0.66, while other error metrics showed similar improvement. Results from this study show the promise of this hybrid data‐driven approach to estimating river discharge from SWOT observations, although a number of enhancements need to be tested to improve the operational applicability of the algorithm.

Simulation on the stochastic evolution of hydraulic geometry relationships with the stochastic changing bankfull discharges in the Lower Yellow River

Extreme weather is an important noise factor in affecting dynamic access to river morphology information. The response characteristics of river channel on climate disturbances draw us to develop a method to investigate the dynamic evolution of bankfull channel geometries (including the hydraulic geometry variables and bankfull discharges) with stochastic differential equations in this study. Three different forms of random inputs, including single Gaussian white noise and compound Gaussian/Fractional white noise plus Poisson noise, are explored respectively on the basis of the classical deterministic models. The model parameters are consistently estimated by applying a composite nonparametric maximum likelihood estimation (MLE) method. Results of the model application in the Lower Yellow River reveal the potential responses of bankfull channel geometries to climate disturbances in a probabilistic way, and, the calculated average trends mainly run to synchronize with the measured values. Comparisons among the three models confirm the advantage of Fractional jump-diffusion model, and through further discussion, stream power based on such a model is concluded as a better systematic measure of river dynamics. The proposed method helps to offer an effective tool for analyzing fluvial relationships and improves the ability of crisis management of river system under varying environment conditions.

River Channel Forms in Relation to Bank Steepness: A Theoretical Investigation Using a Variational Analytical Method

Riverbanks vary considerably in anti-scourability and consequently take various profiles. By using an isosceles trapezoid as the generalized form of river channel cross-sections and then incorporating the effects of bank angle into the variational analytical approach developed by Huang and Nanson (2000), this study presents a detailed theoretical investigation of the self-adjustment of alluvial channel forms. It is demonstrated that when alluvial channel flow achieves stable equilibrium, a significant decrease in riverbank steepness leads to a slight decrease in maximum sediment (bedload) discharge, and yet results in a significant increase in optimal channel width and a considerable decrease in optimal channel depth. The hydraulic geometry relations, theoretically derived for bank steepness to vary across a wide range, show that among the multivariant controls, the roles of bed sediment size, channel roughness, flow discharge and sediment (bedload) discharge are independent of bank steepness. While the effects of bank steepness illustrated in the theoretically derived hydraulic geometry relations are highly consistent with the results of threshold theory and previous empirical studies, limitations on using bank angle to reflect the anti-scourability of natural riverbanks are also highlighted.

Stochastic evolution of hydraulic geometry relations in the lower Yellow River of China under environmental uncertainties

Hydraulic geometry relations comprise a classic way to understand characteristics of a river. However, environmental changes pose large uncertainties for the reliability of such relations. In the current study, on the basis of the ordinary differential equations (ODEs) formed through linear treatment of the deterministic power-law hydraulic geometry relations, a set of stochastic differential equations (SDEs) driven by Fractional white noise and Poisson noise are developed to simulate the historical dynamic probability distributions of typical hydraulic geometry variables such as slope, width, depth, and velocity with bankfull discharge variation over time in the lower Yellow River of China. One group of possible stochastic average behaviors within the next 50 years are calculated under three different design incoming water-sediment conditions (including 300, 600, and 800 million t of annual average sediment discharge). In each part of the lower reaches, after estimation of the SDE parameters using a nonparametric maximum likelihood estimation (MLE) method, the model is carefully examined using Monte Carlo simulation as compared with the deterministic control models. The results of this comparison reveal the potential responses of hydraulic geometry characteristics to environmental disturbances, and the average trends mainly agree with the measurements. Comparisons among the three different prediction results reveal the stochastic average solution generally is greater than the deterministic solution. The results also confirm the severe negative impacts that result from the condition of 300 million t of incoming sediment, thus, pointing out the need to raise the level of river evolution alert for the lower Yellow River of China in the future. Moreover, with the help of the stochastic computation, the stream power and hydraulic width/depth ratio could be representative of an effective systematic measure for river dynamics. The proposed stochastic approach is not only important to development in the field of fluvial relations, but also beneficial to the practical design and monitoring of a river system according to specified accuracy requirements.

Downstream hydraulic geometry across headwater channels in Upper Ogun River Basin, Southwestern Nigeria

ABSTRACT Hydraulic geometry is widely applicable in different environments and is quite essential across different channel units. In this study, downstream hydraulic geometry was used to ascertain differences in exponents across headwater channels within a Basement Complex in a humid tropical region. This study was conducted within the Upper Ogun River Basin, Southwestern Nigeria. The basin is approximately 200 km in length and 140 km wide. Eighty-three (83) reaches were sampled across third-order basins within the Upper Ogun River Basin. Hydraulic geometry variables were measured and derived at bankfull using appropriate techniques and basic hydraulic equations, respectively. For the six-individual basins covered, it was found that the exponents (b, f and m) of the downstream hydraulic geometry relations for Qbf covered a range of: b = −0.12–0.51; f = 0.44–0.67; m = 0.04–0.46. The channels of four basins out of six becomes progressively narrowed and deepened downstream while that of the remaining two becomes progressively wider and shallower downstream.

A study of the stochastic evolution of hydraulic geometry relationships

AbstractUncertainty resulting from climatic and environmental changes creates barriers to the accurate acquisition of information about rivers. In this study, a set of stable stochastic differential equations is developed to simulate the dynamic probability distributions of typical hydraulic geometry variables represented by slope, width, depth, and velocity with variations in bankfull discharge over time for a river system. Random parts of the equations are modelled based on single Gaussian white noise and further on combined Gaussian/fractional white noise with Poisson noise. Consistent estimates of the equation parameters are made using a composite nonparametric maximum likelihood estimation (MLE) method. The proposed models are examined through a Monte Carlo simulation of the lower Yellow River, and the results successfully reveal the potential responses of hydraulic geometries to stochastic disturbance and that average trends largely synchronize with the measured values. Comparisons of the three different models confirm the advantages of fractional jump‐diffusion model, and according to further discussion, stream power on the basis of such a model is concluded to serve as the better systematic measure of river dynamics. The proposed stochastic approach is new to the field of fluvial relationships, and its application could help to design and monitor river systems with specified accuracy requirements.

Roles of Bank Material in Setting Bankfull Hydraulic Geometry as Informed by the Selenga River Delta, Russia

AbstractA semi‐empirical bankfull Shields number relation as a function of slope, bed, and bank sediment grain size is obtained based on a field data set that includes the delta of the Selenga River, Russia, and other rivers from around the globe. The new Shields number relation is used in conjunction with continuity, flow resistance, and sediment transport equations to deduce predictive relations for bankfull width, depth, and slope of sand‐bed rivers. In addition, hydraulic geometry relations are obtained specifically for the Selenga River delta. Key results of this study are as follows: (1) bankfull width is strongly dependent on water discharge and is directly related to bank sediment size; (2) bankfull shear velocity is weakly dependent on bed sediment size and is inversely related to bank sediment size; (3) sand‐bed deltas with multiple distributary channels maintain smaller bankfull Shields numbers than is typical of alluvial rivers. This analysis is the first of its kind to include bank sediment size into a predictive bankfull Shields number relation to obtain relations for bankfull hydraulic geometry. The relations presented here can be utilized in morphodynamic models that explore how fluvial and deltaic systems respond to a range of imposed conditions, such as variable base level, sediment, and water supply.

Revisiting the drivers of at-a-station hydraulic geometry in stream reaches

Knowledge of temporal variations in river hydraulic characteristics (i.e., width, depth, velocity) across stream networks is a key element for catchment management because hydraulics influence physical habitats and biodiversity, water temperature, nutrient fluxes, sediment transport and associated ecosystem services. Reach scale at-a-station hydraulic geometry describes the variation of mean water depth and width with discharge within a stream reach. The ability to understand and predict the form of these hydraulic geometry relationships across river networks therefore represents a powerful tool for river managers. Although variations of these relationships between rivers have been widely documented, they are still largely unexplained. This study provides an analysis of a unique data set of hydraulic geometry collected in 492 stream reaches in France. Relationships between the hydraulic geometry parameters and many variables describing catchment- and reach-scale characteristics of reaches were analyzed using stepwise linear regression and discriminant analysis. Results show that width-discharge relationships across reaches are well predicted by longitudinal and lateral descriptors of reaches: the ratio of median to bankfull width, the median Froude number, the width to depth ratio, the active channel relative to the catchment area and the fluvial pattern (braided or not). Fluvial pattern, reach averaged active channel width and bankfull width can be accurately estimated using aerial imagery, making application of our models over river networks possible. Fewer relationships significantly explained depth-discharge relationships, despite a weak influence of reach Froude number, flow resistance (i.e., relative grain size, relative bedform submergence) and width to depth ratio. Unavailable descriptors of channel resistance would probably improve these models (e.g., describing bank stability, spill and form resistance). Despite the uncertainties of hydraulic geometry relationships, this study shows that predictions of hydraulic geometry exponents across river networks are possible, offering a large range of potential applications.

Investigating the geomorphic characteristics of an Amazonian headwater stream draining a páramo ecosystem

ABSTRACTPáramos are neotropical alpine grasslands located in the northern Andes of South America. Although they cover important headwater regions, little is known about the hydro-geomorphic characteristics of páramo river systems, which are increasingly being impacted by human use and climate change. The objective of this research is to characterize the geomorphology of the Ningar River, Ecuador, an Amazonian headwater river that drains a 22.7 km2 páramo sub-basin, by (1) classifying the geomorphology based on common geomorphic classifications, (2) deriving downstream hydraulic geometry relationships, and (3) performing a global comparison with mountain river systems. Common geomorphic field surveying techniques were used to acquire the necessary data. Results suggest that the Ningar River has similar form-function characteristics as other known mountain headwater streams and corresponds to commonly known stream classification systems, but displays more of an alluvial character than might be expected for montane headwater streams as a result of a convexity in the stream’s longitudinal profile. Additionally, preliminary analyses suggest that other páramo headwater streams may exhibit similar characteristics; thus, the findings of this research are important for future management and protection of these valuable headwater ecosystems.