Hydrogeomorphic Approach Research Articles

Developmental framework for a desktop hydrogeomorphic wetland functional assessment derived from field-based data

With loss of wetlands and their associated ecosystem services within landscapes, it is imperative to be able to understand the change in ecological functions underlying these services. Field-based functional assessments can produce a range of specific scores among a robust set of functions but are time and cost prohibitive as the number of wetlands assessed increases. Remote-based functional assessments are an alternative for broad scale assessments, but trade-off cost for limitations in scoring and functional assemblage. To address these concerns, we created a framework for the development of the Hydrogeomorphic Remote Assessment of Wetland Function (HGM-RAWF). Rooted in the hydrogeomorphic approach of an existing field-based functional assessment and its underlying models, this remote functional assessment substitutes field-based assessment methods with remotely assessed proxies. As potential remote proxies were determined through literature review and statistically screened for use in the remote assessment, a field-based reference wetland database of 222 freshwater wetlands in the Mid-Atlantic Region provided a baseline by which remote data could be compared and calibrated. The resulting HGM-RAWF protocol remotely assesses seven hydrology and biogeochemistry functions in the Mid-Atlantic with assessment scores similar to its field-based counterparts. With noted limitations, the HGM-RAWF framework provides the means to create desktop functional assessments across broad geographic scales with the diversity and specificity of field-based assessments at the reduced costs associated with remote assessments. Its basis in the HGM approach and use of public spatial datasets allows the framework to be adopted regionally and can be used as a model for national wetland functional assessment.

A hydrogeomorphic approach to river characterization in the Breede River catchment, South Africa

A hydrogeomorphic approach to river characterization in the Breede River catchment, South Africa

Wetland functional assessment and uncertainty analysis using fuzzy α-cut-based modified hydrogeomorphic approach.

Wetlands are significant ecosystems which perform several functions such as ground water recharge, flood control, carbon sequestration, and pollution reduction. Accurate evaluation of wetland functions is challenging, due to uncertainty associated with variables such as vegetation, soil, hydrology, land use, and landscape. Uncertainty is due to the factors such as the cost of evaluating quality parameters, measurement, and human errors. This study proposes an innovative framework based on modified hydrogeomorphic approach (HGMA) using fuzzy α-cut technique. HGMA has been used for wetland functional assessment and α-cut technique is used to characterize uncertainty corresponding to the input variables and wetland functions. The most uncertain variables were found to be the density of wetlands and basin count in the landscape assessment area with the scores of 4.38% and 3.614% respectively. Among the functions, the highest uncertainty is found in functional capacity index (FCI) corresponding to water storage (1.697%) and retain particulate (1.577%). The quantified uncertainty can help the practitioners to make informed decisions regarding planning best management practices for preserving and restoring the wetland functionality.

Evaluating topography-based approaches for fast floodplain mapping in data-scarce complex-terrain regions: Findings from a Himalayan basin

Despite a proven record of accurate floodplain mapping, complex hydrodynamic models lack efficiency due to their data-intensive approach and high computation time. As fast-computing low-complexity alternatives, topography-based hydrogeomorphic approaches are being increasingly used in recent times. Yet, there is little evidence to suggest whether and to what extent such topography-based approaches, simply relying on Digital Elevation Models (DEMs), can effectively delineate floodplains/flood hazard zones in data-scarce, highly complex mountainous terrains. We fill this knowledge-gap by conducting a floodplain mapping comparative assessment with three topography-based approaches along a 56-km river reach in the North West Himalayas (Beas River, India). Specifically, we generated floodplain extent using Height Above the Nearest Drainage (HAND), Topographic Wetness Index (TWI), and Slope Position (SP), and estimated their relative differences compared to a reference inundation extent simulated by MIKE11 hydrodynamic model. The unique feature of our study was an extensive field survey to collect longitudinal and cross-sectional elevation data across 223 locations, which allowed us to verify vertical accuracy across multiple alternative DEMs and subsequently improve the selected DEM via bathymetry integration. Statistical measures estimating the degree of consistency across three topography-based approaches suggested that HAND and TWI produce more reasonable floodplain maps than SP. HAND-based floodplain demonstrated greater agreement with the model-simulated reference map. TWI showed moderate predictability with a tendency of underestimating floodplains. SP was largely inconsistent, demarcating floodplains in areas where the hydrodynamic model found uplands and vice versa. Our study can offer critical insights to support floodplain hydrological, biological, and habitat studies across the world’s developing countries where locally relevant delineation of floodplains remains challenging due to data scarcity.

Flood Risk Assessment and Mapping in the Hadejia River Basin, Nigeria, Using Hydro-Geomorphic Approach and Multi-Criterion Decision-Making Method

Flood risk management is crucial for climate change resilience. The Hadejia River basin is known for severe and frequent floods, which have destroyed houses and farmlands and claimed many lives. This study developed a GIS-based flood risk and vulnerability mapping assessment using the Analytical Hierarchical Process (AHP) to outline scenarios that reduce risk and vulnerability associated with floods in the Hadejia River basin. The risk mapping of the basin integrated seven hydro-geomorphological indicators influencing extreme events (elevation, mean annual rainfall, slope, distance from rivers, soil type, and drainage density) and six socio-economic vulnerability indicators (population density, female population density, literacy rate, land use, employment rate, and road network) using a multi-criterion analysis. The average annual rainfall data of 36 years (1982–2018) were used for flood plain mapping in this study. Combining the flood hazard and socio-economic vulnerability indices of the basin revealed high-to-very high flood risk in the downstream and central upstream portions of the basin, which cover about 43.4% of the basin area. The local areas of Auyo, Guri, Hadejia, Ringim, Kafin Hausa, and Jahun were identified as zones at a very high flood risk. The study also revealed that flood hazard and vulnerability indicators have different influences on flood risk. The validated results resonate with the records of previous flood distribution studies of the basin. This research study is significantly important for developing strategic measures and policy revision through which the government and relief agencies may reduce the negative impact of floods in the Hadejia River basin.

Case study: On hydrological function improvement for an endemic plant habitat in Gangcheon wetland, Korea

Wetlands are one of the most important ecosystems for the biodiversity of plants and animals. Especially, Gangcheon wetland in NamHan river, Korea is a very valuable one because Aster altaicus var. uchiyamae, which is one of endemic plants is inhabited. However, Gangcheon wetland was impaired by a river improvement project called ‘Four Major Rivers Project’. After the project, Gangcheon wetland restoration work was performed, for the rehabilitation of wetland functions but the habitat of Aster altaicus var. uchiyamae could not be restored. Actually, Aster altaicus var. uchiyamae can grow in a habitat made by mixing of gravel and sand from flood inundation of the river but there was no inundation after the project because of the rise of levee height. Therefore, this study evaluated wetland functions using Hydrogeomorphic(HGM) approach and analyzed flood inundation using HEC-GeoRAS model after the project for diagnosis of the functions and the habitat. Then we proposed a plan to improve the functions of Gangcheon wetland as a habitat for Aster altaicus var. uchiyamae. The reference wetland is Gangcheon wetland before the project and the wetland functions after the project were compared with the reference one. As a result of the function assessment, hydrological, biogeochemical, and plant habitat functions were deteriorated. The study wetland has three zones of A, B, and C for Aster altaicus var. uchiyamae habitats and particularly, hydrologic functions for zone C which is poor as the habitat should be improved. In particular, the habitat of Aster altaicus var. uchiyamae was adversely affected by the decrease in inundation depth and water level of the river. These hydrologic functions should be improved and the levee height be lowered for obtaining more proper habitat of Aster altaicus var. uchiyamae. This suggestion might be helpful for establishment of the habitat of Aster altaicus var. uchiyamae. Also, it could be expected that the overall function of Gangcheon wetland will be improved because biogeochemical and plant habitat functions are rehabilitated by the improved hydrological function.

Determining the occurrence of potential groundwater zones using integrated hydro-geomorphic parameters, GIS and remote sensing in Enugu State, Southeastern, Nigeria

In many parts of Nigeria, water resource is scarce, and where available, determining their abundance is difficult. In the present paper, various groundwater potential zones for the evaluation of groundwater availability in Enugu State have been delineated using remote sensing and GIS techniques. The satellite images and conventional data obtained from US Geological Survey, World Soil Resources Office in Cooperation with Land and Water Development Division/FAO and Nigerian Geological Survey Agency are used to prepare the thematic layers viz. drainage density, geomorphology, slope, landcover/land use, soil, geology, rainfall and lineament density were converted to raster data adopting feature to raster converter device in ArcGIS. The raster maps of abovementioned factors are assigned a definite score and weight computed from multi-influencing factor approach. Additionally, each weighted thematic layer is statistically computed to generate groundwater potential zones map of the study area. The groundwater potential zones thus obtained were divided into four categories, viz., super-abundant, moderately abundant, abundant and scarce zones. The groundwater resources map demonstrates that the study area is dominated by abundant and scarce groundwater potential zones which covers surface area of about 6073.44 km2 (73.27%) of the study area while the remaining 2294.98 km2 (26.73%) are dominated by super-abundant and moderately abundant groundwater potentials. However, the result validation with boreholes/wells yield data collected from the study area showed good correlations with respect to groundwater potential zones map. It is concluded that the use of hydro-geomorphic approach is very efficient for the determination of groundwater potential zones.

Modified hydrogeomorphic approach for estimating quantitative change of riverine wetland functions

HydroGeoMorphic (HGM) approach could examine relatively more details for wetland functions. However, HGM cannot be utilized in assessing the functional improvement of wetlands because it is limited to evaluating the similarity between the reference and the target wetlands. Therefore, this study proposes the Modified HydroGeoMorphic (MHGM) approach for considering better functions of target wetlands. The values of Index of Function (FCI) and variables in HGM are in the range of 0.0 to 1.0 and so, in MHGM, we redefine the values of variables in 0.0 to 2.0 to find a better function for the target wetland. Based on the monitored variables, FCIs for the wetland functions were estimated and the functions of dynamic surface and subsurface water storage, spatial structure of habitat, and maintaining the distribution and abundance of vertebrates in Imjin riverine wetland as a target wetland showed better FCIs than those of Hwapo which is a reference. This means that MHGM reflects an actual change in FCI, leading to a more favorable evaluation of the target compared to the reference wetland. This indicates that MHGM considers actual functional progress of wetlands by improving HGM's limitations in assessing change.

Flood risk assessment in the Kosi megafan using multi-criteria decision analysis: A hydro-geomorphic approach

Floods are one of the most devastating natural events that lead to enormous and recurring loss of life, properties, and resources around the globe. In India, floods remain a major hazard during the monsoon season in many parts of the country but most seriously in the flat and monotonous Gangetic plains in the Himalayan foreland. One of the most flood-prone rivers in India is the Kosi in north Bihar, eastern India, which also forms the largest active megafan in the world. The Kosi River is known as the “sorrow of Bihar” because of its anomalous behavior and the damage it causes due to frequent floods in this region. This study evaluates the flood hazard and flood vulnerability as separate entities and combines them to assess the flood risk in the Kosi megafan region. Geomorphological, hydrological, and socio-economic data have been integrated in a GIS framework using a multi-criteria decision tool called the Analytical Hierarchy Process (AHP) to generate a process-based flood risk map for 105 blocks (administrative units) of both Nepal and India (Bihar). Such maps should encourage soft engineering solutions for flood mitigation aimed at minimizing the consequences of flooding and reducing flood risks. This study has significant implications for developing measures and plans that will help government and relief agencies in the identification of flood-prone areas and for planning emergency management strategies in this region.

A Classification System for Colombian Wetlands: an Essential Step Forward in Open Environmental Policy-Making

Knowledge about the distribution and diversity of wetlands has become an essential tool for environmental management and policy-making. Yet, while recent estimates indicate that 27% of the area of Colombia is covered by wetlands and despite a number of regional studies, information about the diversity of wetlands nationally is scarce. In response, we present a national wetland classification system that is based on an ecological approach, from the perspective of wetland scientists, and which builds upon the assumptions underlying the flood pulse concept and hydrogeomorphic approach. Thus, the approach and structure of the Brazilian wetland classification system are used, with geomorphological adjustments made according to Colombia’s topography. The classification is hierarchical, multi-scale, functional, and organized according to four levels (system, macroregion, subsystem, and class), with the wetland diversity of Colombia represented nationally by 89 macrohabitats across marine-coastal, inland, and anthropogenic systems. The primary purpose of this classification is to provide integrated and organized information on the distribution and diversity of Colombian wetlands that will serve as a baseline for transparent environmental policy-making.

Investigating hydrogeomorphic floodplain mapping performance with varying DTM resolution and stream order

ABSTRACT Hydrogeomorphic models allow parsimonious, fast and effective floodplain extent mapping using topographic data as the main input. Hydrogeomorphic approaches enforce the principle that floodplains are well-distinguished and unique landscape features within river corridors. We investigated the sensitivity of a hydrogeomorphic floodplain delineation algorithm, based on a hydrological power law, relating flow depth to contributing area, digital terrain model (DTM) resolution and river network hierarchy. In addition, we compared the results to other common floodplain mapping methods using standard flood-hazard maps as a reference. Taking the Arno River Basin, Italy, as a case study, our results show a dependency between the optimal power law parameters and DTM resolution, with larger parameter values required to reach optimal consistency with flood-hazard maps as DTM resolution increased. Floodplain mapping performance was also found to depend on stream order. We further tested the model consistency at a larger scale to evaluate its performance with respect to inundation maps in Hungary, Italy, Spain and the UK. Our study suggests that pre-defined power law parameters can be assumed, considering DTM resolution and stream order, supporting the use of the presented hydrogeomorphic model for large-scale floodplain mapping in ungauged basins where reference flood-hazard maps are not available.

Quantifying Functional Increases Across a Large-Scale Wetland Restoration Chronosequence

Over 300,000 ha of forested wetlands have undergone restoration within the Mississippi Alluvial Valley region. Restored forest successional stage varies, providing opportunities to document wetland functional increases across a large scale restoration chronosequence using the Hydrogeomorphic (HGM) approach. Results from >600 restored study sites spanning a 25 year chronosequence indicate that: 1) wetland functional assessment variables increased toward reference conditions; 2) restored wetlands generally follow expected recovery trajectories; and 3) wetland functions display significant improvements across the restoration chronosequence. A functional lag between restored areas and mature reference wetlands persists in most instances. However, a subset of restored sites have attained mature reference wetland conditions in areas approaching or exceeding tree diameter and canopy closure thresholds. Study results highlight the importance of site selection and the benefits of evaluating a suite of wetland functions in order to identify appropriate restoration success milestones and design monitoring programs. For example wetland functions associated with detention of precipitation (a largely physical process) rapidly increased under post restoration conditions, while improvements in wetland habitat functions (associated with forest establishment and maturation) required additional time. As the wetland science community transitions towards larger scale restoration efforts, effectively quantifying restoration functional improvements will become increasingly important.

Vulnerability assessment of wetland landscape ecosystem services using driver-pressure-state-impact-response (DPSIR) model

Wetlands exist in complex ecological conditions that are changeable in time and space in terms of function and structural diversity. In recent decades, wetlands have been exposed to a wide range of threats. Assessment of these threats is essential to develop an understanding of the state of a wetland ecosystem and to develop a suitable management strategy. This paper discusses wetland vulnerability in terms of analysis of human and environmental systems from application of the driver-pressure-state-impact-response (DPSIR) framework. This assessment presented a systematic methodology for assessment of wetland vulnerability in a social-ecological approach applying broad-scale ecosystem services and vulnerability functions. The method combined the hydro-geomorphic approach with estimations of vulnerability indicators and DPSIR analysis. The aim of this paper was to assess vulnerability of wetland ecosystem services and to characterize the threat indicators according to importance, severity, and probability of occurrence. Quantitative and qualitative methods were applied to characterize values for these three indicators. The Multi Criteria Decision Making (MCDM) method was used to prioritize threats and impacts of the wetland on the basis of experts’ opinions. The proposed methodology was applied to the Choghakhor international wetland landscape in south-western Iran. Vulnerability assessment revealed that water requirement of the lowland and the water transfer system were the most important factors threatening the wetland. Agricultural activities, settlements and urban areas, drought, tourism, population growth, and mining activities in the upland were the next most important priorities, in that order. Hydrological balance was determined as the most vulnerable function and was considered as the most important function in the Choghakhor wetland. The DPSIR model was used to determine a management strategy to reduce vulnerability of ecosystem services in response to drivers, pressures, states and impacts indicated by modelling.

HGM: a call for model validation

The hydrogeomorphic (HGM) approach to wetland functional assessment has been in place for more than 20 years, yet most models developed to date have not been validated. Although HGM models are typically calibrated to a data set, we lack true validation efforts, especially as wetland scientists and managers continue to assert that measuring structure equates to an assessment of function. This paper is a call for a renewed effort at HGM validation in order to fully assure that we know when structure is measured we are also measuring function.

The development of a classification system for inland aquatic ecosystems in South Africa

A classification system is described that was developed for inland aquatic ecosystems in South Africa, including wetlands. The six-tiered classification system is based on a top-down, hierarchical classification of aquatic ecosystems, following the functionally-oriented hydrogeomorphic (HGM) approach to classification but incorporating structural attributes at the lower levels of the hierarchy. At Level 1, a distinction is made between inland, estuarine and shallow marine systems using the degree of connectivity to the open ocean as the key discriminator. Inland systems are characterised by the complete absence of marine exchange and/or tidal influence. At Level 2, inland systems are grouped according to the most appropriate spatial framework for the particular application. At Level 3, four primary Landscape Units are distinguished (Valley floor, Slope, Plain, Bench) on the basis of the topographic position within which a particular inland aquatic ecosystem is situated, in recognition of the influence that the landscape setting has over hydrological and hydrodynamic processes acting within an aquatic ecosystem. Level 4 identifies HGM Units, defined primarily according to landform, hydrological characteristics and hydrodynamics. The following primary HGM Units (or HGM Types), which represent the main units of analysis for the classification system, are distinguished at Level 4A: (1) River; (2) Floodplain Wetland; (3) Channelled Valley-Bottom Wetland; (4) Unchannelled Valley-Bottom Wetland; (5) Depression; (6) Seep; (7) Wetland Flat. Secondary discriminators are applied at Level 5 to classify the hydrological regime of an HGM Unit, and Descriptors at Level 6 to categorise a range of biophysical attributes. The HGM Unit at Level 4 and the Hydrological Regime at Level 5 together constitute a Functional Unit, which represents the focal point of the classification system. The utility of the classification system is ultimately dependent on the level to which ecosystem units are classified, which is in turn constrained by the type and extent of information available.

Floodplain forest succession reveals fluvial processes: A hydrogeomorphic model for temperate riparian woodlands

River valley floodplains are physically-dynamic environments where fluvial processes determine habitat gradients for riparian vegetation. These zones support trees and shrubs whose life stages are adapted to specific habitat types and consequently forest composition and successional stage reflect the underlying hydrogeomorphic processes and history. In this study we investigated woodland vegetation composition, successional stage and habitat properties, and compared these with physically-based indicators of hydraulic processes. We thus sought to develop a hydrogeomorphic model to evaluate riparian woodland condition based on the spatial mosaic of successional phases of the floodplain forest. The study investigated free-flowing and dam-impacted reaches of the Kootenai and Flathead Rivers, in Idaho and Montana, USA and British Columbia, Canada. The analyses revealed strong correspondence between vegetation assessments and metrics of fluvial processes indicating morphodynamics (erosion and shear stress), inundation and depth to groundwater. The results indicated that common successional stages generally occupied similar hydraulic environments along the different river segments. Comparison of the spatial patterns between the free-flowing and regulated reaches revealed greater deviation from the natural condition for the braided channel segment than for the meandering segment. This demonstrates the utility of the hydrogeomorphic approach and suggests that riparian woodlands along braided channels could have lower resilience than those along meandering channels and might be more vulnerable to influences such as from river damming or climate change.

Using the landform tool to calculate landforms for hydrogeomorphic wetland classification at a country-wide scale

Hydrogeomorphic approaches to wetland classification use landform classes to distinguish wetland functionality at a regional scale. Space-borne radar technology enabled faster regional surveying of surface elevations to digital elevation models, which allowed for automated terrain attribute and landform classification using geographical information systems. Country-wide mapping of landforms remain a challenge though, because of the diversity of landscapes and non-exclusive attributes of each landform class. This article presents the approach, method and steps taken to calculate a country-wide data-set of landforms for wetland-type classification in South Africa, using a freely available Landform Tool. The Landform Tool primarily uses standard deviation from the average elevation, calculated for both small and large neighbourhood distances. The results were compared with 2820 random points, classified manually using Google Earth imagery and topographical maps, and showed a 43% accuracy within 50 m of the manually identified landform class. The Landform Tool tended to overestimate benches and valley floors, and underestimate the extent of the slope class, regardless of changes made in the neighbourhood settings or standard deviation settings. Though the data-set was acceptable as a general reference framework at national scale, improvements will be essential for fine-scale wetland delineation and classification.

The Relative Importance of Groundwater and its Ecological Implications in Diverse Glacial Wetlands

Abstract The hydrogeomorphic approach, which assesses a wetland's geomorphic setting, water sources, and hydrodynamics, has proven to be a useful framework for characterizing wetlands. Yet, estimating wetland water sources quantitatively across more than a few study sites remains impractical for larger comparative studies due to the time-intensive measurements required. In this research we tested the efficacy of using dissolved magnesium (Mg2+) as a semiconservative tracer of wetland water sources in southern Lower Michigan. Because concentrations of magnesium in groundwater are high due to equilibrium with dolomite in the glacial deposits, dissolved magnesium distinguished the relative importance of groundwater vs. precipitation as wetland water sources. We examined a set of 24 wetlands to consider relationships between a wetland's water sources and its geomorphic setting, water level variation, and biogeochemistry. Fens and swamps were generally groundwater-dominated, whereas wetlands dominated by Sphag...

High Spatial-Resolution Land Cover Classification and Wetland Mapping over Large Areas Using Integrated Geospatial Technologies

Land Use and Land Cover (LULC) and wetland classification maps are an important prerequisite for many environmental studies. In order to produce accurate LULC and wetland maps at high spatialresolution, a new approach was developed to integrate image classifications, spatial data layers, and analysis methods using Python scripting. Both Maximum Likelihood and Object-based Feature Extraction were adopted into the LULC classification. A spatial analysis approach was applied to wetland mapping based on available wetland inventories and soil data. Python scripts were created and used to automate these processes for each of the 30 reference sites across Minnesota and Wisconsin of the United States, which encompassed the entire study site. Results demonstrated that the proposed method allowed for the integration of geospatial data of varying sources and qualities to produce accurate LULC and wetland maps effectively. The results of accuracy assessment indicated that the classification maps for Minnesota and Wisconsin were of comparable quality. The objectbased classifier extracted LULC effectively from the Wisconsin imagery with acceptable accuracy despite lacking of the NIR spectral band. These maps were used as inputs to create a hydro geomorphicap-proach (HGM) guidebook (Hauer and Smith 1998) for both states (Cook et al. unpublished). The Python-based technique was found to be especially beneficial when dealing with big datasets over large study areas, as it allowed batch processing.

Assessing Natural and Anthropogenic Variability in Wetland Structure for Two Hydrogeomorphic Riverine Wetland Subclasses

The hydrogeomorphic approach (HGM) to wetland classification and functional assessment has been applied regionally throughout the United States, but the ability of HGM functional assessment models to reflect wetland condition has limited verification. Our objective was to determine how variability derived from anthropogenic effects and natural variability impacted site assessment variables within regional wetland subclasses in central Oklahoma. We collected data for nine potential assessment variables including vegetation physiognomy (e.g., tree basal area, herbaceous cover, canopy cover, etc.) and soil organic matter at wetlands of two HGM riverine subclasses (oxbow and riparian) in May and June, 2010. Using Akaike Information Criteria, we identified limited relationships between landscape disturbance metrics and assessment variables within subclasses. The high degree of natural variability from climatic and hydrologic factors within both subclasses may be masking the impact of landscape disturbance on the other measured assessment variables. Precipitation had significant effects on assessment variables within each of the subclasses. To reduce natural climatic variability, the reference domain may need to be further subdivided. The approach used in this study provides fairly rapid and quantitative methods for evaluating the effectiveness of using HGM assessment variables in assessing wetland condition regionally.