Rebecca Manners Diehl

University of Vermont | UVM · Department of Geography

Centuries of human development have altered the connectivity of rivers, adversely impacting ecosystems and the services they provide. Significant investments in natural resource projects are made annually with the goal of restoring function to degraded rivers and floodplains and protecting freshwater resources. Yet restoration projects often fall s...

Centuries of human development have altered the connectivity of rivers, adversely impacting ecosystems and the services provided. Significant investments in natural resource projects are made annually with the goal to restore function to degraded rivers and floodplains and protect freshwater resources. Yet restoration projects often fall short of t...

Floodplain reconnection and wetland restoration projects are increasingly implemented to enhance flood resiliency, and these nature-based solutions can also achieve co-benefits of nutrient storage and improved habitats. Considering the multiple and sometimes incompatible objectives of stakeholders for uses of riverside lands, a decision-support too...

The capacity for floodplains to capture sediment and filter pollutants is spatially variable and depends on the complex interactions of geomorphic, geologic, and hydrologic variables that operate at multiple scales. In this study, we integrated watershed‐scale and local assessments to improve our understanding of floodplain depositional patterns. W...

Wetlands are valuable ecosystems because they are highly productive, support a wide range of wildlife, and serve as hotspots for biogeochemical cycling. Historically, vast areas of wetlands in the United States (US) were drained and converted to agriculture. Efforts are currently underway to restore wetland and floodplain functioning across the US...

The strength of interactions between plants and river processes is mediated by plant traits and fluvial conditions, including above‐ground biomass, stem density and flexibility, channel and bed material properties, and flow and sediment regimes. In many rivers, concurrent changes in 1) the composition of riparian vegetation communities as a result...

1. The combined impacts of climate change and ecological degradation are expected to worsen inequality within society. These dynamics are exemplified by increases in flood risk globally. In general, low-income and socially vulnerable populations disproportionately bear the cost of flood damages. Climate change is expected to increase the number of...

As runoff patterns shift with a changing climate, it is critical to effectively communicate current and future flood risks, yet existing flood hazard maps are insufficient. Modifying, extending, or updating flood inundation extents is difficult, especially over large scales, because traditional floodplain mapping approaches are data and resource in...

Riparian ecosystems are shaped by interactions among streamflow, plants, and physical processes. Sustaining functioning riparian ecosystems in the face of climate change, growing human demands for water, and increasing water scarcity requires improved understanding of the sensitivity of riparian ecosystems to shifts in flow regimes and associated a...

• Environmental flow releases are an effective tool to meet multiple management objectives, including maintaining river conveyance, restoring naturally functioning riparian plant communities, and controlling invasive species. In this context, predicting plant mortality during floods remains a key area of uncertainty for both river managers and ecol...

Point bars influence hydraulics, morphodynamics, and channel geometry in alluvial rivers. Woody riparian vegetation often establishes on point bars and may cause changes in channel-bend hydraulics as a function of vegetation density, morphology, and flow conditions. We used a two-dimensional hydraulic model that accounts for vegetation drag to pred...

Alternating bars influence hydraulics, morphodynamics, and channel geometry in alluvial rivers. Recruitment of pioneer woody riparian vegetation is tightly coupled with bar building, yet the influence of vegetation on changing bend hydraulics and forces has been unresolved. We use a two-dimensional hydraulic model that accounts for vegetation drag...

The functional trait framework, an ecological tool powerful for its simplicity and ability to facilitate modeling and generalization across environmental gradients, can capture the interactions between ecological and physical processes that shape riparian ecosystems. We demonstrate that ecological-response traits that describe how a plant will resp...

Coupling between riparian vegetation and river processes can result in the coevolution of plant communities and channel morphology. Quantifying biotic-abiotic interactions remains difficult because of the challenges in making and analyzing appropriately scaled observations. We measure the influence of woody vegetation on channel topography at the p...

Stream channels are scaled to the amount of water and sediment they convey. The amount and size of bed sediment, composition of bank material, type of channel vegetation (both riparian and in-stream), and valley morphology (slope and width) influence channel size and shape. Interactions and feedbacks among these six bio-hydro-geomorphic controls di...

Plants influence river channel topography, but our understanding of the interaction among plants, flow, and sediment is limited, especially when sediment supply is variable. Using laboratory experiments in a recirculating flume with live seedlings in a mobile sand bed, we demonstrate how varying the balance between sediment supply and transport cap...

Flow and sediment regimes shape alluvial river channels, yet the influence of these abiotic drivers can be strongly mediated by biotic factors such as the size and density of riparian vegetation. We present results from an experiment designed to identify when plants control fluvial processes and to investigate the sensitivity of fluvial processes t...

The lower Yampa River in Yampa Canyon, western Colorado serves as a natural, field-scale experiment, initiated when the invasive riparian plant, tamarisk (Tamarix spp.), colonized an unregulated river. In response to tamarisk's rapid invasion, the channel narrowed by 6% in the widest reaches since 1961. Taking advantage of this unique setting, we r...

Improved understanding of the connection between riparian vegetation and channel change requires evaluating how fine-scale interactions among stems, water, and sediment affect larger scale flow and sediment transport fields. We propose a spatially explicit model that resolves patch-scale (submeter) patterns of hydraulic roughness over the reach sca...

Recently, an interest has emerged in the role of aquatic biota as geomorphic agents. Although it is difficult to untangle the interconnectedness of the biotic and abiotic constituents within channel networks, a few theoretical efforts and several recent empirical studies have capitalized on this interconnectivity, providing research that narrows th...

Recently, an interest has emerged in the role of aquatic biota as geomorphic agents. Although it is difficult to untangle the interconnectedness of the biotic and abiotic constituents within channel networks, a few theoretical efforts and several recent empirical studies have capitalized on this interconnectivity, providing research that narrows th...

Channel narrowing and planform simplification have been ubiquitous processes on those parts of the Colorado River, the Green River and its tributaries, and the Rio Grande where suspended sediment loads are large. These rivers have been subject to (1) significant flow regime changes caused by dams and diversions and (2) large-scale invasion of non-n...

An enduring question in geomorphology is the role of riparian vegetation in inducing or exacerbating channel narrowing. It is typically difficult to isolate the role of vegetation in causing channel narrowing, because narrowing typically occurs where there are changes in stream flow, sediment supply, the invasion of non-native vegetation, and somet...

Vegetation plays a fundamental role in controlling channel form and influencing channel processes. Experimental work has shown that stem density, stem spacing, relative submergence, and stem flexibility are key indicators of the effectiveness of vegetation in altering the flow field. These parameters are likely to be species dependent and change ov...

The resiliency and sensitivity of western rivers to future climate change may be partly anticipated by the response of these rivers to past perturbations in stream flow and sediment supply. Predictions of earlier spring runoff and reduced peak flows of snowmelt-dominated streams mimic hydrologic changes caused by the closure and operation of large...

Although certain characteristics of the El Niño-Southern Oscillation (ENSO) are well known on contemporary timescales, less is known about the magnitude–frequency relationships of this atmospheric phenomenon on longer timescales or its relationship to widespread flooding, especially in its core zone along the sub-tropical Andes where La Niña or El...

The natural tendency of woody debris to accumulate into complex debris jams has been adapted by the restoration industry because of the morphological and ecological benefits of these structures. While much work has been done on woody debris, there is a lack of understanding of the dynamics of debris jams including the controls on their formation an...

1. Stream ecosystems are the products of interactions between hydrology, geomorphology and ecology, but examining all three components simultaneously is difficult and rarely attempted. Frequently, either geomorphology or hydrology is treated as invariable or static. 2. To examine the validity of treating either hydrology or geomorphology as static,...

Using field-mapping, remote-sensing (ASTER, aerial photography), and GIS/GPS, we identified and analyzed reach-scale geomorphic responses to contemporary floods along a 20-km valley length in hyperarid southern Peru. We combined these data with alluvial stratigraphy of remnant terrace patches recording late Holocene aggradation and incision. In thi...

Numerous studies exist on the hydraulics of woody debris jams and the mechanisms driving their geomorphic influence. While most hydraulic studies treat jams as single, solid objects, jams are clearly not individual cylindrical logs but rather an accumulation of pieces ranging in size from leaves and twigs to entire trunks. Here we treat debris jams...

Numerous studies exist on the hydraulics of woody debris jams and the mechanisms driving their geomorphic influence. While most hydraulic studies treat jams as single, solid objects, jams are clearly not individual cylindrical logs, but rather an accumulation of pieces ranging in size from leaves and twigs to entire trunks. Here we treat debris jam...

Varying the hydrologic regime of a system alters the hierarchy of interactions between flow, organic matter, and physical structure. In most systems, storms are the major OM-export events, but their infrequency in natural systems may make them less important in the daily energy dynamics of streams than the geomorphic forms that partially regulate h...

Here we apply the concept of "dominant discharge" from fluvial geomorphology to analyze the influence of flow regime on stream ecology. Quantitative metrics of effective discharge (Qeff) and functionally-equivalent discharge (Qfed) were developed to quantify how discharge drives organic matter transport, algal growth, nutrient retention, macroinver...

The catastrophic effects of large floods have been well documented, on both contemporary and paleo-timecales, especially for the conterminous U.S. Less is known, however, about extreme events in hyper-arid sub-tropical climates where synoptic scale meteorological causes, such as El Nino-Southern Oscillation events, are the driving atmospheric mecha...