More Like this

1. Flood Wave Attenuation as a Function of Floodplain Storage, Secondary Channel Conveyance, and Discharge

   https://doi.org/10.1029/2024WR038582  

   Tull, N; Passalacqua, P (May 2025, Water Resources Research)

   Abstract The elevation of natural river levees can vary considerably along the length of a river, and low‐lying features such as secondary floodplain channels allow for hydrologic exchange between a river and its floodplain over a range of discharges. This hydrologic, “river‐floodplain connectivity” plays a role in attenuating flood waves and transporting fluvial material to floodplain ecosystems. However, flood wave attenuation and transport are also limited by the available storage provided by floodplains. In this study, we explore the combined controls of river‐floodplain connectivity and floodplain width on flood wave attenuation and transport, and how those controls change as flood magnitude increases. We develop idealized river‐floodplain models based on the geometry of the lower Trinity River in Texas, USA, varying floodplain width, peak discharge, and degree of river‐floodplain connectivity, which we prescribe by varying the width of a secondary channel connecting the river to the floodplain. We show that attenuation transitions from connectivity‐limited to storage‐limited as discharge increases. Secondary channel conveyance allows for floodplain inundation at lower discharges, but also fills the floodplain faster and, for larger floods, can cause higher flood peaks downstream. Greater secondary channel conveyance and wider floodplains increase fluxes to the floodplain, but secondary conveyance allows the floodplain to drain faster while wider floodplains have longer average residence times. This study presents a framework for understanding how secondary channel conveyance and floodplain width combine to modulate lateral flow exchange, residence times, and flood wave attenuation, and can guide successful management of river systems and future restoration efforts. 

   more » « less
2. River-floodplain connectivity and residence times controlled by topographic bluffs along a backwater transition

   https://doi.org/10.3389/frwa.2023.1306481  

   Tull, Nelson; Moodie, Andrew J; Passalacqua, Paola (January 2024, Frontiers in Water)

   The morphology of river levees and floodplains is an important control on river-floodplain connectivity within a river system under sub-bankfull conditions, and this morphology changes as a river approaches the coast due to backwater influence. Floodplain width can also vary along a river, and floodplain constrictions in the form of bluffs adjacent to the river can influence inundation extent. However, the relative controls of backwater-influenced floodplain topography and bluff topography on river-floodplain connectivity have not been studied. We measure discharge along the lower Trinity River (Texas, USA) during high flow to determine which floodplain features are associated with major river-floodplain flow exchanges. We develop a numerical model representing the transition to backwater-dominated river hydraulics, and quantify downstream changes in levee channelization, inundation, and fluxes along the river-floodplain boundary. We model passive particle transport through the floodplain, and compute residence times as a function of location where particles enter the floodplain. We find that bluff topography controls flow from the floodplain back to the river, whereas levee topography facilitates flow to the floodplain through floodplain channels. Return flow to the river is limited to locations just upstream of bluffs, even under receding flood conditions, whereas outflow locations are numerous and occur all along the river. Residence times for particles entering the floodplain far upstream of bluffs are as much as two orders of magnitude longer than those for particles entering short distances upstream of bluffs. This study can benefit floodplain ecosystem management and restoration plans by informing on the key locations of lateral exchange and variable residence time distributions in river-floodplain systems. 

   more » « less
3. River‐Floodplain Exchange Influences Basin‐Scale Mixing During Large Fluvial Flood Events

   https://doi.org/10.1029/2026GL122190  

   Brinkerhoff, Craig B; Raymond, Peter A; Gleason, Colin J (May 2026, Geophysical Research Letters)

   Abstract River‐floodplain exchange occurs when high flows inundate the floodplain and exchange water bi‐directionally between substrates and communities. While well‐understood locally, the full spatial heterogeneity of exchange event duration (the residence time) and magnitude (the exchange flux, or discharge) remains poorly constrained, limiting our understanding of the role that underlying structural connectivity and hydrologic regime plays in basin‐scale mixing. Here, we use machine learning to predict river‐floodplain exchange duration and magnitude for over 1.8M rivers in the contiguous United States. We find residence time is on average 3.4 times longer in the floodplain than the river, with that difference decreasing as both event and river size increase. Further, more than 31% of basin water may exchange with the floodplain during large floods. We confirm that the cumulative effect of reach‐scale exchange influences basin‐scale mixing and subsequent biogeochemical processing, though the nature of that influence will be region, river, and constituent specific. 

   more » « less
4. Empirical Evidence of Dynamic Hydrogeomorphic Feature Inundation in a Lowland Floodplain

   https://doi.org/10.1002/hyp.70043  

   Cain, Molly R; Hixson, Jase L; Jones, C Nathan; Rhoads, Bruce L; Ward, Adam S (January 2025, Hydrological Processes)

   NA (Ed.)

   ABSTRACT Floodplains along low‐gradient, meandering river systems contain diverse hydrogeomorphic features, ranging from isolated depressions to hydrologically‐connected channels. These ephemerally‐flooded features inundate prior to river water overtopping all banks, enhancing river‐floodplain connectivity during moderately high flow stages. Predicting when and where ecological functions occur in floodplains requires understanding the dynamic hydrologic processes of hydrogeomorphic features, including inundation and exchange. In this study, we examined storm event‐scale inundation and exchange dynamics along a lowland, meandering river system in central Illinois (USA). We monitored surface water presence/absence, surface water level, and groundwater level across floodplain hydrogeomorphic feature types (i.e., isolated depression, backwater channel, and flow‐through channel). Using these data, we evaluated inundation onset and recession characteristics, drivers of groundwater‐surface water interactions, and direction of hydrologic exchange with the river channel. Surface water presence/absence patterns suggested inundation onset timescales were primarily controlled by microtopography and recession timescales were correlated with floodplain elevation. Employing a novel hysteresis approach for characterising groundwater‐surface water interactions, we observed distinct patterns indicating differences in water sources across hydrogeomorphic units and event characteristics. Finally, differences in hydraulic head along floodplain channels revealed that channels with multiple inlets/outlets (i.e., flow‐through channels) conveyed down‐valley flow and channels with single inlets primarily functioned as sinks of river‐derived water to the floodplain with short source periods. These results highlight the heterogeneity of hydrologic processes that occur along lowland, meandering river‐floodplains, and more specifically, point to the important role hydrogeomorphic features play in controlling dynamic connectivity within the river corridor. 

   more » « less
5. Forensic Hydraulic Analysis of Floodplain Connectivity Driven by Historical Beaver Dams in Colorado Headwater Streams

   https://doi.org/10.1002/rra.70165  

   Schultz, Kayla; Morrison, Ryan R; Rathburn, Sara; Mertz, Connor; Christensen, Nicholas (June 2026, River Research and Applications)

   ABSTRACT As ecosystem engineers, beavers (Castor canadensis) modify river corridor form through dam building. When beavers are removed from a river corridor, their unmaintained dams wash out, altering the stream's hydrologic regime. The assumption that beaver dams increase floodplain connectivity is frequently presumed but has not been directly quantified. To address this gap, we assessed changes in floodplain connectivity caused by the loss of beaver dams at three headwater streams in Colorado, USA. Using a forensic analysis of historical beaver activity, we developed two‐dimensional hydraulic models to compare metrics of floodplain connectivity under historical (beaver‐active) and present (no beaver activity) scenarios. At three simulated flood discharges, we quantified changes in the volume of water on the floodplain, the fraction of flow through the floodplain, the volumetric flux into the floodplain, and mean site and floodplain residence times. The loss of beaver dams decreased floodplain connectivity across all metrics (up to a 96.5% loss in connectivity) except mean floodplain residence time, which increased in the absence of dams. Sensitivity analysis results show that the flow state and condition of beaver dams can have reach‐scale impacts on floodplain connectivity. Notably, while we observed floodplain disconnection due to the loss of beaver dams at each site, the magnitude of change varied depending on both site‐specific characteristics and on the flood magnitude. We conclude that, in headwater streams, beaver dams play an important and quantifiable role in facilitating floodplain connectivity, and floodplain disconnection from the loss of dams has major implications for other ecological and geomorphic floodplain processes. These results are especially timely considering the increasing interest in beaver‐related restoration. 

   more » « less