Abstract
AbstractInundation dynamics are a key driver of ecosystem form and function in river‐valley bottoms. Inundation itself is an outcome of multi‐scalar interactions and can vary strongly within and among river reaches. As a result, establishing to what degree and how inundation dynamics vary spatially both within and among river reaches can be challenging. The objective of this study was to understand how river‐valley morphology, basin size, and flow‐event magnitude interact to affect inundation dynamics in river‐valley bottoms. We used 2D hydraulic models to simulate inundation in four river reaches from Maryland's Piedmont physiographic province, and qualitatively and quantitatively summarized within‐ and among‐reach patterns of inundation extent, duration, depth, shear stress, and wetting frequencies. On average, reaches from confined valley settings experienced less extensive flooding, shorter durations and shallower depths, stronger gradients of maximum shear stress, and relatively infrequent wetting compared to reaches from unconfined settings. These patterns were generally consistent across flow‐event magnitudes. Patterns of within‐reach flooding across event magnitudes revealed complex interactions between hydrology and surface topography. We concluded that valley morphology had a greater impact on flooding patterns than basin size: Inundation patterns were more consistent across reaches of similar morphology than similar basin size, but absolute values of inundation characteristics varied between large and small basins. Our results showed that the manifestation of out‐of‐bank flows in valley floors can vary widely depending on geomorphic context, even within a single physiographic province, which suggests that hydrologic and hydraulic conditions experienced on the valley floor may not be well represented by existing hydrologic metrics derived from discharge data alone. We thus support the notion that 2D hydraulic models can be useful hydrometric tools for cross‐scale investigations of floodplain ecosystems.
Highlights
Inundation dynamics are believed to be the master variable driving the structure and function of floodplain ecosystems (Junk et al 1989, Ward et al 2002)
We asked: (1) How do inundation attributes vary among and within river reaches? (2) What is the relative importance of river reach morphology and basin scale on within-reach distributions of inundation attributes? and (3) How do these relationships change, if at all, across a gradient of flow-event magnitudes? We focused on describing patterns of five inundation attributes believed to be important in the structure and function of floodplain ecosystems: inundation extent, duration, depth, frequency, and shear stress
Physiographic setting and study reaches We examined floodplain inundation dynamics from basins located in the Maryland Piedmont physiographic province of the Chesapeake Bay
Summary
Inundation dynamics are believed to be the master variable driving the structure and function of floodplain ecosystems (Junk et al 1989, Ward et al 2002). Flooding itself is an outcome of multi-scalar interactions among climate, landscape physiography, river-valley morphology, and local channel hydraulics. High upstream transport efficiency can produce frequent flooding if a given river-valley reach (i.e., a segment expressing relatively uniform valley morphology) is incapable of efficiently propagating the flood wave, or energetically intense floods if reach slope or valley width promotes deeper flow depths. Limited upstream conveyance combined with a reduced capacity for transport through the local reach can result in prolonged flooding. Inundation dynamics may vary widely among reaches with different river-valley morphologies and contributing areas, even if they are from the same basin (Baker and Wiley 2009)
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