Deposition Potential and Flow‐Response Dynamics of Emergent Sandbars in a Braided River. Issue 1 (15th January 2020)

• Record Type: Journal Article
• Authors: Alexander, Jason S.; McElroy, Brandon; Huzurbazar, Snehalata; Elliott, Caroline; Murr, Marissa L.
• Is Part Of: Water resources research. Volume 56:Issue 1(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-01-15
• Subjects: sandbar -- braided -- river -- tern -- plover -- habitat; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2018WR024107
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Sandbars are ubiquitous in sandy‐braided rivers throughout the world. In the Great Plains of the United States, recovery and expansion of emergent sandbar habitat (ESH) has been a priority in lowland rivers where the natural extent of sandbars has been degraded. Recovery efforts are aimed at protection of populations of the interior least tern ( Sterna antillarum ) and piping plover ( Charadrius melodus ). But quantitative observations of deposition and erosion dynamics of populations of sandbars across long segments of rivers are rare. We present a three‐part case study which used Bayesian regression models to examine relations between hydrology, channel morphology, and ESH responses in the Platte River, eastern Nebraska. Logistic regression indicates presence of ESH is positively related to the Parker, (1976) stability criterion and a gradient in sediment transport mode, and negatively related to presence of vegetation. Hierarchical linear regression modeling shows direct coupling between sandbar top‐surface height and formative flood magnitude, but the gap between formative flood stage and sandbar top‐surface increases with increasing discharge. Finally, linear regression modeling of sandbar erosion demonstrates rates of ESH erosion are on the order of 10 −1 ha/day during high‐flow periods and 10 −2 during low‐flow periods, but sandbar persistence is largely a function of sandbar starting size. The collective observations highlight the importance of large floods (>3‐year recurrence) in creating very large sandbars that persist as high‐quality ESH over periods of years whereas lower‐magnitude, more‐frequent flood events create lower‐quality ESH that typically does not persist into the following nesting season. Key Points: Potential to deposit emergent sandbars is a positive function of Parker (1976) stability criteria and a gradient in sediment transport mode Emergent sandbar top‐surface height grows linearly with formative flood magnitude at a rate that lags growth of formative flood stage Emergent sandbar persistence is largely dependent on sandbar starting size, which itself is dependent on formative flood magnitude