Browsing by Author "Keys, Tyler A."

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    Effects of Large Wood on Floodplain Connectivity in a Headwater Mid-Atlantic Stream
    Keys, Tyler A.; Governer, Heather; Jones, C. Nathan; Hession, W. Cully; Hester, Erich T.; Scott, Durelle T. (2018-05-08)
    Large wood (LW) plays an essential role in aquatic ecosystem health and function. Traditionally, LW has been removed from streams to minimize localized flooding and increase conveyance efficiency. More recently, LW is often added to streams as a component of stream and river restoration activities. While much research has focused on the role of LW in habitat provisioning, geomorphic stability, and hydraulics at low to medium flows, we know little about the role of LW during storm events. To address this question, we investigated the role of LW on floodplain connectivity along a headwater stream in the Mid-Atlantic region of the United States. Specifically, we conducted two artificial floods, one with and one without LW, and then utilized field measurements in conjunction with hydrodynamic modeling to quantify floodplain connectivity during the experimental floods and to characterize potential management variables for optimized restoration activities. Experimental observations show that the addition of LW increased maximum floodplain inundation extent by 34%, increased floodplain inundation depth by 33%, and decreased maximum thalweg velocity by 10%. Model results demonstrated that different placement of LW along the reach has the potential to increase floodplain flow by up to 40%, with highest flooding potential at cross sections with high longitudinal velocity and shallow depth. Additionally, model simulations show that the effects of LW on floodplain discharge decrease as storm recurrence interval increases, with no measurable impact at a recurrence interval of more than 25 years.
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    Evaluating rare earth elements as tracers of fluvial processes: Fine sediment transport and deposition in a small stream
    Govenor, Heather; Hession, W. Cully; Keys, Tyler A.; Jones, C. Nathan; Stewart, Ryan D.; Krometis, Leigh-Anne H. (ASABE, 2021-01-01)
    Effective sediment management requires an understanding of the lag time between best management practice implementation and observable changes in the target water body. To improve our understanding of sediment lag times, we tested a method to label locally sourced sediments with rare earth elements to quantify fine sediment flow-through and storage in fluvial systems. We injected sediments labeled with lanthanum and ytterbium into a small stream during two artificial flood events. During the floods, we collected and quantified suspended sediments and sediment deposition in the stream channel and floodplain at four cross-sections within our study reach. Two down-gradient (90 m and 850 m) timeintegrated suspended sediment samplers evaluated total travel distance. Sediment tracer observations of particle transport distances ranged from 0 m to at least 850 m at a maximum flow rate of 55 L s-1 (stream 1.5 year flow was 515 L s-1). Sediment deposition per unit area was greater in the channel than in the floodplain. The majority of sediment tracer mass injected into the stream entered storage within the first 69 m of the reach. Some particles that deposited following the first flood were resuspended and either transported downstream or redeposited within the study reach. Our results support the further use of rare earth elements as sediment tracers to inform water quality and sediment transport models, and to provide estimates of lag times between management actions and downstream improvements.