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Browsing Research Data - Other by Subject "logjams"

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    ItemOpen Access
    Data Associated with "Logjam Characteristics as Drivers of Transient Storage in Headwater Streams"
    (Colorado State University. Libraries, 2022) Marshall, Anna; Zhang, Xiaolang; Sawyer, Audrey Hucks; Wohl, Ellen; Singha, Kamini
    Logjams in a stream create backwater conditions and locally force water to flow through the streambed, creating zones of transient storage within the surface and subsurface of a stream. We investigate the relative importance of logjam distribution density, logjam permeability, and discharge on transient storage in a simplified experimental channel. We use physical flume experiments in which we inject a salt tracer, monitor fluid conductivity breakthrough curves in surface water, and use breakthrough-curve skew to characterize transient storage. We then develop numerical models in HydroGeoSphere to reveal flow paths through the subsurface (or hyporheic zone) that contribute to some of the longest transient-storage timescales. In both the flume and numerical model, we observe an increase in backwater and hyporheic exchange at logjams. Observed complexities in transient storage behavior may depend largely on surface water flow in the backwater zone. As expected, multiple successive logjams provide more pervasive hyporheic exchange by distributing the head drop at each jam, leading to distributed but shallow flow paths. Decreasing the permeability of a logjam or increasing the discharge both facilitate more surface water storage and elevate the surface water level upstream of a logjam, thus increasing hyporheic exchange. Multiple logjams with low permeability result in the greatest magnitude of transient storage, suggesting that this configuration maximizes solute retention in backwater zones, while hyporheic exchange rates also increase. Understanding how logjam characteristics affect solute transport through both the channel and hyporheic zone has important management implications for rivers in forested, or historically forested, environments.
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    ItemOpen Access
    Datasets associated with ‘All Logjams Are Not Created Equal’
    (Colorado State University. Libraries, 2021) Livers, Bridget; Wohl, Ellen
    Logjams create diverse physical and ecological effects in stream channels, including at least temporary storage of water, sediment, and particulate organic matter. We hypothesize that logjams that span the entire bankfull channel width in channels < 25 m wide are more effective in storing these materials than non-channel spanning logjams. We test this hypothesis by systematically comparing characteristics of 183 logjams from 17 stream reaches in the Southern Rocky Mountains. Our dataset is novel in that it evaluates naturally occurring logjams in unaltered streams in a single study area specifically based on whether they span the stream channel. We find that channel-spanning logjams have a significantly larger number of wood pieces, longer & wider pieces, more ramp and bridge pieces, and greater logjam height and volume, both as raw data and when standardized by average channel width. Channel-spanning logjams also have significantly greater backwater pool volume and volume of particulate organic matter stored in backwater pools and in logjams. Restoration employing engineered logjams in relatively small channels currently focuses on non-spanning logjams, but could be expanded to include spanning logjams.
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    ItemOpen Access
    Supplementary materials associated with “The Transience of Channel-Spanning Logjams in Mountain Streams”
    (Colorado State University. Libraries, 2022) Wohl, Ellen; Iskin, Emily
    We use 11 years of annual surveys in streams of the Southern Rockies of Colorado, USA to examine the persistence and geomorphic effects of logjams. Each year’s survey includes ~300 logjams along more than 21 km of 4 mountain streams in primarily old-growth subalpine forest. Streams alternate longitudinally between laterally confined reaches with a single channel and wider reaches with multithread channel planform. We distinguish logjam persistence and site persistence. Logjam persistence is the median timespan over which an individual jam is present. Site persistence describes the tendency for jams to disappear and then re-form at the same site. We hypothesize that (i) site persistence is greatest in multithread reaches; (ii) logjam persistence is greatest in multithread reaches; and (iii) average backwater storage at each jam is greater in multithread reaches. We find that spatial and temporal metrics of site persistence differ significantly between single and multithread reaches. Individual logjam persistence does not differ significantly. Backwater storage is significantly greater in multithread reaches. Varying combinations of riparian forest age and average logjams per channel length explain variation in jam and site persistence and backwater storage via multivariate linear regression analyses. Over the 11 years of survey, a total of 429 distinct logjams were observed. Only 2.1% of the population was present for all 11 annual surveys. Median jam persistence is 1-2.5 years; median site persistence is 6-10 years. Despite the transience of most channel-spanning logjams in the population, these jams create persistent effects in channel planform and backwater storage.