A Method for Spatially Explicit Representation of Sub-watershed Sediment Yield, Southern California, USA

Channel evolution models (CEMs) are used to structure the interpretation of observed channel morphology to support long-term restoration of these systems. However, channels reflect the variety of their watersheds' climatological, ecological and physiographic contexts, and so no single CEM can be truly 'global' . Unrecognised differences between the assumptions and the reality of evolutionary trajectories of particular streams can subsequently lead to restoration actions that neither fully achieve their intended objectives nor successfully self-maintain even limited improvements. Despite the daunting variety of biophysical settings, however, urbanisation imposes distinctive, homogenising influences on virtually all watercourses, suggesting that even a relatively small set of evolutionary pathways can embrace much of the diversity of critical watershed drivers on urban channels. CEMs describing single-thread channel response to incision are most common in the published literature, but not every urban disturbance yields this classic sequence, initiated by excess transport capacity followed by incision, bank erosion, widening and ultimately a lowered re-equilibrated channel. A comprehensive urban CEM must also include responses under less common (but locally ubiquitous) conditions, such as excess sediment relative to transport capacity (the 'inverse' of the classic CEM), imposed constraints on vertical and/or lateral adjustment, and multi-thread channels or those influenced by instream or riparian vegetation. An urban CEM also requires a hierarchical framework that acknowledges fundamental differences in the process drivers within any given watershed, because a single observation of channel form can rarely pinpoint the context or evolutionary trajectory of every stream. We present a geomorphic framework for diagnosing and predicting the evolution of urban streams, potentially guiding the selection of restoration targets that are achievable within an urban context and sustainable without ongoing maintenance.

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“…; Booth et al . ). Conversely, channels in regions of intrinsically low watershed sediment delivery (e.g.…”

Section: Watershed Differences and Urban Channel Evolutionmentioning

confidence: 97%

A channel evolution model to guide sustainable urban stream restoration

Booth

Fischenich

2015

Area

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“…Extrapolation of hillslope erosion process to areas under canopy and not field‐accessible was based on ‘geomorphic landscape units’ (GLUs, Booth et al ., ), a representative area approach similar to ‘response units’ in hydrology (Wolock et al ., ; Beighley et al ., ). Land cover, lithology and hillslope steepness were combined at the scale of their respective minimum resolution (i.e.…”

Section: Methodsmentioning

confidence: 99%

Fluvial system dynamics derived from distributed sediment budgets: perspectives from an uncertainty‐bounded application

Downs

Dusterhoff

Leverich³

et al. 2018

Earth Surf Processes Landf

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The utility of sediment budget analysis is explored in revealing spatio‐temporal changes in the sediment dynamics and morphological responses of a fluvial system subject to significant human impacts during the recent Anthropocene. Sediment budgets require a data‐intensive approach to represent spatially‐differentiated impacts adequately and are subject to numerous estimation uncertainties. Here, field and topographic surveys, historical data, numerical modelling and a representative‐area extrapolation method are integrated to construct a distributed, process‐based sediment budget that addresses historical legacy factors for the highly regulated Lagunitas Creek (213 km2), California, USA, for the period 1983–2008. Independent corroboration methods and error propagation analysis produce an uncertainty assessment unique to a catchment of this size. Current sediment yields of ~20 000 t a‐1 ± 6000 t a‐1 equate to unit rates of ~300 t km‐2 a‐1 ± 90 t km‐2 a‐1 over the effective sediment contributing area of 64 km2. This is comparable with yields associated with early Euro‐American settlement in the catchment, despite loss of sediment supply upstream of the two large dams. It occurs because ~57% of the sediment is now derived from incision‐related channel erosion. Further, the highly efficient routing of channel‐derived sediments in these incised channels suggests an efflux of 84% of contemporary sediment production, contrasting with the efflux of ≈10–30% reported for unregulated agricultural catchments. The results highlight that sediment budgets for regulated rivers must accommodate channel morphological responses to avoid significantly misrepresenting catchment yields, and that volumetric precision in sediment budgets may best be improved by repeat, spatially dense, channel cross‐section surveys. Human activities have impacted every aspect of the sediment dynamics of Lagunitas Creek (production, storage, transfer, rates of movement through storage), confirming that, while distributed sediment budgets are data demanding and subject to numerous error sources, the approach can provide valuable insights into Anthropocene fluvial geomorphology. Copyright © 2017 John Wiley & Sons, Ltd.

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“…Episodic mass wasting sources in decadal sediment supply can be estimated through a more detailed sediment budget approach (e.g., Reid and Dunne, 1996), or more simply by increasing the sediment yield in active mass wasting areas based on regional literature values. For example, two similar studies (GMA, 2007;Bigelow et al, 2012b) used digitized maps of active earthflows and local literature values of earthflow rates to appropriately increase the sediment yield estimates at these discrete locations within the watersheds. This approach in part accounts for differences in lithologic erosion rates across the basin, as higher sediment yields from earthflows often occur in specific formations that produce clay-rich soils (e.g., Keefer and Johnson, 1983).…”

Section: Adjustments and Considerationsmentioning

confidence: 99%

“…For example, the Universal Soil Loss Equation (USLE) (Wischmeier and Smith, 1978), the revised USLE (RUSLE) (Renard et al, 1997), and similar approaches (e.g., Booth et al, 2014) simply use a generic reduction (C-factor) based on classes of vegetation cover (e.g., crop type, forest, scrub, etc.) to adjust erosion predictions over vast areas regardless of the individual size of vegetation within the categories.…”

Section: Modifying Erosion Potential By Vegetationmentioning

confidence: 99%

“…are often created by headward incision of the channel network in response to local or regional base-level lowering (Begin et al, 1981;Schumm, 1993), tectonic uplift (Burnett and Schumm, 1983), or disturbances that change the relative balance between sediment transport and supply (Schumm et al, 1984;Schumm, 1999). For example, incision caused by humans can include urbanization that greatly increases runoff and sediment transport (Booth, 1991), or dams and gravel mining that reduce sediment supply (Kondolf, 1997;Surian and Rinaldi, 2003). Examples of natural causes of incision include change to a wetter climate that increases runoff (Balling and Wells, 1990) and catastrophic events that increase sediment supply from volcanic eruptions (Simon, 1992), extreme precipitation (Miller and Benda, 2000), or following wildfire (Benda et al, 1998).…”

Section: Introduction and Objectivementioning

confidence: 99%

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Delineating incised stream sediment sources within a San Francisco Bay tributary basin

2016

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Abstract. Erosion and sedimentation pose ubiquitous problems for land and watershed managers, requiring delineation of sediment sources and sinks across landscapes. However, the technical complexity of many spatially explicit erosion models precludes their use by practitioners. To address this critical gap, we demonstrate a contemporary use of applied geomorphometry through a straightforward GIS analysis of sediment sources in the San Francisco Bay Area in California, USA, designed to support erosion reduction strategies. Using 2 m lidar digital elevation models, we delineated the entire river network in the Arroyo Mocho watershed (573 km 2 ) at the scale of ∼ 30 m segments and identified incised landforms using a combination of hillslope gradient and planform curvature. Chronic erosion to the channel network was estimated based on these topographic attributes and the size of vegetation, and calibrated to sediment gage data, providing a spatially explicit estimate of sediment yield from incised channels across the basin. Rates of erosion were summarized downstream through the channel network, revealing patterns of sediment supply at the reach scale. Erosion and sediment supply were also aggregated to subbasins, allowing comparative analyses at the scale of tributaries. The erosion patterns delineated using this approach provide land use planners with a robust framework to design erosion reduction strategies. More broadly, the study demonstrates a modern analysis of important geomorphic processes affected by land use that is easily applied by agencies to solve common problems in watersheds, improving the integration between science and environmental management.

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A Method for Spatially Explicit Representation of Sub-watershed Sediment Yield, Southern California, USA

Cited by 9 publications

References 50 publications

A channel evolution model to guide sustainable urban stream restoration

A channel evolution model to guide sustainable urban stream restoration

Fluvial system dynamics derived from distributed sediment budgets: perspectives from an uncertainty‐bounded application

Delineating incised stream sediment sources within a San Francisco Bay tributary basin

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