Equilibrium or indeterminate? Where sediment budgets fail: Sediment mass balance and adjustment of channel form, Green River downstream from Flaming Gorge Dam, Utah and Colorado

Rainfall induced landslides and soil erosion are part of a complex system of multiple interacting processes, and both are capable of significantly affecting sediment budgets. These sediment mass movements also have the potential to significantly impact on a broad network of ecosystems health, functionality and the services they provide. To support the integrated assessment of these processes it is necessary to develop reliable modelling architectures. This paper proposes a semi-quantitative integrated methodology for a robust assessment of soil erosion rates in data poor regions affected by landslide activity. It combines heuristic, empirical and probabilistic approaches. This proposed methodology is based on the geospatial semantic array programming paradigm and has been implemented on a catchment scale methodology using GIS spatial analysis tools and GNU Octave. The integrated data-transformation model relies on a modular architecture, where the information flow among modules is constrained by semantic checks. In order to improve computational reproducibility, the geospatial data transformations implemented in ESRI ArcGis are made available in the free software GRASS GIS. The proposed modelling architecture is flexible enough for future transdisciplinary scenario-analysis to be more easily designed. In particular, the architecture might contribute as a novel component to simplify future integrated analyses of the potential impact of wildfires or vegetation types and distributions, on sediment transport from water induced landslides and erosion.

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Dam tailwaters compound the effects of reservoirs on the longitudinal transport of organic carbon in an arid river

Biogeosciences Discussions ◽

10.5194/bgd-12-6081-2015 ◽

2015 ◽

Vol 12 (8) ◽

pp. 6081-6114

Author(s):

A. J. Ulseth ◽

R. O. Hall Jr.

Keyword(s):

Organic Carbon ◽

Base Flow ◽

Green River ◽

Transport And Transformation ◽

Stream Discharge ◽

River Reservoir ◽

Gorge Reservoir ◽

Flaming Gorge ◽

Early Snowmelt ◽

Yampa River

Abstract. Reservoirs on rivers can disrupt organic carbon (OC) transport and transformation, but less is known how downstream river reaches directly below dams contribute to OC processing than reservoirs alone. We compared how reservoirs and their associated tailwaters affected OC quantity and quality by calculating particulate (P) OC and dissolved (D) OC fluxes, and measuring composition and bioavailability of DOC. We sampled the Yampa River near Maybell, Colorado, USA and the Green River above and below Fontenelle and Flaming Gorge reservoirs, and their respective tailwaters from early snowmelt to base flow hydrological conditions. In unregulated reaches (Yampa River, Green River above Fontenelle reservoir), DOC and POC concentrations increased with snowmelt discharge. POC and DOC concentrations also increased with stream discharge below Fontenelle reservoir, but there was no relationship between DOC and stream flow below Flaming Gorge reservoir. The annual load of POC was 3-fold lower below Fontenelle Reservoir and nearly 7-fold lower below Flaming Gorge reservoir, compared to their respective upstream sampling sites. DOC exported to downstream reaches from both reservoirs was less bioavailable, as measured with bioassays, than DOC upriver of the reservoirs. Lastly, tailwater reaches below the reservoirs generated OC, exporting 1.6–2.2 g C m−2 d−1 of OC to downstream ecosystems. Changes in total fluxes from upstream to downstream of reservoirs and their tailwaters do not represent the simultaneous transformation and production of OC, which may lead to the underestimation of the quantity of OC mineralized, transformed, or retained in coupled river-reservoir-tailwater ecosystems.

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