Indirect Environmental Effects of Dikes on Estuarine Tidal Channels: Thinking Outside of the Dike for Habitat Restoration and Monitoring
TL;DR: In this article, the authors analyzed historical photos of the Skagit River delta marshes (Washington, U.S.) and compared changes in estuarine marsh and tidal channel surface area from 1956-2000 in the Wiley Slough area of the South Fork Skagits delta, and from 1937-2000 on the North Fork delta.
Abstract: While the most obvious effects of dike construction and marsh conversion are those affecting the con- verted land (direct or intended effects), less immediately apparent effects also occur seaward of dikes (indirect or unintended effects). I analyzed historical photos of the Skagit River delta marshes (Washington, U.S.) and compared changes in estuarine marsh and tidal channel surface area from 1956-2000 in the Wiley Slough area of the South Fork Skagit delta, and from 1937-2000 in the North Fork delta. Dike construction in the late 1950s caused the loss of 80 ha of estuarine marsh and 6.7 ha of tidal channel landward of the Wiley Slough dikes. A greater amount of tidal channel surface area, 9.6 ha, was lost seaward of the dikes. Similar losses were observed for two smaller North Fork tidal channel systems. Tidal channels far from dikes did not show comparable changes in channel surface area. These results are consistent with hydraulic geometry theory, which predicts that diking reduces tidal flushing in the undiked channel remnants and this results in sedimentation. Dikes may have significant seaward effects on plants and animals associated with tidal channel habitat. Another likely indirect dike effect is decreased sinuosity in a distributary channel of the South Fork Skagit River adjacent to and downstream of the Wiley Slough dikes, compared to distributary channels upstream or distant from the dikes. Loss of floodplain area to diking and marsh conversion prevents flood energy dissipation over the marsh surface. The distributary channel has responded to greater flood energy by increasing mean channel width and decreasing sinuosity. Restoration of diked areas should consider historic habitat loss seaward of dikes, as well as possible benefits to these areas from dike breaching or removal. Habitat restoration by breaching or removal of dikes should be monitored in areas directly affected by dikes, areas indirectly affected, and distinct reference areas.
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TL;DR: A conceptual model of sedimentation is presented that includes submodels for river supply from the watershed to the Delta, regional transport within the Delta and seaward exchange, and local sedimentation in open water and marsh habitats and demonstrates feedback loops that affect the Delta ecosystem.
Abstract: Sedimentation in the Sacramento–San Joaquin River Delta builds the Delta landscape, creates benthic and pelagic habitat, and transports sediment-associated contaminants. Here we present a conceptual model of sedimentation that includes submodels for river supply from the watershed to the Delta, regional transport within the Delta and seaward exchange, and local sedimentation in open water and marsh habitats. The model demonstrates feedback loops that affect the Delta ecosystem. Submerged and emergent marsh vegetation act as ecosystem engineers that can create a positive feedback loop by decreasing suspended sediment, increasing water column light, which in turn enables more vegetation. Sea-level rise in open water is partially countered by a negative feedback loop that increases deposition if there is a net decrease in hydrodynamic energy. Manipulation of regional sediment transport is probably the most feasible method to control
24 citations
TL;DR: In this article, the authors assess the status of channel networks and pools of two tidal salt marshes recovering from more than a century of agricultural reclamation on the Bay of Fundy, Canada.
Abstract: We assess the status of channel networks and pools of two tidal salt marshes recovering from more than a century of agricultural reclamation on the Bay of Fundy, Canada. A process of largely unmanaged restoration occurred at these sites since abandonment of agricultural activities during the first half of the twentieth century. Each recovering marsh was compared to a reference marsh that was never drained or ditched. We field mapped channel networks at all marshes and used aerial photographs to map the pre-abandonment channel network at one of the sites. The recovering marshes have hybrid channel networks that feature highly variable channel morphologies, loss of original channels, and incorporation of drainage ditches. Although channel networks in recovering marshes integrate agricultural ditches, the recovering marsh networks may not be substantially increased in length or density. Our aerial photograph analysis shows that channel density at one of the recovering marshes is comparable to the pre-abandonment density, but with reduced sinuosity. Field mapping of permanent tidal pools on the lower Bay marshes revealed that pools cover 13% of the recovering marsh, compared to ∼5% of the reference marsh. This study demonstrates that these essential marsh features can be regained through restoration or simple abandonment of drainage infrastructure.
23 citations
Cites background from "Indirect Environmental Effects of D..."
...Drainage of salt marshes has resulted in significant habitat loss on North American coasts (Hood 2004), but our knowledge of how these intertidal habitats respond to human disturbances is sparse for many regions (McIvor and Odum 1988)....
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06 Dec 2007
TL;DR: The third annual report of a six-year project to evaluate the cumulative effects of habitat restoration action in the Columbia River Estuary (CRE) was published in 2006 as discussed by the authors, and the overall objectives of the 2006 study were to continue to develop techniques to assess cumulative effects, refine the standard monitoring protocols, and initiate development of an adaptive management system for Corps of Engineers habitat restoration monitoring efforts in the CRE.
Abstract: This report is the third annual report of a six-year project to evaluate the cumulative effects of habitat restoration action in the Columbia River Estuary (CRE). The project is being conducted for the U.S. Army Corps of Engineers (Corps) by the Marine Sciences Laboratory of the Pacific Northwest National Laboratory, the Pt. Adams Biological Field Station of the National Marine Fisheries Service, and the Columbia River Estuary Study Taskforce. Measurement of the cumulative effects of ecological restoration projects in the Columbia River estuary is a formidable task because of the size and complexity of the estuarine landscape and the meta-populations of salmonids in the Columbia River basin. Despite the challenges presented by this system, developing and implementing appropriate indicators and methods to measure cumulative effects is the best way to enable estuary managers to track the overall effectiveness of investments in estuarine restoration projects. This project is developing methods to quantify the cumulative effects of multiple restoration activities in the CRE. The overall objectives of the 2006 study were to continue to develop techniques to assess cumulative effects, refine the standard monitoring protocols, and initiate development of an adaptive management system for Corps of Engineers’ habitat restoration monitoring efforts in the CRE. (The adaptive management effort will be reported at a later date.) Field studies during 2006 were conducted in tidal freshwater at Kandoll Farm on the lower Grays River and tidal brackish water at Vera Slough on Youngs Bay. Within each of area, we sampled one natural reference site and one restoration site. We addressed the overall objectives with field work in 2006 that, coupled with previous field data, had specific objectives and resulted in some important findings that are summarized here by chapter in this report. Each chapter of the report contains data on particular monitored variables for pre- and post-restoration conditions at both the Kandoll and Vera study areas.
21 citations
TL;DR: A case study of the most extensive area of saltmarshes in Tasmania, on the north-west Circular Head coast, was presented in this article, where a mixture of aerial photographs and ground-truthing data were used to determine human impacts and saltmarsh loss between 1952 and 2006.
Abstract: Coastal saltmarshes of temperate Australia are in decline and have recently been listed as a threatened ecological community under Federal legislation. Further research is required to better understand both the extent and nature of their decline in order to plan their recovery. A case study is presented of the most extensive area of saltmarshes in Tasmania, on the north-west Circular Head coast. A mixture of aerial photographs and ground-truthing data were used to determine human impacts and saltmarsh loss between 1952 and 2006. There was an absolute loss of 219 ha since 1952, largely due to the effects of a 24.5 km network of levees. Of the 1 153 ha of saltmarshes that remained in 2006, a further 752 ha (65%) was associated with one or several of land-based human impacts. This left 401 ha (35%) of saltmarshes that had no recorded human impacts and a contiguous vegetative buffer zone of 50–100 m. These areas represent some of the least disturbed saltmarshes in Tasmania and warrant adequate conservation measures. Future planning for conservation and the use of land and marine resources should strive to promote both the extent and functional health of saltmarshes.
21 citations
TL;DR: In this article, a review of methods for ecological enhancement of sea dikes is presented and limitations and challenges related to these methods are discussed in order to increase environmental awareness and climate change adaptation needs.
Abstract: Sea dikes protect low-lying hinterlands along many coasts all around the world. Commonly, they are designed as embankments with grass covers or grey revetments accounting for the prevailing hydraulic loads. So far, incorporation of ecological aspects in the dike design is limited. With regard to increasing environmental awareness and climate change adaptation needs, the present study reviews methods for ecological enhancement of sea dikes and discusses limitations and challenges related to these methods. In doing so, one key aspect is to maintain dike safety while increasing the ecological value. Potential for ecological enhancement of sea dikes has been found regarding natural or nature-based solutions in the foreshore, dike surface protection measures (vegetated dike covers, hard revetments and dike roads) and the dike geometry. While natural and nature-based solutions in the foreland are investigated thoroughly, so far only few experiences with ecological enhancements of the dike structure itself were gained resulting in uncertainties and knowledge gaps concerning the implementation and efficiency. Additional to technical uncertainties, engineers and ecologists meet the challenge of interdisciplinary collaboration under consideration of societal needs and expectations.
21 citations
Cites background from "Indirect Environmental Effects of D..."
...Dikes are conventionally built as hard engineering structures that withstand the forces of wind, waves and flooding, whereby constituting an interference with nature [9,10]....
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References
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TL;DR: This book is a blend of erudition, popularization, and exposition, and the illustrations include many superb examples of computer graphics that are works of art in their own right.
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TL;DR: A blend of erudition (fascinating and sometimes obscure historical minutiae abound), popularization (mathematical rigor is relegated to appendices) and exposition (the reader need have little knowledge of the fields involved) is presented in this article.
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"Indirect Environmental Effects of D..." refers background in this paper
...Tidal channel allometry follows from a more general fractal theory of landforms (RodriguezIturbe and Rinaldo 1997), and the scaling of perimeter with surface area is a common reflection of landform fractal geometry (Mandelbrot 1983; Sugihara and May 1990)....
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"Indirect Environmental Effects of D..." refers background in this paper
...Greater adjustment in width relative to depth with changing discharge is consistent with hydraulic geometry theory (Leopold et al. 1964)....
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...Because high sinuosity is associated with small channel width relative to depth (Leopold et al. 1964), the observed correlation between changes in sinuosity and in mean channel width suggests that distributary channel widths changed to a greater degree than channel depths....
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...As a final error check, meander bends in tidal channels were examined at scales ranging from 1:1,000 to 1:10,000 to determine whether erosion had occurred in the cut banks of the meanders and sediment deposition at the point bars, in accord with theoretical expectations (Leopold et al. 1964)....
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...Sinuosity was the ratio of sinuous length to straight length (Leopold et al. 1964)....
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