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The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

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River deltas are among the world's most imperiled landscapes. Their low elevations, combined with their typically low elevation gradients, make them particularly vulnerable to changes in sediment supply, eustatic sea-level rise (Cazenave & Llovel, 2010) and subsidence (Erickson, 2006), as their sustainability largely hinges on the relative balance between these factors (Syvitski, 2008). With over 500 million people

ABSTRACT:The entrance channel at the Mouth of the Columbia River requires annual dredging of 3 to 5 million cu m (3.9 to 6.5 million cu yd) of fine-to-medium sand to maintain the navigation channel at the authorized depth. The sandy dredged material is placed in EPA-approved Ocean Dredged Material Disposal Sites (ODMDS). Exceedance of ODMDS capacity at the Mouth of the Columbia River creates two operational problems for the Portland District: (a) The overall footprint of disposed dredged material extends beyond the existing ODMDS formally permitted boundaries by as much as 915 m (3,000 ft) in some cases, and (b) dredged material within the ODMDS has accumulated to such an aerial and vertical extent that adverse sea conditions are created. In some cases, mounds rise 18.3 to 21.4 m (60 to 70 ft) above surrounding bathymetry. Mariners report that the ODMDS mounds cause waves to steepen and/or break in the vicinity of the sites, and that these wave conditions are hazardous to navigation.The objectives of the MCNP monitoring at the Mouth of the Columbia River were to: (a) Analyze existing data to document historic bathymetric response at the Mouth of the Columbia River entrance and the ODMDS due to anthropogenic and environmental conditions at the Mouth of the Columbia River; (b) monitor selected Mouth of the Columbia River ODMDS locations to observe bathymetric response with respect to dredging disposal operations and the forcing environment; (c) explain qualitatively and quantitatively the rates of sediment dispersion at the Mouth of the Columbia River ODMDS, and relate observed sediment dispersion of ODMDS citing and management practice; (d) assess the suitability of new USACE Dredging Research Program sediment fate models (STFATE, LTFATE, and MDFATE) and RCPWAVE, and synthetically-generated input data from HPDPRE, HPDSIM, and ADCIRC for predicting sediment dispersion in the environment off the Mouth of the Columbia River; and (e) develop a standardized method for data collection and management that can be used by other Corps District offices using as ODMDS.The FATE models had previously suffered from a lack of quality field data for their calibration and verification. As the new MCNP data were being acquired and processed, enhancements to the FATE models were incorporated to ensure these models would accurately predict the ultimate disposition of future dredged material disposal at such exceedingly energic locations. Finally, predictive techniques for determining sediment transport processes under both waves and currents were developed to assess the movement of disposed material at the Mouth of the Columbia River for assessing capacity and to determine the useful life of the ODMDS.The MCNP Mouth of the Columbia River study approach consisted of the execution of four fundamental tasks: (a) a regional coastal processes analysis, (b) oceanographic field data collection and analysis, (c) state-of-the-art numerical modeling, and (d) a comprehensive analysis of sediment transport processes. DISCLAIMER:The contents of t...

River deltas are maintained by a continuous supply of terrestrial sediments that provide critical land-building material to help sustain and protect coastal communities. In order to examine the mechanisms of sediment delivery, a field study was conducted at Wax Lake Delta located in St. Mary Parish, LA. Instrumented platforms equipped with wave, current, tide and sediment sensors were installed on Mike Island, an interdistributary island located near the centerline axis of the delta complex. This report focuses on the hydrodynamic measurements, which imply multiple regimes of sediment delivery based on seasonal differences in climate and biological activity. In winter, vegetation is absent, and the primary flow is driven by tides. In the spring, increased river discharge inundates the island producing lateral flows and increase in suspended sediment concentrations that supply large quantities of terrestrial sediments to interior regions. In late spring, persistent southeasterly winds create setup along the coast and higher water levels over the island allowing waves to more easily penetrate the island interior. The emergence of American lotus (Nelumbo lutea) in summer forms a dense canopy over the island reducing wave and current energy, increasing the potential for sediment deposition.