Tidal-Fluvial and Estuarine Processes in the Lower Columbia River: II. Water Level Models, Floodplain Wetland Inundation, and System Zones

Abstract

Spatially varying water-level regimes are a factor controlling estuarine and tidal-fluvial wetland vegetation patterns. As described in Part I, water levels in the Lower Columbia River and estuary (LCRE) are influenced by tides, river flow, hydropower operations, and coastal processes. In Part II, regression models based on tidal theory are used to quantify the role of these processes in determining water levels in the mainstem river and floodplain wetlands, and to provide 21-year inundation hindcasts. Analyses are conducted at 19 LCRE mainstem channel stations and 23 tidally exposed floodplain wetland stations. Sum exceedance values (SEVs) are used to compare wetland hydrologic regimes at different locations on the river floodplain. A new predictive tool is introduced and validated, the potential SEV (pSEV), which can reduce the need for extensive new data collection in wetland restoration planning. Models of water levels and inundation frequency distinguish four zones encompassing eight reaches. The system zones are the wave-and current-dominated Entrance to river kilometer (rkm) 5; the Estuary (rkm-5 to 87), comprised of a lower reach with salinity, the energy minimum (where the turbidity maximum normally occurs), and an upper estuary reach without salinity; the Tidal River (rkm-87 to 229), with lower, middle, and upper reaches in which river flow becomes increasingly dominant over tides in determining water levels; and the steep and weakly tidal Cascade (rkm-229 to 234) immediately downstream from Bonneville Dam. The same zonation is seen in the water levels of floodplain stations, with considerable modification of tidal properties. The system zones and reaches defined here reflect geological features and their boundaries are congruent with five wetland vegetation zones.

Storm‐driven particulate organic matter flux connects a tidal tributary floodplain wetland, mainstem river, and estuary

“…Of this mobilized H-POM, 100% passed the Below KF transect, 65% passed through the Confluence of Seal Slough and the Grays River, and about 52% passed through the mouth to Grays Bay (Fig. 2d), which is located on the main stem of the Columbia River in the estuary system zone (Jay et al 2016). H-POM was redistributed to the floodplain during the peak flood events and was then available for transport during moderate flow conditions.…”

“…d), which is located on the main stem of the Columbia River in the estuary system zone (Jay et al. ). H‐POM was redistributed to the floodplain during the peak flood events and was then available for transport during moderate flow conditions.…”

“…The study site, Kandoll Farm (KF site), is~7 km upstream from the confluence of the Grays and Columbia Rivers. The confluence, at Grays Bay, is within the energy minimum reach (i.e., where the turbidity maximum normally occurs) of the Columbia River estuary system zone between river kilometers 21 and 39 (Jay et al 2016). The 65-ha KF site was disconnected from Grays River and its floodplain by dikes along the river and across the floodplain, forming a parcel isolated from all but the most extreme annual flood events ( Fig.…”

Decadal variability of tidal dynamics in the Pearl River Delta: Spatial patterns, causes, and implications for estuarine water management

“…Previous studies on the long‐term evolution of tidal dynamics mainly focused on tidal properties in terms of the tidal range and tidal datum level (e.g., lower low water, higher high water, and MWL). The underlying causes of historic changes can then be diagnosed either by trend tests, change‐point detections (Zhang et al, , , ), or by harmonic analysis that allows to describe the tidal behaviour using tidal species or constituents (Kukulka & Jay, ; Jay, Leffler, & Degens, , , ; Zhang et al, ). However, gradients of the tidal range or tidal datum levels are of greater practical interest because they are directly related to the magnitude of tidal dynamics.…”

Juvenile Salmonid Assemblages at the Mirror Lake Complex in the Lower Columbia River before and after a Culvert Modification

“…; Jay et al. ). As part of the effort to restore Columbia River salmonids, attention has been increasingly focused on improving and increasing available estuarine rearing habitat for juvenile salmonids in the LCRE (Bottom et al.…”