Stage‐discharge relationship in tidal channels

Water Resources Research, 2009

1] Acoustic Doppler current profilers (ADCPs) can be mounted horizontally at a river bank, yielding single-depth horizontal array observations of velocity across the river. This paper presents a semideterministic, semistochastic method to obtain continuous measurements of discharge from horizontal ADCP (HADCP) data in a tidal river. In the deterministic part, single-depth velocity data are converted to specific discharge by applying the law of the wall, which requires knowledge of local values of the bed roughness length (z 0 ). A new filtration technique was developed to infer cross-river profiles of z 0 from moving boat ADCP measurements. Width-averaged values of z 0 were shown to be predominantly constant in time but differed between ebb and flood. In the stochastic part of the method, specific discharge was converted to total discharge on the basis of a model that accounts for the time lag between flow variation in the central part of the river and flow variation near the banks. Model coefficients were derived using moving boat ADCP data. The consistency of mutually independent discharge estimates from HADCP measurements was investigated to validate the method, analyzing river discharge and tidal discharge separately. Inaccuracy of the method is attributed primarily to mechanisms controlling transverse exchange of momentum, which produce temporal variation in the discharge distribution over the cross section. Specifically, development of river dunes may influence the portion of the discharge concentrated within the range of the HADCP.

Estuaries, 1988

Considering a year as a finite population of tidal cycles, annual net flux can be estimated using a regression estimator. In the case of the flux of dissolved nitrite plus nitrate, the marsh was found to be a statistically significant sink for nitrogen (in this form) from adjacent tidal creeks.

Journal of Geophysical Research: Earth Surface, 2014

1] The hydrologic processes by which tide affects river channel and riparian morphology within the tidal freshwater zone are poorly understood yet are fundamental to predicting the fate of coastal rivers and wetlands as sea level rises. We investigated patterns of sediment accretion in riparian wetlands along the nontidal through oligohaline portion of two coastal plain rivers in Maryland, U.S., and how flow velocity, water level, and suspended sediment concentration (SSC) in the channel may have contributed to those patterns. Sediment accretion was measured over a 1 year period using artificial marker horizons, channel hydrology was measured over a 1 month period using acoustic Doppler current profilers, and SSC was predicted from acoustic backscatter. Riparian sediment accretion was lowest at the nontidal sites (mean and standard deviation = 8 ± 8 mm yr À1 ), highest at the upstream tidal freshwater forested wetlands (TFFW) (33 ± 28 mm yr À1 ), low at the midstream TFFW (12 ± 9 mm yr À1 ), and high at the oligohaline (fresh-to-brackish) marshes (19 ± 8 mm yr À1 ). Channel maximum flood and ebb velocity was twofold faster at the oligohaline than tidal freshwater zone on both tidal rivers, corresponding with the differences in in-channel SSC: The oligohaline zone's SSC was more than double the tidal freshwater zone's and was greater than historical SSC at the nontidal gages. The tidal wave characteristics differed between rivers, leading to significantly greater in-channel SSC during floodplain inundation in the weakly convergent than the strongly convergent tidal river. High sediment accretion at the upstream TFFW was likely due to high river discharge following a hurricane.

Limnology and Oceanography, 1980

Estuarine and Coastal Marine Science, 1979

Earth Surface Processes and Landforms, 2003

During a one-year period temporal and spatial variations in suspended sediment concentration (SSC) and deposition were studied on a salt and freshwater tidal marsh in the Scheldt estuary (Belgium, SW Netherlands) using automatic water sampling stations and sediment traps. Temporal variations were found to be controlled by tidal inundation. The initial SSC, measured above the marsh surface at the beginning of inundation events, increases linearly with inundation height at high tide. In accordance with this an exponential relationship is observed between inundation time and sedimentation rates, measured over 25 spring-neap cycles. In addition both SSC and sedimentation rates are higher during winter than during summer for the same inundation height or time. Although spatial differences in vegetation characteristics are large between and within the studied salt and freshwater marsh, they do not affect the spatial sedimentation pattern. Sedimentation rates however strongly decrease with increasing (1) surface elevation, (2) distance from the nearest creek or marsh edge and (3) distance from the marsh edge measured along the nearest creek. Based on these three morphometric parameters, the spatio-temporal sedimentation pattern can be modelled very well using a single multiple regression model for both the salt and freshwater marsh. A method is presented to compute two-dimensional sedimentation patterns, based on spatial implementation of this regression model. Figure 3. Whisker boxplots of sedimentation datasets, obtained by measurements over 25 spring-tidal cycles at 17 sampling sites. The boxplots are plotted with respect to the position of sampling sites along the transects, situated as shown on Figure 2 SEDIMENTATION IN TIDAL MARSHES 745 Figure 4. Typical example of the temporal evolution of the inundation height above the marsh surface (in solid lines) and suspended sediment concentration (SSC; in symbols and lines) during a tidal inundation at the Paulina marsh (thin lines and white symbols) and Notelaar marsh (thick lines and black symbols) S. TEMMERMAN ET AL. = k lH mD nD (1) where SR = the sedimentation rate (g m −2 per spring-neap cycle), H = the intensity of tidal inundation (this parameter will be further specified below), D c = the distance to the nearest creek or marsh edge (m) and D e = the SEDIMENTATION IN TIDAL MARSHES 749 Figure 7. (a) Mean sedimentation rate per spring-neap cycle in relation to marsh surface elevation (expressed relative to local mean high water level) for all sampling sites. White dots indicate data points from levees (sites 3, 6, 7, 12) and are incorporated in the construction of the broken regression line but omitted in the construction of the solid regression line. (b) Relative mean sedimentation rate in relation to distance from the creek or marsh edge for all sampling transects situated within different vegetation types (see Figure 2 for location of the transects). (c) Absolute mean sedimentation rate next to creek or marsh edges in relation to distance from the marsh edge, measured along the creek system distance to the marsh edge (m), measured along the nearest creek. For sampling transects perpendicular to the marsh edge, D e is set to zero. The model parameters k, l, m and n are determined using a non-linear regression procedure in SAS/STAT (SAS Institute Inc., 1989). First, regression analysis was carried out with sedimentation rates averaged over the one-year measuring period as the dependent variable and incorporating the spatial variation between all salt and freshwater marsh 750 S. TEMMERMAN ET AL.

2015

A foundational element in determining Total Maximum Daily Loads (TMDLs) is the determination of the relative impacts of point and nonpoint source impacts on the dissolved oxygen concentration (DO) of an impaired stream. It is not uncommon that the ultimate oxygen demand during a rain event can be greater than the effects of the fully permitted point source loading to the stream. Traditionally, the loading of oxygen consuming constituents is often estimated with a watershed model which is then coupled with a mechanistic model of the receiving stream. Calibrating coastal system applications of watershed models and mechanistic models to match the behavioral variability observed in actual field data is particularly difficult due to low watershed gradients, poorly defined drainage areas, chaotic forcing functions, and insufficient understanding of watershed and marsh process physics and chemistry. Data mining offers an alternative approach for analyzing and modeling tidal DO signals to q...

2012

The hydrologic regime of bottomland hardwood swamps is typically characterized as being determined by the inundation period caused by flood events. However, in the lower coastal plain of South Carolina there are large areas of bottomland hardwood swamps that adjoin freshwater tidal creeks. There has been little work in South Carolina to ascertain whether the tidal creek affects the hydrologic regime of the forested riparian zone. We established a stream stage gauge in Huger Creek, a tidal freshwater creek that drains into the Charleston harbor estuary, and a network of wells in the adjoining riparian zone to assess the hydrologic linkages between the stream and riparian zone. Groundwater levels were influenced by the tidal stream with decreasing affect as distance from the channel increased. Water table behavior adjacent to the creek was primarily controlled by tidal forcing. Groundwater levels in the interior wetland were closely related to stream stage, but mostly lacked the daily...

2010

A foundational element in determining Total Maximum Daily Loads (TMDLs) is the determination of the relative impacts of point and nonpoint source impacts on the dissolved oxygen concentration (DO) of an impaired stream. It is not uncommon that the ultimate oxygen demand during a rain event can be greater than the effects of the fully permitted point source loading to the stream. Traditionally, the loading of oxygen consuming constituents is often estimated with a watershed model which is then coupled with a mechanistic model of the receiving stream. Calibrating coastal system applications of watershed models and mechanistic models to match the behavioral variability observed in actual field data is particularly difficult due to low watershed gradients, poorly defined drainage areas, chaotic forcing functions, and insufficient understanding of watershed and marsh process physics and chemistry.

Estuaries, 2005

This study provides new insights in the relative role of tidal creeks and the marsh edge in supplying water and sediments to and from tidal marshes for a wide range of tidal inundation cycles with different high water levels and for marsh zones of different developmental stage. Net import or export of water and its constituents (sediments, nutrients, pollutants) to or from tidal marshes has been traditionally estimated based on discharge measurements through a tidal creek. Complementary to this traditional calculation of water and sediment balances based on creek fluxes, we present novel methods to calculate water balances based on digital elevation modeling and sediment balances based on spatial modeling of surface sedimentation measurements. In contrast with spatial interpolation, the presented approach of spatial modeling accounts for the spatial scales at which sedimentation rates vary within tidal marshes. This study shows that for an old, high marsh platform, dissected by a well-developed creek network with adjoining levees and basins, flow paths are different for tidal inundation cycles with different high water levels: during shallow inundation cycles (high water level Ͻ 0.2 m above the creek banks) almost all water is supplied via the creek system, while during higher inundation cycles (high water level Ͼ 0.2 m) the percentage of water directly supplied via the marsh edge increases with increasing high water level. This flow pattern is in accordance with the observed decrease in sedimentation rates with increasing distance from creeks and from the marsh edge. On a young, low marsh, characterized by a gently seaward sloping topography, material exchange does not take place predominantly via creeks but the marsh is progressively flooded starting from the marsh edge. As a consequence, the spatial sedimentation pattern is most related to elevation differences and distance from the marsh edge. Our results imply that the traditional measurement of tidal creek fluxes may lead in many cases to incorrect estimations of net sediment or nutrient budgets.