Hydrometeorological controls on water level in a vegetated Chesapeake Bay tidal freshwater delta

Abstract

ABSTRACT.Wind vectors, watershed discharge, and subestuarine water levels were monitored in a vegetated delta at the head of the Bush River, an upper Chesapeake Bay tributary in Maryland, during an El Niño/La Niña cycle 1995-1996 to investigate hydrometeorological processes that affect the tidal freshwater ecosystem located there. Time series of these processes were analyzed in both the time and frequency domains using such methods as flood frequency analysis, harmonic analysis, averaged and evolutionary power spectral analysis, and coherency spectral analysis. Wind speed variations with periods of 3-4 and 7 days were found to have both high spectral power and high statistical significance. The frequencies of these variations fluctuated over weeks to months and the amplitudes modulated seasonally, but the variations persisted interannually. Significantly greater subtidal wind speed variations in the prinicipal wind direction occurred during the cold and stormy La Niña winter of 1996 relative to the warm and dry El Niño winter of 1995. Data from 5 hurricanes occurring in the region during the study provided high-resolution snapshots of the mechanisms revealed by the time series analyses.Water level quickly responded to S-N directed wind speed fluctuations during the aperiodic hurricanes, illustrating the strong coupling between wind and water levels in this system. The magnitude of the response was large enough to determine the extent and duration of flooding over tens of hectares in important intertidal marsh habitats. Subtidal water level variations were greater during the La Niña period. During El Niño conditions, the E-W wind component played a larger role than during the La Niña period. Variations in local watershed discharge as well as Susquehanna River outflow had no measurable impact on water levels in the upper reaches of the Bush River tributary during the study.

Oceanic and Hydrologic Influences on Flow and Water Properties in the St. Jones River Estuary, Delaware

“…Hence, local wind effects within the St. Jones River estuary basin are limited to forcing along its axis, and externally by winds in Delaware Bay. Similar influences of basin orientation with respect to wind direction have been observed in a wide range of subestuaries and tidal wetland basins fringing larger estuaries and bays (e.g., Pasternack and Hinnov 2003;Snedden et al 2007).…”

“…Locally generated wind waves, particularly over shallows and intertidal flats, resuspend bed sediments, and increase concentrations of suspended matter (De Jonge and van Beusekom 1995;Talke and Stacey 2008;French et al 2008). Remote wind forcing of large estuaries and bays is well-documented (Wang and Elliott 1978;Wong and Moses-Hall 1998;Ryan and Noble 2007;Reed et al 2008), and related effects on adjoining tidal wetland basins are receiving increased attention among researchers (e.g., Pasternack and Hinnov 2003;Wong et al 2009). …”

Long-Term Variability of Nutrients and Chlorophyll in the Chesapeake Bay: A Retrospective Analysis, 1985–2008

“…The impacts of ENSO on the southwest US and across the northern plains are well known (Andrade andSellers 1988, Bunkers et al 1996), and the impacts on the northeast are mostly associated with the ENSO impacts on hurricane activity (Saunders et al 2000). Using a very short time series of the water level at the head of the Bush River in the upper Chesapeake Bay, Pasternack and Hinnov (2003) concluded that subtidal wind speed variations were statistically stronger during the cold ENSO winter of 1996 compared to the warm ENSO winter of 1995. They did not consider the impact of NAO on their data, which is known to impact wintertime variability over parts of the US (Notaro et al 2006).…”

Hydrological regime and water budget of the Red River Delta (Northern Vietnam)

“…Estimating the water balance of a tidal hydrological system is a complex task due to the large variations that occur in time and space in its components (Cook et al, 1998;Pasternack and Hinnov, 2003). In this study, we assembled a database of rainfall, evapotranspiration and water discharge in the river network of the RRD for a period of 10 years using (i) official recorded data, (ii) direct field measurements and (iii) the results of hydrological modelling.…”