An inverse mathematical estuarine eutrophication model has been developed. The model provides a framework to estimate unknown parameters by assimilation of the concentration data of those state variables. The inverse model developed is a laterally integrated, two-dimensional, real-time model which consists of a hydrodynamic model, an eutrophication model and an adjoint model. The hydrodynamic model provides the dynamic fields for both the eutrophication model and the adjoint model. The eutrophication model simulates eight water quality state variables which are phytoplankton, organic nitrogen, ammonium nitrogen, nitrite-nitrate nitrogen, organic phosphorus, inorganic (ortho) phosphorus, carbonaceous biochemical oxygen demand and dissolved oxygen. The adjoint model is used during the processes of parameter estimation to provide the gradients of the cost function with respect to the unknown parameters. to increase the computational efficiency and reduce computer storage space, a decoupling scheme is implemented in the inverse model, in which the kinetic processes are decoupled from the physical transport for the purpose of numerical computation. An efficient preconditioning technique is introduced in the inverse model to speed up the rate of convergence. The experiments conducted in this study provide the information of the parameter identifiability and the field data requirement for the model calibration. The model experiments with hypothetical data sets show that the parameters can be accurately estimated for short period and long period model simulations under both constant and time-varying boundary conditions. The inverse model is convergent with different initial guess parameter values and under different environments. The inverse model was successfully applied to aid calibration of the eutrophication model of the tidal Rappahannock River, Virginia. With the use of the inverse model, the eutrophication model can be calibrated efficiently and systematically. The agreement between the model predictions and observations are very satisfactory. The studies show that the inverse model is also useful in addressing the important questions of whether the estimated parameters are unique and whether the sample data are sufficient to calibrate a model. Therefore, the inverse model may also serve as a tool in helping design a field program to collect data for model calibration.

Two of the most important processes in cohesive sediment transport, erosion rate and settling velocity, were the focus of this study. Settling velocities were estimated by the Owen tube method and the acoustic Doppler velocimeter (ADV) method. A novel erosion model, namely a constant erosion rate model, was implemented in a three-dimensional hydrodynamic eutrophication model (HEM-3D) to simulate the turbidity maximums in the York River system, Virginia. Two one-month periods of model simulations were conducted to mimic typical dry (November--December, 2001) and wet (March--April, 2002) seasons. In order to have enough data to verify the model, four slack water surveys were carried out during each period to measure salinity and total suspended solid (TSS) profiles. Because of the unexpected extremely low freshwater discharge during both those periods, all survey results showed similar salinity and TSS distributions. The estuarine turbidity maximums were abnormally located about 30 km upstream from West Point, with TSS concentrations on the order of 102 mg/L. Laboratory Owen tube experiments showed that the settling velocity was related to the TSS concentration, highlighting the importance of sediment availability on settling velocity and the less important salinity effect. The estimated settling velocities from four sets of ADV field measurements were much higher than that from the Owen tube laboratory experiments and better reproduced the turbidity maxima for slackwater simulations. These suggested that turbulence may have a dominant effect on settling velocity, and the ADV method seems to be an effective and suitable way to estimate the settling velocity in turbulence dominated environments. Based on a newly found erosion behavior, a constant erosion rate model was implemented in a three-dimensional numerical model such that erosion occurs only during accelerating phases of the tide. Specifically, the Four Factor Model was suggested that consists of (i) a reference constant erosion rate, (ii) hydrodynamic effects, (iii) spatial variability of the bed condition, and (iv) temporal variability of the bed condition. The Four Factor Model successfully simulated the turbidity maximums in the York River system.

Although precipitation and runoff for the entire Yangtze River watershed have changed little since 1950, the increase of runoff in Yangtze southern sub-basin has been much larger than that of precipitation, reflecting decreased temperatures and evapotranspiration, In contrast, the marked decreases in runoff in northern Yangtze have been due mainly to increased water consumption. Since the 1980s, the Yangtze sediment load has declined dramatically, and 2004 loads at Yichang (just below the Three Gorges Dam - TGD) and Datong (lower stream) were only 12% and 33% of those in the 1950s and 60s, reflecting precipitation decline, landuse change, and most importantly, construction of >50,000 dams. Following the impoundment of the TGD, annual sediment load at Yichang dropped by 164 million tons (mt), but in the preceding 16 years it had decreased by ∼300 mt/yr. Future dams and diversions will decrease the load to <100 mt/yr, thereby endangering the Yangtze coasts. Sediments on the inner shelf of the East China Sea reflect illite-dominated mud from the Yangtze River in the north as well as sandy silt and fine sand (low feldspar/quartz and low K-feldspar/plagioclase) from small mountainous rivers draining Taiwan to the south. Both sediments are significantly different from muds derived from the Yellow (smectite-rich) and Min (kaolinite-dominated) rivers. Grain-size distribution further confirms that ∼25% of coarse sediments in northern Taiwan Strait (south of 26??N) are Taiwan-derived. Along the inner shelf, an elongated (800 km) mud wedge, ∼40 m thick at the 30-m isobath, overlies a transgressive sand layer; the mud wedge thins offshore to <2 m at 80-m isobath. Four acoustic facies can be delineated: late-Pleistocene, Transgressive System Tract (TST), and early and late High-Stand System Tracts (HST). The thin (<3m) and acoustically transparent TST is only located between 40- and 90-m isobaths south of 30??N. In contrast, early (2-11 ka BP) and late (0-2 ka BP, more opaque) sigmoidal HSTs are widely distributed shallower than 70- and 50-m isobaths, respectively. The average Yangtze sediment flux between 2 and 11 ka BP was 215 mt/yr, but increased to 330 mt/yr after 2 ka BP, primarily reflecting increased deforestation and agriculture.

Many studies have focused on hydrological and geochemical fluxes from land to the ocean via groundwater discharge, however few have assessed groundwater flow in deltaic settings. Hydrological budgets indicate that 1,000 to 5,000 m3s-1 of water flow from the Mississippi River (MR) to its delta (MRD) via subterranean pathways, however the spatial and geological controls on these processes are less known. This study suggests that deltaic lithofacies of paleoenvironments related to the delta cycle allow for groundwater to discharge out of the MR main channel and into the MRD through organic sediment-rich and silt-sand overbank and mouth bar facies. This study employs geophysical data, including chirp sonar subbottom profiling and continuous resistivity profiling (CRP), to detect the location of these sediments in Barataria Bay, a coastal bay located in the MRD. Chirp data indicate paleochannel features in the MRD, whereas CRP data indicate freshwater seepage into MRD embayments during high river stage events. Analyses of bulk properties of sediment cores are used to characterize delta facies sediments and determine variability in hydraulic conductivity values, which range from 10-7 to 10-2 ms-1. These geophysical and sediment core data show the potential for groundwater flux through deltaic sediments, and will contextualize geochemical tracer data collected by project collaborators. Results indicate that groundwater discharge in the MRD is directly controlled by the geological constraints of the delta region. These results illustrate the potential for substantial groundwater fluxes in other large river deltas, and present implications for urban and coastal infrastructure planning, as many large global deltas sustain significant populations. / 1 / Alexander M Breaux

The concept of the submarine equilibrium profile has long been established. / This dissertation first proposes a conceptual model based on the well established concept. Then it proposes an analytical model with a differential equation which is based on the Airy wave theory and the wave-induced asymmetrical onshore/offshore sediment particle movement proposed by Cornaglia. / A "SIMPLEX" non-linear regression algorithm was used to write a computer program "SIMPYA" in GWBASIC. The computer program approaches two unknown parameters in the equation using sample profile data plotted on some coasts around continental U.S., namely, the southeastern U.S. Atlantic coast, the Gulf of Mexico coast and the Pacific coast. The sample profiles were selected according to criteria derived from the conceptual model. The result of regression analysis was very encouraging. This model permitted a more perceptive geological interpretation of various profile morphology features. / A wave tank, a wave generator and an adjustable platform were designed and constructed by the author, and were used in an effort to verify the analytical model. The unique platform provides independently adjustable settings of slope and depth of the platform, on which the sand behavior under the wave can be observed. This design eliminates the need of a very long flume (up to several thousand foot long) and bulky handling of sand, which are conventional in marine profile experimental research. However, scale problems were too great to be overcome completely. / The Application of the model may include assessment of profile stability, profile evolutionary trends, development of transitional models and coastal engineering calculations. / Source: Dissertation Abstracts International, Volume: 52-04, Section: B, page: 1917. / Major Professor: William F. Tanner. / Thesis (Ph.D.)--The Florida State University, 1991.

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Hydrology, particularly the water table position below the surface, is an mportant control on biogeochemical and ecological processes in peatlands. The position of the water table is a function of total storage changes, drainable porosity and peatland surface oscillation (PSO). Because the absolute level of the peat surface (ASL) oscillates in a peatland, we can assign two different water table positions: the water table depth below the surface (relative water level, RWL) and the water table position above an absolute elevation datum eg. sea level (absolute water level, AWL). A review of 37 studies that report peatland surface oscillation indicate awide range (0.4-55 cm), which is to the same order as (or one order smaller than) water storage changes and RWL fluctuations. PSO can vary substantially across a single peatland and through time. A set of mechanisms (flotation, compression/shrinkage, gas volume changes and freezing) is hypothesised to cause ASL changes. The potential of PSO to reduce RWL fluctuations trended (mean in %) floating peatlands (63) greater than bogs (21), fens (18) greater than disturbed peatlands (10) with respect to peatland types. To investigate the spatiotemporal variability of peatland surface oscillation, AWL and ASL were monitored continuously over a one-year period (one site) and monthly (23 sites) in a warm-temperate peatland that is dominated by Empodisma minus (Restionaceae). A new measurement method was developed by pairing two water level transducers, one attached to a stable benchmark (AWL) and one attached to the peat surface (RWL). From August 2005 until August 2006 the ASL oscillated at one site through a range of 22 cm following AWL fluctuations (in total 47 cm). Consequently, RWL fluctuations were reduced on average to 53% of AWL fluctuations. The strong AWL-ASL relationship was linear for 15 sites with manual measurements. However, eight sites showed significantly higher rates of peatland surface oscillation during the wet season (ie. high AWLs) and thus a non-linear behaviour. Temporary flotation of upper peat layers during the wet season may have caused this non-linear behaviour. On the peatland scale AWL fluctuations (mean 40 cm among sites) were reduced by 30-50% by PSO except for three sites with shallow and dense peat at the peatland margin (7-11%). The reduction of RWL fluctuation was high compared to literature values. The spatial variability of PSO seemed to match well with vegetation patterns rather than peat thickness or bulk density. Sites with large PSO showed high cover of Empodisma minus. Surface level changes exhibited surprisingly hysteretic behaviour subsequent to raised AWLs, when the rise of ASL was delayed. This delay reversed the positive ASL-AWL relationship because the surface slowly rose even though AWL started receding. Hysteresis was more pronounced during the dry season than during the wet season. The observed hysteresis can be sufficiently simulated by a simplistic model incorporating delayed ASL fluctuations. PSO has wide implications for peatland hydrology by reducing RWL fluctuations, which feed back to peat decomposition and plant cover and potentially to (drainable) porosity. Stable RWL also reduce the probability of surface run-off. It is further argued that the gas content of the roots of plants, particularly Empodisma minus, added enough buoyancy to detach the uppermost peat layers resulting in flotation.

Thesis (M.S. in biological and agricultural engineering)--Washington State University, December 2007. / Includes bibliographical references (p. 53-57).