Solvability and multiquadric analysis as applied to investigations of vertical crustal movements

A variety of geodetic measurements can be combined, in network fashion, to yield adjusted velocities of elevation change. However, it is not always apparent which network junctions have solvable point velocities. When a velocity surface is desired, it is not always apparent how many coefficients should be used. A solvability algorithm, devised to operate on observation equations, answers these questions, and therefore permits the adjustment process to continue with the assurance that the result will be mathematically justified. Using both the hyperboloid and the reciprocal hyperboloid as quadric forms, multiquadric (MQ) analysis has been applied to leveling and tide gauge data in the vicinity of Puget Sound, to obtain heights corresponding to a selected date, and coefficients which collectively define a velocity surface. The solvability algorithm was used to tell which junctions in the level network had solvable point velocities, and consequently where MQ nodal points should be placed for an optimized solution. Networks of simulated data were also used with the solvability algorithm to help determine data requirements for height—velocity adjustments, and to evaluate the ability of MQ analysis to predict velocities.     

Wave-forced resuspension of upper Chesapeake Bay muds

Moored instruments were used to make observations of near bottom currents, waves, temperature, salinity, and turbidity at shallow (3.5 m and 5.5 m depth) dredged sediment disposal sites in upper Chesapeake Bay during the winters of 1990 and 1991 to investigate time-varying characteristics of resuspension processes over extended periods. Resulting time series data show the variability of two components of the suspended sediment concentration field. Background suspended sediment concentrations varied inversely with salinity and in direct relation to Susquehanna River flow. Muddy bottom sediments were also resuspended locally by both tidal currents and wind-wave forcing, resulting in short-term increases and decreases in suspended concentration, with higher peak concentrations near the bottom. In both years, episodes of wave-forced resuspension dominated tidal resuspension on an individual event basis, exceeding most tidal resuspension peaks by a factor of 3 to 5. The winds that generated the waves responsible for the observed resuspension events were not optimal for wave generation, however. Application of a simple wind-wave model showed that much greater wave-forced resuspension than that observed might be generated under the proper conditions. The consolidated sediments investigated in 1990 were less susceptible to both tidal and wave-forced resuspension than the recently deposited sediments investigated in 1991. There was also some indication that wave-forced resuspension increased erodibility of the bottom sediments on a short-term basis. Wave-forced resuspension is implicated as an important part of sediment transport processes in much of Chesapeake Bay. Its role in deeper, narrower, and more tidally energetic estuaries is not as clear, and should be investigated on a case-by-case basis.     

Controls of Wellbore Flow Regimes on Pump Effluent Composition

Where well water and formation water are compositionally different or heterogeneous, pump effluent composition will vary due to partial mixing and transport induced by pumping. Investigating influences of purging and sampling methodology on composition variability requires quantification of wellbore flow regimes and mixing. As a basis for this quantification, analytical models simulating Poiseuille flow were developed to calculate flow paths and travel times. Finite element modeling was used to incorporate influences of mixing. Parabolic velocity distributions within the screened interval accelerate with cumulative inflow approaching the pump intake while an annulus of inflowing formation water contracts uniformly to displace an axial cylinder of pre‐pumping well water as pumping proceeds. Increased dispersive mixing forms a more diffuse formation water annulus and the contribution of formation water to pump effluent increases more rapidly. Models incorporating viscous flow and diffusion scale mixing show that initially pump effluent is predominantly pre‐pumping well water and compositions vary most rapidly. After two screen volumes of pumping, 94% of pump effluent is inflowing formation water. Where the composition of formation water and pre‐pumping well water are likely to be similar, pump effluent compositions will not vary significantly and may be collected during early purging or with passive sampling. However, where these compositions are expected to be considerably different or heterogeneous, compositions would be most variable during early pumping, that is, when samples are collected during low‐flow sampling. Purging of two screen volumes would be required to stabilize the content and collect a sample consisting of 94% formation water.     

Is the present stellar birthrate really determined by gas density?

Observed supernovae rates in Sb and Sc galaxies, and a recent re-examination of the mean gas density in these galactic types, implies that if the clumpiness of gas in the disks of Sb and Sc galaxies is similar, the gas density isnot the primary factor in determining the overall present stellar birthrate.     

Tracer mass recovery in fractured aquifers estimated from multiple well tests

Forced-gradient tracer tests in fractured aquifers often report low mass recoveries. In fractured aquifers, fractures intersected by one borehole may not be intersected by another. As a result (1) injected tracer can follow pathways away from the withdrawal well causing low mass recovery and (2) recovered water can follow pathways not connected to the injection well causing significant tracer dilution. These two effects occur along with other forms of apparent mass loss. If the strength of the connection between wells and the amount of dilution can be predicted ahead of time, tracer tests can be designed to optimize mass recovery and dilution. A technique is developed to use hydraulic tests in fractured aquifers to calculate the conductance (strength of connection) between well pairs and to predict mass recovery and amount of dilution during forced gradient tracer tests. Flow is considered to take place through conduits, which connect the wells to each other and to distant sources or sinks. Mass recovery is related to the proportion of flow leaving the injection well and arriving at the withdrawal well, and dilution is related to the proportion of the flow from the withdrawal well that is derived from the injection well. The technique can be used to choose well pairs for tracer tests, what injection and withdrawal rates to use, and which direction to establish the hydraulic gradient to maximize mass recovery and/or minimize dilution. The method is applied to several tracer tests in fractured aquifers in the Clare Valley, South Australia.