Fluctuation of hyporheic zone thickness due to inflow and outflow across the water-sediment interface
Determination of hyporheic zone thickness in streams is an important step for study of stream-aquifer interactions. Knowledge about hyporheic zone thickness is useful in stream restoration. However, because there is a lack of standard techniques for such study, evaluation of the hyporheic zone thickness for a given stream reach remains a challenge task for researchers. This paper presents Galerkin finite element flow and stream function models that can simulate the hyporheic zone thickness. The flow and stream function equations are solved for 2-D profile domains that can be across a stream or parallel to a stream. The numeral schemes for solving the flow and stream function equations and the treatment of boundary conditions are described. Hypothetical streams are used for simulation of the control of hyporheic zone thickness by the magnitude of inflow and outflow that occur at the stream-sediment interface. Groundwater flow velocity field is generated to examine the flow dynamics in hyporheic zones. The magnitude of groundwater flow velocity in hyporheic zone is greater than that of regional groundwater flow.
Vertical and seasonal distribution of hyporheic invertebrates in streams with different glacial histories
Abstract.We investigated the vertical, lateral, and seasonal distribution of hyporheic invertebrates at five stream sites in Idaho (unglaciated areas) and seven sites in Montana (glaciated areas), U.S.A. Conservative tracer releases and transient storage zone analyses were conducted to help characterize study sites. Hyporheic invertebrates and substrate were sampled by freeze-coring with electro-shocking, and mini-piezometers were used to measure other hyporheic conditions, including vertical hydraulic gradient (VHG). Wells were installed at some Montana sites (range: 5–175 m lateral to the channel) and shallow pits were excavated at some Idaho sites (5 m lateral to the channel) to sample hyporheic invertebrates in these saturated sediments regions. Environmental conditions varied widely among sites and between surface and hyporheic zones at each site, and most hyporheic habitat measures differed significantly between glaciated and unglaciated streams. In-channel invertebrate density and taxa richness generally decreased with increasing depth into the streambed, regardless of geographic location, history of glaciation, or season. Although hyporheic invertebrate mean density and (to a lesser extent) richness values at individual depth layers (e.g., 10–20 cm, 20–30 cm) mostly were greater in the glaciated region than the unglaciated region, density and richness between 10–50 cm did not differ significantly between the two regions. Hydrologic variables (VHG; AS/A [ratio of transientstorage- zone- to channel- cross-sectional areas]; TTS [turnover time of storage]; and Rh [hydraulic retention factor]) provided the best explanation for differences in sub-channel invertebrate density and richness patterns. The observation that benthic invertebrates occurred in freeze-core, well, and open-pit samples contributes to existing evidence that aquatic invertebrates occupy habitats that extend considerable distances from the active channel.
Thermodynamic Evaluation of Solar Integration into a Natural Gas Combined Cycle Power Plant
The term integrated solar combined-cycle (ISCC) has been used to define the combination of solar thermal energy into a natural gas combined-cycle (NGCC) power plant. Based on a detailed thermodynamic cycle model for a reference ISCC plant, the impact of solar addition is thoroughly evaluated for a wide range of input parameters such as solar thermal input and ambient temperature. It is shown that solar hybridization into an NGCC plant may give rise to a substantial benefit from a thermodynamic point of view. The work here also indicates that a significant solar contribution may be achieved in an ISCC plant, thus implying substantial fuel savings and environmental benefits.