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.
Potential interaction between transport and stream networks over the lowland rivers in Eastern India.
Extension of transport networks supports good accessibility and associated with the development of a region. However, transport lines have fragmented the regional landscape and disturbed the natural interplay between rivers and their floodplains. Spatial analysis using multiple buffers provides information about the potential interaction between road and stream networks and their impact on channel morphology of a small watershed in the Lower Gangetic Plain. Present study is tried to understand the lateral and longitudinal disconnection in headwater stream by rural roads with the integration of geoinformatics and field survey. Significant (p < 0.001) growth of total road length and number of road-stream crossing in the last five decades (1970s-2010s) contribute to making longitudinal and lateral disconnection in the fluvial system of Kunur River Basin. Channel geometry from ten road-stream crossings shows significant (p = 0.01) differences between upstream and downstream of crossing structure and created problems like downstream scouring, increased drop height at outlet, formation of stable bars, severe bank erosion, and make barriers for river biota. The hydro-geomorphic processes are also adversely affected due to lateral disconnection and input of fine to coarse sediments from the river side growth of unpaved road (1922%). Limited streamside development, delineation of stream corridor, regular monitoring and engineering efficiency for the construction of road and road-stream crossing might be effective in managing river geomorphology and riverine landscape.
Redistribution of rare-earth elements during diagenesis of carbonate rocks from the Mid-Proterozoic Newland Formation, Montana, U.S.A.
Abstract REE data for carbonate rocks from the Mid-Proterozoic Newland Formation, Belt Supergroup, show variable degrees of relative REE enrichment when normalized to a composite shale of the Newland Formation. Most conspicuous are relative enrichments in LREE's and positive Eu anomalies. Possible coprecipitation of REE's in carbonates from seawater is much too small to account for the REE enrichment, thus only diagenetic REE enrichment has to be considered. By far the strongest LREE enrichment is observed in carbonates with interbedded shales. During diagenesis REE apparently moved from the shale partings to the adjacent limestone beds. Massive limestone units have considerably smaller REE enrichments (except in proximity to shales), suggesting that REE addition from formation waters is less efficient for supplying REE's than is local redistribution between shale and limestone beds. Early precipitation of diagenetic silica in pore spaces reduces REE enrichment in limestone beds by reducing their permeability. Dolostones are cemented by pervasive early-diagenetic silica and lack significant REE enrichment except for Eu, probably because silica cement prohibited access of REE-bearing pore waters. Positive Eu anomalies indicate reduction of Eu to the divalent state during diagenesis and relatively large mobility of divalent Eu.