摘要:

AbstractA field study of surface water and groundwater interactions during baseflow and stormflow conditions was performed at the Reedy Creek watershed in the Virginia Coastal Plain. Three estimates of the average saturated hydraulic conductivity (Ks) of the unconfined aquifer were in reasonable agreement (ranging from 0.0033 to 0.010 cm/s), indicating that baseflow in the creek is entirely from the drainage of shallow groundwater from the relatively thin (1–6 m thick) unconfined aquifer. This relatively permeable surficial aquifer was found to be underlain by dark, olive grey, clay‐silt and diatomaceous Miocene deposits of low permeability known as the Calvert Formation, which is believed to function as a confining bed in the area.A chemical hydrograph separation technique was used to resolve the contributions of [old] (pre‐event) and [new](event) water to stormflow. Results from a major rainstorm indicated that old water dominated the stormflow response of the watershed, although the new water contribution approached 40% at the hydrograph peak. Stormflow at Reedy Creek appears to result from saturation overland flow from variable source areas which include the stream channels and a significant part of the riparian wetland area. This response appears to be attributable to the transient dynamics of the shallow groundwater flow system and to the formation of localized groundwater mounds which raise the water‐table to the wetland

ISSN:0885-6087    

DOI:10.1002/hyp.3360080503

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractAn intensive study was conducted on the biogeochemical processes controlling the acid‐base chemistry of Reedy Creek, a wetland‐influenced coastal plain stream located near Ashland, Virginia. In the context of the hydrological processes determined by Eshlemanet al., the present research sought to: (1) identify the sources and sinks of anthropogenic and organic acidity within the watershed, (2) determine the seasonal and spatial variability in the stream base flow chemistry, (3) determine the episodic variability in stream stormflow chemistry and (4) quantify a watershed sulphate budget for the 1990 water year. Sulphate is the primary acidic anion in groundwater and surface water at the Reedy Creek watershed. Dissolved organic carbon (DOC) and anion deficit data suggest that organic acids are less important than sulphate in contributing acidity to the stream. In groundwater sampled from wells installed along two transects perpendicular to the stream, sulphate concentrations were higher and alkalinity lower in the groundwater in the hill‐slope than in the stream. Sulphate concentrations and alkalinity observed in groundwater in the wetland were usually between those of the hillslope and stream. These data suggest that the wetland is a sink for sulphate and acidity; sulphate reduction may be an important mechanism for generating alkalinity in the wetland. The DOC concentrations were higher in the stream and wetland groundwater than in hillslope groundwater. No consistent spatial patterns in sulphate concentrations were observed in surface water chemistry under base flow conditions. Anion deficit, DOC and the sum of base cation concentrations were usually higher at upstream sites than downstream sites. At all sites, sulphate concentrations were higher and alkalinity lower in winter and spring than during summer and autumn. Calculated anion deficits were lower in winter and spring than during summer and autumn, reflecting an increase in the contribution of organic acidity during the growing season. Seasonality was not observed in DOC concentrations. Stream discharge was found to be positively correlated with base flow sulphate concentrations and inversely correlated with alkalinity. A sulphate mass balance indicated that approximately 30% of the estimated 24.9kg SO2−2/ha yr wet atmospheric input was exported from the watershed as sulphate in stream runoff in the water ye

ISSN:0885-6087    

DOI:10.1002/hyp.3360080504

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractAs pumping proceeds in an unconfined aquifer the water‐table is lowered and slowly drains out of the initially saturated material giving a delayed yield from storage. Although considerable work has been carried out on delayed yield, a definitive solution is still lacking. The unsaturated zone was treated here as a significant factor in delayed yield analysis. The one‐dimensional unsaturated flow equation was solved numerically to simulate the flow in the zone located between successive water levels in the unconfined aquifer for the case with zero flux at the upper boundary. The moisture content distribution curve was integrated numerically to determine the amount of water drained with time. The study shows that the numerical results are in close agreement with the monitored field data, which implies the important role of the unsaturated zone and the reliability of the numerical simulation in describing this physical phenomenon. The results show that the relationship between the flux and time is sensibly in exponential form, which agrees with the general applicability of Boulton's assumpt

ISSN:0885-6087    

DOI:10.1002/hyp.3360080505

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe ability to continually monitor several meteorological parameters is needed to estimate snow surface energy balance components in mountainous terrain. In remote mountainous locations, limited accessibility and extreme weather conditions limit the use of delicate meteorological instrumentation. Robust instrumentation and radio telemetry are often needed to measure snow surface energy exchanges. This study examined the practicality and effectiveness of robust instrumentation in estimating radiative and turbulent exchanges in the forested Bear River Mountains of northern Utah. Measurement of reflected shortwave radiation was problematic due to possible selective absorption in the infra‐red range. This resulted in overestimates of reflected shortwave radiation and decreased estimates of now surface albedo. During high snowfall, the pyranometer and net radiometer were occasionally covered with snow, resulting in inaccurate radiation measurements. Snow typically melted from instrument surfaces in less than one day under full sun. A relative humidity measurement accuracy of ± 4% may have resulted in a possible error of 20% in the calculation of vapour pressure. Snow depth measurement with an acoustical sensor was affected by new or blowing snow, which resulted in inaccurate snow depth measurement 16.2% of the time. The longest period without a valid snow depth measurement was 19.5 hours. A new snow temperature thermocouple ladder was designed and constructed and provided accurate within‐pack temperature measurements throughout the pre‐melt and melt

ISSN:0885-6087    

DOI:10.1002/hyp.3360080506

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe interesting suggestion by Knight and Tweed (1991) that a link exists between glacier velocity changes and the filling and draining of a marginal ice‐dammed lake at Sólheimajökull, southern Iceland, is examined. The main problem lies not with plausibility, but with a lack of field data to substantiate the argument. Some pertinent hydrological, glaciological and meteorological data from the area are presented here, many of which do not entirely support certain inferences and observations made in their paper. It is shown that this very small lake is likely to have limited quantitative significance in the operation of the glacio‐hydrological or solute and sediment transfer systems in this basin. Further, specific, difficulties include the absence of crucial observations on glacier velocity variations and the precise timing and pattern of lake drainage in relation to such velocity changes, the lack of evidence for a significant relationship between precipitation receipt and ice velocity here [a component of the Knight and Tweed (1991) proposition], and the occurrence of the lake drainage event in arain‐freeperiod (contrary to the authors' suggestion). The opportunity is also taken to correct some incidental

ISSN:0885-6087    

DOI:10.1002/hyp.3360080507

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractDissolved organic carbon (DOC) was measured at four or eight hour intervals between mid‐1989 and mid‐1991 in two catchments in west central Scotland. The experimental catchment had been recently clear‐felled and the control remained under forest. The amount of DOC varied during individual storm events following the stream hydro‐graph. Maximum variations were found in the summer half‐year and in the clear‐felled catchment. There was also evidence of the exhaustion of DOC in the later events of a sequence. Differences between the catchments were related to catchment characteristics and to land‐use change. The reduced magnitude of variation in DOC with discharge in the control stream was due to the influence of a wetland area through which the stream flowed. The mean DOC concentrations were similar in the two streams and annual exports were 15 g m−2from the control and 16g m−2from the felled catchment. The stream draining the clear‐felled catchment had greater high flow DOC concentrations in the summer half‐year, probably due to the effect of greater mean summer temperatures on DOC release and of the greater supply of organic debris

ISSN:0885-6087    

DOI:10.1002/hyp.3360080508

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractUntil now, alpine glacial meltwaters have been assumed to consist of two components, dilute quickflow and concentrated delayed flow, the mixing of which has been regarded as chemically conservative for the major dissolved ions and electrical conductivity. Dye tracing results suggest that this two‐component model adequately represents the sub‐glacial hydrology of the Haut Glacier d'Arolla, Switzerland. However, laboratory dissolution experiments in which various concentrations of glacial rock flour are placed in dilute solutions show that this rock flour is highly reactive and suggest that bulk meltwaters may acquire significant amounts of solute through rapid chemical reactions with suspended sediment which occur after mixing of the two components. This view is supported by detailed analysis of variations in the hydrochemistry of meltwaters draining from the Haut Glacier d'Arolla over three diurnal cycles during the 1989 melt season. Variations in the composition of bulk meltwaters are controlled by two main factors: dilution of the delayed flow component by quickflow, and the extent of post‐mixing reactions. The latter depends on the suspended sediment concentration in bulk meltwaters and on the duration of contact between these waters and suspended sediment. Seasonal changes in the magnitude of these factors result in changes in the character and causes of diurnal variations in meltwater chemistry. In June, these variations reflect discharge‐related variations in residence time within a distributed subglacial drainage system; in July, when a channelized drainage system exists beneath the lower glacier, they primarily reflect the dilution of delayed flow by quickflow; in August, when suspended sediment concentrations are particularly high, they reflect varying degrees of solute acquisition by post‐mixing reactions with suspended sediment that take place in arterial channels at the gl

ISSN:0885-6087    

DOI:10.1002/hyp.3360080509

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMajor‐ion variability related to discharge was analysed in a forested 187 km2mafic Piedmont Province watershed using statistical (both parametric and non‐parametric), graphical (box‐plots) and curve‐fitting (log concentration‐log discharge) techniques. Baseflow alkalinity and base cation concentrations show systematic temporal variations as a result of the influx of additional water that occurs during the late autumn to early spring. Regression analyses indicate that storm‐related discharge and baseflow generated during periods of water surplus are characterized by similar dilution slopes. Mass balance estimates indicate that the additional water, which comprises storm/recession discharge and base‐flow from late autumn to early spring, is between about 30 and 80% as concentrated as summer low‐flow.The thick clay‐rich soil mantle represents a key control on solute concentrations in that it stores water for periods of time sufficient for a high degree of water‐mineral interaction to occur. Hence solute‐discharge relationships (C= aQb, wherebis typically<0) are characterized by relatively low slope values and there is ample acid neutralizing capacity throughout the range of discharge. Owing to the predominance of amphibolite, solute efflux related to rock weathering from the Falling Creek watershed is much greater than other more felsic locations within the region. Statistical analyses (Mest and the non‐parametric Mann‐Whitney‐Wilcoxon test), along with accompanying box‐plot representations, provide a useful method of describing systematic annual hydrochemical variation within streamflow. These methods are particularly effective for those instances in which a long‐term data set exists, but is limited to relativel

ISSN:0885-6087    

DOI:10.1002/hyp.3360080510

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360080502

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY