bluuebunny/crossref_metadata_2025 huggingface dataset:
Lateral moisture flow beneath a sandy hillslope without an apparent impeding layer
Authors: McCord James T. , Stephens Daniel B.
Published: February 2007

Part of a small drainage basin on the Sevilleta National Wildlife Refuge (about 25 km north of Socorro, NM) was intensively instrumented with soil monitoring equipment to estimate natural ground‐water recharge. Soil‐moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand. Moisture content data were obtained by the neutron scattering technique, and hydraulic head data were obtained using tensiometers. In addition, tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water. The results indicate that there is a strong lateral component to unsaturated flow on a hillslope, even in the absence of apparent sublayers of much lower permeability. Darcian calculations estimate the long‐term, steady, deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm. The deep soil water flux downward varied by several orders of magnitude during the 17 month period of record.
Flow dynamics and suspended sediment properties in arid zone flash floods
Authors: Reid I. , Frostick L. E.
Published: February 2007

Hydrological process in arid zones differs substantially from that in better documented humid environments. The ponding point for infiltration is reached within 10 mins of first rain and overland flow forms the major component of basin runoff. Drainage densities are high, approaching 100 km.km−2, maximising the opportunity for both water and eroded soil to reach the channel network. The typical flood bore is not as abrupt as the mythology of desert streams would suggest. Nevertheless, the time of rise of the flood hydrograph is usually between 4 and 16 mins, giving credance to the notion of ‘flash flood’. Measured flows remain subcritical in the main, though Froude number exceeds unity for short periods around peak discharge. Flow is exceedingly turbulent, with Reynolds number > 105 even for much of the recession limb. As a result, suspended sediment concentrations by size grade are shown to be hydraulically controlled. However, the high degree of turbulence and wide availability of sediment from hillslope and channel sources also means that the mean size of the suspended load varies systematically with flow parameters. In this respect, ephemeral streams differ from perennial counterparts in humid environments where no clear‐cut relationships exist. There is greater prospect of deriving a physically deterministic model of suspended sediment transport in desert streams. Implications for soil erosion and reservoir siltation are discussed, and sediment is traced from its source to its various sinks within the drainage basin.
A dynamic, process‐based, user‐oriented model of forest effects on water yield
Authors: Schulze R. E. , George W. J.
Published: February 2007

The effects of afforestation on water yield from catchments are reviewed. In the light of research findings and an assessment of the method currently used in South Africa to determine reductions of water production associated with afforestation, the ACRU agrohydrological model is adapted to account for changes in critical land use related processes as a forest grows in time by incorporation of a dynamic land use information file. First tests with this model on a catchment at Cathedral Peak in the Natal Drakensberg, which was afforested in 1951, indicate that forest hydrological effects can be modelled successfully with a dynamic land use file. Further model development is outlined.
A study of the three‐dimensional groundwater flow system in an upland area of Japan
Authors: Bae S. K. , Kayane I.
Published: February 2007

A three‐dimensional finite difference model was developed to study the groundwater flow system in an upland area bordering a lake. For a general perspective of the groundwater flow system, a steady state three‐dimensional flow was employed. Having determined the flow net by using a three‐dimensional model, the flow volumes under natural conditions have been used to establish the parameter values and for the analyses of flow patterns. Further, to study the effects of human impact and precipitation on groundwater flow conditions in a small area, a transient three‐dimensional simulation was performed. Environmental tritium was used to trace the regional groundwater movement to verify the three‐dimensional mathematical model. Results obtained using the three‐dimensional mathematical model approach and tritium concentration analyses were in close agreement. The results demonstrated that the groundwater flow system should be analysed using a three‐dimensional geometric concept of groundwater movement.
Effects of wildfire and logging on streamwater chemistry and cation exports of small forested catchments in Southeastern New South Wales, Australia
Authors: MacKay S. M. , Robinson G.
Published: February 2007

In January 1979 four experimental catchments in forests of southeastern New South Wales were burnt by wildfire. Logging before the fire had no detectable effect on concentrations of Ca, K, Mg, Na, Cl, NO3, nor on pH of stream waters.

In all burnt catchments mean K concentrations increased by from 20 per cent to 60 per cent for a 12 month period and nitrate concentrations increased by factors of about ten in severely burnt catchments. In one of the catchments (unlogged) Ca also increased. From one year to four years after the fire, concentrations of all ions were either close to or less than levels predicted from the control but, during the fifth and sixth years, concentrations of Mg and Na were higher by 20 per cent to 60 per cent.

In all burnt catchments, cation exports increased considerably during the first three years after the fire but major components of these increases were elevated levels of runoff. Exports of Mg and Na were higher than those of the control during the fifth and sixth years after the fire, although runoff had returned to pre‐fire levels in the two unlogged catchments and was 10 per cent to 20 per cent greater than the control in the two logged catchments. During this final period, increased ion concentrations were the main factors which contributed to the elevated exports.

Post‐fire logging in one catchment had no detectable effects on streamwater parameters measured in the study but was associated with a further increase in runoff.
Sources and sinks of nutrients in a New Zealand hill pasture catchment II. Phosphorus
Authors: Cooke James G.
Published: February 2007

The management of the riparian zone has been suggested as a technique for controlling the amounts of phosphorus (P) entering watercourses draining pasture catchments. A study was therefore made of P entering a stream from various sources (rainfall, surface and subsurface derived runoff, direct fallout from aerial topdressing), with the object of providing a rational basis for the design of effective riparian management schemes.

P entrained in surface runoff could account for virtually all of the P entering the stream during storms. Approximately 20 per cent of the annual P export from the catchment could be accounted for by direct aerial input of P to the stream during autumn fertilizer topdressing. More than 85 per cent of the P was exported from the catchment as particulate P. Stream sediment had higher P sorption capacities, and were enriched with P relative to the soils from which they were derived. There was a pronounced seasonal variation in sediment enrichment which could be predicted (r2 = 0.92) by the logarithm of the rainfall since fertilizer topdressing (LNFERT) and flood intensity. The amount of P lost in streamflow during any flood event was predicted (r2 = 0.94) by peak flow, seven day antecedent peak flow and LNFERT. Approximately 40 per cent of the 1.3 kg P ha−1 exported during 1981 occurred in four storms with recurrence intervals of more than three months. From a P budget compiled from nine events it was hypothesized that the stream acted as a net sink for P at baseflow and low‐medium intensity floods but was a source of P at higher flood intensities.

It was concluded that P losses from hill pasture catchments could be reduced by avoidance of direct application of P fertilizer to the stream channel, and by fencing out stock from seasonally saturated areas during periods of saturation. The ultimate success of the latter technique would depend on whether buffer vegetation could retain accumulated P during extreme storm events.
The quantity of stormwater runoff from ten stretches of road, a car park and eight roofs in Hertfordshire, England during 1983
Authors: Hollis G. E. , Ovenden J. C.
Published: February 2007

Rainfall and runoff were monitored simultaneously for one year from a residential road, a car park, nine sections of road draining to individual gullies, two house roofs, two garage roofs, and three types of factory roof. The sites, which included an automatic weather station, were in Redbourn, Hertfordshire on Flood Studies Report Soil Type 1. The 2906 quality controlled ‘station‐storms’ represented 193 rain storms and involved 57.2 per cent of the annual rainfall. 1732 storms were of less than 1.4mm of rain, whilst 77 had over 10mm.

The percentage runoff averaged 11.4 per cent for roads and 56.9 per cent for roofs (28.3 per cent and 90.4 per cent respectively for rainfalls >5mm). Percentage runoff from the roads was cyclic with a peak during the summer months but there was a marked variation in monthly percentage runoff within and between sites. Regression analysis to explain percentage runoff was undertaken with various subsets of data for: each site; roads; and roofs. The regression analysis considered all storms; >1 percent runoff events; >5mm rainfalls; and events with > = 4 mm rain and > = 5 per cent runoff. The variable values in percentage runoff could not be explained satisfactorily with statistical methods. Only eight of the 72 equations explained more than 57 per cent of the variance. The most important explanatory variables for roads were short term rainfall intensity and rainfall amount, the former was the most important for roofs. ‘Seasonal’ variables had a positive relation ship for roads which shows that the percentage runoff from roads is higher in summer than winter. The antecedent variables showed that percentage runoff from roads and roofs is increased by antecedent rainfall. Seasonal factors and evaporation were unimportant for the percentage runoff from roofs.

Depression storage, assessed by examining rainfalls that did and did not produce runoff, showed a diversity of monthly values. The depression storages derived by the regression intercept method were usually smaller. There were no relationships between depression storage and catchment or roof slope. The mean values for roofs and roads respectively were 0.52 mm and 1.23 mm for the classification method and 0.42 mm and 0.6mm with the regression approach.

Peak runoff from the roads showed an attenuation to 12.8 per cent for 1 minute rainfall intensities and 24.2 per cent for 5 minute intensities. For roofs the attenuation averaged 36.8 per cent for 1 minute intensities and 92.6 for 5 minute intensities. Regression for peak runoff coefficients from roofs and roads explained negligible amounts of the variance except when events with 1 minute rainfall intensities of over 30 mm hr−1 over the roads were analysed. Total rainfall was an important explanatory variable as was the slope of the road. There was evidence that peak coefficients for roads are greater during the summer.
The physical framework of the dependence between channel flow hydrographs and drainage network morphometry
Authors: Garbrecht J. , Shen H. W.
Published: February 2007

The physical basis of the linkage between magnitude and timing of channel flow hydrographs and drainage network morphometry is reviewed. Small Hortonian and structurally Hortonian networks are analysed using numerical runoff simulation. For Hortonian networks the variability of the geometry of individual channels and subcatchments within each Strahler order has generally little effect upon the overall character of the hydrograph in channels of higher order. If the network is also structurally Hortonian, the analysis of the simultaneous formation, travel, and concentration of the hydrographs in all channels of the network can be simplified to a sequence of one representative hydrograph per channel order. This approach is used in this study. Three major runoff processes control the flow hydrograph characteristics: the overland flow process which determines the water supply to the drainage network; the channel flow process which translates the hydrograph in space and time; and the drainage network process which concentrates and magnifies the flow at the junctions of the drainage network. Functional relations for the hydrograph peak, timing, and flow velocity are presented. For a given uniform rainfall and infiltration rate, the peak of the channel flow hydrograph is shown to increase geometrically with channel order, and its magnitude is directly related to the bifurcation ratio. The travel time of the peak also increases geometrically with channel order, and it is directly related to the channel length ratio over velocity ratio. The flow velocity of the peak changes in a downstream direction as a function of the bifurcation and slope ratio. It was also found that for negligible channel storage the channel flow and drainage network processes do not contribute significantly to the observed nonlinear response of a watershed to precipitation.
Water use by intensively cultivated willow using estimated stomatal parameter values
Authors: Grip Harald , Halldin Sven , Lindroth Anders
Published: February 2007

Large land areas in Sweden are planned to be planted with high producing, short rotation forest stands of willow in the beginning of the 1990s. Since willow is a highly hydrophilic species, this new land use may have strong implications on water resources. To assess these implications, evaporation of Salix viminalis and Salix viminalis x caprea stands in lysimeters was analysed with the simple, yet physically realistic KAUSHA model. Parameter values for the Lohammar equation were deduced (b = 100 m3 kg−1, kmax = 0.01 m s−1), believed to be applicable to other sites. Simulated evaporation during the 1980 growth season for a normal stand with a production of 12 tonnes of dry matter per hectare per season was 526 mm, of which 375 mm was transpiration, 56 mm interception evaporation, and 95 mm soil evaporation. For an optimally irrigated 20‐tonnes stand, the total evaporation was 584 mm, of which 430 mm was transpiration. As a comparison, Penman open water evaporation was 430 mm. To avoid soil water stress in the 20‐tonnes stand, 140 mm was needed as irrigation, equivalent to 25 per cent of the mean annual precipitation. Since intensively cultivated willow plantations seemed to be using much water, it was concluded that introduction of this agri‐forestry practice must be carefully planned to make use of this property, e.g. in biological filters or in reclaiming water‐logged land.
Recovery and concentration of suspended solids in the upper rhone river by continuous flow centrifugation
Authors: Burrus D. , Thomas R. L. , Dominik J. , Vernet J.‐P.
Published: February 2007

Six stations along the Rhône River from the Rhône Glacier to Lake Geneva were sampled by continuous flow centrifuge for recovery of suspended sediment. The samples were taken four times in the year in both 1982 and 1983. In addition, the mouth of the river was sampled in a like manner every two weeks during 1982 until August 1983. Concentration of sediment and composition did not vary as a function of depth or location across the river. Concentrations varied in time and as a function of flow and samples showed both increasing concentration in suspension and an increase in the proportion of finer particles moving downstream from source to mouth. Only slight variations in texture could be observed down the river as a function of time and appeared to relate to freezing and melting of the Rhône and other headwater glaciers as the primary sediment source. Little variation was observed annually in the texture and composition of the sediment at the river mouth despite large changes in concentration between the high flow summer and low flow winter discharges. These findings are consistent with a well‐mixed system in which the suspended sediments are directly related to the primary supply of material from the glaciers.
Hydrogeochemical processes involved in salt‐dissolution zones, texas panhandle, U.S.A.
Authors: Dutton Alan R.
Published: February 2007

Permian evaporite deposits have been extensively dissolved beneath the perimeter of the Southern High Plains in the Texas Panhandle. Hydrologic and geochemical data were collected from six test wells to determine hydrogeochemical processes involved and the source and flow paths of ground water moving in salt‐dissolution zones. Geochemical similarities and hydraulic‐head relationships indicate that ground water dissolving halite and anhydrite moves downward from aquifers in post‐Permian formations and follows flow paths influenced by topography. Holocene salt‐dissolution rates probably are lower than Tertiary and Pleistocene rates owing to regional changes in physiography and climate that probably decreased the amount of recharge to salt‐dissolution zones. Present as well as palaeohydrologic ground‐water velocities and salt‐dissolution rates are probably less beneath the Southern High Plains than in adjacent, peripheral salt‐dissolution zones because of lower hydraulic conductivities and lower hydraulic‐head gradients. Salinities in peripheral salt‐dissolution zones are low (67 000 to 95 000 mg L−1) despite high solubility of halite, reflecting relatively open circulation of ground water. In interior salt‐dissolution zones beneath the Southern High Plains, ground‐water circulation is low and water composition tends to reach halite saturation.
The nature of iron and manganese species in dam waters
Authors: Chiswell Barry , Zaw Myint
Published: February 2007

The molecular weight (M. W.) distributions of iron and manganese species in dam water samples were investigated by use of gel filtration, while the ion‐exchangeable and non‐ion‐exchangeable fractions of these metals were also analysed by ion‐exchange chromatography. For the samples studied, more than 96 per cent of the manganese species present were found to be ion‐exchangeable, whilst less than 35 per cent of iron species were ion‐exchangeable. These results correlated with the finding that all the manganese species had molecular weights less than 700, but that the molecular weights of the iron species were mostly in excess of 5000. Electron paramagnetic resonance (EPR) spectroscopy has been used to support the finding that manganese is almost totally present in the form of simple aquated Mn(II) ions.
The prediction of aquatic sediment‐associated trace element concentrations using selected geochemical factors
Authors: Horowitz Arthur J. , Elrick Kent A. , Hooper Richard P.
Published: February 2007

Multiple linear regression models calculated from readily obtainable chemical and physical parameters can explain a high percentage (70 per cent or greater) of observed sediment‐trace element variance for Cu, Zn, Pb, Cr, Ni, Co, As, Sb, Se, and Hg in a widely divergent suite of 61 sediment samples. The independent variables used in the models may be single parameters, principal component scores, or principal component scores combined with their cross‐products. The most useful type of variable must be determined on a case‐by‐case basis.

The independent variables (geochemical parameters) incorporated in the models calculated during this study probably are applicable to many aquatic sediments; albeit, use of a larger data set (>61) could alter the magnitude of the calculated coefficients. The geochemical parameters included in the models were of a physical (e.g. grain size, surface area) and a chemical (e.g. organic matter, amorphous iron oxides) nature. Comparison between actual and predicted trace element concentrations obtained from the models may provide a means of defining ‘average’ sediment‐trace element concentrations. In this context, the models may also help identify either naturally or anthropogenically impacted sites for additional study.
The transformation and export of phosphorus from Wetlands
Authors: Gehrels Jim , Mulamoottil George
Published: February 2007

There is widespread acceptance of the phosphorus retention capability of wetlands even though research findings are often inconclusive and contradictory. The results of a one year phosphorus budget study indicate that internal wetland processes may transform sediment bound phosphorus to plant available orthophosphorus. While total phosphorus imports were nearly double the total phosphorus exports for the study wetland, orthophosphorus exports were 22 per cent greater than imports. This study supports the recent finding that wetlands have limited capability to retain orthophosphorus and indicates that wetlands may even increase the export of orthophosphorus. The generally accepted nutrient retention function of wetlands and their possible role in eutrophication is thus questionable.
Characteristics of suspended sediment in the upper rhone river, switzerland, including the particulate forms of phosphorus
Authors: Burrus D. , Thomas R. L. , Dominik B. , Vernet J.‐P , Dominik J.
Published: February 2007

Six stations along the Upper Rhone River above Lake Geneva were sampled by continuous flow centrifuge for recovery of suspended sediment. The samples were taken four times, once in 1982 and three times in 1983. In addition the mouth of the river was sampled in a like manner every two weeks during 1982 until August 1983. Samples were analysed for the major elements SiO2, Al2O3, K2O, MgO, Na2O, CaO, and Fe2O3; for trace elements, Zn, Cu, Ni, Mn, and Cr; for Org. C and Kjeldahl N; and the forms of phosphorus bound as Organic P (OP), Apatite P (AP), and Non Apatite Inorganic P (NAIP). The major elements and trace metals confirmed that there is virtually no change in the major geochemical characteristics of the suspended solids in the Rhone, spatially or temporally, indicating that this river is a well‐mixed sedimentary system. AP also remained consistent in concentration throughout the year. Sediment recovered during the winter low flow, low turbidity period has been designated SED 1 whereas sediment from the high flow, high turbidity summer condition of the river has been designated SED 2. Org C, OP, and NAIP show a dramatic decrease in concentration from SED 1 to SED 2. The decline is ascribed to dilution of a relatively constant supply of organic matter and phosphorus derived mainly from point source sewage treatment plants to the Rhone. This results in variable partitioning of the OP/NAIP and Org C under the different turbidity condition in the river between winter and summer. This interpretation is confirmed by a low and consistent C‐N ratio which except for March remains below 10. Higher values in March may be indicative of soil erosion during spring melt in the agricultural lands of the Rhone Valley. The estimated proportion of particulate bio‐available phosphorus is 14 per cent for SED 1 and 7 per cent for SED 2. These low values would suggest that there would be no observable direct effect on the primary production of the receiving waters of Lake Geneva, which would thus respond only to the cumulative loading of phosphorus from the Rhone River.
One‐dimensional dispersion in unsteady flow in an adsorbing porous medium: An analytical solution
Authors: Yadava Raja Ram , Vinda Ram Raj , Kumar Naveen
Published: February 2007

Analytical solutions describing the concentration distribution along one‐dimensional unsteady seepage flow through adsorbing saturated finite porous medium have been obtained. An exponential function concentration is enforced at the source of the dispersion, while the change in the concentration is zero at the other boundary. A new time variable has been introduced to solve the unsteady flow problem and the solution is illustrated.
Rainfall interception in two tropical montane rain forests, Colombia
Authors: Veneklaas E. J. , Van Ek R.
Published: February 2007

Rainfall interception was studied during one complete year in two montane rain forests in the Colombian Andes at altitudes of 2550 and 3370 m. Additional measurements were made in a subsequent period at 3370 m, comparing two plots with different tree genera. Special attention was paid to the possible consequences of the abundant epiphytic vegetation, representing a high but spatially variable storage capacity. On an annual basis, interception amounted to 262 mm (12.4 per cent) of 2115 mm incident precipitation at 2550 m, and to 265 mm (18.3 per cent) of 1453 mm incident precipitation at 3370 m. There was no evidence for fog precipitation. The fact that, in spite of lower annual rainfall and lower evaporation rate, absolute quantity of interception at 3370 m was not lower than at 2550 m is probably related to differences in rainfall distribution and canopy storage capacities. The different responses of the two tree genera (characterized by distinct epiphyte cover) and the lower interception after prolonged wet periods support the idea that epiphytes play a significant role in the interception process. A realistic description of the water balance of such ecosystems will require the adaptation of existing interception models.
Processes of water movement through a chalk coombe deposit in Southeast England
Authors: Hodnet M. G. , Bell J. P.
Published: February 2007

The processes of water movement through the Coombe Deposit in a chalk dry valley near Eastbourne in Southeast England were investigated using simple methods based on regular weekly measurements of rainfall, soil water content, and soil water potential. The drainage flux (recharge) through the soil was determined using the water balance method during the winter and the zero flux plane (ZFP) method after the appearance of the ZFP in the spring. The unsaturated hydraulic conductivity was derived applying Darcy's Law in a novel way using the measured potential gradients and weekly drainage fluxes. The derived conductivity characteristics were adequate to identify the flow mechanisms, to illustrate the difference in behaviour between the horizons of the soil profile, and to give some indication of pore water velocities.

The mean daily drainage flux at 2.85 m depth during the recharge period from 10 October 1980 to 29 May 1981 was 1.6 mm d−1. Weekly mean rates of up to 3.7 mm d−1 were observed, but peak short term rates must have considerably exceeded this figure. It was shown that, in the lower part of the Coombe Deposit, when drainage fluxes are large, much of the flux passes through a very small proportion of the wetted cross‐sectional area of the soil. This gives rise to pore water velocities of at least 3 m d−1 at a depth of 2.85 m and 0.5 m d−1 between 0.5 m and 2.5 m depth. These results show that pollutants may be moved very rapidly through the profile in this, and similar, material. The core sampling techniques normally used to monitor pollutant movement in the chalk are unlikely to succeed in detecting this movement, not only because it is transient but also because it occupies only a very small proportion of the water filled pores.
Digital terrain modelling: A review of hydrological, geomorphological, and biological applications
Authors: Moore I. D. , Grayson R. B. , Ladson A. R.
Published: February 2007

The topography of a catchment has a major impact on the hydrological, geomorphological, and biological processes active in the landscape. The spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques. Many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems. Furthermore, topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology. Digital elevation models are the primary data used in the analysis of catchment topography. We describe elevation data sources, digital elevation model structures, and the analysis of digital elevation data for hydrological, geomorphological, and biological applications. Some hydrologic models that make use of digital representations of topography are also considered.
The prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models
Authors: Quinn P. , Beven K. , Chevallier P. , Planchon O.
Published: February 2007

The accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways. This paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using TOPMODEL. Distributed moisture status is predicted in TOPMODEL on the basis of spatial indices that depend on flow path definition. The sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients. A strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application.
Periodic drainage of ice‐dammed lakes as a result of variations in glacier velocity
Authors: Knight Peter G. , Tweed Fiona S.
Published: February 2007

Previous discussions of the catastrophic drainage of ice‐dammed lakes have centred on mechanisms where characteristics of the lake are crucial to drainage initiation, for example dam flotation or tunnel formation at a critical lake depth. This paper describes a mechanism for lake drainage where drainage initiation depends on the characteristics of the glacier and is independent of the characteristics of the lake. Prediction of this mechanism must be based on glacier dynamics, whereas the mechanisms most commonly discussed previously are best predicted primarily on the basis of lake evolution.

An ice‐dammed lake at the margin of the glacier Solheimajokull, in southern Iceland, was observed to drain rapidly into the sub‐ or englacial drainage system, supplying water and debris to the bed or interior of the glacier. Geomorphological evidence suggests that the lake drains and refills periodically, discharging up to 13300 m3 of water into the glacier‐hydrological system. The depth of the maximum lake is insufficient to cause either flotation of the ice margin or tunnel opening by plastic deformation of the ice, and we suggest that sudden drainage is related to ice‐bed separations associated with specific glacier flow states rather than to a critical lake depth threshold. This mechanism of lake drainage has implications for conditions at the glacier bed, for the development of basal ice and for the entrainment of debris into the glacier, as well as for the prediction of potentially hazardous catastrophic drainage events and jokulhlaups from ice‐dammed lakes.
The use of 137Cs as a tracer in an erosion study in south limburg (the Netherlands) and the influence of chernobyl fallout
Authors: De Roo A. P. J.
Published: February 2007

The 137Cs radioactivity of soils was used as a tracer of soil erosion in a catchment in the Netherlands: 143 samples were analysed to map the 137Cs redistribution using geostatistical interpolation methods. Caesium‐137 activities on grassland are significantly higher than on arable land. Also, 137Cs activities on waning slopes are higher and activities on steep slopes are lower. The soil erosion estimates, derived from the 137Cs data, are used to validate the USLE erosion model. The recent Chernobyl nuclear accident also contributed to the 137Cs activity. However, the Chernobyl input of 137Cs, with a constant ratio of 1.765:1 to 134Cs, cannot be used as a tracer of soil erosion. Because of the rapid decay of 134Cs, we will not be possible to separate the sources of 137Cs in the near future in areas significantly influenced by Chernobyl fallout and in these areas 137Cs can no longer be used as a soil erosion tracer.
II: Wind related errors in different methods of solid precipitation measurement
Authors: Günther Th. , Graf B.
Published: February 2007

Using data sets assembled within the WMO Solid Precipitation Measurement Intercomparison, the paper deals with the wind related losses in national methods of solid precipitation measurement. Fourteen different types of precipitation gauges are included in the Harzgerode/GDR intercomparison field. Initial results of the comparisons between the Valdai double fence reference method and the other gauges in terms of dependence on wind speed and type of precipitation are presented. These results reveal that the national unsheltered HELLMANN gauge catches only 24 per cent to 70 per cent of the daily totals of solid precipitation as compared with the reference gauge. Results of the analysis of monthly totals and individual events reveal a similar dependence of gauge deficiencies on wind speed and type of precipitation. Case studies of single snow falls and the wind field conditions around and within the double fence reference are also described.
III: Methods of correcting for systematic errors in atmospheric precipitation measurements in Czechoslovakia
Authors: Lapin M. , Šamaj F.
Published: February 2007

The methods of correcting for systematic errors in precipitation measurements using the Czechoslovak gauge METRA 886 are presented. This gauge has an orifice area of 500 cm2 and is elevated 1 m above the ground. The wetting correction amounts to 0.1–0.2 mm per measurement. The evaporation correction ranges from 3 per cent in frost‐free periods to 10 per cent in frost periods. The wind‐induced correction amounts to 5 per cent for rain and 45 per cent for snow. The total sum of corrections on average 10–15 per cent per year in lower localities.
Variation in suspended sediment concentration during storm discharges in three small streams in upper osun basin, Central Western Nigeria
Authors: Jeje L. K. , Ogunkoya O. O. , Oluwatimilehin J. M.
Published: February 2007

The suspended sediment concentration response of three small streams draining quartzites and quartz‐schists in southwestern Nigeria to storms of varying magnitude are presented. A total of 1468 water samples from 62 storm responses with peak stream discharge values ranging from 80 to 120 l s−2 were analysed and storm and suspended sediment concentration hydrographs and hysteresis loops were used to depict the response patterns. The six different types of responses identified include the single and multiple discharge peak rises with sediment lead and lag and also the mixed response patterns. Both valley slope and channel erosion constituted important sources of suspended sediment. However, sediment availability, exhaustion, and flushing effects determined the variation in the different response types.
Continuous measurement of the depth of water table (inundation) in wetlands with fluctuating surfaces
Authors: Roulet Nigel , Hardill Steven , Comer Neil
Published: February 2007

Assessment of the water table in compressible and/or floating peatland mats requires a remote sensor that can measure simultaneously the elevation of the peat surface and the water level. A simple device, comprising two potentiometers, a float and ‘bog shoe’ was used to measure the water level and peat surface witin 0‐3 mm. The water table (depth of water level relative to the peat surface) was then calculated.
Subsurface flow responses of a small forested catchment in the Ouachita mountains
Authors: Turton Donald J. , Haan Charles T. , Miller Edwin L.
Published: February 2007

Despite considerable research performed on forested catchments in the Ouachita Mountains of Oklahoma and Arkansas, little information on hydrological processes in operation is available. Based on catchment physical characteristics, subsurface flow was thought to be an important hydrological process in the region. Therefore, this study was undertaken to determine the occurrence, rates, timing and volumes of subsurface flow, and to estimate the importance of subsurface flow as a streamflow generating process. Subsurface flow was collected from three hillslope sites on a 7.7 ha forested catchment. Hillslope sites drained through natural seepage faces located near stream channels. Subsurface flow was collected from three depths at each hillslope site, below the litter layer, below the a horizon, and within the B horizon (Bt21). Subsurface flow occurred and was measured during 11 of 31 rainfall events. Subsurface flow responded rapidly to the initiation of and to changes in intensity of rainfall at all depths. the rapid response was indicative of flow through soil macropores. B horizon subsurface flow commenced within 10 to 180 min of the initiation of rainfall. Multiple linear regression showed that the volume of subsurface flow generated during a given storm was directly related to rainfall depth and a 7‐day antecedent precipitation index used to represent antecedent water content. About 67 per cent of the total subsurface flow collected during the study was produced in one large storm under wet antecedent conditions. the storm was equal to the 2‐year, 24‐hour storm for the region. Measured subsurface flow volumes were extended to the watershed scale to provide estimates of catchment‐wide contributions to streamflow. It was estimated that subsurface flow contributed from 1 to 48 per cent of total quickflow measured at the catchment outlet. Based on the timing of subsurface flow, it was estimated that subsurface flow May, contribute up to 70 per cent of quickflow before and soon after peak flow.
A laboratory investigation of the leaching of solute from snowpack by rainfall
Authors: Tranter M. , Tsiouris S. , Davies T. D. , Jones H. G.
Published: February 2007

Under controlled laboratory conditions, artificial rain leaches solute from snow columns, and gives rise to leachate with a composition similar to snowmelt, in addition to the solute initially present in the artificial rain. the initial concentration of ions in the leachate, normalized to the concentration of ions found in the original snow and corrected for the solute present in the artificial rain, is similar to those reported in other laboratory and field studies of snowmelt composition, but there is some evidence that the concentration of leached ions declines more rapidly than during snowmelt. Similarly, as in snowmelt studies, not all ions are leached with the same efficiency. Bearing in mind the confounding influences of snow crystal morphology and snow column hydrology, it seems likely that rain will leach solute from snowpack during rain‐on‐snow events, in a manner similar to leaching by snowmelt, and that the precise composition of the leachate will depend on the hydrological routing of rain‐meltwater mixtures through the snowpack.
Future of distributed modelling
Authors: Jensen Karsten Høgh , Mantoglou Aristotelis
Published: February 2007

The state of the art of modelling hydrological systems using distributed modelling techniques is discussed and the theoretical problems caused by the heterogeneities always present in field soil systems are emphasized. It is argued that such heterogeneities need to be considered to develop physically based large‐scale models applicable at the scale of the numerical discretization blocks. Stochastic approaches seem to provide a rational framework for treating the difficult to characterize spatial variability and for establishing a link between parameter uncertainty and prediction uncertainty. It is emphasized that more research in theory development and testing is required before complete large‐scale models are obtained and this had to be carried out jointly with field tests. More research is also required in field measurement techniques to accurately supply the deterministic and statistical parameters required in distributed models.
Future of distributed modelling: The Systeme Hydrologique Europeen
Authors: Bathurst J. C. , O'Connell P. E.
Published: February 2007

Current and projected UK activities with the Système Hydrologique Européen (SHE) hydrological modelling system are examined. Development of the SHE arose from the need for a new modelling approach for use in assessing the environmental impacts of river basin development and the system is particularly suited to predicting the impacts of land use and climatic changes and to applications to basins with sparse data sets. the basic hydrology model is now being developed into a powerful contaminant and sediment transport modelling system called SHETRAN‐UK and components are also being proposed to account for landslide and gully erosion. Applications of the SHE have been made at spatial scales ranging from 30 m2 to 5000 km2 and in a variety of environments. These have demonstrated an ability to achieve calibration on the basis of short time series records and field evaluation of parameters, to provide multiple outputs on a spatially and temporally distributed basis, and to explore basin response mechanisms. They have also indicated the importance of integrating field measurements within the calibration process. the effect of the scale of model grids on parameter evaluation and on simulation results still needs to be investigated and there is a need for field process studies in areas where there is a poor understanding, to improve certain of the process representations within the SHE. However, new ideas are being explored to account for subgrid spatial variability in parameter values and to develop a validation methodology for testing the predictive capability of the SHE. Future developments will include the use of geographical information systems and data processing packages to aid data handling, expert systems to improve the efficiency of calibration, and parallel processing and other new computational techniques. an expanding range of applications will see physically based hydrological modelling systems at the core of decision support systems and integrated at the continental scale with general circulation modelling systems.
The future of distributed models: Model calibration and uncertainty prediction
Authors: Beven Keith , Binley Andrew
Published: February 2007

This paper describes a methodology for calibration and uncertainty estimation of distributed models based on generalized likelihood measures. the GLUE procedure works with multiple sets of parameter values and allows that, within the limitations of a given model structure and errors in boundary conditions and field observations, different sets of values May, be equally likely as simulators of a catchment. Procedures for incorporating different types of observations into the calibration; Bayesian updating of likelihood values and evaluating the value of additional observations to the calibration process are described. the procedure is computationally intensive but has been implemented on a local parallel processing computer. the methodology is illustrated by an application of the Institute of Hydrology Distributed Model to data from the Gwy experimental catchment at Plynlimon, mid‐Wales.
Stochastic modelling of groundwater flow and solute transport in aquifers
Authors: Jim Yeh T.‐C.
Published: February 2007

This paper presents an introductory overview of recently developed stochastic theories for tackling spatial variability problems in predicting groundwater flow and solute transport. Advantages and limitations of the theories are discussed. Lastly, strategies based on the stochastic approaches to predict solute transport in aquifers are recommended.
Deposition and resuspension of fine particles in a riverine ‘dead zone’
Authors: Tipping E. , Woof C. , Clarke K.
Published: February 2007

Particulate matter suspended in the River Severn (Shropshire, UK) consists chiefly of clay‐sized mineral particles, together with living and dead micro‐organisms (algae and bacteria). Its concentration depends strongly on discharge, but the particle size distribution shows no systematic variability. For most samples, the particle volume is log‐normally distributed with respect to diameter, the mean diameter being ca. 9 μm. The particles are mainly aggregates, including some with linear dimensions of the order of tens or hundreds of micrometres. Particle density depends appreciably on size, decreasing from ca. 2.5 × 106 g m−3 at a diameter of 2.5 μm to ca. 1.3 × 106 g m −3 at 20 μm. The collision efficiency factor for particle aggregation is estimated to be 0.01–0.03. At low discharge, the ‘dead zone’ in the River Severn at Leighton is a well defined region of stagnant water behind a gravel bar. The rate of deposition of fine particles on its bed is of the order of tens of grams per square metre per day. Resuspension requires a critical bed shear velocity of 0.03–0.04 m s−1, which occurs at main river discharges greater than about 150 m3 s−1. Under such conditions the gravel bar is underwater and the dead zone is a region of highly turbulent return flow. A simple mechanistic model of particle dynamics in the dead zone accounts reasonably well for particle accumulation rates when run with parameter values based on measured particle and hydraulic properties. Calculations with the model suggest that most of the sedimentation flux to the dead zone bed is due to particles with equivalent sphere diameters in the range 30–240 μm. Simulations indicate that deposition proceeded continuously during spring and summer, whereas repeated deposition and resuspension occurred in autumn and winter.
Hydrological flow paths at the allt A' mharcaidh catchment: An analysis of plot and catchment scale observations
Authors: Wheater H. S. , Tuck S. , Ferrier R. C. , Jenkins A. , Kleissen F. M. , Walker T. A. B. , Beck M. B.
Published: February 2007

An integrated programme of hydrological monitoring at the 10 km2 Allt a' Mharcaidh catchment in north‐east Scotland has been based on observations at plot, hillslope and catchment scale. The resonse of the principal soil types has been characterized from a combination of throughflow and three‐dimensional tensiometer data at plot scale, and plot sequences have been used to investigate hillslope scale effects. Seep emergence is associated with downslope drainage and local topographic convergence; in parallel preferential pathways generate a highly dynamic throughflow response. Catchment and subcatchment hydrographs mirror the twin dynamic observed at hillslope scale, and a unified hypothesis of response is presented which is consistent with all scales of observations.
Streamflow routing in the indian arid zone
Authors: Sharma K. D. , Murthy J. S. R. , Dhir R. P.
Published: February 2007

A lumped model for streamflow routing in arid ephemeral channels has been developed. The governing equations for movement of flood waves subjected to transmission losses are simplified through a time averaging process to develop an ordinary differential equation describing transmission losses as a function of distance, inflow, channel width, time parameters of flow and effective hydraulic conductivity. The resulting equation has an analytical solution and simulates runoff volume and peak discharge rates for individual storm events. The outflow hydrograph is fairly well approximated with a triangular approximation. The model is simplified and constructed to require a minimum of observed data for calibration. It can also be used for ungauged basins in arid regions through parameterization.