bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling long term stream acidification trends in upland wales at plynlimon
Authors: Whitehead P. G. , Reynolds B. , Hornung M. , Neal C. , Cosby J. , Paricos P.
Published: February 2007

Historical reconstructions and predictions of streamwater acidification are presented for moorland and afforested catchments in the Welsh Uplands at Plynlimon. MAGIC (Model of Acidification of Groundwater In Catchments) is validated by application to an afforested catchment. MAGIC is used to illustrate that atmospheric deposition is primarily responsible for stream acidification but that conifer afforestation can enhance stream acidity. The historical trends determined by the model illustrate that long‐term acidification has been present since the turn of the century and will continue unless either deposition levels are reduced significantly or liming is undertaken on a major scale.
A unique flood event in an arid zone
Authors: Walter Michael O.
Published: February 2007

Arid regions generally lack surface water records for developing flood characteristics for hydraulic design purposes. Consequently good records of floods, particularly large ones, are a data asset to arid zone hydrology.

A large rainfall and runoff event which occurred on 23 April 1985 has been fully recorded on Wadi Ghat, a 597 km2 catchment in southwest Saudi Arabia.

Maximum point rainfall intensity was 115.4 mm hr−1. The peak discharge was 3200 m3 s−1. Point rainfall has an expected frequency of occurrence in excess of once every 200 years. The peak discharge is expected to occur on an average once in 143 years.
Sea‐salt induced streamwater acidification
Authors: Langan S. J.
Published: February 2007

The paper describes three episodes of short‐lived streamwater acidification for a remote site in southwest Scotland. During the third of these storms stream pH decreased from 5.5 to 4.4. The apparent mechanism for acidification is one of ion‐exchange within the catchment soil following precipitation inputs heavily laden with sea‐salt. Verification of such a process is provided by a series of soil experiments. Comparison of data from three catchments under differing land‐use indicates the additional role land management can play in streamwater acidification.
A terrain‐based watershed information system
Authors: Band L. E.
Published: February 2007

A framework for a watershed information system is presented in which the topology of the drainage basin is closely followed in the data structure. The topography is partitioned into a set of subcatchments and hillslopes that are organized around the drainage network, automatically extracted and defined from standard digital elevation data. A set of recursive algorithms perform the actual topographic feature extraction and synthesis into a full basin model, and also serve as the basis for processing registered information. The techniques are particularly well suited to support and parameterize distributed components runoff models as full hydrologic connectivity throughout the basin is explicitly defined. Full scale flexibility in terms of the representation of the topography and aggregation of physical units is achieved by the recursive nature of the data stucture, allowing straightforward translation between scales and the investigation and choice of the appropriate scale for various hydrologic applications.
Soil hydrophobic effects on infiltration and catchment runoff
Authors: Burch G. J. , Moore I. D. , Burns J.
Published: February 2007

After dry summers or drought, eucalypt forest soils at two sites in southeastern Australia developed hydrophobic or non‐wetting surface characteristics that reduced infiltration, measured using a sprinkling infiltrometer. At one site the development of hydrophobic conditions caused the rainfall to runoff conversion efficiency of a forested catchment to increase from 5 per cent to 15 per cent. Under non‐hydrophobic conditions at this site, grassland always generated more runoff than forest. However, one major rainfall‐runoff was recorded at a time of highly hydrophobic forest soil conditions and this storm generated greater runoff on the forested catchment than the grassland catchment.

At the second site forest soils have naturally highly conductive surface layers because of a dense network of macropores and pathways for preferential flow. Hydrophobic conditions produced by drought caused soil water movement to be confined to only a few of the larger macropores exposed to surface ponded water. Even so, infiltration rates remained relatively high so that the impacts of hydrophobic soils were not translated into increased catchment runoff as at the first site.
Field measurement and associated controlling factors for ground water seepage in a piedmont impoundment
Authors: Bruckner Amy E. , Hornberger George M. , Mills Aaron L.
Published: February 2007

Knowledge of groundwater seepage to and from lakes can be an important component of scientific investigations involving water and geochemical budgets. Measurements of groundwater seepage at Lake Anna, a man‐made lake in central Virginia, show that inflow to the lake occurs even under dry summer conditions. Seepage rates were found to be correlated with the elevation of the near‐shore water table, which responded rapidly to rainfall events in the fractured rock terrane in which Lake Anna is located. Seepage rates did not decline uniformly with distance offshore. This result contrasts with those for lakes underlain by relatively homogeneous porous media where measurements generally confirm the prediction that seepage rates drop off exponentially with distance from shore. The along shore variability of seepage rates in Lake Anna was related to a topographic index that is used to describe drainage from hillslopes. This suggests that seepage in impoundments such as Lake Anna may be strongly controlled by drainage pathways that pre‐date the lake.
The response of headwater stream channels to urbanization in the humid tropics
Authors: Ebisemiju Fola S.
Published: February 2007

Analysis of the bankfull cross‐sections of headwater streams in Ado‐Ekiti region of Southwestern Nigeria and their comparison with data from other tropical environments and temperate latitudes reveal that the channel capacities of streams in the humid tropics are relatively smaller than those of temperate regions, averaging 1.51 m2with a coefficient of variation of 87 per cent. This is attributed to the small stream discharge, the predominantly low and highly seasonal flows of the streams, the low shear stress of stream load, and the stabilizing and protective influence of riparian vegetation and surface incrustations. The chanel capacities of the urban streams (mean = 1.13m2) are about 47 per cent smaller than those of the natural streams (mean = 2.12 m2) in the same ecological zone. In terms of hydraulic efficiency, the urban streams also have relatively inefficient cross‐sections and larger width/depth ratios than their rural or natural counterparts. Resurveys of seventeen monumented cross‐sections reveal that while channel shoulder width increased by only 6 per cent over a one‐year period, channel depth and capacity decreased by 16 per cent and 4 per cent respectively; the observed decrease in channel size occurs entirely in the channel depth dimension. Thus the response of stream channels to the urbanization of small headwater catchments in the humid tropics is probably more of vertical accretion of channel bed and reduction in channel capacity rather than the widely‐reported anomalous enlargement of urban streams through channel widening. The rapid rate of channel aggradation is attributed to excessive rates of sediment production and delivery to streams in urbanized catchments in the humid tropics, rapid deposition of sediments during small runoff events and on the falling stage of storm hydrographs, and the inability of the streams to evacuate the sediments delivered to them despite the increased discharge and peak flow associated with urbanization. The low competence of the urban streams is attributed to the predominance of low flows, very gentle bed slopes, and most importantly the widespread dumping of refuse into the channels thereby reducing flow velocity and promoting backwater flooding, ponding, and sedimentation. The correlations between drainage basin area, a surrogate for stream discharge, and channel capacity are very strong for the rural watersheds, and the regression analysis indicates a tendency towards a steady‐state isometric relationship. Urban channels are, to a large extent, in disequilibrium with the urban hydrological state. However, spatial variations in the degree of urbanization of the catchments, and, therefore in runoff volume and velocity, exercise strong control on channel width, depth, and size. A model of the sequence of stream channel adjustment to the urbanization of small headwater catchments in the humid tropics is presented.
Use of caesium‐137 measurements to investigate erosion and sediment sources within a small drainage basin in the loess plateau of China
Authors: Xinbao Zhang , Shaolong Li , Chenghua Wang , Wanpei Tan , Qingchang Zhao , Yiyun Zhang , Meiqiong Van , Yalun Liu , Jingjiang Jiang , Jule Xiao , Jie Zhou
Published: February 2007

The contributions of sediment from different geomorpholigical units within a small basin in the Loess Plateau have been determined using caesium‐137 as a tracer. The mean caesium‐137 content of sediment originating from the hill area, where sheet and rill erosion are predominant, was 3–37 Bq kg‐1, whereas no caesium‐137 was detected in the sediment originating from the gully area where gullying and gravitational erosion are predominant. The mean caesium‐137 content of sediment from two flood deposits was 0–23 Bq kg‐1 and 0–89 Bq kg‐1. The relative contribution from the hill area in the two floods was 7 per cent and 26 per cent, whilst that from the gully area was 93 per cent and 74 per cent.
Changes in physical properties of young and old volcanic surface soils in Costa Rica after clearing of tropical rain forest
Authors: Spaans E. J. A. , Baltissen G. A. M. , Bouma J. , Miedema R. , Lansu A. L. E. , Schoonderbeek D. , Wielemaker W. G.
Published: February 2007

Large areas of tropical rain forests are being cleared and used for agricultural purposes. As a result, fragile soil structure degrades which alters soil hydraulic properties. Soil physical methods and micromorphometrical analysis were used to analyse effects of changes in vegetation on soils of different ages. Measurements were made in topsoils of a relatively old Humoxic Tropohumult and of a relatively young Oxic Humitropept, both under forest and under pasture.

The crust test was used to measure hydraulic conductivities (K) in relation to pressure head (h). Moisture retention data were obtained by measuring outflow from undisturbed core samples placed in porous cups at certain negative pressure heads. Micromorphometric analysis of thin sections supplied quantitative descriptions of macroporosity patterns and pore types.

Ksal of the Humult decreased from 1000 cm day−1 under forest to 50 cm day−1 under pasture. Macroporosity of the forest topsoil consisted mainly of compound packing voids. In the pasture topsoil predominantly vughs and more planar voids were present and macroporosity was significantly lower.

Ksat was equal at 70 cm day−1 under both types of vegetation of the Tropept. Compound packing voids as well as vughs were present under both forest and pasture. Under pasture more planar voids appeared and macroporosity decreased significantly.

Both total porosity and bulk density, before and after clearing of forest, were not significantly different in the two soil types. Obviously, puddling occurred in both soil types. Structure degradation in the relatively old Humu't was, however, more severe in shorter time than in the relatively young Tropept over a longer time span.
Mechanisms of water storage in salt marsh sediments: The importance of dilation
Authors: Nuttle William K. , Hemond Harold F. , Stolzenbach Keith D.
Published: February 2007

Direct observation of surface displacement in two New England salt marshes shows that shrinking and swelling of the sediment is an important mechanism for water storage. This mechanism accounts for 20 per cent of the total change in water content of the sediment in Belle Isle marsh, Massachusetts, and for as much as 36 per cent and 86 per cent of the total at separate sites in Sippewissett Marsh, Massachusetts. Swelling in response to infiltration appears to follow the infiltration model of Hemond et al. (1984). Shrinkage decreases the aeration of the sediment compared to soils that do not shrink, and reduced aeration represents a physiological stress to vegetation. For a given depth of water loss, e.g. one day's evapotranspiration, more shrinkage, less aeration, and higher stresses on vegetation will occur in deeper sediment deposits.
Hydrochemical processes in ground water‐discharge playas, Central Australia
Authors: Jankowski Jerzy , Jacobson Gerry
Published: February 2007

A large groundwater system in the Amadeus Basin, central Australia, discharges to a chain of playa lakes 500 km long. The playas contain highly concentrated brines; these are sodium‐chloride rich waters with appreciable magnesium and sulphate and very low concentrations of calcium and bicarbonate. Gypsum, glauberite, and other evaporite minerals are precipitating in the playas. The groundwaters evolve to brine by concurrent processes of dissolution, evaporative concentration, mineral precipitation, and mineralogical change. Chemical evolution is considered with reference to a concentration factor based on chloride. Ion transfer calculations demonstrate losses of magnesium and bicarbonate throughout, as a result of precipitation. Sodium, potassium, calcium, and sulphate are gained initially as a result of dissolution but lost subsequently as a result of precipitation.

Larger playas in the chain, exemplified by Lake Amadeus, have dual shallow and deep groundwater flow paths whereas the smaller playas, exemplified by Spring Lake, have only shallow flow paths. Brines in the larger playas are diluted by deep groundwaters and this is reflected in the degree of saturation attained with respect to particular minerals. Thus, saturation with respect to gypsum and glauberite is attained earlier in Spring Lake than in Lake Amadeus. Saturation with respect to halite is attained in Spring Lake but not in Lake Amadeus. Both playas are undersaturated with respect to hexahydrite and sylvite although these minerals occur in efflorescent crusts in Spring Lake.
Case study evaluation of geomorphologic rainfall ‐ runoff model, incorporating linear infiltration expression
Authors: Allam Mohamed Nasr
Published: February 2007

This paper presents case study applications for the hydraulically‐based geomorphologic Instantaneous Unit Hydrograph (IUH), developed by Diaz‐Granados et al. (1986). This IUH was derived as a function of watershed geomorphology and stream response to lateral inflows. This response was determined by solving one‐dimensional linearized equations of motion including a simple infiltration expression approximated by an infiltration coefficient multiplied by the streamflow discharge. Three gauged watersheds in Saudi Arabia are selected as case studies. A procedure for estimating the stream response parameters (the flow depth, the flow velocity, and the infiltration coefficient) is provided. A comparison is made between the observed and computed hydrographs and an evaluation of the IUH results and limitations is provided.
Groundwater cation concentrations in the riparian zone of a forested headwater stream
Authors: Hill Alan R.
Published: February 2007

Groundwater cation concentrations in relation to hydrologic flow paths were studied in the riparian forest zone of a small headwater catchment near Toronto, Ontario. Groundwater entering the riparian zone from uplands showed significant differences in cation concentrations between slope‐foot and near‐stream locations. Mean Ca, Mg, K, and Na concentrations in shallow groundwater at the upland perimeter of the riparian forest were 65‐0, 11‐2, 0‐7, and 1‐8 mg L−1 respectively. Mean Ca, Mg, K, and Na concentrations in deep groundwater flowing upwards through glacial sands beneath the riparian zone were 52‐1, 15‐1, 1‐3, and 2‐6 mg L−1 respectively. Shallow groundwater emerged as slope‐foot springs producing surface rivulets which crossed the riparian zone to the streams. Deep groundwater flowed upward through organic soils into the rivulets and also discharged directly to the streams as bed and bank seepage. Springs had higher Ca concentrations and lower Mg, K, and Na values than rivulets entering the streams. Conversely, Mg, K, and Na concentrations were higher and Ca concentrations were lower in bank seeps in comparison to rivulets. These results suggest that differences in cation concentrations in groundwater entering the streams result from initial contrast in the chemistry of shallow and deep groundwater rather than from the effects of riparian soils and vegetation.
Partitioning of rainfall in a eucalypt forest and pine plantation in southeastern australia: I throughfall measurement in a eucalypt forest: Effect of method and species composition
Authors: Crockford R. H. , Richardson D. P.
Published: February 2007

A seven year event‐based study partitioning of rainfall into throughfall, stemflow, and interception was conducted in a dry sclerophyll eucalypt forest and a Pinus radiata plantation. Resulting information will be of use for process modelling.

Stemflow was influenced by event type, rain angle having a major effect; and the yields of the different species are compared. Tree characteristics that influenced stemflow yields are outlined and discussed.

The canopy storage capacity of the eucalypt forest was determined and the influence of species composition is shown. The likely influence of climate variations is discussed. The canopy storage capacity is compared to the interception values estimated for continuous events of various sizes.

The interception of the eucalypt forest and the pine plantation are compared on event basis for event size classes and on an annual basis. The comparative interceptions for continuous events are also discussed, while the effect of thinning the pine plantation on throughfall, stemflow, and interception is shown.

The hydrological consequences of this study are: more informed judgment can be made about techniques for measurement of throughfall, tree structural characteristics (species related) can more adequately be considered when selecting trees for measurement of stemflow, and the stemflow yields can in some cases be better understood from the information about effect of event type.

This paper deals with the influence of measurement method, species composition, and tree characteristics on the estimation of throughfall in the eucalypt forest. The site is near Canberra, lat. 35°S, 145°E, with annual rainfall about 650 mm.

Two methods of measuring throughfall are compared: randomly placed, 200 mm cylindrical gauges (standard) and 50 mm square opening wedge type gauges (plastic), and randomly placed 5 × 0–22 m troughs. Despite the high placement density (150 to 225 ha−1), throughfall estimates from gauges has high variance and consistently underestimated those of the troughs, which had a total opening equivalent to 2325 raingauges (200 mm diameter) per hectare.

Local concentration of stemflow into drip points provided by detaching bark pieces of one smooth barked species, Eucalyptus mannifera, is believed to be the principal cause of the lower collection and greater variance of the gauges. The low leaf area index (1–3) and large wood area of the forest together with a pendulous vertical habit of the leaves also contributed. The presence of E. mannifera is shown to substantially affect the relative values of throughfall as measured by troughs and gauges. The plastic receivers were found to underestimate rainfall or throughfall relative to the standard gauges, particularly for fine drop rainfall in multiperiod events.
Partitioning of rainfall in a eucalypt forest and pine plantation in southeastern australia: II stemflow and factors affecting stemflow in a dry sclerophyll eucalypt forest and a pinus radiata plantation
Authors: Crockford R. H. , Richardson D. P.
Published: February 2007

Stemflow of a dry sclerophyll eucalypt forest and a nearby Pinus radiata plantation was studied on a rainfall event basis. The stemflow yields of the forests are quantified, compared, and presented on an annual basis for four years. Yields of the individual eucalypt species are compared and the tree characteristics responsible for the yield differences are discussed. The influence of event size, type, and season on stemflow are also shown. Rainfall angle is shown to have a significant effect on stemflow yield.
Partitioning of rainfall in a eucalypt forest and pine plantation in southeastern australia: III determination of the canopy storage capacity of a dry sclerophyll eucalypt forest
Authors: Crockford R. H. , Richardson D. P.
Published: February 2007

The canopy storage capacity of a dry sclerophyll eucalypt forest was determined. This required destructive sampling of three major species of trees and development of a water soakage method for the measurement of water holding capacity of all above ground components.

The influence of antecedent weather conditions on canopy storage capacity was assessed. It was shown that the interactive effects of leaf area and water holding capacity of all tree components were such that the estimated canopy storage capacity (0‐39 mm) was likely to change little except under extreme conditions of drought and rainfall.

The effect of species composition on forest canopy storage capacity is also presented.

The wetting processes are described and compared with those discussed in other studies. They are shown to be relevant to the estimation of canopy storage capacity in almost any forest.
Monitoring spatial variability of forest interception
Authors: Durocher M. G.
Published: February 2007

Field instrumentation was designed and installed to quantify the influence of forest interception on the spatial and temporal distribution of water flux onto and into the forest soil at the plot scale. An application is presented which demonstrates that the instrumentation has the required resolution to monitor the spatial variability and dynamics of the flux processes. The observations show that spatial variability of interception may play an important role, not only in small scale soil moisture heterogeneity, but also in the hydrological response of a forested catchment at the hillslope scale. They also highlight the need of gathering more field information on the effects of vegetation on the spatial variability of soil surface water input.
Seasonal, hydrological, and land management factors controlling dissolved organic carbon concentrations in the loch fleet catchments, Southwest Scotland
Authors: Grieve Ian C.
Published: February 2007

Dissolved organic carbon (DOC) was measured at hourly or two‐hourly intervals during more than 30 events in one forested and two moorland subcatchments of the Loch Fleet catchment in southwest Scotland. The dominantly peaty soils in the catchments resulted in small discharge‐related DOC variations within individual events, with a maximum range of about 2 mg 1−1. Seasonal variations were larger with an amplitude of 8‐9 mg 1−1 and maximum concentrations in the summer months. The forested stream had the highest mean DOC, twice as large as the comparable moorland stream in the preliming phase. Applications of lime to the catchments increased stream DOC concentrations, with the largest increases in the moorland catchments.
Seasonal soil water dynamics in the jarrah forest, Western Australia. I: Results from a hillslope transect with coarse‐textured soil profiles
Authors: Ruprecht J. K. , Schofield N. J.
Published: February 2007

Seasonal soil water dynamics were measured on a hillslope transect in the jarrah forest of southwest Western Australia over the period 1984‐86 using mercury manometer tensiometers, gypsum blocks, and a neutron moisture meter. The soil water potential gradients indicated downward vertical drainage flux through winter and spring. There was generally a change to an upwards flux in early summer which was sustained through to autumn. A shallow ephemeral saturation zone was identified in and above a duricrust layer, lasting up to three days after heavy, late winter rainfall. The annual maximum to minimum unsaturated soil water storage on the hillslope was approximately 400 mm to 6 m depth and 480 mm to 15 m depth. This did not change significantly in years of substantially different winter rainfall. The magnitude of seasonal soil water storage was similar to other forested areas with deep soil profiles. The depth of observable infiltration was dependent on annual rainfall. This was consistent with the observation that groundwater levels responded to rainfall over the whole hillslope in wet years but only responded on the lower slopes in dry years. The average summer drying rate of the soil profile to 6 m depth of 3.5 mm day−1 was within the range of values reported for forests elsewhere. In late summer, following an extended drought period, the drying rate decreased downslope but increased midslope.
Further discussion on the intercomparison of the trace metal concentrations and particle size of fluvial sediment recovered from two centrifuge systems
Authors: Santiago S. , Thomas R. L. , Loizeau J.‐L. , Favarger P.‐Y. , Vernet J.‐P.
Published: February 2007

A single large volume water sample taken at the mouth of the Upper Rhone River on Lake Geneva was processed directly in parallel through two continuous flow centrifuges, a Westphalia and an Alfa‐Laval. Sediment was recovered from the Westphalia, and separately from the bowl and brass core of the Alfa‐Laval. The three sediment samples were analyzed for particle size and the following elements: Zn, Cu, Mn, Cr, P, Co, B, V, Be, Sr, Na, Pb, Ni, Ba, Fe, Ca, and Mg. Results indicate that the particle size recovery of both machines is similar when sediment from the brass core and bowl of the Alfa‐Laval are combined, and that the recovery for all elements other than Cu, V, B, and Pb are the same when the particle size differences are taken into account. Sediment from the Alfa‐Laval brass core is clearly contaminated by Cu, B and is also elevated in V and Pb but not to a significant extent. The sediment recovered from the bowl of the Alfa‐Laval is contaminated only with Cu, with a 10 ppm increase over the 52 ppm recovered in the Westphalia sediment. Operating procedures involve the discarding of the brass core sediment and the mixing of the Alfa‐Laval bowl sediment with that from the Westphalia. The consequent increase in Cu is estimated at less than 5 ppm or within the confidence level of the analysis. These procedures are recommended to all operators of non modified Alfa‐Laval units.
Transpiration of plantation pinus radiata estimated by the heat pulse method and the bowen ratio
Authors: Hatton Thomas J. , Vertessy Robert A.
Published: February 2007

The heat pulse method was used to estimate stand transpiration from a radiata pine (Pinus radiata) plantation in southeastern Australia over a period of four days. The diurnal pattern of sapflow was related to net radiation with a time lag of about 1.5 hours. Despite high soil moisture levels, sapflow did not keep up with evaporative demand in the afternoon. Sapflow estimates of transpiration exceeded estimates for evaporation based on Bowen ratio measurements for all four days of the study.
Use of practical aspects of soil behaviour to evaluate different methods to generate soil hydraulic functions
Authors: H. M. Wösten J. , Schuren C. H. J. E. , Bouma J. , Stein A.
Published: February 2007

Soil hydraulic functions can be obtained with methods that range from complex and costly to simple and cheap. Decisions as to which is the most appropriate method for a specific application have to be based on a comparison of generated hydraulic functions. This comparison should preferably be based on a statistical comparison of practical applications calculated with the different hydraulic functions rather than on a statistical comparison of the functions themselves. In this study four different methods were used to generate hydraulic functions: (A) direct on‐site measurement, (B) measurement in soil horizons in the area, (C) use of a national data set, and (D) use of Van Genuchten parameters correlated with soil texture and organic matter content. The four methods were compared by their effect on two practical aspects of soil behaviour: (1) evapotranspiration deficit and (2) flux through a plane at 30 cm below soil surface. These two aspects are highly relevant for agricultural and environmental use. However, direct measurement is not feasible. A validated simulation model was used for the calculations and results obtained with method A were taken as a reference. Calculations were performed for three soil profiles for a period of seven years. Deficits and fluxes, calculated with the four methods to generate hydraulic functions, were not significantly different using the data of the seven‐year period. However, methods were significantly different when rainfall deficits were used as a covariable. This is true with the exception of downward fluxes in the period October until March which are most important for leaching of pollutants. The user has to decide whether differences between methods are sufficiently large to justify repeated, expensive on‐site measurements (method A) or whether an investment will be made to make standard series of curves to be used everywhere (methods C and D).
Design and application of a constant head well permeameter for shallow high saturated hydraulic conductivity soils
Authors: Bell R. W. , Schofield N. J.
Published: February 2007

A new constant head well permeameter has been designed to measure saturated hydraulic conductivities (Ks) ranging from 10−6 to 10−3 ms−1. Application to shallow soils of Western Australia in this Ks range highlighted problems with different aspects of the borehole discharge response. Firstly steady‐state borehole discharge was only reached in 13 out of 50 tests conducted. This was a consequence of the constraint placed on the volume of water storage (40 L) of the permeameter. For some non‐steady‐state cases, techniques of estimating steady‐state discharge from the available data are examined. Secondly borehole discharge was observed to increase with time in 34 per cent of cases. A satisfactory physical explanation of this phenomenon is not presently available. Other limitations in the application of the constant head well permeameter are noted.

Examination of a number of recent theoretical developments in the determination of Ks led to a preference of saturated‐unsaturated flow solutions by Philip (1985) and Reynolds et al. (1985). These solutions involve the ‘sorptive number’ to which the solutions were sensitive but not critically sensitive. The theory was used to establish design criteria for the permeameter and to identify an optimum application strategy in terms of well dimensions and heads. Error estimation indicated that the designed permeameter was a practically useful field instrument.
Hydrology of a headwater basin wetland: Groundwater discharge and wetland maintenance
Authors: Roulet Nigel T.
Published: February 2007

The link between groundwater and surface hydrology in a small headwater drainage basin in the zone of glacial deposition of southern Ontario south of the Precambrian Shield was examined for two years. The basin is situated in a discharge zone of a regional aquifer and contains a small treed spring‐fed swamp. The swamp exists because of the groundwater and has little effect on the maintenance of streamflow. Groundwater input to the swamp is an order of magnitude larger than precipitation. Groundwater of local and regional origin passes through the swamp by two routes: surface streamlets, where groundwater that emerges at specific seepage points in the swamp is conveyed over the ground surface with little interaction with the swamp itself, and by diffuse seepage in the swamp and through the bed of the stream. While the diffuse seepage input is the smaller component of groundwater it maintains the swamp's saturation. Groundwater input to the swamp from the specific seepage points and diffuse flow varies little over a year; therefore the saturation of the swamp and baseflow from the basin display little seasonal variation compared to other wetland types. The existence of the valley bottom in the headwater basin alters the seasonal and storm hydrology and is important to biogeochemical transformation of emerging groundwater.
A continental hydrological assessment of a new grid‐based digital elevation model of Australia
Authors: Hutchinson M. F. , Dowling T. I.
Published: February 2007

A rectangular grid digital elevation model (DEM) for Australia, with a horizontal resolution of 1/40 degree of latitude and longitude (approximately 2.5 km), has recently been calculated from continent‐wide coverages of point elevation and stream line data using an elevation gridding technique which incorporates a drainage enforcement algorithm. An automated drainage basin analysis of this DEM is in close agreement with existing basin analyses, both for the better surveyed coastal areas with well‐defined relief, and for large areas of low relief that make up much of the interior Lake Eyre basin and the Murray‐Darling basin. The analysis of the arid western plateau region differs from the currently accepted analysis but is in broad agreement with a previous analysis of palaeodrainage systems based on topographic and geological information. The drainage analyses is used to calculate cumulative distributions of spatially distributed, hydrologically significant, terrain parameters for the Murray‐Darling and Derwent River basins. The adequacy of the resolution of the DEM for continental hydrological analyses is assessed by comparing drainage basin analyses and cumulative distributions of terrain parameters at resolutions of 1/40th and 1/20th degree of latitude and longitude.
Terrain analysis for urban stormwater modelling
Authors: Djokic Dean , Maidment David R.
Published: February 2007

A geographic information system (ARC/INFO) is used to develop a model of the urban environment for storm drainage analysis. The drainage system is divided into surface terrain, stormwater intakes, and the drainage network. The intakes hydrologically connect surface and subsurface flow elements. The drainage network consists of both man‐made structures (pipes and channels) and overland flow paths that connect them. The land surface terrain is defined by a triangulated irregular network (TIN), which is used to determine necessary parameters for design flow calculations. Each of the three basic elements of the urban terrain representation, inlets‐defined as points, drainage network‐defined as lines, and surface terrain‐defined as TINs, has its own specific data structure. The three databases are fully integrated, and the stored information is used to determine whether inlets and pipes can convey 10‐and 25‐year design flows, using the rational method.

An ‘intelligent network builder’, is developed using the Nexpert Object expert system shell, to test for completeness of databases and flow paths prior to hydrological computations. If necesssary, the intelligent network builder starts up ARC/INFO procedures that fill in missing links in the drainage network and missing flow properties of its components. An example application is made to the drainage system of a section of City of Asheville, North Carolina.
Hydrological consequences of artificial drainage of grassland
Authors: Armstrong Adrian C. , Garwood E. A.
Published: February 2007

Soil water regimes and water balances are presented for a series of drained and undrained experimental grassland plots, intended to examine the agronomic consequences of drainage. Although drainage has lowered the watertables and reduced the duration of waterlogging in the drained plots, its effects in terms either of the total water quantities leaving the site or of peak flows is quite small. The major effect of drainage is to alter the route of water loss from the site. In its undrained state, the soil is waterlogged for the majority of the winter, incident rainfall cannot infiltrate, and water leaves as surface runoff or near‐surface flow. The introduction of fissures by mole drainage both provides an outlet and enhances the macroporosity, so that the rain moves rapidly through the soil and appears as drainflow. Consequently, the additional delay in generating peak runoff through the drainage system is only of the order of 30 minutes on this site.
Use of a single‐bowl continuous‐flow centrifuge for dewatering suspended sediments: Effect on sediment physical and chemical characteristics
Authors: Rees Terry F. , Leenheer Jerry A. , Ranville James F.
Published: February 2007

The use of a single‐bowl continuous‐flow centrifuge (CFC, Sharples‐Pennwalt Model AS‐12) for dewatering suspended sediment from large volumes of river water is evaluated. Sediment‐recovery efficiency of 86‐91 per cent is comparable to that of other types of CFC units. The recovery efficiency is limited by the particle‐size distribution of the feed water and by the limiting particle diameter that is retained in the centrifuge bowl. The limiting particle diameter, using the parameters for this study (bowl radius = 10.5cm; bowl length = 71.1 cm; rotational velocity = 16000 r min−1; flow rate = 2 L min−1, and an assumed hydrated particle density = 1.7 gm cm−3), is 370 nm. There seems to be no particle‐size fractionation within the centrifuge bowl—the median particle size was the same at the top as at the bottom. Particle electrophoretic mobility plays some role in fractionation of particles within the centrifuge. The mobility ranged from −1.19 to −2.01 × 10−8 m2 V−1 s−1, which is typical of clays coated with organic matter, the charge of which is partially neutralized by divalent cations and iron. Contamination by trace metals and organics is minimized by coating all surfaces that come in contact with the sample with either FEP or PFA Teflon and using a removable FEP Teflon liner in the centrifuge bowl. Because of the physical and chemical factors affecting particle fractionation within the centrifuge, care must be exercised in interpreting the environmental consequences of particles collected by continuous‐flow centrifugation.
IV: EPSAT‐NIGER study of rainfall over the Sahel at small time steps using a dense network of recording raingauges
Authors: Thauvin V. , Lebel T.
Published: February 2007

The high density, static memory raingauge network of the EPSAT‐NIGER experiment was designed with the aim of: (1) studying the rainfall spatial variability in the Sahel, as may be seen from ground networks of varying density, and (2) providing reference values for the calibration of a C band radar system. A first subset of 37 raingauges was installed in 1988 and the remaining 43 in 1989, thus providing a network of 80 stations, spread over a 100 × 100 km square area. The data analysis is based on the indentification of the structural function for each rainfall event. This permits classification of the events into three main categories with respect to their spatial organization. Furthermore the differences between the shower body and the trail are important and it is shown that the analysis of the spatial organization at the event scale may not be applicable to the calibration of high temporal resolution radar data. Estimation of the areal rainfall over two reference areas is also carried out.
V: Daily catchment rainfall estimated from meteosat
Authors: Dugdale G. , Hardy S. , Milford J. R.
Published: February 2007

Meteosat data for 1986 to 1988 have been used to estimate the daily rainfall over catchments of tributaries of the river Senegal in Mail and Guinea. The technique uses the methodology of the TAMSAT group of the University of Reading, which involves the selection of an appropriate cloud top temperature threshold to determine whether the cloud is producing rain and the rainfall is estimated from the period during which storm clouds remain over a site. After calibration against all available raingauges in the catchments, the daily rainfall estimates derived by this technique were used as inputs to rainfall‐runoff models. The results indicate that the streamflow models, which had themselves been calibrated using raingauge data, performed as well or better when the satellite derived estimates were used as inputs than when gauge data were used. An economical, automated operational system is described.
A model of dissolved organic carbon concentrations in soil and stream waters
Authors: Grieve Ian. C.
Published: February 2007

The release of dissolved organic carbon (DOC) into drainage waters was modelled using the hydrology of the Birkenes model of stream water chemistry and estimated parameters for the formation and decay of soluble organic matter in the soil. The model was first tested against soil water DOC concentrations over a three year period in the Loch Dee catchment in southwest Scotland. It predicted annual cycles in DOC at one site, but underestimated maximum DOC in the first year, overestimated in the following year, and predicted values very similar to the measured values in the third year. With small modifications to the parameters controlling organic matter addition and decay it successfully predicted DOC variations at two other soil water sites with smaller mean DOC.

Further tests were made against short‐term DOC variations in a stream draining a subcatchment of Loch Ard in west‐central Scotland, using the same decay and addition parameters. Prediction of temporal variation was good, although predicted concentrations were about 25 per cent less than measured values. Considerable potential for the use of fully optimized models of DOC production in soil and stream waters is identified on the basis of these results.
Estimation of soil moisture status using near infrared reflectance
Authors: Whalley W. R. , Leeds‐Harrison P. B. , Bowman G. E.
Published: February 2007

The use of a prototype near infrared reflectance meter for estimating the water content of soil is described. The instrument, developed from one used for estimating the water content of forage is based on the measurement of reflectance of infrared light emitted at wavelengths of 1450 nm, a strong water absorption band, and 1300 nm a weak water absorption band. Calibration curves of reflectance and reflectance ratio versus moisture content for pure sands and sand/clay mixes are presented. Problems associated with the measurement of moisture content using this technique on swelling soils are highlighted. The use of a modified form of this instrument for estimating soil moisture status in the field is discussed.
Water repellency in a dry sclerophyll eucalypt forest — measurements and processes
Authors: Crockford H. , Topalidis S. , Richardson D. P.
Published: February 2007

The magnitude of soil water repellency in a dry sclerophyll eucalypt forest was measured periodically over four years. The varying responses from a range of sites within the forest are discussed and the effect of amount and frequency of rainfall is shown.

It was found that some weeks of consistently wet weather were required for water repellency breakdown, and a frequency of rainfall much greater than normal in the study area for it to remain broken down. Even after an extended period of breakdown, it was found that repellency can be reestablished after one week of hot dry weather.

Laboratory tests were used to examine the major repellency processes; three were identified and the relative importance of each considered in the context of the field study. The relative influence of each depended on the physical and chemical characteristics of the sites.

The repellent soil samples were more repellent to water of throughfall origin, and even more repellent to stemflow than to distilled water. The repellency response also varied with the type of vegetative cover present. The influence of these phenomena on the preservation of water repellency and the relevance of repellency in macropore infiltration processes are discussed.
Measurement and prediction of water movement in a field soil: The matrix‐macropore dichotomy
Authors: Smettem K. R. J. , Ross P. J.
Published: February 2007

The saturated and unsaturated flow properties of a field soil under two tillage treatments were obtained with ponded rings and disc permeameters of dissimilar radii. No difference was observed between tillage treatments but the flow properties displayed a distinct macropore‐matrix dichotomy, with K changing by an order of magnitude as ψ0 went from just ‐ 30 mm to zero.

Accurate prediction of time to incipient ponding was achieved using both numerical and analytical models calibrated with field hydraulic properties that were characteristic of the soil matrix. However, extension of the numerical model to the prediction of the wetting front development under non‐ponded conditions was less accurate due to localized preferred wetting

It is hypothesized that at this site, localized concentration of rainfall and hence, preferred wetting, May, occur by interception and stemflow associated with lines of standing stubble present in the original seeding slots.
A water balance study in lateritic terrain
Authors: Langsholt Elin
Published: February 2007

The water balance of a 600 m2field site on a lateritic hillslope in Kerala, southwest India, has been studied during two southwest monsoon seasons. Surface runoff was of minor importance while infiltration and evapotranspiration were the major components amounting to approximately 2/3 and 1/3 of the rainfall, respectively. Groundwater response was rapid, involving fluctuations of several metres. Recharge mechanisms hypothesized are water movement via preferred pathways from the ground surface to the capillary fringe where rapid rise in groundwater level is brought about by a transmitted pressure pulse. Groundwater recharge was found normally to take place during the southwest monsoon season only. the field study demonstrates that seasonal shallow groundwater recharge representing the major portion of the rainfall May, be observed in this lateritic terrain in the humid tropics. It indicates a good potential for further groundwater development. Moreover, conditions are conducive to a considerable contribution to possible recharge to deeper aquifers. the observed groundwater recharge is the result of a complex process on which further research will throw more light.
Systematic parameter estimation of watershed acidification model
Authors: Chang Fi‐John , Delleur J. W.
Published: February 2007

A joint strategy for parameter estimation which can systematically identify the important model parameters is presented. the strategy includes a regionalized sensitivity analysis (RSA) and an automatic parameter calibration technique (APCT). the RSA is based on a large number of Monte‐Carlo simulations to identify the sensitive parameters and to establish a range of appropriate values for each sensitive parameter. the APCT adjusts the values of the sensitive parameters based on changes in the residual variances between the predicted and observed values. the strategy is applied to the watershed acidification model—ILWAS. the strategy succeeds in identifying the sensitive parameter and increases the likelihood of obtaining a global optimal parameter set. Improvements in the model prediction of the streamflow and chemistry are obtained.