bluuebunny/crossref_metadata_2025 huggingface dataset:
Drawdowns at the Free Water Table During Pumping Tests in Artesian and Semiartesian Aquifers
Authors: Kærgaard Henrik
Published: May 2018

In an earlier paper I have shown an example of how long term drawdowns can be used for the computation of long term storage in artesian and semiartesian areas. In most cases the long term storage is more or less equivalent to the specific yield at the water table; the storage mechanisms of consolidation playing a minor role in long term situations. The specific yield in artesian areas is a very important parameter in the prediction of long term effects of ground water withdrawal. Especially the stream depletion will often mainly be governed by draw-downs in upper nonpumped aquifers near the water table, and these drawdowns depend to a great extent on the specific yield at the water table.

A determination of long term storage will often necessitate long term draw-down data, however, under certain circumstances a determination can be made on the basis of a pumping test of limited duration (3-5 weeks) provided drawdown observations at the water table can be made. In this paper some formulas dealing with water table drawdowns in different geohydrologic systems are reviewed, and two cases in which these formulas have been used in practice are presented.
Snow Surface Measurements from Digital Landsat MSS Data
Authors: Lichtenegger J. , Seidel K. , Keller M. , Haefner H.
Published: May 2018

The snow cover is an important parameter for water run-off prediction in high mountain areas. At present its seasonal changes can be monitored regularly by satellite. The paper presents a new method for a more accurate classification of snow from multispectral Landsat data with the aid of a digital terrain model (DTM). A reflectance map derived from the DTM was used to register the Landsat data onto the map applying the cross-correlation function. The DTM makes the independent evaluation of snow possible with respect to elevation, exposure and slope angle. For areas with climatologically similar conditions, it becomes possible to extrapolate the snow cover of the total catchment area supposed to be partially obscured by clouds from a small “cloud free” zone.
Instruments for Mountainous Areas
Authors: Strangeways Ian
Published: May 2018

Because of the difficulty of data collection, little is known about the climate and hydrology of high mountain basins. Following the development of an automatic weather station (AWS) in the 1960s for use in upland Britain, the Institute of Hydrology is now engaged in developing an AWS for operation in more mountainous areas. To this end, and using the summit of Cairn Gorm in Scotland as a proving-ground, investigations are being carried out into methods of preventing ice accretion, new ways of deploying temperature sensors, alternative ways of exposing radiation sensors consistent with the deicing techniques, the sensing of wind by static sensors, the choice of the most appropriate method of sensing humidity, and the measurement of rain and snowmelt. This paper describes these new techniques.
On the Heat Exchange Between Rivers and Atmosphere
Authors: Stang Ole
Published: May 2018

In order to be able to predict water temperatures in rivers which are to be harnessed for hydro power, it is essential to take into account the heat exchange with the atmosphere. It is often sufficient to predict average temperatures and temperature changes for periods of some days. A simple model for the heat exchange between flowing water and atmosphere has been developed for this purpose. The model offers a semi-empirical relationship between air temperature and water temperature.

In this paper the model is applied to the Orkla river in Central Norway, and it is demonstrated how analyses of diurnal variations of water and air temperatures make it possible to predict the downstream decay of temperature changes originating from man-made releases. As a result an average heat exchange coefficient is calculated for Orkla for the summer of 1980. This calculation indicates that the cooling/heating rate in the flowing water in Orkla is considerably greater than the one for lakes under the same meteorological conditions.
A Modified Sediment Transport Model for Natural Streams
Authors: Thomsen Thorkild
Published: May 2018

In an earlier investigation of the behaviour of tracer particles for determination of bed load transport in an alluvial stream (Thomsen 1980), specific records were taken of the particle velocities in the upper bed layer. These data aroused the interest for more detailed investigations.

The result of the measured surface particle velocities with radioactive tracers, performed in five locatities with different hydraulic conditions in natural alluvial rivers, has been used for determination of the relation UG/Uf'vs. √θ'/θ0.

The obtained results have been inserted in the parameters of Engelund and Fredsøe's sediment transport model (1976) and compared with experimental data (Guy et al. 1966).

Some reservations and methods for possible improvements of the sediment transport model are finally discussed.
Combination of a Conceptual Model and an Autoregressive Error Model for Improving Short Time Forecasting
Authors: Lundberg Angela
Published: May 2018

An autoregressive error model has been tested on the residuals of the conceptual HBV-model for the Emån catchment. The autoregressive model gives considerable improvements for real shorttime forecasting, but for long range (10 days or more) forecasting no improvement is achieved compared to the conceptual model. Separation of the error functions for high and low discharges does not give any further improvement.
The Hydrological Suså-Study
Authors: Hansen Eggert , Dyhr-Nielsen Mogens
Published: May 2018

The paper gives a short description of a 4 ½-years hydrological research project constituting a Danish contribution to UNESCO's International Hydrological Programme. The Suså-project was a joint effort among many different institutions working within all parts of the hydrological cycle. The main objective of the project was to investigate the potential of applying distributed hydrological catchment models in integrated water resources management, taking into account in particular consequences of increased groundwater abstraction.
A Distributed Groundwater/Surface Water Model for the Suså-Catchment
Authors: Refsgaard Jens Chr , Hansen Eggert
Published: May 2018

A distributed physically based model of the entire land phase of the hydrological cycle has been developed for the Suså-area, covering about 1,000 km2 of Zealand, Denmark. The model is described in part I of the paper, also presented in this volume. The model's ability to simulate the streamflow depletion caused by a groundwater abstraction from a confined aquifer, overlaid by Quaternary drift deposits, has been tested on historical streamflow data from the catchment of Køge Å. This catchment has been heavily influenced by a major groundwater abstraction started in 1964.

The physical mechanisms of streamflow depletion are discussed, and the effects of a groundwater abstraction on the recharge to the confined aquifer and on the streamflow are illustrated. General conclusions regarding streamflow depletion due to groundwater abstraction are made.
Selected Effects of Field Variability on Predictions from a Soil Water Finite Difference Model
Authors: Anderson Malcolm G.
Published: May 2018

Known field variability of soil hydrologic parameters is incorporated into a general finite difference scheme for the prediction of near surface soil water conditions, including runoff. It is shown for the situations examined that the resolution of predictions obtained is relatively robust against ‘within soil group’ changes in the soil water retention characteristics, but that a significant deterioration in resolution occurs when all input parameters are subjected to stochastic sampling from specified distributions. Nevertheless, even under these relaxed conditions spatial probability fields of relative saturation exceedence retain good resolution. Runoff predictions are shown to exhibit low variation generally, and to accord well with the SCS curve prediction method, suggesting the possibility of using finite difference schemes incorporating field variability for ‘ungauged’ catchment modelling.
Predictive Aggregation Models in Hydrology
Authors: Şen Zekâi
Published: May 2018

A prediction model capable of aggregation with recursive unbiased minimum variance estimation algorithms based on the Kalman filter technique has been formulated and applied for predicting monthly flows such that their summation is equal to annual flow in the same year. The model represents a discrete linear stochastic system where the states are defined as monthly flows in addition to the measurement equation with time invariant measurement matrix and annual flow measurement. Provided that observed or generated annual flows are available then the proposed model can be employed to predict monthly flows so that their aggregation yields the total annual flow.
A Hydrodynamical Model for Calculating the Vertical Temperature Profile in Lakes During Cooling
Authors: Sahlberg Jörgen
Published: May 2018

A one-dimensional hydrodynamical model is used for simulating the vertical temperature profile in a lake during cooling conditions. The vertical mixing rate is calculated by solving the equations for turbulent kinetic energy, k, and dissipation of energy, ε. The heat exchange between the water and atmosphere consists of the radiation fluxes, sensible and latent heat flux. Temperature measurements from Lake Väsman during November-December, 1981, were used in the verification study. The agreement between calculated and measured temperature profiles is very good. This indicates that both the mixing processes and the net heat flux are well described in the model.
Utilization of Satellite Snow-Cover Observations for Seasonal Streamflow Estimates in the Western Himalayas
Authors: Dey B. , Goswami D. C. , Rango A.
Published: May 2018

The results presented in this study indicate the possibility of seasonal runoff prediction when satellite-derived basin snow-cover data are related to point source river discharge data for a number of years. NOAA-VHRR satellite images have been used to delineate the areal extent of snow cover for early April over the Indus and Kabul River basins in Pakistan. Simple photo-interpretation techniques, using a zoom transfer scope, were employed in transferring satellite snow-cover boundaries onto base map overlays. A linear regression model with April 1 through July 31 seasonal runoff (1974-1979) as a function of early April snow cover explains 73% and 82% of the variance, respectively, of the measured flow in the Indus and Kabul Rivers. The correlation between seasonal runoff and snow cover is significant at the 97% level for the Indus River and at the 99% level for the Kabul River. Combining Rango et al.'s (1977) data for 1969-73 with the above period, the April snow cover explains 60% and 90% of the variance, respectively, of the measured flow in the Indus and Kabul Rivers. In an attempt to improve the Indus relationship, a multiple regression model, with April 1 through July 31, 1969-79, seasonal runoff in the Indus River as a function of early April snow-covered area of the basin and concurrent runoff in the adjoining Kabul River, explains 79% of the variability in flow. Moreover, a significant reduction (27%) in the standard error of estimate results from using the multi-variate model. For each year of the study period, 1969-79, a separate multiple regression equation is developed dropping the data for the year in question from the data-base and using those for the rest of the years. The snow cover area and concurrent runoff data are then used to estimate the snowmelt runoff for that particular year.The difference between the estimated and observed dircharge values averaged over the 11 year study period is 10%. Satellite derived snow-covered area is the best available input for snowmelt-runoff estimation in remote, data sparse basins like the Indus and Kabul Rivers. The study has operational relevance to water resource planning and management in the Himalayan region.
Representativeness of Chemical Analysis of Groundwater
Authors: Aastrup Mats , Axelsson Carl-Lennart
Published: May 2018

This paper raises the question of the representativeness of a single chemical analysis of groundwater. This is undertaken with the knowledge of the variations in chemical constituents obtained in the groundwater chemistry programme of the Groundwater network of SGU.

The variations in time and space are described for an area of 30 km2. The main geological feature of the area is a glaciofluvial esker. The esker is surrounded by littoral sand and till. The measurements show that the pH varies in a similar way in the three types of aquifers, but the variations in alkalinity, calcium content and conductivity are much greater within the till aquifer than in the aquifers consisting of glaciofluvial and littoral material.

An example is also given of the significance of depth and hydrogeological location within a small till aquifer on the level of concentration of some chemical substances in groundwater.
Simulation of Water Resources Development Projects in the Nam Kam Basin, Thailand
Authors: Nielsen M. Dyhr , Storm Børge
Published: May 2018

The Nam Kam basin is located in north east Thailand, discharging into the Mekong river. At present, a hydropower project has been constructed in the basin, and Nong Han, a natural lake, is regulated for fish-production purposes. In addition, four potential reservoir sites for irrigation projects have been identified.

The water availability resulting from various combinations of project developments has been analyzed by a simulation model.

Rainfall-runoff-models were calibrated on typical subcatchments. Based on 30 years of rainfall data, a long time series of natural inflow to the various project sites was simulated. Water level variations in the reservoirs were simulated based on inflows, reservoir losses and releases. A plant-soilwater model was developed for simulation of irrigation requirements of rice paddy and upland crops.

For various cropping alternatives, the total irrigation water availability for the basin was determined under the assumption that shortages may occur in one out of five years. The simulations formed the basis for a water master plan of the basin.

For the Lower Nam Kam Project, a detailed simulation of the operation of a 14,000 ha pump irrigation project was carried out. Based on 30 years of simulated data for inflow and irrigation requirements, pumping needs and power consumption of 4 irrigation pump stations and a feeder pump station at Mekong was determined. The results formed part of the basis for the feasibility study of the project.
Hydrogeology of the Bist Doab and Adjacent Areas, Punjab, India
Authors: Bowen Robert
Published: May 2018

In India, as elsewhere, groundwater is a vital component of the ecosystem and its controlled use should not interfere adversely with the natural hydrologic cycle. However, its misuse causes many problems and may be observed in the Bist Doab and adjacent areas of the Punjab state where difficulties arise from water-logging, pollution by industrial toxic wates and overdraft in the phreatic aquifer. Remedial measures should include artificial recharge to groundwater in recharge areas by means of check impoundments and infiltration basins in order to overcome serious over-exploitation currently in progress.
A Comparison of Water Lag Times for Converging and Plane Surfaces
Authors: Ağiralioğlu N.
Published: May 2018

In order to examine the influence of the degree of convergence for converging geometry on lag time, a comparison of surface water lag times for converging and plane surfaces is made using the Overton lag time concept. Assuming that four physical characteristics, watershed length, slope, roughness and rainfall excess are the same, an expression of the ratio of the lag time for converging surface to the lag time for plane surface is derived. The expression is solved numerically, and evaluated graphically for practical purposes. And the findings are compared with those of a previous study.
Oxygen Depletion in the Kattegat
Authors: Jacobsen T.S. , Ottesen Hansen N.-E.
Published: May 2018

A mathematical model driven by meteorological forcing and sea level differences has been established in order to describe the water exchange and vertical mixing in the Kattegat and Samsø Belt.

The model has been run with a time-step of 1 day for the period April - October from 1961 to 1981. The mixing has been represented by equations from the theory of turbulence with the normally used coefficients, i.e. no calibration has been necessary. Results from earlier investigations have been used to describe the flows in the Belts and the Sound.

The vertical exchange between the upper, brackish and the lower, saline water is strongly dependent on the meteorology. A small meteorological activity results in small exchange flows which implies that the oxygen supply to the lower layer becomes smaller and unfavourable biological conditions may occur. A simple calculation has been carried out on the assumption that the chemical and biological oxygen demand is a first order process with a time scale for the oxygen decay, which is halfed for each 10° increase of temperature. Thus the model describes the effect of the meteorological activity on the oxygen concentration, all other parameters kept constant.
Spring Characteristics and Hydrological Models of Catchments
Authors: Englund Jens-Olaf
Published: May 2018

The Åstdalen catchment (373 km2) represents largely a natural ecosystem, typical for the higher central and southern parts of the Scandinavian Peninsula. It is underlain by fractured sedimentary rocks with a thin cover of unconsolidated Quaternary deposits.

The runoff process in Åstdalen is mainly determined by: Large accumulation of precipitation as snow, large areas covered by peatlands, and a high waterstorage capacity in the bedrocks. Groundwater discharge occurs in river beds, in springs and as flow towards the soil surface, especially toward peatland areas.

The discharges of the main river Åsta and of investigated springs rise rapidly following snowmelt and rainstorms during the two water-years of study, 1 October 1980 to 30 September 1982. This shows that the catchment has a high infiltration capacity, and that water moves rapidly downslope in the saturated zone, following macropores in soils, peatlands and bedrock fractures. Groundwater, especially shallow groundwater, plays an important role of streamflow peak generation, even during snowmelt. About 60-70 % of the river discharges during the melting periods in 1981 and 1982 were baseflow.

There is a net gain of protons, ammonium, potassium, nitrate and chloride to the catchment from the atmosphere during the year, and a net loss of calcium, magnesium sodium and sulfate. Constituents showing a net loss have an internal geologic and/or organic source in addition to the atmosphere.

The concentration of most substances in river Åsta and in the investigated springs are lowered during peak flows. The concentration of protons is on the other hand typically increased during snowmelt. This indicates that fresh rain and/or snowmelt water dominates such flow periods and not older prestorm water.

About 56 % of the protons needed to supply the weathering-derived ions to river Åsta come from precipitation.
Mixing Effects of Carbonate Dissolving Waters on Chemical and 13C/12C Compositions
Authors: Staniaszek P. , Halas S.
Published: May 2018

Seasonal variations in chemistry and 13C/12C ratios of total inorganic carbon of carbonate dissolving waters are considered in the frame-work of a simplified approach dealing explicitly with major ionic species. The unidirectional evolution models of Deines et al. (1974) are supplemented by taking mixing effects into consideration (Wigley and Plummer 1976). These effects, caused mainly by the redistribution of carbon-bearing species in the mixture, are to a great extent nonlinear and unsymmetric with respect to the fraction of the second solution in a binary mixture. The theoretical considerations are supported by observations of many samples taken during a period from January to May 1977 in SW Lublin Upland.

The parameters PCO2 and δ13C of a reservoir lose their primary meaning in the case of mixing of waters but investigation of their changes may help in studying some conditions in the soil. During the period of observation (except March) the estimated values of PCO2 of a reservoir tended to he in a narrow range of values from 10−1.3 to 10−1.4 atm. In March those values were higher due to the large inflow of CO2-rich waters into the aquifer. The estimated δ13C values of a reservoir CO2 spread from –17 to –27 permil during January to March. In April and May those values focused in a narrow range from –22 to –26 permil. This tendency indicates that waters inflowing in March and April transported isotopically lighter CO2.

Both HCO3− content and δ13C of total carbon versus pH allowed to search inflows of infiltrating water into particular areas of the aquifer. It has been shown that δ13C investigations are necessary to notice the admixing of waters in certain cases.
On the Correction of Liquid Precipitation
Authors: Allerup P. , Madsen H.
Published: May 2018

The paper discusses a bi-linear statistical model for correcting aerodynamic errors, earlier presented by Allerup and Madsen, 1980. Further data from Finland, USA and Australia testing the model will be presented. A simplification of the bi-linear model in order to cover different gauge types and varying measuring levels will be demonstrated. The simplification will extend the applicability of the correction model when implemented into automatic correction systems.

The paper will discuss the problems of fit by the simplified model and attention will be given to physical interpretation of the mathematical structure in the model.

Besides aerodynamic errors, wetting losses influence the correction values. It will be demonstrated how these effects cause too large corrections for small amounts of precipitation and too small corrections for large amounts.
Modelling of Unsaturated Flow in Heterogeneous Soils
Authors: Høgh Jensen K. , Butts M. B.
Published: May 2018

Modelling of soil moisture conditions in spatially variable fields is treated using stochastic methods. Spatial variability of moisture content in a vegetation covered field is partly caused by field variability in soil physical parameters. In the present study a physically based model is coupled with a statistical description of retention properties and saturated hydraulic conductivity respectively to simulate moisture conditions in heterogeneous soils.

Results are compared with measurements obtained from two 0.5 ha field sites.

Simulations based on the variation in retention properties are shown to account for much of the observed variation in soil moisture conditions with some deficiencies evident close to the soil surface. Variations in saturated hydraulic conductivity alone give an incomplete description of observed variability in soil moisture conditions.
Operational Spring Time Forecasting Difficulties and Improvements
Authors: Vehviläinen Bertel
Published: May 2018

A modified version of HBV-3 model has been used since 1981 for operational spring-time forecasting in Finland. This model is ready now for eleven river basins ranging from 500 to 30,000 km2. From the experience with these models in forecasting we have learned to know the common difficulties and errors in real-time forecasting and some methods to improve forecasting results.

The main difficulties with forecasting during spring time in Finnish conditions have been: unstable parameters in snowmelt models, heavy unforecasted rainfall, evaluation of areal water equivalent of snow and ice-dams in rivers.

The methods to overcome these difficulties are: the development of more physically based snowmelt models, new methods to determine initial value of areal water equivalent of snow, the use of statistical error models with hydrological model, the automatization of observation and transport of hydrological and meteorological data and the improvement of areal precipitation calculations.
Lateral Mixing in Channels due to Secondary Currents
Authors: Larsson Rolf
Published: May 2018

Different mechanisms generating secondary currents in channels are presented. It is shown by an order-of-magnitude analysis that secondary currents of magnitude 1% of the downstream velocity are as important for lateral mixing as turbulent diffusion. Results from numerical simulations that support the analysis are presented.
Digital Simulation Model for Brine Coning in Unconfined Anisotropic Aquifers
Authors: Rajagopalan S. P. , Jose U. V.
Published: May 2018

A digital simulation model has been presented for locating the steady state stable brine cone position beneath partially penetrating wells tapping from the fresh water zone overlying a saline zone in an unconfined anisotropic aquifer. A graphical procedure developed by Morris Muskat has been converted into a numerical one and is used to successively approximate the brine cone position. The truncation in the fresh water zone both due to the brine cone and the depression in the water table are taken care of by repeated adjustment of the hydraulic conductances of the affected branches in the numerical model of the aquifer. An iterative version of the alternating direction implicit method has been used to solve the flow equations repeatedly till successively modified fresh water flow zones converge within a specified tolerance level. The results from the simulation model for a range of expected field conditions of aquifer, well and fluid density contrast have been presented in the form of graphs making use of appropriate non-dimensional parameters. These results can find applications in designing wells so that the discharge from those wells are limited to levels below which fresh water alone is drawn without any contamination by the underlying salt water.
Determination of Steady State Drawdowns in a Horizontal Double Aquifer System
Authors: Pandey V. S. , Pandey S. K. , Pandey R. N.
Published: May 2018

Using Ditkin's operator the exact analytical expressions for drawdowns for coupled two finite aquifer system in which pumpage from the upper and lower aquifer is balanced by a reduction in evapotranspiration from the upper aquifer are obtained. Also, the expressions for drawdowns for the limiting cases (viz. when the horizontal dimension of the aquifers is considered to be infinite) are deduced from one of the general results. It is observed that these results are the same as obtained by Motz. The application of Ditkin's operator in obtaining the solution for such problems is new and to our knowledge it has not been reported elsewhere in the literature.
Spring Discharge and Aquifer Characteristics in a Sandy Till Area in Southeastern Sweden
Authors: Johansson Per-Olof
Published: May 2018

Spring discharge and groundwater levels were used to study groundwater outflow recessions, groundwater reservoir sizes, water yielding properties and saturated hydraulic conductivities in a sandy till area in southeastern Sweden. Water chemistry was used as an indicator of flow paths. The catchment areas of the five springs, ranging from approximately 0.01 km2 to 0.2 km2 in size, were all mainly covered with coniferous forest. The maximum active groundwater storages of the catchment areas of the springs varied from 75 to 145 mm. As a comparison the maximum total groundwater storage of the till in the catchment area of the largest spring was estimated to 1,250 mm. Two springs were chosen for detailed studies. The highest peak discharge of the smallest of these springs was 1.7 mm/day and it usually dried up in summer. The discharge from the largest spring was evenly distributed and varied between 0.2 and 0.8 mm/day. Frequent analyses of water chemistry during a spring with intense snowmelt revealed no change of water composition in spite of a great increase in discharge; for the smallest spring by more than 30 times. Integrated values of the specific water release from the unsaturated zone to the groundwater reservoir were calculated from runoff volumes and decreasing groundwater levels for the catchment area of the largest spring. The different values obtained from dry summer and winter periods, 0.024 and 0.047 respectively, indicated a strong influence from evapotranspiration. It the same spring, an areally integrated value of the saturated hydraulic conductivity was estimated to 6 × 10−5 m/s from a linearized solution of the Boussinesq equation.
Estimation of Catchment Rainfall Uncertainty and its Influence on Runoff Prediction
Authors: Storm B. , Jensen K. Høgh , Refsgaard J. C.
Published: May 2018

Interpolation of spatially varying point precipitation depths introduces uncertainties in the estimated mean areal precipitation (MAP). This paper describes a geostatistical approach – the Kriging method – to calculate the daily MAP on real-time basis. The procedure provides a linear unbiased estimate with minimum estimation variance. The structural analysis of the random precipitation field is automatized by relating the time-varying semivariogram model to the sample variance. This is illustrated on data from a Danish IHD catchment.

The conceptual rainfall-runoff model NAM incorporated into a Kalman-filter algortithm is applied to investigate the effects of uncertainties in MAP on the runoff predictions. Measurement and processing errors are not included in the investigation.
Movement of Meltwater in Small Basins
Authors: Bengtsson Lars
Published: May 2018

A kinematic approach is applied to compute moisture flux and particle velocities in the unsaturated zone. The computations are compared with observations of tracer marked meltwater particles. Groundwater flow is computed accounting for storage and assuming constant particle velocity. It is found that meltwater particles that reach the groundwater not very close to the ground surface do not contribute to runoff until several months after the melt event. The meltwater constitutes a significant part of the melt runoff only when saturated overland flow occurs or when the percolated water flows along the rock beneath a thin soil layer.
Swedish Evaporation Research A Review
Authors: Halldin Sven
Published: May 2018

Swedish evaporation research has gone through a rapid development, and there is now a need to overview the results. This review presents the research in a broad sense. The brilliant research by Wallerius between 1739 and 1747 clarified the basic nature of the evaporation process. After him, research has been concentrated to two periods. The first, in the beginning of this century, was connected with the establishment of the meteorological and hydrological services in Sweden. The second period of progress started with the International Hydrological Decade (1965-1974). Recent evaporation research has been strongly focused on forest, and aimed at establishing the causal relationship between changes in land use and changes in the hydrological cycle. Applications to problems of clcarfellirig, large-scale introduction of water-demanding energy forests, and effects of atmospheric pollution have shown the great importance of the evaporation component of the water budget. Present evaporation research in Sweden is directed along three main lines. Firstly the development of reliable methods to measure evaporation. Secondly sophisticated turbulence measurements within and immediately above a vegetation cover. Thirdly the development of simple, yet physically realistic models of evaporation from plant covers.
Calcium Budgets for Catchments as Interpreted by Strontium Isotopes
Authors: Jacks Gunnar , Åberg Göran , Joseph Hamilton P.
Published: May 2018

Strontium isotopes in precipitation, soil and runoff water can be used to establish a ratio of wet plus dry deposited Sr to Sr released by weathering. This ratio is especially enhanced in areas with old acid Proterozoic rocks (0.6-2.5 Ga) and Archean rocks (>2.5 Ga). Since Sr and Ca behave in an analogous way in the coniferous forest ecosystem the results for Sr can be used for the determination of Ca. If the deposition of calcium can be calculated reasonably accurately the weathering rate can also be estimated. Five catchments have been investigated using this approach. Three of them seem to be close to a steady state, wherein the losses and gains of calcium to the system are equal. In the two southern-most catchments there seems to be an ongoing loss of exchangeable calcium. The loss by runoff occurs with sulphate being the dominant anion. Weathering rates of 1.5 to 4.8 kg Ca/ha year have been estimated.
A Simple Approximation of the Hydrograph Downstream of a Flooded Area
Authors: Corradini C. , Melone F. , Singh V.P.
Published: May 2018

A simple model for estimating the hydrograph at the outlet of a reach crossing a flood-prone area is investigated. The first part of the model involves routing of the inflow hydrograph through an ideal reach with infinite vertical extension of the walls. The second part routes the flow which determines a two-dimensional flooding (outbank flow) through a linear reservoir whose storage coefficient is linked with geometric features of the flood plain. The model was applied to various geometric configurations representative of real areas in Central Italy. Its calibration and validation were carried out by comparison of the results of a diffusion hydrodynamic model. The hydrodynamic model incorporates two-dimensional overland flow and one-dimensional open channel flow. The two models were in substantial agreement, as revealed by similar shape characteristics of the corresponding hydrographs and by the values of the peak runoff error which were lower than 15% of the maximum outbank flow. Model validity was also confirmed by a comparison of its results with observed outflow hydrographs.
Estimating the Variance of Airborne Snow Water Equivalent Estimates Using Computer Simulation Techniques
Authors: Carroll Steven S. , Carroll Thomas R.
Published: May 2018

Estimates of snow water equivalent derived from measurements of the attenuation of terrestrial gamma radiation vary as a function of several known sources of error. In this study, a computer simulation of the physically-based model used to obtain estimates of snow water equivalent is developed and the variance in estimates of snow water equivalent is investigated using simulation techniques. Several of the principle sources of error in the estimating model are simulated and studied for various conditions under which snow water equivalent estimates are obtained. The simulation results indicate that the error in airborne snow water equivalent estimates made in both forested and open environments with up to 60 cm of snow water equivalent is less than 12 per cent of the estimate for typical flight lines. The results of this study can aid National Weather Service hydrologists in improving river and flood forecasts, water supply forecasts, and spring flood outlooks for large areas of the United States and Canada.
Assessing the Effect of Longitudinal Density Gradient on Estuarine Hydrodynamics
Authors: Aiyesimoju Kolawole O.
Published: May 2018

If the impact of longitudinal density gradient on the hydrodynamics of estuaries is negligible, then in water quality simulations, the hydrodynamics can be decoupled from the mass transport which would lead to substantial savings in computational time and storage requirements. It is thus important to be able to assess this impact beforehand.

The impact of longitudinal density gradients is evaluated analytically in the context of a one-dimensional wide rectangular channel taking into account the influence of bed slope, bottom friction, type of boundary condition and transient effects. The analysis predicts actual errors that would arise in numerical computations from near exactly in the best cases to within a factor of 6 in the worst cases. It should thus be useful for at least an order of magnitude prediction of the errors that would arise from the neglect of the effect of longitudinal density gradient on estuarine hydrodynamics.
The Speed of Two Moving Rainfall Events in Lund
Authors: Diskin M. H.
Published: May 2018

The speed and direction of movement of rainfall patterns, assumed constant during any given storm, can be derived from data sets comprised of the coordinates (x, y) of a number of rainfall recording stations and the times of arrival (T) of some prominent feature of the recorded hyetographs. The result depends on the nature of the feature adopted. A measure of the significance of the result can also be derived by computing the reduction in the value of the RMS deviation of arrival times due to the assumption of a moving storm in contrast to the alternative assumption of random fluctuations about an equal arrival time. The paper also outlines a procedure for estimating the accuracy of the results based on repeated computations of the speed and direction using subsets of the data obtained by removing records of one rainfall measuring station. The procedure is demonstrated with data recorded in the city of Lund, Sweden, by a network of 12 stations for two different storms.
Spatial Variability of Physical Parameters and Processes in Two Field Soils
Authors: Høgh Jensen K. , Refsgaard J. C.
Published: May 2018

Natural field systems exhibit a large degree of soil heterogeneity which affects the movement of water and solutes and thus leads to highly varying observations of water content and solute concentration. To investigate this problem comprehensive field investigation programs were carried out at two field sites in Denmark representing two different soil types, a coarse sand and a sandy loam, respectively.

The field investigations included collection of soil samples for analysis of textural composition, retention, and hydraulic conductivity, measurements of water content and suction, and measurements of radioactive tracer concentration, all carried out at a number of positions within the two field sites.

Models for one-dimensional vertical unsaturated flow and solute transport were applied to the two field sites, and the simulation results were compared to field measurements of water content, suction and solute concentration. This paper describes results from model simulations in individual soil profiles, while the variability issues at field scale are described in the two accompanying papers. The modelling approach was based on numerical solutions to Richards' equation for water flow and the convection-dispersion equation (CDE) for solute transport. The model results from the coarse sand field site compared relatively well to measurements of water content, suction, and concentration except for the upper soil layer (∼ 10 cm depth) where the measured water contents appeared to be somewhat uncertain.

Due to the neglecting of hysteresis and macropore flow (by-pass) in the model the measured retention curves (drainage based) and the hydraulic conductivity functions at the sandy loam field site had to he modified empirically through the calibration procedure in order to match the measurements.
Worldwide Testing of the Snowmelt Runoff Model with Applications for Predicting the Effects of Climate Change
Authors: Rango A.
Published: May 2018

The Snowmelt-Runoff Model (SRM), a simple degree-day model, has been applied to over 50 basins in 15 countries around the world. Where results have been reported, the average R2 has been 0.84 and the average seasonal volume difference, Dv, has been 3.8 %. The testing of SRM has taken place on basins in different climatic regions, thus setting the stage for using SRM in evaluations of the hydrological effects of climate change. A method for using SRM in evaluations of climate change has been established and tested on several basins. Initial results show some potentially serious problems involving water supply, flooding, and drought. More testing in a variety of climatic regions is necessary along with improved specification of the changes in temperature and precipitation by region.
A Neural Network Approach to Inversion of Snow Water Equivalent from Passive Microwave Measurements
Authors: Chang A.T.C. , Tsang L.
Published: May 2018

The inversion of snow water equivalent, SWE, from passive microwave remote sensing measurements may be accomplished by using a neural network trained with a dense media multiple scattering model. Brightness temperatures from 19 GHz vertical and horizontal polarizations, 22 GHz vertical polarization and 37 GHz vertical and horizontal polarizations which are available from the SSM/I sensors, are used as input to the neural network. The percentage error for estimated SWE varies from 9 % to 57 % for different snow conditions.
Linear or Nonlinear Covariance of Seasonal Snowmelt and Snow Cover in Western Himalayas
Authors: Dey B. , Sharma V. K. , Rango A.
Published: May 2018

Log-linear, exponential and fractional relations for estimating seasonal snowmelt from early-spring snow accumulation in the Indus and Kabul river basins in the western Himalayas are developed with a view to improve the prediction given by bivariate linear regression models earlier developed by the senior author in collaboration with others. This study shows that although the transformed data may improve the above prediction, they fail to satisfy the condition of nonlinearity; a property that must be borne in mind before recommending any nonlinear regression model. Any further improvement in the prediction of seasonal flow volume from basin snow cover area, therefore, has to come from within the domain of linear regression models only or from improvements in the original input data.
Analysing Hydrometeorological Time Series for Evidence of Climatic Change
Authors: Kite Geoff
Published: May 2018

Considerable scientific attention has been focused on a measured increase in atmospheric CO2 and a suspected corresponding change in climate. Such a change in climate, if it occurred, might be expected to have a magnified effect on hydrologic time series and, indeed, projections have been made of major changes in water resources.

If the climatic changes are indeed magnified in hydrologic time series then, by detecting trends in such series, it should be possible to work backwards and identify the causative climatic change. This paper looks at two data sets: 1) long-term temperature, precipitation and streamflow data from sites across Canada and 2) long-term levels of large lakes in Africa and North America.

The study assumes that time series may be modelled by trend, periodic, autoregressive and random residual components. The trend component of a time series is generally associated with changes in the structure of the time series caused by cumulative natural or manmade phenomena. Periodicities in natural time series are usually due to astronomical cycles such as the earth's rotation around the sun. Autoregressive components reflect the tendency for an event to be dependent on the magnitude of the previous event(s), a memory effect.

The analyses of temperature, precipitation and streamflow data show some significant linear trends but no pattern is apparent. The analyses of longterm lake levels also identify linear trends but these are all explainable without invoking climate change due to greenhouse gases.
Field Evaluation of Sulphide Oxidation Rates
Authors: Elberling B. , Nicholson R.V. , David D.J.
Published: May 2018

The generation of acidic waters and the release of dissolved metals from inactive sulphide mine-tailings disposal is a well-known environmental problem. The flux of oxygen across the surface of the tailings was determined under different physically-controlled environmental conditions and related to the oxidation rate of pyrrhotite mine-tailings. This work was conducted to verify, i) the consistency in oxygen flux rate measurements in the field within small areas and, ii) the importance of moist layers near the ground surface in the control of the oxygen flux. The flux of oxygen across the surface is related to a relative oxidation rate of the tailings, and it can be concluded from the study that differences in the degree of saturation as a result of fine-grain layers, hardpan formation or a general high water table can control the overall rate of oxygen flux into tailings and reduce the relative rate of tailings oxidation by more than three orders of magnitudes. The oxygen flux method used in the study is shown to be a useful field mapping tool for distribution of relative oxidation rates in field settings.
Low Flow Estimation and Hydrogeology in a Chalk Catchment
Authors: Clausen B. , Rasmussen K. Rømer
Published: May 2018

Procedures to estimate low flow statistics at ungauged sites and their relation to hydrogeology are presented. The discussion is based on an example of a Danish chalk catchment of 242 km2, within which the climatic variation is small compared to the physiographical variation. The spatial and temporal variation of streamflow was studied using synchronous discharge measurements and the application of a numerical model. The synchronous discharge measurements showed the runoff is unequally distributed within the catchment and depends primarily on the regional hydrogeology, but also on the lithology of the valley deposits. The numerical model was used to obtain an understanding of the hydrogeological effect on the temporal variation of the runoff from small subcatchments. This was not possible from the discharge measurements because of the high uncertainty of estimating the difference in flow between two nearby gauging stations. The temporal variation was found to be strongly related to the hydraulic gradient along the river. A knowledge of catchment processes and variability of runoff from modelling studies is shown to assist in low flow estimation.
PDS-Modelling and Regional Bayesian Estimation of Extreme Rainfalls
Authors: Madsen H. , Rosbjerg D. , Harremoës P.
Published: May 2018

Since 1979 a country-wide system of raingauges has been operated in Denmark in order to obtain a better basis for design and analysis of urban drainage systems. As an alternative to the traditional non-parametric approach the Partial Duration Series method is employed in the modelling of extreme rainfalls The method is applied to two variables: the total precipitation depth and the maximum 10-minute rain intensity of individual storms. On the basis of the at-site modelling a regional analysis is carried out. It is shown that the previous assumption of spatial homogeneity of extreme rainfalls in Denmark cannot be justified. In order to obtain an estimation procedure at non-monitored sites and to improve at-site estimates a regional Bayesian approach is adopted. The empirical regional distributions of the parameters in the Partial Duration Series model are used as prior information. The application of the Bayesian approach is derived in case of both exponential and generalized Pareto distributed exceedances. Finally, the aspect of including economic perspectives in the estimation of the design events is briefly discussed.