bluuebunny/crossref_metadata_2025 huggingface dataset:
Forecasting Watercooling in the Kattegat, the Öresund, the Belt Sea and the Arkona Basin
Authors: Omstedt Anders
Published: May 2018

Some problems associated with forecasting water cooling in the entrance to the Baltic Sea are examined, using a diagnostic study from the severe ice winter of 1986/87 as a starting point. In the study, measured and numerically simulated data demonstrate that surface water cooling can be well simulated with the mathematical model presented by Omstedt (1987). Forecast tests during the same winter also indicate that the model may provide useful forecast information. However, because of the limited numbers of temperature and salinity profile measurements, the forecasts had to be accomplished with diagnostic calculations. These calculations will then produce the necessary initial data for the forecasts.
Snowmelt Runoff in Suburban Environments
Authors: Buttle J. M. , Xu F.
Published: May 2018

While snowmelt and rain-on-snow events have received considerable attention in rural watersheds they have been largely ignored in urban hydrology, despite the fact that they may result in severe flooding. The runoff responses of two subcatchments of a small drainage basin in Peterborough, Ontario were investigated for the spring snowmelts of 1984 and 1985. One of the catchments has undergone substantial suburbanization, while the other is largely in rural land use. Measurements in each catchment included snowpack water-equivalent depths, snowmelt and precipitation, fluxes of net radiation over snowpacks, infiltration capacities of pervious surface types, and streamflow.

Suburban development appears to have produced substantial increases in spring quickflow yields from the entire basin. A comparison of the responses of the two subcatchments reveals that the suburban catchment reacts more rapidly to snowmelt and rain-on-snow inputs and generates larger initial quickflow response ratios than the rural basin as a result of the microclimatic, pedologic and hydraulic characteristics of built-up areas. However, the dynamic behaviour of the runoff contributing area of the rural catchment results in a marked increase in its quickflow yield as melt progresses. The results suggest that the distinct nature of the processes of snow accumulation, melt and runoff generation in built-up areas should be considered when modelling suburban snowmelt runoff.
Interpretation of the Positive-Degree-Days Factor by Heat Balance Characteristics – West Greenland
Authors: Ambach W.
Published: May 2018

From heat balance measurements in the ablation area of West Greenland (EGIG-profile, 1,013 m a.s.l., 69°40'N, 49°38'W) the positive-degree-days-factor is interpreted by the heat balance characteristics. The positive-degree-days-factor depends on the heat transfer coefficient and is a function of the share of the sensible heat flux density to the heat of melt. Using simple approximations the calculated positive-degree-days-factor is in good agreement with the measured value.
Application of Satellite Data to Monitoring Snow Cover and Runoff in Greenland
Authors: Søgaard Henrik , Thomsen Thorkild
Published: May 2018

Based on NOAA-AVHRR satellite data and runoff records from one of the major drainage basins in Western Greenland methods for monitoring snow cover, snowpack water equivalent and runoff have been elaborated and evaluated by use of field observations and hydrological simulation. Data from six years and more than 40 satellite scenes have been used in the analysis. A procedure for snow cover mapping in areas with alpine relief is presented, and it is shown that the snowpack water equivalent can be derived by applying either a hydrological simulation or a degree-day approach. Finally, the applicability of the results with respect to hydro-power production in Greenland is discussed.
The Importance of Phytoplankton Photoadaptation in Influencing Estimates of Integral Photosynthesis
Authors: Pierson D. C.
Published: May 2018

The rates of light limited (αB) and light saturated (PmaxB) photosynthesis per unit chlorophyll often showed significant differences between samples collected from the top and the bottom of the mixed layer in Lake Erken (59° 51′ N). The importance of these vertical variations to the photosynthetic rate of the lake as a whole was examined by systematically changing the vertical weighting given to the biomass specific photosynthetic rates associated with each depth, when calculating integral photosynthesis. These simulations, carried out over the 3 month period from July to September of 1987, suggest that vertical variations in rates of biomass specific photosynthesis could account for at most a 24 to 36 percent change in monthly rates of integral photosynthesis, this variance in integral photosynthesis was similar to that which could result from inaccurate estimates of integral biomass, but was less than the measured temporal variability in integral photosynthesis. It was not possible to identify the specific processes responsible for the vertical variations in biomass specific photosynthesis, but evidence does suggest that photoinhibition of the surface phytoplankton was partially responsible, particularly when biomass increased at the surface in the presence of blue-green algae. Simulations which increasingly redistributed the total integral biomass to the upper 1-4 m of the water column suggest that while the upward migration of blue-green algae may lead to enhanced levels of photoinhibition, the effect on integral photosynthesis may be partially offset by increased concentrations of biomass at surface light intensities.
Infiltration into a Frozen Heavy Clay Soil
Authors: Thunholm Bo , Lundin Lars-Christer , Lindell Sten
Published: May 2018

The infiltration of snow melt water on arable land influences both the water storage and the nutrient budget. The infiltration rate during thawing was assumed to depend on the ice content of the soil. Field measurements of soil temperature, water content and infiltration rate were made and used to test a numerical model. Efforts were made to create different ice contents in three plots by adding different amounts of water before freezing as well as during winter. The total water content in spring was not influenced by the pre-freezing addition of water, but slightly increased by water added during the winter. The simulated total water content was constant throughout the winter. The measured infiltration rates were high, at maximum 8 mm/min, and the differences between the plots were small, although lower infiltration rates were found in plots with higher amounts of added water. Simulated infiltration rates never exceeded 0.1 mm/min. The discrepancy was probably due to water flow in the partially unfrozen crack system, which the model was not capable to simulate, and to a time lag in the simulated soil temperature during thawing. Low infiltration rates were probably caused by high ice content in the cracks, originating from the added water. It should be possible to predict the infiltration capacity during thawing using a simple model which treats the crack system, the water content before freezing, and the number and intensity of warm spells during the winter.
Renewal Theory Criteria of Evaluation of Water-Resource Systems: Reliability and Resilience
Authors: Kundzewicz Zbigniew W.
Published: May 2018

The alternative concepts of reliability and resilience criteria of evaluation of water-resource systems are reviewed. The potential of the renewal theory is illustrated that covers many alternative criteria and suggests relations between them.
Simulation of Runoff and Nitrate Transport from Mixed Basins in Sweden
Authors: Brandt Maja
Published: May 2018

A conceptual model for simultaneous computation of runoff and inorganic nitrogen leaching is described. The model is semi-empirical with coefficients that are calibrated against observed data. It has been developed and tested for mixed basins consisting of forest, arable land and lakes. In two of the basins, lakes have a major impact on the transport of nitrate. The results show that a major part of the variations of inorganic nitrogen in runoff can be explained by the model, but details in the modelling of nitrogen turnover can be masked by biological and physical processes in the lakes.
Effects of Spatially-Distributed Rainfall on Runoff for a Conceptual Catchment
Authors: Watts L.G. , Calver A.
Published: May 2018

A physically-based rainfall-runoff model is used to investigate effects of moving storms on the runoff hydrograph of throughflow dominated idealised catchments. Simulations are undertaken varying the storm speed, direction, intensity, the part of the catchment affected by rainfall, and the spatial definition of rainfall zones. For a 100 km2 catchment, under the circumstances investigated, an efficient spatial resolution of rainfall data is around 2.5 km along the path of the storm. Storms moving downstream produce earlier, higher peaks than do storms moving upstream. Error is most likely to be introduced into lumped-rainfall predictions for slower storm speeds, and the likely direction of this error can be specified. Differences in magnitude of peak response between downstream and upstream storm directions reach a maximum at a storm speed and direction similar to the average peak channel velocity. These results are qualitatively similar to those reported for overland flow dominated catchments, but differences in peak runoff between downstream and upstream storm directions are much smaller where rainfall inputs are modified by a period of hillslope throughflow.
Development of a Process Oriented Calibration Scheme for the HBV Hydrological Model
Authors: Harlin Joakim
Published: May 2018

A process oriented calibration scheme (POC), developed for the HBV hydrological model is presented. Twelve parameters were calibrated in two steps. Firstly, initial parameter estimates were made from recession analysis of observed runoff. Secondly, the parameters were calibrated individually in an iteration loop starting with the snow routine, over the soil routine and finally the runoff-response function. This was done by minimizing different objective functions for different parameters and only over subperiods where the parameters were active. Approximately three hundred and fifty objective function evaluations were needed to find the optimal parameter set, which resulted in a computer time of about 17 hours on a 386 processor PC for a ten-year calibration period. Experiments were also performed with fine tuning as well as direct search of the response surface, where the parameters were allowed to change simultaneously. A calibration period length of between two and six years was found sufficient to find optimal parameters in the test basins. The POC scheme yielded as good model performance as after a manual calibration.
Principles and Confidence in Hydrological Modelling
Authors: Bergström Sten
Published: May 2018

General principles in development and application of hydrological models are discussed and related to the confidence in the results. The presentation is mainly based on the experience from the work with the HBV and PULSE models at the Swedish Meteorological and Hydrological Institute between 1971 and 1990 but has also been influenced by other modelling work. It covers a discussion on the optimal complexity of models, use of observations, calibration, control and sensitivity analysis. Special attention is given to the uncertainties encountered when using hydrological models for the simulation of extreme floods and long-term scenario simulations. Finally a few ethical problems in modelling are mentioned.
Snow Cover Mapping using Microcomputer Image Processing Systems
Authors: Baumgartner M. F. , Rango A.
Published: May 2018

For many years, digital snow cover mapping using satellite data had to be carried out on large and expensive image processing systems. Recently, small computer systems (microcomputers) have been developed for image processing. Snowmelt runoff forecasting models have also been developed to run on microcomputers. Digital snow mapping procedures were surveyed, and a general snow mapping approach was developed that allows use in various snowpack regions. Tests were conducted to determine if satellite snow cover mapping could be carried out effectively on the microcomputers and which combination of software and hardware provided optimum performance. A range of computer facilities was tested and recommended capabilities for snow cover image processing were established. It was discovered that adequate microcomputer image processing systems were already on the market, and that the Snowmelt Runoff Model (SRM) could easily be run on the same microcomputer system. Further improvements will result as the 40486 microcomputers image processing systems become widely available. The microcomputer approach, as opposed to operation on larger, more expensive, and non dedicated systems, has much appeal for hydroelectric power companies and other small users who need economical, yet powerful, processing systems where both snow mapping and snowmelt runoff forecasting can be conducted.
Modelling Streamflow Recession in Two Danish Streams
Authors: Clausen Bente
Published: May 2018

The streamflow recession for two Danish streams is found not to follow the traditionally used single exponential expression Q= Q0Kt, where K is the recession constant. Three alternative equations, based on a simple hydrogeologic model, are applied. A good fit is obtained by use of the equation Q = B + C Kt, where K is a constant for each catchment and B and C are constants within each recession. Recessions with constant evapotranspiration are used to determine some of the hydraulic parameters for one of the two catchments.
Sensitivity of Streamflow Simulation to Changes in Climatic Inputs
Authors: Ng H.Y.F. , Marsalek J.
Published: May 2018

Sensitivity of streamflow simulations to changes in temperature and precipitation were evaluated for a small basin (A ≡ 53 km2) characterized by low evapotranspiration and high conversion of precipitation into streamflow. Using a calibrated HSPF model, such sensitivities were studied for temperature increases up to 4° C and precipitation fluctuations of ± 10%. Temperature increases barely affected annual streamflow, led to larger and earlier winter runoff when precipitation was stored in the snowpack, and increased winter/spring streamflow peaks. Effects of precipitation fluctuations were more direct - annual and seasonal streamflow fluctuations were directly proportional to precipitation changes and monthly peaks increased about twice as much as precipitation.
Estimating Evaporation Using Stable Isotopes: Quantitative Results and Sensitivity Analysis for Two Catchments in Northern Canada
Authors: Gibson J.J. , Edwards T.W.D. , Bursey G.G. , Prowse T.D.
Published: May 2018

The stable isotope-mass balance method can provide useful water balance information in ungauged catchments. The method has been used to evaluate evaporation and water balance at two contrasting sites in northern Canada. Areally weighted evaporative discharge from an 850 km2 tundra catchment in south-central District of Keewatin is estimated to be about 7 % of total water discharge (≈ 16 mm/yr), compared to about 19 % (≈ 65 mm/yr) from a 300 km2 forested watershed in the Upper Mackenzie Valley. Lakes in both watersheds exhibit broad ranges of evaporation/inflow ratios related to local water balance. The potential errors in the estimates are evaluated through consideration of possible variations in basin storage, humidity, and the isotopic composition of atmospheric vapour.
The Potential of Satellite Remote Sensing of Snow over Great Britain in Relation to Cloud Cover
Authors: Archer D.R. , Bailey J.O. , Barrett E.C. , Greenhill D.
Published: May 2018

Whilst satellite monitoring of snow cover is already operational in some countries, the maritime climate of the United Kingdom poses special problems for assessment of snow cover by satellite, including the short snow duration, its intermittent occurrence and associated conditions of cloud. Both satellite and ground-based observations of cloud have been used to assess the limitations imposed by cloud over broad regions and also for individual sites at different elevations and during periods of snow accumulation, stability and ablation. It is concluded that satellite sensing based on visible and infrared images alone is restricted by cloud cover, but can often provide helpful ancillary information in support of ground based measurements and satellite images from other spectral bands.
The Potential of Real Time Control to reduce Combined Sewer Overflow
Authors: Broks K. , Geenen A. , Nelen F. , Jacobsen P.
Published: May 2018

The potential of Real Time Control (RTC) to reduce the overflow volume from a combined sewer system has been investigated for a catchment in Copenhagen, named Strandvaenget. The results have been compared with the alternative of increasing the storage volume of the system. The RTC strategy has been derived using a mathematical optimization and a rule based method. As the only objective is to reduce the Combined Sewer Overflow (CSO), the developed rule based control algorithm can achieve almost the same results as the optimization method.

From the results of time series calculations, it can be concluded that the introduction of RTC appears very promising when the mean yearly CSO volume has to be reduced. In this research, the potential of RTC is investigated for an increasing amount of storage volume and for an increasing demand for reduction of CSO volume.
The Effect of Climate Change on Rainfall Trends and Flooding Risk in the West of Scotland
Authors: Mansell M.G.
Published: May 2018

Evidence is presented of a general increase in river flows in four catchments in the West of Scotland in the last 30 years. The increase has been significantly higher than the increase in rainfall over the same period. It is postulated that the more than proportionate increase is due to changes in the distribution and pattern of rainfall events although changes in evapotranspiraiion rates are also considered.
Comparison of Simulated Water Balance for Willow, Spruce, Grass Ley and Barley
Authors: Persson Gunn
Published: May 2018

Evaporation from four cropping systems, i.e. willow, spruce, grass ley and barley, was compared in this simulation study. The physically based soil model had previously been used to simulate a wide variety of soil-plant systems. Climatic data obtained over six years from two stations in southern Sweden were used as model input. The stand parameters were mostly taken from the literature. The mean seasonal “crop coefficient” for the period from April through October, defined as the relation between the potential transpiration calculated by the Penman-Monteith (1965) formula and the Penman (1948) estimate, Eto, was about the same for willow and spruce (0.9), but was lower for grass ley (0.7) and barley (0. 4). Seasonal evaporation was highest for spruce (516 mm), slightly lower for willow (497 mm), and much lower for grass ley (419 mm) and barley (347 mm). Total evaporation and transpiration decreased linearly with the precipitation deficit, P< Eto, indicating reduced transpiration for all six years at the east coast and two years at the west coast. The difference in total evaporation between the trees (willow, spruce) and grasses (grass ley, barley) was most pronounced during growing seasons with a precipitation excess, P> Eto, and decreased linearly with the precipitation deficit to near zero at a deficit of 350 mm. Runoff increased with the precipitation excess, but for willow and spruce it was generally equal to or less than the excess. For the grass ley and barley, runoff exceeded the precipitation excess, P-Eto, by about 150 mm on a yearly basis.
Temperature and Salt Content Regimes in Three Shallow Ice-Covered lakes
Authors: Malm J. , Terzhevik A. , Bengtsson L. , Boyarinov P. , Glinsky A. , Palshin N. , Petrov M.
Published: May 2018

A field study on the temperature, salt content, and density regime in three shallow ice-covered Karelian lakes is presented. The measurements show that the heat content increases during the whole ice-covered period. At ice formation a weak stable stratification existed in the lakes, with average temperatures about 1°C. Thereafter, the stability of the stratification gradually increased, mainly due to pronounced temperature increases in the bottom layers. In mid-winter the bottom layer in the deep parts of the lakes obtained temperatures above 4°C. The density stratification in these layers was stable, however, due to higher salt contents (increasing continuously during the winter) in the vicinity of the bottom. The horizontal variations in temperature and salt content were very small, and both parameters can be considered to be horizontally homogeneous.

Under-ice convection was developed in two of the three investigated lakes during the second half of April, when heating due to penetrating solar radiation became apparent. Although no under-ice convection in the conventional sense occurred in the third lake (Uros), interior convection developed when the temperature exceeded 4°C (the temperature of maximum density) there. The absence of under-ice convection in Lake Uros is most likely due to the higher vertical temperature gradient in the lake before spring heating and smaller extinction coefficient than in the other two lakes.
Characteristics of Turbulent Cross and Alongshore Momentum Exchanges During a Thermal Bar Episode in lake Ontario
Authors: Gbah Messon B. , Murthy Raj C.
Published: May 2018

Time series flow data obtained during the thermal bar episode of 17 April to 24 May 1990 in Lake Ontario are analyzed to provide a kinematic description of the coastal flow and cross-margin exchange characteristics. A thermal bar is a shore-parallel front which separates descending waters at or near the fresh water temperature of maximum density (4°C) during Spring and Fall seasons. Thermal bars are important because of their influence mixing, cross-shore exchanges, and the variability of biotic factors in coastal zones.

The analysis shows that cross-frontal exchange coefficients, Ky, are nearly constant and consistently smaller than along-frontal counterparts, Kx. Moreover, these exchange coefficients are several orders of magnitude smaller than typical coastal and oceanic values in the absence of the bar. The turbulent kinetic energy represents less than 6% of the total kinetic energy in the flow. These results suggest that small-scale horizontal fluctuations and cross-frontal turbulent momentum exchanges are severely inhibited in the spring during the thermal bar.
Contributions of Snow to the Annual Water Balance in Moshiri Watershed, Northern Hokkaido, Japan
Authors: Ishikawa N. , Nakabayashi H. , Ishii Y. , Kodama Y.
Published: May 2018

Characteristics of the water balance were investigated in an experimental watershed where there is a seasonal snow cover. To estimate the basin-wide snowmelt by the heat balance method, seven observation sites were established in the watershed and the dependencies of meteorological parameters on elevation, slope, and forest density were examined. In the snowmelt season, the net radiation and sensible heat flux increased with elevation because of the decrease in forest density, an increase in wind speed, and the temperature inversion phenomenon, which resulted in an increase in the snowmelt rate with elevation. The solid precipitation accounted for 53% of the annual precipitation and snowmelt runoff accounted for 45% of the annual runoff. The runoff/precipitation ratio was 0.75 in the snowmelt season. Evaporation was negligibly small during the winter season, but it increased during the snow-free period. The total water loss due to evaporation was about a quarter of the annual precipitation.
The Effects of Frozen Soils on Groundwater Recharge and Discharge in Granitic Rock Terrane of the Canadian Shield
Authors: Thorne G. A. , Laporte J. , Clarke D.
Published: May 2018

Hydrologic measurements on groundwater flow systems of the Canadian Shield during the winter period provide insight into groundwater dynamics and can support conclusions based on measurements of the more “active” spring-to-fall, open-water period. To illustrate this, we present the results of detailed and continuous year-round measurements of parameters such as groundwater levels, air/soil temperatures, soil heat flux and soil moisture content which were made in upland recharge and wetland discharge areas of a local groundwater flow system in granitic terrane of the Canadian Shield.

Recharge to the groundwater flow system in the rocks of the study area occurs as rain or snowmelt waters infiltrate exposed vertical and/or sub-horizontal soil-infilled fractures in outcrops of the upland area. During winter, soils in the fractures of the recharge area do not normally freeze below 0.5 m depth and shallow (5-20 cm depth) soil temperatures are most often only 1-2°C below freezing. During the spring melt period the temperature of these frozen soils remains near 0°C for several weeks as the pore ice absorbs thermal energy necessary for the phase transition from ice to water. However, despite these soils being completely or partially frozen, infiltration and recharge to the groundwater flow system in the rock occurs as shown by large and rapid rises in watertable and piezometric levels.

In the groundwater discharge area of this flow system, near-surface soil temperatures (5 cm depth) reached minimums of about -12°C during the 1996 winter and freezing soils extended downward to more than 75 cm depth. During the spring melt period, as meltwaters add heat to the substrate, these shallow soil temperatures also, rise to near 0°C and remain frozen for several weeks as latent heat of fusion of ice becomes a factor. However, during the spring melt period, while ice covers ithe surface and soils are still frozen in the discharge area, groundwater level rises are recorded in both the overburden and bedrock of the discharge area. This is attributed to hydraulic pressure being rapidly transmitted to the discharge area through the low storativity groundwater flow system in the rock from the large waterlevel increases occurring in the rock of the adjacent upland recharge area.
Sediment Bound Contaminants in a Remote Northern Delta
Authors: Milburn David , Prowse Terry D.
Published: May 2018

Deltas of major rivers are among the most productive and environmentally sensitive components of riverine systems in cold regions, and are of great hydrological and ecological importance. Much of their productivity stems from the supply of nutrient-rich sediments that rejuvenate in-channel, perched and riparian habitats. Such sediments, however, can also be a source of organic contaminants and deltas, because of their natural tendency to accumulate sediments, may become retention zones or sinks of these. The objective of this research was to determine the nature of sediment-related organic contaminant deposition in the Slave River Delta, Canada – a remote area that is now experiencing the effects of rapid upstream development. A special focus was placed on the protracted low-flow period that characterizes the winter period during which there should be a significant deposition of fine-grained sediment – size fractions with an affinity to adsorb organic contaminants. Results of an exploratory field program conducted during the 1997 pre-breakup and pre-freeze-up periods support the concept that the under-ice period is a time of significant fine-grained sediment deposition. Moreover, the contaminant load was found to be higher at the end of the winter flow recession rather than in late autumn following the major summer flow events. Comparisons of the observed contaminant levels measured in the delta are also made with those recorded by others in the upstream river that feeds the Slave Delta and in Great Slave Lake downstream of the delta.
An Energy Budget Approach to Urban Snow Deposit Melt
Authors: Sundin Eva , Andreasson Patrik , Viklander Maria
Published: May 2018

In urban areas in cold regions snow handling is a significant part of municipal activity. The snow is usually ploughed off the streets and then transported to a snow deposit. As a consequence the snow is mechanically blended, packed, polluted and piled up, giving it a characteristic texture, shape, and size. To predict snow deposit melt an energy budget model that uses general meteorological data has been derived. The model is a synthesis of available energy balance terms developed for natural snow covers, and general mass and heat transfer considerations. This approach was found applicable for estimating snow deposit melt. Only geometry, radiation, sensible and latent heat are included to the model. Radiation was found to be the major source of snow deposit melt. Very little difference was found between top and side energy fluxes. Model predictions were compared with measurements of two pilot snow deposits which were constructed with snow collected from the streets of Luleå, Sweden. The degree day approach also seems to be an applicable method to estimate snow deposit melt.
Field Observations of Small Scale Spatial Variability of Snowmelt Drainage and Infiltration
Authors: French H. K. , van der Zee S. E. A. T. M.
Published: May 2018

De-icing chemicals (containing 1,2 propane diol and potassium acetate) used on airports in winter time mix with snow and start infiltrating along the runways in spring. The distribution of the chemicals over the area, and the infiltration pattern during the snowmelt period will strongly affect the efficiency of the unsaturated zone for degradation of these chemicals before entering the groundwater. Transport of de-icing chemicals and tracers in the unsaturated zone was studied in a lysimeter trench at Gardermoen, Norway during the snow melt periods of 1994 and 1995. Simultaneously, volumes of meltwater were registered from melt plates. Observations in 1994 indicated a typical diurnal process in contrast to observations in 1995 where large volumes of meltwater entered from each melt plate within a limited number of days. Temperature seemed to be the main regulating factor and cause for the observed differences between years. The overall melt pattern was well captured by a simple model based on air temperature and global radiation. Large differences in melt volumes collected from melt plates on the surface indicated a spatially variable drainage pattern strongly related to micro-topography. Infiltration rates estimated from breakthrough curves of tracers moving through the unsaturated zone at the same location were in the same order of magnitude as drainage rates found from melt plates.
Fracture Systems and Groundwater Flow in the København Limestone Formation
Authors: Jakobsen Peter Roll , Klitten Kurt
Published: May 2018

In connection with large construction works in the Copenhagen and Øresund area a large number of investigations were conducted on the København Limestone Formation. By combining the different investigations made on the København Limestone Formation a renewed analysis of the fracture controlled groundwater flow is given. An analysis of the fracture systems is presented, with regard to the spatial distribution and their genesis. Three main fracture systems are recognized in the København Limestone Formation: An upper brecciated zone, horizontal fractures and vertical fractures. The uppermost part of the limestone has previously always been expected to have a high transmissivity due to glacial brecciation. It is shown that this is not as common as expected. Most of the water in-flow to boreholes occurs as peak in-flow in rather few horizons which are identified as lst-order horizontal fractures generated by unloading. The transmissivity varies stratigraphically within the København Limestone Formation. It is larger in the Upper- and Lower København Limestone Formation than in the Middle København Limestone Formation.
Large Scale Basins With Small to Negligible Slopes
Authors: Silveira Luis
Published: May 2018

In the first of this two-paper series, the main mechanisms for generation of runoff from rainfall in large basins with small to negligible slopes are analyzed using available data from the Río Negro basin in Uruguay. Topography and soils were examined in order to identify physical features that may influence the flow patterns. Soil moisture storage in space and soil moisture variability in time were also evaluated to relate rainfall and runoff generation. The study revealed the existence of strongly developed horizontal layers. Soil moisture depends essentially on vertical water transport processes due to the low morphological energy of the terrain. Surface and subsurface flow occurs during the season of low evapotranspiration where soils become progressively wet. Extreme storms in terms of accumulated rainfall are required to produce surface and subsurface flow during the season of high evapotranspiration. In the following paper, these observations and hypotheses are used to model a large basin with small to negligible slopes.
Large Scale Basins With Small to Negligible Slopes
Authors: Silveira Luis
Published: May 2018

Large basins with small to negligible slopes are seldom considered in the hydrological literature. An example of such basins is the Río Negro catchment in Uruguay. The first of this two-paper series showed the following special features: a) the existence of strongly developed horizontal layers and an essentially impervious B-horizon, b) significantly high soil moisture storage in terms of normally expected rainfall during a storm and c) the importance of vertical water transport processes to establish the soil moisture condition prior to a storm and its role concerning basin runoff response. These observations and hypotheses were taken into account by the lumped conceptual hydrological model called Hidro-Urfing through the percolation function and the basin runoff response function. This second paper shows its application to the Laguna I basin, a sub-basin of the Río Negro catchment with a surface area of 13,945 km2, and its ability to model the major storm hydrographs without any subdivision into smaller sub-basins. Modelling of low flows requires disaggregation of spatial-scale issues. A hydrological model of the entire Río Negro catchment did not previously exist.
Preferential Flow and Melt Water Retention in Cold Snow Packs in West-Greenland
Authors: Bøggild Carl Egede
Published: May 2018

Runoff from seasonal snow covers in Greenland provides the major source of stream flow in the non-glacierized catchments, and has gained interest in relation to hydropower potentials and water supply. During a two-month period the seasonal snow cover is melted and the discharge generated constitutes a major part of the annual runoff.

Motivated by discrepancies between modelled and observed hydrographs during the early melt period in the Tasersuaq basin, we have performed tracer experiments in several pits and at different levels below the snow surface, to improve our understanding of water flow and storage in cold snow. It is observed that vertical percolation more readily occurs the deeper in the snow pack the tracer is sprinkled. At places where preferential vertical flow is established, we believe the water will eventually reach the bottom of the snow pack once it has passed the wind crusts on the top of the snow pack.

From observations a parameterization of melt-water retention in the cold snow is suggested. We propose a time dependent term for the thermal and the gravity component, respectively, of storage in the snow pack. This time dependent term describes the fraction of snow which is exposed to melt water at the time when the water reaches the base of the snow. Incorporating such a term in hydrological models would improve them by providing an explanation of the observed fast hydrological response in the early melt period and by limiting the magnitude of the modeled peak flow.
Turbulent Exchange Characteristics in the Hypolimnion Layer of Lake Ontario
Authors: Gbah Messon B. , Rao Y.R. , Murthy Raj C.
Published: May 2018

Flow regime and turbulence characteristics in a hypolimnion of Lake Ontario are determined using time series current measurements from a vertical string of moored current meters and a bottom mounted Acoustic Doppler Current Profiler (ADCP). The diffusion and turbulent structures of the water column are parameterised in terms of horizontal exchange coefficients for momentum (Kx and Ky) during these deployments. The analysis suggests that the structure of the turbulent fluctuations is isotropic. The kinetic energy and horizontal exchange coefficients decrease with depth. The mean flow at all moorings appears to be strongly correlated with the zonal surface wind stress. Fifteen to twenty metres above the bottom, the flow is marked by an increase in kinetic energy, turbulence intensities, and eddy viscosity coefficients. Strong episodic wind impulse decreases horizontal exchange coefficients through the water column but probably enhances the vertical mixing due to increase in current shear. It is suggested that the associated current-induced sediment resuspension may contribute to the establishment and maintenance of a Nepheloid layer in Lake Ontario.
Sources of Major Chemical Constituents in Surface Water and Groundwater of Southern Sweden
Authors: Maxe Lena
Published: May 2018

The chemistry of groundwater has been altered to a large degree through the influence of human activities. Addition of acids through precipitation and dry deposition, nitrogen from agriculture and sewage systems, and chloride from deicing are quantitatively the most important sources. In this paper the chemical characteristics of groundwater are discussed for a crystalline bedrock area located above the highest marine shoreline in southern Sweden. The aim of the study is to establish the background levels for the main chemical constituents in these waters. Focusing on sulphate and chloride, contributions from deposition are evaluated and a comparison with surface water chemistry is performed. Approximately 50% of the base cations in the lakes with extremely low alkalinity originate directly from deposition, while the corresponding figure for lakes with higher, though still low alkalinity, is approximately 39%, and for shallow wells the figure is 36%. There is evidence that the lakes receive water from a shallower depth than the shallow wells, but both groups receive the base cations mostly from the exchange store, or from weathering where the alkalinity produced is consumed by acid inputs. Deposition levels of sulphate and chloride are better approximated by lake water than by groundwater.
Calibration of Time Domain Reflectometry for Water Content in Peat Soil
Authors: Kellner Erik , Lundin Lars-Christer
Published: May 2018

Since peat soil differs from mineral soil in several respects, mineral-soil calibration functions for time domain reflectometry (TDR) are not necessarily applicable. This paper evaluates a number of calibration functions, both empirical polynomial and theoretical mixing models, on the basis of laboratory measurements on undisturbed Sphagnum peat samples. Deviations between different samples within this study indicate dissimilarities in dielectric properties between peats with different degrees of humification. Connections to physical properties such as amount of bound water and structural orientation are likely to exist. There is, however, a lack of methods to measure and quantify parameters expressing these properties. Therefore, until further studies on physical properties are accomplished, empirical or semi-empirical calibration curves are preferred. The best fit was obtained by an empirical, third order polynomial model. This model also gave a better fit than the mixing models when data were grouped into humification classes. However, all models reproduced pooled data with an r2 better than 0.93.
Modelling Mountainous Water Systems Between Learning and Speculating Looking for Challenges
Authors: Burlando Paolo , Pellicciotti Francesca , Strasser Ulrich
Published: May 2018

For many years considerable efforts have been put into investigating and modelling hydrological processes of mountainous catchments. On the one hand, the complexity and intrinsically high variability of the involved processes as well as insufficient knowledge of the underlying physical mechanisms still induce large uncertainties in understanding observed phenomena and predicting the behaviour of the system. On the other hand, the demand for models that are able to simulate mountainous water resource systems is increasing because of the needs related to both water exploitation and water conservation, which clearly call for an integrated vision and modelling of these systems.

Accordingly, this paper moves from a brief survey of the most significant achievements in mountain hydrology to discuss what could be future challenging issues related to the broader spectrum of questions, which hydrologic modelling of mountainous river systems may face in the next decades. Firstly, reference is made to existing methodologies for modelling alpine water systems, focussing on some specific aspects that provide a basis for the discussion of the weaknesses and perspectives of present simulation tools. The future is thus discussed, delineating some of the research challenges that may foster a comprehensive and integrated vision of water related issues in mountainous regions.
Film and Pulse Flow in Artificial Macropores
Authors: Tofteng Charlotte , Hansen Søren , Jensen Henry E.
Published: May 2018

It is generally recognized that macropore flow may occur in unsaturated soil and that this should be taken into account when modelling flow of water and solutes in soil. The objective of the present study was to examine the water pressure potential conditions at which macropore flow may occur and to elucidate the nature of macropore flow. A laboratory setup consisting of a sand column 20 cm in diameter and 20 cm high with outlet into a 50 cm long glass tube was used. The outlet characteristics of the glass tube was either free to the atmosphere or the glass tube terminated in gravel. The tube diameters used were 3, 4, and 6 mm while the water application rates used were 1.2, 2.2, 12, and 18.5 mm h −1. Experiments covering 26 combinations of tube diameter, water application rate and outlet characteristics were conducted. Water entered the macropores at a water pressure potential in the overlying sand more or less equivalent to the water entry pressure potential of the macropore according to capillary theory. The nature of flow in the macropore was for the tubes of 3 mm and 4 mm in diameter predominantly pulse flow while film flow was more likely to occur in the tube of 6 mm in diameter. During pulse flow events a pressure potential gradient was consistently created in the sand column, the pressure potential decreasing to -20 cm to -30 cm corresponding approximately to the air entry pressure potential of the sand. The pulse flow events occurred repeatedly during the infiltration as long as water application was continued. When film flow occurred after a pulse flow event, the film flow continued at a water pressure potential less than -20 cm in the sand close to the opening of the artificial macropore.
An Energy Balance Based HBV- Model with Application to an Arctic Watershed on Svalbard, Spitsbergen
Authors: Bruland Oddbjørn , Killingtveit Ånund
Published: May 2018

In several studies of snowmelt using the temperature index method from the original HBV-model, the model fails to predict the timing of the snowmelt and underestimates the intensities on occasions with high solar radiation and low air temperatures. This is especially evident at high latitudes such as catchments on Svalbard, but can also be the case for catchments at lower latitudes but at higher elevations and thus of importance to hydropower production. In this study, an energy balance calculation replaces the simple temperature index model in a spreadsheet version of the HBV-model. Calculation of average snow pack temperatures is included, and a new method is introduced to account for uneven snow distribution and glacial melt. This energy balance based HBV-model gives a better simulation of both snow and glacial melt. It was also found that estimates of sensible heat were improved by using a function with a non-linear wind speed dependency.
Suspended Sediment Transport from the Dokriani Glacier in the Garhwal Himalayas
Authors: Singh Pratap , Ramasatri K. S. , Kumar Naresh , Bhatnagar N. K.
Published: May 2018

Estimation of sediment load from glacierized basins is very important for planning, designing, installation and operation of hydro-power projects, including management of reservoirs. In the present study, an assessment of suspended sediment concentration, load, yield and erosion rate has been undertaken for the Dokriani Glacier drainage basin located in the Garhwal Himalayas. About 60% of the total drainage area of this basin is glacierized. Data were collected for four ablation seasons (1995-1998). The mean daily suspended sediment concentrations for June, July, August and September were 452, 933, 965 and 275 mg 1-1, respectively, indicating highest suspended sediment concentration in August, followed by July. Similar trends were also found for the sediment load and about 88% of the total suspended sediment load of the melt period was transported during the months of July and August. Sediment yield for the study basin was computed to be about 2,800 t km-2 yr-1, which is comparable with glacierized basins (10-30% glacierized) in the Pamir region. For the entire ablation period, the erosion from the Dokriani Glacier basin is estimated to be about 1.0 mm. There was a poor relationship between suspended sediment concentration and discharge. The average percentages of clay, silt and sand were found to be 1.4, 67.3 and 31.3%, respectively, which suggest maximum content of silt followed by sand. There was limited variation in the content of clay, silt and sand in the suspended sediment during the ablation period.
Investigation of Ice and Water Properties and Under-ice Light Fields in Fresh and Brackish Water Bodies
Authors: Leppäranta Matti , Reinart A. , Erm A. , Arst H. , Hussainov M. , Sipelgas L.
Published: May 2018

Light transmission through ice and light conditions beneath ice have been investigated in the mild winter of the year 2000 in eight Estonian lakes arid in one brackish water basin, Santala Bay in the Gulf of Finland. A new system designed for optical measurements beneath the ice was successfully tested. In the water body the vertical profiles of photosynthetically active radiation (PAR), temperature and oxygen were mapped. The concentrations of optically active substances (dissolved organic matter, chlorophyll a, particles) were estimated for water samples and meltwater of ice samples. The PAR band albedo was 0.28-0.76 and transmittance was 1-52% for the ice/snow cover. The light field below ice was much more diffuse than in open water conditions. Euphotic depth was 0.1-5.5 m. The amount of yellow substance in lake ice is very small in comparison with the lake water; lake ice may contain a lot of particles, but their source is atmospheric fallout rather than the water body. In some lakes a depletion of oxygen was observed. There were considerable differences between the fresh and brackish water ice (structure, stratigraphy, amount of impurities), which influenced the underwater light field.