Comparison of the MODFLOW modules for the simulation of the river type boundary condition

The aim of this article is the comparison of input options of river boundary condition of MODFLOW - three-dimensional numerical simulation model of groundwater flow. The water level in stream flowing through territory of hydrogeological layer can be computed via three built-in modules: River, Stream and Streamflow-Routing. In this study the code MODFLOW is used to simulate idealized aquifer and stream. The differences between computed groundwater table showed to be minimal, thus in case of modules Stream and Streamflow- Routing they are equally usable as using module River with external one or two-dimensional simulation of surface water flow, which is more time-consuming process. However, this applies only to idealized, simplified conditions of the modeled environment. For more complex simulation of flow in streams with irregular structure of the streambed is necessary to use either an external simulation or use the Streamflow-Routing module, which includes the possibility to enter more complex hydraulic flow parameters in the model

Application of asymmetrical statistical distributions for 1D simulation of solute transport in streams

Analytical solutions of the one-dimensional (1D) advection–dispersion equations, describing the substance transport in streams, are often used because of their simplicity and computational speed. Practical computations, however, clearly show the limits and the inaccuracies of this approach. These are especially visible in cases where the streams deform concentration distribution of the transported substance due to hydraulic and morphological conditions, e.g., by transient storage zones (dead zones), vegetation, and irregularities in the stream hydromorphology. In this paper, a new approach to the simulation of 1D substance transport is presented, adapted, and tested on tracer experiments available in the published research, and carried out in three small streams in Slovakia with dead zones. Evaluation of the proposed methods, based on different probability distributions, confirmed that they approximate the measured concentrations significantly better than those based upon the commonly used Gaussian distribution. Finally, an example of the application of the proposed methods to an iterative (inverse) task is presented

Water regime simulation along Gabčíkovo – Topoľníky chanel (Vrakúň junction) case study

Gabčíkovo – Topoľníky channel is one of three main channels in the irrigation and drainage channel network of Žitný ostrov. Žitný ostrov is a lowland area in south – western Slovakia with high degree of agricultural use and thanks to its bed composed mainly of fluvial gravel sediments it is a significant storage of high quality groundwater. The Vrakúň junction location was chosen due to the presence of regulation measures (floodgates)along the boundary of the area of interest and also due to the occurrence of both agricultural and urban areas. The aim of this paper is to evaluate surface water – groundwater interactions between the channel and its surroundings considering the significant increase in volume of silts in the channel over the past years and comparison of the interaction between the current state and state with no aggradation in the channel. The simulation was done using finite – difference groundwater (MODFLOW) (Harbaugh et al., 2000) model in the Aquaveo GMS interface

Consumption of fertilizers in districts of Slovakia in the period 2006–2015

Consumption of fertilizers in districts of Slovakia in the period 2006–2015 Water quality in the surface streams is influenced by several factors. One of important information which can help us to solve problems with quality of water in water body is a distribution of point and non-point pollution sources in a river basin and also amount of pollutants released from them to surface streams. An example of a point source of pollution is the outlet from wastewater treatment plants (industry, urban areas, farms, etc.). On the other hand the most significant non-point source of pollution is considered the application of fertilizers in agriculture. In this paper we have evaluated consumption of organic and industrial fertilizers in Slovakia in the period 2006–2015. Total (in tonnes) and average (in kg ha-1) consumption of industrial and organic fertilizers was analyzed. In monitored period, the amount of applied organic fertilizers was much higher than the amount of applied industrial fertilizers and in addition a significant part of total fertilizers consumption had nitrogenous fertilizers in a group of industrial fertilizers. In a group of industrial fertilizers during the period 2006–2015 we observed just moderately increasing in their consumption, while in the period 2010–2015 the average amount of applied industrial fertilizers per hectare of agricultural land increased by about 20 kg ha-1. On the other hand, in a group of organic fertilizers we observed a decreasing in consumption of fertilizers

An approximate method for 1-D simulation of pollution transport in streams with dead zones

Analytical solutions describing the 1D substance transport in streams have many limitations and factors, which determine their accuracy. One of the very important factors is the presence of the transient storage (dead zones), that deform the concentration distribution of the transported substance. For better adaptation to such real conditions, a simple 1D approximation method is presented in this paper. The proposed approximate method is based on the asymmetric probability distribution (Gumbel’s distribution) and was verified on three streams in southern Slovakia. Tracer experiments on these streams confirmed the presence of dead zones to various extents, depending mainly on the vegetation extent in each stream. Statistical evaluation confirms that the proposed method approximates the measured concentrations significantly better than methods based upon the Gaussian distribution. The results achieved by this novel method are also comparable with the solution of the 1D advection-diffusion equation (ADE), whereas the proposed method is faster and easier to apply and thus suitable for iterative (inverse) tasks

Sedimentace v malých vodních nádržích

V současné době roste počet malých vodních nádrží v Česku i na Slovensku, které mají dva hlavní úkoly – protipovodňová ochrana a zásoba vody pro období sucha. Tyto malé vodní nádrže se často objevují v zemědělských oblastech, kde je velký potenciál jejich využití. Problém těchto oblastí je silná eroze půdy, která vede k odnosu a následnému uložení erodovaného materiálu v nádržích či nad jinými překážkami. Takto uložené sedimenty snižují retenční kapacitu nádrže, zvyšují koncentraci chemických látek, což vše může vést ke zhoršení kvality vody v nádrži i pod ní. Tento příspěvek se zaměřuje na dvě malé nádrže vybudované v roce 2011, u kterých se od uvedení do provozu sleduje množství uložených sedimentů. Jsou zde představeny dvě různé metody, jak odvodit množství sedimentů z měření vývoje dna nádrže, včetně možné aplikace empirických erozních modelů pro stanovení potenciálního množství erodovaného materiálu. Důraz je také kladen na terénní průzkum pro odběr vzorků půdy a jejich následnou laboratorní analýzu. Takto získané informace mohou pomoci k pochopení transportních i depozičních procesů v nádrži a odpovídající přispívající ploše (povodí). Výsledky poukazují na relativně rychlé zanášení malých vodních nádrží v zemědělské krajině zejména díky intenzivním srážkovým událostem. Množství sedimentů nezávisí na typu nádrže (suchá nebo se stálou hladinou), ale na charakteru povodí (fyzicko-geografické vlastnosti území), využití území a pěstovaných plodinách.The uncontrolled reservoir siltation presents a hazard together with the rising number of reservoirs and current climate change. This paper presents the possible methodologies to measure siltation in small reservoir and how to calculate the potential soil water erosion and deposition of the contributing area. The results show that the USLE-based erosion models are suitable for estimation of erosion processes, especially USPED model, which is capable to model erosion and deposition of the material in the same time. Also, both approaches to investigate the development of the reservoir bottom were verified. The use of AUV EcoMapper is appropriate for reservoirs with stable water level between 1 and 100 meters, however the second approach is more suitable for shallow reservoirs. According to observed and modelled sediment budget of reservoirs the supposed reservoir lifetime was determined from 100 to 400 years. The siltation is much higher in the Svacenický reservoir in contrast to Němčický reservoir (Suchý creek catchment), which corresponds to bigger catchment area, higher percentage of arable land and more variable relief

Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems

Experiments focused on pollution transport and dispersion phenomena in conditions of low flow (low water depth and velocities) in sewers with bed sediment and deposits are presented. Such conditions occur very often in sewer pipes during dry weather flows. Experiments were performed in laboratory conditions. To simulate real hydraulic conditions in sewer pipes, sand of fraction 0.6–1.2 mm was placed on the bottom of the pipe. In total, we performed 23 experiments with 4 different thicknesses of sand sediment layers. The first scenario is without sediment, the second is with sediment filling 3.4% of the pipe diameter (sediment layer thickness = 8.5 mm), the third scenario represents sediment filling 10% of the pipe diameter (sediment layer thickness = 25 mm) and sediment fills 14% of the pipe diameter (sediment layer thickness = 35 mm) in the last scenario. For each thickness of the sediment layer, a set of tracer experiments with different flow rates was performed. The discharge ranges were from (0.14–2.5)·10−3 m3·s−1, corresponding to the range of Reynolds number 500–18,000. Results show that in the hydraulic conditions of a circular sewer pipe with the occurrence of sediment and deposits, the value of the longitudinal dispersion coefficient Dx decreases almost linearly with decrease of the flow rate (also with Reynolds number) to a certain limit (inflexion point), which is individual for each particular sediment thickness. Below this limit the value of the dispersion coefficient starts to rise again, together with increasing asymmetricity of the concentration distribution in time, caused by transient (dead) storage zones

The influence of channel network silting up at Žitný Ostrov to range of interaction between surface and groundwater

The movement of water resources, especially the possibilities of their regulation by interaction between surface and groundwaters are the subject matter of attention particularly during the occurrence of extreme hydrologic situation. This work presents the overview of knowledge and results which were achieved at IH SAS in this question. It can show the ways how to optimize the adjudicated processes which emerge during the requirement of emergency intervention. The solution of this task was located at the Žitný Ostrov area because this territory with their existence of channel network is suitable for studying the surface and groundwater interaction. The channel network at Žitný Ostrov was built up for drainage and also to safeguard irrigation water. The water level in the whole channel network system has an effect on groundwater level on the Žitný Ostrov and vice versa. It was been necessary to judge the impact of the channel network silting up by bed silts on the interaction between channel network and groundwater on the Žitný Ostrov. The aim was to evaluate the changes of bed silt state of Žitný Ostrov channel network and consecutively their influence on interaction processes between groundwater and surface water along the channels in the period from 1993 to present. The measurements of bed silt thickness in Žitný ostrov channel network had been started from1993, later they continued at selected profiles of three main channels – channel Gabčíkovo-Topoľníky, Chotárny channel and Komárňanský channel (for checking of the silting up variability). From 2008 the detailed field measurements of cross-section profiles aggradations along these selected three channels have been started. The objective of detailed field measurements was the determination of the silt permeability which is expressed by parameter of saturated hydraulic conductivity. This parameter was determined by two ways – as the saturated hydraulic conductivity obtained from disturbed samples of silt Kp and as the saturated hydraulic conductivity obtained from undisturbed samples of silt Kn. In the first case the granularity of silts was determined as a first step and then was computed their Kp from the empirical formulas according Bayer-Schweiger and Spacek. From undisturbed samples of silts which were extracted along the channels from top, middle and bottom layer of silts, were determined the values Kn by the laboratory falling head method. The valid values Kp on channel Gabčíkovo-Topoľníky ranged from 4,33 10-7 to 4,46.10-5 m s-1, on Chotárny channel from 5.98 10-5 to 2.14 10-6 m s-1 and on Komárňanský channel fluctuated from 1.93 10-6 – 6.09 10-5 m s-1. The valid values Kn on on channel Gabčíkovo-Topoľníky ranged from 5.21 10-8 – 4.18 10-3 m s-1 , on Chotárny channel ranged from 8.54 10-8 – 2.70 10-4 m s-1 and on Komárňanský channel fluctuated from 4.72 10-7 – 1.26 10-5 m s-1. The remarkable results were noticed by comparison of values of saturated hydraulic conductivity from disturbed and undisturbed samples Kp and Kn. On Chotárny channel the values of silt saturated hydraulic conductivity from undisturbed samples Kn approximately hundredfold decreased (from 10-6 to 10-8 m s-1). On Komárňanský channel the comparison of values Kp and Kn shown that the values Kn from undisturbed samples approximately tenfold descended against Kp. Simultaneously, the bed silts‘ impact on the groundwater recharge (saturated hydraulic conductivity of silt) was also examined. Determination of the total recharge amount was done by numerical simulation (model SKOKY) and by the so-called method of interaction formulas. These two approaches were applied at the Žitný Ostrov channel network. There were field measurements performed in monitored three main channels and adjacent to obtain correct input data. These characteristics were used for simulation and computation of total recharge along the channels. The total recharge amount was calculated for four alternatives of the surface water levels in the channel and the surroundings groundwater respectively. We chose four simplified variants with the same geological conditions in surroundings area of channels, only water levels of groundwater and in channels were modified. The results of the simulations seem to show greater impact of the silt in the case of outflow from the channels to the surroundings than the inflow into the channel from the surroundings. &nbsp