Completed PhD thesis:




Completed PhD thesis:

Identification a range of ecological acceptable dicharges

Author: Ing. Jana Caletková
Supervisor: RNDr. Dana Komínková,Ph.D.

In present epoch it is necessary deal with one of the biggest global problems join with development of water management. For a long period of time interest about all these problems were limited only on changes of hydraulic and hydrological conditions in running waters as resource of water for different users (delivery of required amount of water). The delivery of required water amount was supported by technical changes of rivers (creeks) character (reservoirs, damps, etc). This effort to deliver required amount of water to all users and a flood protection did not impact the water body always positively and rivers (creeks) were significantly changed. The present European legislation, especially Directive 2000/60/ EC, requires that all water bodies will reach good ecological status until year 2015. The first step is to monitor quality of aquatic ecosystem from different point of view; chemical, morphological and hydraulic and finally biological status. The monitoring of chemical quality is done for a few decades and also biological quality is observed during the last two decades with increasing emphasis. But the impact of changes in morphology and discharge on aquatic ecosystem was neglected for a long time. Changes in morphology and discharges play an important role especially in small urban creeks, which are heavily impacted by urban drainage and discharge from sewer system. Frequent overflows from sewer and discharge variation in the creek put a high demand not only on the watercourse but also on the aquatic biota. Impact of these events makes either deficient discharge or discharges, which cause an artificial flood. Both cases could destroy the watercourse and aquatic life so heavily, that it would exceed their recovery potential. Identification of ecological discharge range is necessary to avoid these types of negative impacts and also it is important for sustainable water management and revitalization of impacted watercourses.
One of the potential approaches is the methodology IFIM – Instream Flow Incremental Methodology The IFIM is most often used for determination of ecologically acceptable discharges in watercourses and for design of operating regulations. Further the IFIM can be implemented into the process of EIA (Ecological Impact Assessment) for minimization of ecological impacts caused by hydraulic structures construction and management.
One of the basic instruments of IFIM is a simulation tool Physical HABitat SIMulation system (PHABSIM). It is used for modelling of habitat changes in dependence on discharge changes and connected to the ecological consequence for particular species and their life stages.

Goals:

  • Application of PHABSIM for small streams in urban drainage
  • Biological diversity determination
  • Habitat Suitability Index creation
  • Determination of:
       - Optimum discharge range
       - Minimum discharge range
       - Maximum discharge range
  • Proposal of measures from view of urban drainage

Unsteady Free Surface Flow Analysis in Circular Tube

Author: Ing. Vojtěch Bareš
Supervisor: Prof. Ing. Jaroslav Pollert, DrSc.

Poster_cz (pdf, 490 kB)
Poster_en (pdf, 624 kB)

Unsteady free-surface flows in circular pipe over smooth pipe wall as well as over rough sediment bed have been experimentally and theoretically investigated.

The theoretical equation for the mean longitudinal, for the friction velocity, for the bottom shear stress were rewied and defined based on the theory of turbulent boundary layer flow and basic equations, particulary the Reynolds equations of motion, the Saint-Venant equation and the equation of continuity. Sediment transport theory has been discussed with respect to specific hydraulic conditions in the sewer flow.

Experimental track were made of plexiglass pipe with constant bottom slope. The hydraulic system were controlled via PC. An Ultrasonic Velocity Profile Monitor (UVP Monitor) was used to obtain experimental data on the velocity profiles. Complex information about flow and turbulent characteristics, such a flow depth, mean velocities and turbulence intensities has been given by data analysis. For decomposing the instantaneous signals (longitudinal velocity u etc) different methods were tested.

Preliminary and reference experiments were carried out under steady uniform flow conditions. A number of experiments have been done with different flow depth smaller than h/D = 0.55. The experimental results show that: a) the tests of flow dimensionality show contradictory results. The aspect ratio during experiments has been smaller then critical value B/h=3.5 proposed in the literature for rectangular channels. On the other side, the Dip-value of the centre line velocity profile was found smaller than 0.2 in all experimetns; b) the mean velocity profiles can be expressed by the log law with Bs 5.0 in the inner region. Coles wake law can describe the velocity distribution in the outer region of the turbulent boundary layer. Wake strength parametr has had the average value of The values above mentioned distribution parameters have been in the same range as other observations in rectangular channels; c) fitting the mean velocity distribution data in the inner region the local friction velocity u*loc has been estimated; d) the ratio between calculated local bottom shear stress 0loc and average value 0av estimated from hydraulic radius R and bottom slope i0 has been found in the range 1.1 1.3.

Unsteady flow experiments have been carried out in hydraulic smooth flow regime. Different shapes of hydrograph were generated with data acquisition system. The first experimental results shows that: a) during the hydrograph passage the longitudinal velocity near the water surface reaches maximum values earlier than that near the bottom; b) the velocities in the profiles are generaly higher in the rising than in falling branch of the hydrograph for the same flow depth h; c) the comparison of the velocity profiles for the same vertically averaged velocity U shows crossing of the profiles. Close to the bottom the velocity is less for the rising branch then for the falling branch of the hydrograph and vice versa for velocity close to the free surface; d) The friction velocity u* was determined using the Saint-Venant equation of the motion and using the Clauser method for velocity profile in the inner region of turbulent layer. In both cases has the friction velocity u* similar time behaviour. For the same flow depth the values are higher in the rising branch than in the falling one. The observed peak deviation was close to 100 percent. The diference to steady flow values was defined; e) it was shown, that bottom shear stress 0 cannot be estimated with steady flow formula under unsteady flow conditions.

UVP method provides successfully data of unsteady turbulent flow with free surface in circular pipe. Applicability of that method in non-intrusive measuring mode has been confirmed.

Predikce potreby vody pomocí neuronových sítí

Author: Ing. Marek Nemec
Supervisor: Doc. Ing. Iva Ciháková, CSc.

Completed PhD thesis (pdf, 519 kB)

Heavy Metals in the Environment of Small Urban Streams

Author: Mgr. Jana Nábělková, Ph.D.
Supervisor: Dr. Ing. Ivana Kabelková

Completed PhD thesis (pdf, 15 kB)

Heavy metals belong to the most dangerous contaminants, which get to watercourses in urban areas particularly from point sources (combine sewer overflows and storm sewer outlets). They are toxic for fishes and other water organisms and via food chain they can get to higher trophic levels (birds and human), where they can take toxic (carcinogenic or teratogenic) effect showing already in low concentrations. Their toxicity often depends on form, in which they occur in water environment. The form of occurrence is influenced by water composition and physico - chemical properties. Moreover, they tend to cumulate in bottom sediment and water biota (bioaccumulation). High concentrations of heavy metals can be bound in solid matrix (bottom sediment) for a long time without toxic effect on aquatic biota (particularly fishes), because actual concentrations of metals in water is insignificant. But during change of physico - chemical conditions release of metals from solid faze to liquid can occur and metals become available for organisms and can cause toxic effects.

The research is applied to actual problems, which have been solved a little in our country till this time and which are in accordance with ideas of EU about achievement of good ecological status of watercourses in member countries till 2015. PhD thesis results will be basis for creation of complex methodology of assessment of streams affected by pollution input from sewer systems and creation of a system for assessment of ecological status of watercourses in accordance with EU legislation, as regards ecotoxicological impact on ecosystem.

The questions solved in terms of PhD thesis::

  • What techniques of sampling, treatment and analysis of bottom sediment samples is the best? Are results obtained by different techniques comparable?
  • How long does establishing of equilibrium of metal partition between solid and liquid phase take? How does this period vary for different heavy metals and how does it depend on environmental conditions (shaking, grain size and composition of solid material, temperature…..)?
  • How does distribution coefficient change with modification of environmental conditions for chosen heavy metals (Cu and Zn)?
  • Does found dependence from point 3) hold also for other heavy metals (Ni, Pb)?
  • What is behaviour of metals if they are bound into contaminated sediment?
  • What is the role of grain size during binding of metals onto sediment?
  • Are conditions in environment of small urban streams changed so far (e.g. by effect of outlets of sewer system), that remobilization of heavy metals from sediment to water can occur? - research based on results from points 2)-5).

Reliability of sewer systems designed by rational formula

Author: Ing. David Stránský
Finished: 2004
Supervisor: Prof. Ing. Jaroslav Pollert, DrSc.

The rational formula is a classic tool for design of sewer systems. It has been developed more than 100 years ago and it is still used in many parts of the world. As a design criterion is used rain intensity of certain frequency, which is mostly chosen from IDF (intensity-duration-frequency) curves. Frequency of the design storm cannot be interpreted as frequency of surcharge, because relation between them is not linear and homogenous in space. Frequency of the design rain is chosen according to the national legislative. In Czech Republic there are used rain intensities occurring once per year or once per two years in average (the first one is used for municipalities up to 5000 thousand inhabitants and storm sewers, the second one for lager cities). Based on operation experience, it is clear, that surcharge occurs less often. We can deduct, that reliability of sewer system is unknown during its design. However it is very important information for specialist (lack of knowledge of design consequences), operation companies (real time control, mitigation strategies), authorities (city development planning) as well as consumers (protection of property).

The first part of the thesis is focused on definitions of sewer system reliability and safety, which are not included in Czech legislative. The sewer system can operate in five different regimes, which are defined by water level and/or discharge. The mildest regime is situation, when discharge in sewer is under design values (design discharges), the most dangerous regime occurs when wastewater escapes from sewers and causes flooding in urban areas. The nomenclature for all regimes has been suggested.

The second part of the thesis shows methods and results of analysis of rational formula uncertainties, which arises from uncertainties of included parameters, i.e. design intensity, runoff coefficient and area. Uncertainties has been defined, described and then quantified. It has been find out, that major uncertainties in design intensity include inaccuracy of measuring devices, errors in data processing, length of historical rain series and definition of rain. Quantification has been done by analysis of 78-year record of rains. For example, the random parts of rain series have been processed in order to obtain IDF curves. It allows to quantify uncertainties in length of the record. Subjectivity of determination and time variation has been studied as important uncertainties of the runoff coefficient. Mathematical deduction and experiment have been used for quantification. Effect of previous rainfall history of watershed has been investigated on small experimental catchment (about 60 ha), where five rain gauges were installed. It allows decrease errors of space variation of rain. Catchment area appears as a less important parameter of the rational formula from uncertainty point of view. Uncertainties have been studied on abstract example, which shows that value of the parameter is the less certain in upper catchment and decreasing downstream.

Determination of the runoff coefficient causes large decrease of expected value of design discharge. The greatest uncertainty should be expected in situation, when design intensity has been derived from short (less than 20 years) historical series, a catchment is lowly urbanised and designed pipe is placed in upper part of the catchment. The lowest uncertainty occurs in opposite case. At the end of the thesis the suitability of the rational formula for sewer system design is discussed in comparison with use of simulation tools. The rational formula is very fast and cheap method, but it oversimplifies the problem at the expense of accuracy of results. Simulation tools are much more sophisticated, using up to date knowledge and advantages of computational aids, which were not at disposal few decades ago. On the other hand, simulation tools have to be calibrated a verified in order to get credible results. It is not possible for sewer systems, which are in stage of planning. There are also great gaps in methods of determining parameters of the rational formula. The combination of simulation tools and the updated rational formula seem to be future way of sewer system design, which will include the reliability of sewer system as a key parameter.

Mathematical Modelling of Sewer System Objects

Author: Ing. Jaroslav Pollert ml.
Finished: 2002
Supervisor: Doc. Ing. Zdeněk Koníček

Hydraulics of Sewer System - Criterion of Sediment Transport

Author: Ing. Pavel Koudelák
Finished: 2001
Supervisor: Prof. Ing. Jaroslav Pollert, DrSc.

Urban Drainage Role in Water Management Planning

Author: Ing. Jan Krejčík
Finished: 2000
Supervisor: Doc. Ing. Zdeněk Koníček, CSc.
Abstract of disertation thesis (pdf, 22 kB)