COMPARATION OF ORIGINAL AND CURRENT STATUS DIGITAL
BOTTOM MODELL FOR ASSESSMENT OF BOTTOM SEDIMENTS
QUANTITY OF SMALL WATER BASINS
Ing. JAKUB FUSKA, Ing. JOZEF GABČO, doc. Ing. VILIAM BÁREK, CSc.
Departmenta of Landscape Engineering, Horticulture and Landscape Engineering Faculty, Slovak
University of Agriculture in Nitra
fuska.jakub@gmail.com, viliam.barek@uniag.sk,
Abstract
The important water-management problem of small water basins is sedimental alluviation
caused by erosion processes in the watershed of rivers and streams.
For the right functionallity of small water basins it is necessary to periodically purify the
bottom. For the scheduling of purification, quantification of water mass capacity is necessary
to know the physical, biological and chemical composition and estimation of removed
sediments quantity. This article is about the last, but not least point- estimation of water basin
sediment mass.
The comparation of original and current bottom model is a viable option. For this purposes,
a GIS application creates two models from different data sources.
Digital model of original bottom can be created from original project documentation using
original maps, technical drafts or geodetical measurings of bottom in the time of creation of
water basin.
Digital model of original bottom can be created from a variety of geodetical measurings as
sections, topographical measurings of drained basins and so on. The other option is to
measure the bottom in almost any status (filled or drained water basin) by using of GPS
measuring for position assessment and SONAR measuring for depth assessment.
Comparation of this two models provides the GIS application, which allows us to determine
the quantity of bottom sediments, actual water capacity of water basin, maximal depth and
other characteristics. This data can be used for ecological, technical and watermanagement
planning.
Key words: water basin bottom model , assessment of bottom sediments
Introduction
STN 73 6824 says, that small water basins are those, which have the following characteristics:
-
Mass of basin is smaller than 2 mil. m³
-
Maximum depth is 9 mQ
-
100 is smaller than 60m³/s
(STN 73 6824)
Small water basins are in accordance to water source divided to:
-
Rain basins (water source – rain or snow water)
-
Spring basins (water source – spring in bottom or waterside)
-
River or stream basins (water source – natural water flow)
(Rybársky, a kol.,1991)
Bottom sediments are erosion particles from agricultural or forest soils from watershed of
main waterflow and tributarry waterflows, which are its watersources. They have
characteristics same as the ground layer of eroded soils.
Chemical, physical and mechanical composition of sediments is function to the geologic build
of area and the human activities in this area, and that determines its heterogenity. Quality and
characteristics of bottom sediments shows all the inputs to agricultural soil and industry (with
waste water).
(Holobradý a kol., 1997)
One of the options for the manipulation with bottom sediments is application to agricultural
soils. This manipulation is described in Law nr. 188 / 2003 about application of wastewater
treatment plant sludge and bottom sediments to the soil, Law nr. 223/2001 abut waste
and STN 46 5735 – Industrial composts. In
STN 46 5735 there are determined the
requirements for characteristics of industrial composts, which describes the bottom sediments
too. Industrial compost must be brown, gray-brown or black homogene mater with lumpy
structure, wihout inseparable particles.
(STN 46 5735)
MATHERIAL AND METHODS
The installation of GPS reciever and sonar seems to be the best solution for bottom
mapping of small water basins. The measuring will be done from small rubber boat. The
bottom will be measured in points during the sailing. In accordance to high precission of GPS
measuring, the RTC reciever will be used.
The installation will measure the position of points (GPS reciever) and the water depth
in the point of measuring (SONAR). If GPS position in X and Y axis describes the point in
bottom, then we have to subtract the sonar-measured depth and distance between GPS and
sonar to get the Z coordinate of point in bottom of water basin (Fig. 1).
Figure 1.: GPS – sonar instalation
The thickness of sediment layer will be done with comparation of nowadays bottom
with original bottom. The measurings will be used to create the model of the bottom in
nowadays. The second model – model of original bottom, will be created from the older plans
of basin construction, geodetic measurings and other parts of project documentation. Then we
can compare these models and asset the mass of bottom sediments. The main idea of
comparation is shown in fig. 2.
Figure 2.: Comparation of original and actual bottom
The crucial part of this method is data collection of GPS measurings.
GPS system
Global position system (GPS) is system based on satellites in the cosmos managed
from the control stations on Earth. The services of this system are accesable from almost any
part of the Earth surface. The only limitation is the direct visibility to the sky for recieving the
signal from satellites.
Cosmic segment of system is made of 24 satellites, which send navigation signals to
the Earth’s surface. They are recieved by GPS reciever. Reciever is small, mobile electronic
device, which recieves navigation signals, process them and based on signals determines the
position.
(Rapant, 2002)
Principle of position determination
This principle is quite simple. Satellites orbit the Earth in distace 20200km from the
earth surface and emmits Navigation codes, which are decoded by reciever. This signal is in
form of time of emmit. Simultaneously the reciever compare the time os recieve the signal
and use this comparation to calculate the distance between satelite and reciever. The position
is then calculated from the signals of 3 and more satellites as the transection of distances from
satellites with known position.
(Rapant, 2002)
Refinement of GPS measurings
Averaging
Average value of measuring in the duration of few hours on the measured point.
Practic results shows that after 8 hours of measuring the precision is not getting better in time.
Postprocessing
This method does not require direct communication with GPS reciever in real timethe data are obtained later (mostly via internet) for the time period of measuring
Real-time corrections (RTC)
Reciever obtains the satelite signals and the data about ionosphere. Ionospheric data
are distributed from correction stations on the Earth’s surface, where is made continuous
position measuring of known points, which provides the determination of ionospheric changes
in actual time of measuring.
(Klimánek, 2006)
Sonar system
Typic sonar consists of two basic components – reciever and recorder. Reciever is
combination of emmiter and reciever (hydrophone). Reciever sends the signal (sound
vibration), which is reflected from the bottom. This reflected signal travesl back to the
reciever. From the calculation with known time from sending and recieving the signal and the
velocity of sound in liquids the recorder calculate and record the data of depth form reciever
to bottom.
(Lurton, 2002)
RESULTS AND DISCUSSION
For the assessment of quantity of bottom sediments it is necessary to get the precise
measuring of the bottom, but also prepare the representative model of original bottom.
Comparation of these two models provides the quantification of actual water mass in
water basin and mass of sediments.
Nowadays the GIS applications offers a few types and methods of creation of models.
Because of character of water bottom relief and sedimentation process we assume, that the
direction of bottom will be continuous, without the presence of expressive breaks
(singularities). This is why we will use the polyedric model.
Basic surface of polyedric model is created of points (vertex), which creates the
edges.These edges determines the faces of model. Input data are created of X, Y,
Z coordinates of vertex. That means the edge connects two points and divide two faces. The
face is bordered by three edges and represents the flat surface.
(Klimánek, 2006)
Final comparation of models (model of actual and original bottom) then describe many
characteristics as:
-
Total amount of sediments
-
Maximum thickness of sediments
-
Total water capacity of water basin
-
Bottom slope, depth and profile of water basin in any point or direction
CONCLUSION
The usage of this method will confirm or disconfirm the expectations of precision,
time and economic effectivity of this method and the options of usage of this methot for
watermanagement, environmental, engineer, agricultural and ecological purposes.
LITERATURE
Holobradý, K., Ilka, P. 1997. Metodika priamej aplikácie stabilizovaných čistiarenských
kalov a dnových sedimentov 1997. 11,12 s. ISBN 80 – 85361 – 25 – 6
Klimánek, M., 2006. Digitální modely terénu. Mendelova zemědělská a lesnícká univerzita
v Brně, 2006. 85 s. ISBN 80-7157-982-3
LURTON, X., 2002. An introduction to underwater acoustics: principles and applications.
Chichester: Springer. 2002. 480 s. ISBN 3-540-42967-0
Rapant, P., 2002. Družicové polohové systémy. VŠB-TU Ostrava 2002. 202 s. ISBN 80-2480124-8
Rybársky, I., Švehla, F., Geissé, E., 1991. Pozemkové úpravy. Bratislava 1991. 213, 222 s.
ISBN 80-05-00873-2
STN 46 5735, 1991: Priemyselné komposty
STN 73 6824, 1978: Malé vodné nádrže
Contact adress:
Ing. Jakub Fuska, Slovak University of Agriculture in Nitra, Horticulture and Landscape
Engineering Faculty, Departmenta of Landscape Engineering,
Hospodárska 7 Nitra, Slovakia,
E-mail: fuska.jakub@gmail.com,