Geography Reference
In-Depth Information
is supplemented with specific geodesic measurements and the follow-up GIS
analyses. The geodatabase of DIBAVOD (Digital Database for Water Management
managed by T. G. Masaryk Water Research Institute) was the source of the
hydrological data. The altitude data come from the ZABAGED data set (Funda-
mental Base of Geographical Data managed by Czech Office for Surveying,
Mapping and Cadastre) data set. On the basis of this group of data, hydrological
attributes of the basins in question were determined, such as length, average
descent, shape of the basin—expressed by the basin shape coefficient
(De Blij
et al. 2006 ), and type of streaming—expressed by the Froude number Fr (Chanson
2004a , b ). The software used is ArcGIS 10.2 (ESRI) and its extensions HEC-RAS
and HEC-GeoRAS.
The longitudinal slope, the transversal profiles and parameters of all transversal
objects, such as pipes and bridges, were measured for the two streams flowing
through the village build-up area with the geodesic GPS using RTK (real time
kinematics) of the CZEPOS (the network of permanent GNSS stations in CR)
network. This group of data was used to determine the flow rate limits for all
transversal objects, two of which were used for creating the water gauges of
category C. Flood limits, i.e. state of alert (1), state of emergency (2), state of
danger (3), were determined for these water gauges using hydrological calculation.
The drainage from the village build-up area is limited by the maximum flow
rates of the piped parts of the streams. This regards 13 piped parts, namely 8 piped
parts on the stream B ´ l´ potok and 5 piped parts on the stream Hr ´ zkov´ potok. All
of these passages were geodesically measured together with the longitudinal verti-
cal alignment of the stream bottoms for purposes of hydrological calculation of the
maximum flow rates. In front of the entries to specific pipes, the transversal stream
profile was measured to determine the Hmax level for the flow rate limits of
individual pipes using the Ch ´ zy equation and the continuity equation (Landau
and Lifshitz 1987 ). The Hmax value thus gives the maximum depth of the flow
before going through the pipe when the limit flow rate (for the pipe given) goes
through the streambed. The Manning coefficient of friction 0.033 was used for fully
fortified streambeds, the value of 0.04 was taken for unfortified streambeds (Chan-
son 2004a , b ).
With respect to the currently running campaign of laser surface scanning of the
Czech Republic, the altitude data for Moravia are not yet available with sufficient
precision to model the flood zones in the village. This analysis will be carried out as
soon as the 4G data subbase is processed by the Czech Office for Surveying,
Mapping and Cadastre—spring of 2014 is the expected date. Selection of the
buildings under threat, for the time being, is based on historical experience only.
The western part of the build-up area in the village of Hostaˇovice is situated in a
terrain depression which is surrounded from three sides by slopes with permanent
grass growth and forests. In case of burst rainfall events in combination with the
saturation of the soil horizon, accumulation of surface water occurs on the slopes in
a great measure, which is a threat to some properties during flood events in the
village. In case of improper management on the surrounding slopes (planting wide-
rowed crops, plowing in lines parallel with the descent, and the like), the soil wash-
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