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| Titel |
Spatio-temporal flow structures and morphological changes in a meander bend during a spring flood: a unique ADCP mini-boat approach |
| VerfasserIn |
Leena Laamanen, Claude Flener, Petteri Alho |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090634
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| Publikation (Nr.) |
 EGU/EGU2014-4890.pdf |
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| Zusammenfassung |
| To date, measuring flow structure of rivers has been time consuming and mostly
based on a cross-sectional survey approach. Therefore temporal and spatial scales
of earlier studies on flow dynamics have been rather limited. The development
of acoustic measurement techniques has improved knowledge of flow structure
and their dynamics. Especially Acoustic Doppler Current Profiler (ADCP) has
regenerated field of flow studies. ADCP is used in most cases for discharge measurements
and cross-sectional flow structure measurements. However, flow measurements
covering the whole meander bend are still uncommon. Our measurement approach
enables to acquire spatially well-covered and accurate 3D flow data for the whole
reach.
We studied the changes in near-bed flow structure and bed morphology in a sandy
meander bend. Flow measurements were undertaken during nine days field work period in the
rising state of a spring flood. During the field investigation the water level rose 1.3 meters
with discharge increasing from 35 to 66 m3/s.
3D flow structures and the associated bed morphologies were studied using ADCP
coupled with high accuracy VRS-GNSS. Both ADCP and VRS-GNSS were placed on remote
controlled mini-boat in order to measure the meander bend effectively. This combination
enables spatially accurate measurement of flow structure and bed morphology.
Plotting frequency of both devices was 1 Hz, which allowed dense measurements of
flow structure and bed morphology. Average density of flow measurements was 1.2
pts/m2.
The day-to-day changes in flow structure and bed morphology were studied and
compared. Spatial and temporal changes in near-bed flow velocity and direction were
investigated and compared with depth-averaged flow velocity and direction. Subsequently,
morphological changes were detected and compared to daily changes in flow velocity,
direction, depth and other flow characteristics. In total, changes from nine days of
measurements were analysed daily during the rising state of the flood. Flow velocities varied
from 0.5 to 1.3 m/s in the upstream part and 0.6 to 1.0 m/s in the downstream part of the
meander bend.
Highly accurate spatial and dense temporal scale measurements of flow structure and bed
morphology can be undertaken only by using a remote controlled platform that is capable of
navigating in river channel with high position flow measurement accuracy. Our remote
controlled mini-boat in combination with a state-of-the-art VRS-GNSS and ADCP system
opens a new perspective on studying fluvial dynamics on a very detailed spatio-temporal
scale. |
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