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Universität Innsbruck (2015)

Determination of Discharge Information for Arid Areas with Ephemeral Flow with the Help of Remote Sensing Techniques

Mett, Michael

Titre : Determination of Discharge Information for Arid Areas with Ephemeral Flow with the Help of Remote Sensing Techniques

Auteur : Mett, Michael

Université de soutenance : Universität Innsbruck

Grade : Doctoral Thesis 2015

Résumé
In arid areas, typically the availability of discharge data is limited due to a lack of gauging stations and highly variable river systems, which are difficult to observe. However in the context of decreasing water resources and population growth the demand for such data is enormous. Braided wadi streams, which are characterised by highly dynamic runoff and sedimentation processes, are the most typical river types in arid areas. Ephemeral discharge events with high peak flows and short durations significantly alter the braiding patterns of the wadis. By optical space born sensor data, these fluvio-morphologic changes can be observed and judged. Within the scope of the work, twelve wadis in Jordan and the Sultanate of Oman are being investigated regarding morphologic changes which were caused by flash floods.
Change detection is performed with multitemporal satellite pictures from different sensors for a timespan of two decades. From the image subsets braiding indexes like absolute sinuosity, sinuosity of the main channel, channel count, island count and effective flow width are determined by GIS analysis and digital image processing. The monitored structural changes are related with discharge measurements which were raised in the test sides. The analysis is supported by hydraulic data from extensive field work. It is observed that the values of absolute sinuosity, channel count, island count and effective flow width are proportional to the magnitude of the discharge. In contrast, the sinuosity of the main channel decreases. Power functions and linear functions are most suitable to explain the relationship between the observed pattern changes and the discharge. Mostly they exhibit coefficients of determination between 0.7 and 0.98. The most sensitive results are displayed by the development of the effective flow width and the island count index. Both parameters are used to develop discharge formulas, which enable the estimation of flow volumes for arid areas with ephemeral flow. Three types of formulas are distinguished, based on the slope and the braiding behaviour of the wadi system. Furthermore the “Fluvio Morphological Activity Index – FMAI” considers the site-related intensity of pattern changes for a more general calculation of flood volumes. The methods are verified with the help of historical discharge data and satellite imagery from wadis in Israel and Namibia. The developed approaches enable to re-calculate discharge amounts of discrete flood events from the past within certain accuracy. If considering the accumulated discharge volume for a wadi over a period of several years, the methodology allows significantly improved estimations of the total available water resources. The approaches turned out to be a promising tool for estimating discharge volumes in arid areas – even long after the related floods. Because of the large spatial coverage of satellite data, also remote areas can be monitored in a fast and economic way regarding potential water resources. The ex post assessment of important flood data becomes a realistic option to make accessible these valuable resources.

Mots clés : Hydrologie / Aride Gebiete / Abflussvolumen / Strukturänderungen / Braided river / Fraktale Analyse / Verblassungs Kompensierungsfaktor / Effektive Fließbreite / Wadi / Flash flood / Fernerkundung / Multi Sensor Approach / FMAI — Hydrology / Arid areas / Structural changes / Braided river / Fractal analysis / Desaturation compensation factor / Effective river width / Discharge volumes / Wadi / Flash flood / Remote sensing / Multi Sensor Approach / FMAI

Présentation (österreichischen Bibliothekenverbundes)

Page publiée le 22 novembre 2015, mise à jour le 13 mars 2019