17 research outputs found
EIN NEUFUND DES MUCICOLEN CHYTRIDIOMYCETEN PLEOTRACHELUS WILDEMANII
Volume: 19Start Page: 431End Page: 43
Potentials and constraints of different type of soil moisture observations for flood simulations in headwater catchments
Flood generation in mountainous headwater catchments is governed by rainfall intensities,
by the spatial distribution of rainfall and by the state of the catchment prior to the rainfall,
e.g. by the spatial pattern of the soil moisture, groundwater conditions, and possibly
snow. The work presented here explores the limits and potentials of measuring soil moisture with
different methods and in different scales and their potential use for flood simulation. These
measurements were obtained in 2007 and 2008 within a comprehensive multi-scale experiment in the
Weisseritz headwater catchment in the Ore-Mountains, Germany. The following technologies have
been applied jointly thermogravimetric method, Frequency Domain Reflectometry (FDR) sensors,
Spatial-Time Domain Reflectometry (STDR) cluster, Ground Penetrating Radar (GPR), airborne
polarimetric synthetic aperture radar (polarimetric-SAR) and Advanced Synthetic Aperture Radar
(ASAR) based on the satellite Envisat. We present exemplary soil measurement results, with spatial
scales ranging from point scale, via hillslope and field scale to the catchment scale. Only the Spatial-
TDR cluster was able to record continuous data. The other methods are limited to the date of over
flights (airplane and satellite) or measurement campaigns on the ground. For possible use in flood
simulation, the observation of soil moisture at multiple scales has to be combined with suitable
hydrological modelling, using the hydrological model WaSiM-ETH. Therefore, several simulation
experiments have been conducted in order to test both the usability of the recorded soil moisture data
and the suitability of a distributed hydrological model to make use of this information.
The measurement results show that airborne-based and satellite-based systems in particular provide
information on the near surface spatial distribution. However, there are still a variety of limitations,
such as the need for parallel ground measurements (Envisat-ASAR), uncertainties in polarimetric
decomposition techniques (Polarimetric-SAR), very limited information from remote sensing methods
about vegetated surfaces, and the non-availability of continuous measurements.
The model experiments showed the importance of soil moisture as an initial condition for physically
based flood modelling. However, the observed moisture data reflect the surface or near-surface soil
moisture only. Hence, only saturated overland flow might be related to these data. Other flood
generation processes influenced by catchment wetness in the subsurface, such as subsurface storm
flow or quick groundwater drainage cannot be assessed by these data. One has to acknowledge that, in
spite of innovative measuring techniques on all spatial scales, soil moisture data for entire vegetated
catchments are still today not operationally available. Therefore, observations of soil moisture should
primarily be used to improve the quality of continuous, distributed hydrological catchment models
that simulate the spatial distribution of moisture internally. Thus, when and where soil moisture data
are available, they should be compared to their simulated equivalents in order to improve the
parameter estimates and possibly the structure of the hydrological model