This project deals with the possible amount of floating debris as a result
of landslide activity along the Lule river. Some kinds of debris can be
considered harmless while others may be harmful to the dam by clogging the
spillways, depending on their size and density. In any case different forms
of floating debris have different impacts, which is why both, amount and
distribution of characteristics, are to be determined in this study.
Using all the input data described in chapter 2 a basic impression about
the slope stability situation in the working area was gained. Those
locations, well known already at that point, gave a comparatively good
estimation of the slope stability in these limited areas, but in order to
get a slope stability assessment over the entire working area it was
necessary to find correlations between slopes and apply characteristics
known for some locations onto slopes with similar features in terms of
geometry, material or vegetation. The field investigations performed during
that stage offered opportunities to collect data not only for these tasks,
but also about the vegetation characteristics of the working area. Four
vegetation classes were defined during the field work. Already during that
stage the number of dams that might become confronted with significant
amounts of floating debris was narrowed down to only three, namely
Vittjärv, Laxede and Porsi. With the help of the data collected during the
fieldwork all potentially hazardous locations were classified in terms of
extensions, geometrical characteristics and vegetation.
Based on the findings during the field investigations the total potentially
unstable surface area was calculated to a value of 326605 m². A value which
was slightly corrected later on to 324585 m², after the SlopeW calculations
indicated that not always the entire slope has to be considered unstable
and that the land surface right behind the crest of a slope might have to
be considered unstable terrain as well.
Calculations using the SlopeW software were performed mainly in order to
find conditions under which slopes can be considered stable or unstable
considering water levels in a 10.000 year flood event. Out of the 28
locations identified during the fieldwork as much as 25 were considered
potentially unstable.
Finally the information concerning extent and vegetation class of these 25
locations was combined in order to compute values for the total amount of
trees over the entire unstable surface area, which resembles the amount of
floating debris. The total amount of trees, as it can be observed in
appendix III, was highest for the Porsi dam (46699 logs) followed by
Vittjärv (23257) and finally Laxede (14021). On the first impression the
results might suggest that Porsi should require most attention in terms of ...
