Post-Fire hidrological and sediment delivery dynamics of two Mediterranean nested catchments
- Publication date
- Publisher
Abstract
A continuous monitoring network of nested catchments
was set
-
up as soon as possible after the
largest wildfire that affected Mallorca, which occurred in July 2013. The Sa Font de la Vila
catchment is a Mediterranean afforested catchment of 4.8 km
2
, which is located in the western
part of the island. Altitude
s range between the 71 to 515 m with an average gradient slope of
38%. The lithology is mainly composed by Keuper clays and loams in the bottom valleys with
gentle gradient slopes ca. <10%. Meanwhile, Raethian dolomites and Lias limestones
predominate in t
he upper parts of the catchment. The intensive agricultural use in the past is
witnessed by the widespread occurrence of traditional soil conservation structures (i.e., terraces
and valley bottom terraces), occupying 65% of the area. It was affected by 2 l
arge wildfires in
the last 20 years, i.e. in 1994 and 2013 affecting 44% and 71% of the area, respectively. The Sa
Murtera is a headwater sub
-
catchment
of 1.2 km
2
representative of lithology, land uses and fire
affection. Altitudes range between the 185 to
515 m with an average gradient slope of 36%. In
October 2013, the outlet of both the Sa Font de la Vila and Sa Murtera was instrumented with a
gauging station, which recorded water level, average turbidity, electric conductivity and
temperature at 15 minu
te intervals (average values based on 1 minute readings). Within the
study area, also precipitation, air temperature and soil moisture content were measured also
continuously with a meteorological station and a humidity probe.
The results
indicate a very
low sediment yield in the two post
-
fire hydrological years, showing
important differences between the two nested catchments, although monitoring problems during
the first year (2013
-
14) caused that results were only available from the Sa Font de la Vila. In
this station, total runoff and sediment yield were 5 mm and 23 t
km
-
2
respectively, with a total
sediment load of 111 t, although 99% was exported in the first event after the wildfire when 50
mm were accumulated in only 15 minutes. During the second post
-
fire year (October 2014
-
July
2015) in Sa Font de la Vila the tota
l runoff was higher with
23
mm. However, the sediment
yield was lower
–
0.5 t km
-
2
–
showing a significant decrease. At Sa Murtera, the
31
m
m of
runoff and 3.3
t km
-
2
of sediment yield showed greater results, indicating that most of the
sediment yield from t
he upstream parts of the catchment must have been deposited before
reaching the outlet of the Sa Font de la Vila. Despite the
fire effects on erosion and delivery
processes,
sediment is therefore progressively trapped along the main channel during its
tran
sport due to the downstream gradient reduction