76 research outputs found
Hydrological processes and their seasonal controls in a small Mediterranean mountain catchment in the Pyrenees
The Vallcebre catchments are located in a middle mountain area of the Pyrenean ranges, built up by sedimentary rocks and loamy soils. The vegetation cover is pastures and forests of <i>Pinus sylvestris</i>, mostly occupying former agricultural terraces. Some relatively small, heavily eroded landscapes (badlands) occur in the catchments, playing a relevant hydrological and geomorphic role. Annual precipitation is 924 mm and potential (reference) evapotranspiration is about 700 mm. Rainfall interception in forests represents about 24% of precipitation; interception rates were similar throughout the seasons because of a compensation between rainfall intensities and atmospheric conditions. Soil moisture showed a temporal pattern characterised by the occurrence of marked deficit periods in summer and also, but less pronounced, in winter. During most of the year, subsurface flows on hillslopes drove the spatial organisation of soil moisture and the occurrence of saturated areas. Nevertheless, this spatial organisation was also controlled by the patterns of vegetation cover. During dry periods, subsurface flow ceased, saturated areas disappeared and the spatial patterns of soil moisture changed. Stream flow from these catchments was dominated by storm flow, and the runoff generating mechanisms showed a clear seasonal pattern, controlled mainly by the soil moisture and the extent of saturated areas. During the dry periods, runoff was produced only on impervious areas and badlands. At the end of the dry periods, some large rainfall events generated significant runoff because of the perched saturation of the shallow soil horizons. Thereafter, runoff generation was dominated by the role of saturated areas. Stream waters in catchments with badlands had very high suspended sediment concentrations. The seasonal pattern of erosion processes in badlands was characterised by physical weathering during winter, regolith breakdown and vigorous hillslope erosion during spring and summer, and efficient transport of sediments in autumn
Análisis de la variabilidad temporal de la infiltración en un gradiente de degradación de usos del suelo en el Pirineo central
20 págs, 4 figs, 5 tablas[ES] Se analiza
la
capacidad
de
infiltración
con
respecto
a
las
condiciones
físicas
superficiales
(humedad
y
resistencia
mecánica)
de
suelos
en
el
Pirineo
Central,
considerando tres
escenarios:
bosque
natural,
campos
abandonados
y
cárcavas.
El
estudio
se
ha
realizado
en
tres
cuencas
experimentales
(San
Salvador,
Arnás
y
Araguás)
situadas
en
un
contexto
geográfico,
geológico
y
climático
similar.
La
información
se
ha
obtenido
mediante
ensayos
con
un
infiltrómetro
de
doble
anillo
entre
otoño
de
2008
y
verano
de
2009.
Los
resultados
sugieren
cierto
efecto
de
las
condiciones
físicas
previas
sobre
la capacidad
de
infiltración.
Sin
embargo,
el
uso
del
suelo
y
la orientación
de
las
laderas
(N‐S) se
han
revelado
los factores más
determinantes.
Esto
se
relaciona
con
la
variabilidad
estacional del
estado
físico
antecedente
y
su
dinámica
durante
los
ensayos.
Las
diferencias
de la
infiltración
asociada
a
la
orientación
de
las
laderas
incluso
pueden
superar
a
las
observadas
entre
usos
del
suelo.[EN] The
infiltration
capacity
has
been
analysed
related
to
the
variation
of
surface
physical
conditions
(moisture
and
mechanical
r esistance)
of
soils
from
the
Central
Spanish
Pyrenees,
taking
into
account
the
most
representative
situations
of
land
uses
and
vegetal
covers.
The
study
was
carried
out
in
three
experimental
catchments,
each
representative
of
different
environments
in
terms
of
soil
use
and
vegetation
cover:
forested
(San
Salvador),
field
abandonment
(Arnás)
and
badlands
(Araguás).
The
three
catchment s
are
located
near by
and
have
similar
geologica l
and
climatic
conditions.
The
study
was
done
through
experimental
infiltration
s et s
using
a
big
double
ring
instrument
(50
cm
water
column
height.
Experiments
were
performed
from
autumn
2008
to
summer
2009.
The
infiltration
process
was
analysed
on
six
land
uses
situations:
bare regolith,
grass
c overed
regolith,
north‐facing
slope
in
forested
soil,
south‐facing
slope
in
forested soil,
north‐facing
slope
in
meadow
soil
and
south‐facing
slope
in
pasture
soil.
Before and
after
each
experiment
soil
was
sampled
in
order
to
estimate
moisture
content
(0‐1,
0‐5
and
5‐10
cm
depth)
and
surface
mechanical
resistance
was
measured
with
the
help
of
a
pocket
penetrometer,
providing
an
idea
a bout
previous
conditions
and
its
variation.
The
results
suggest
a
certain
effect
of
moisture
conditions
on
infiltration
capacity.
However,
soil
use
and
slope
exposition
(North
and
South)
seem
to
be
the
most
determinant
factors.
This
is
related
to
the
seasonal
variability
of antecedent
soil
conditions
and
its
dynamics
during
the
experiments.
The
differences
on
infiltration
capacity
associated
with
slope
e xposition
can
be
higher
than
those
observed
between
land
uses.Este
estudio
se
ha financiado
mediante
fondos
del
proyecto
CETSUS
(CGL2007‐66644‐C04‐01/HID)
del
Plan
Nacional
I+D+I
2004‐207
(Ministerio
de
Ciencia
e
Innovación).
El
mantenimiento
y
parte
de
la
monitorización
de
las
cuencas
experimentales
se
ha
logrado
a
partir
de
la
financiación
proporcionada
por
el
convenio
RESEL (Ministerio
del
Medio
Ambiente‐CSIC). E.
Nadal‐Romero
y
N.
Lana‐Renault
contaron
durante
2009
y
2010
con
un
contrato postdoctoral
del
Ministerio
de
Ciencia
e
Innovación,
mediante
el
Programa
Nacional
de
Movilidad
de Recursos
Humanos
del
Plan
nacional
de
I‐D+I
2008‐2011
y
en
la
actualidad
están
contratadas
gracias
al
programa
Postdoctoral
Juan
de
la
Cierva
(Ministerio
de
Ciencia
e
Innovación).Peer reviewe
La investigación hidrogeomorfológica en cuencas experimentales de montaña media en el Pirineo Central (1996-2014)
10 páginasPeer reviewe
Seasonal differences in runoff between forested and non-forested catchments: a case study in the Spanish Pyrenees
[EN] The hydrological response of two neighbouring catchments in the central Spanish Pyrenees with similar lithology and topography but different land use was compared. One catchment (2.84 km 2 ) was extensively cultivated in the past, and the other (0.92 km 2 ) is covered by dense natural forest. Differences in runoff were strongly related to catchment wetness conditions and showed a marked seasonality: under dry conditions runoff tended to be greater in the former agricultural catchment, whereas under wet conditions it tended to be greater in the forested catchment. One explanation for this switching behaviour could be an increase in the hydrological connectivity within the slopes of the forested catchment as it becomes wetter, which favours the release of large amounts of subsurface flow. Differences in land use (vegetation and soil properties) dictate the contrasting dominant runoff generation processes operating in each catchment, and consequently the differences between their hydrological responses. Key words water yield; seasonal controls; hydrograph characteristics; forestSupport for this research was provided by the following projects: PROBASE (CGL2006-11619/HID), RespHiMed (CGL2010-18374) and MONTES (CSD2008-00040), financed by the Spanish Commission of Science and Technology; ACQWA (FP7-ENV-2007-1), financed by the European Commission; and PI032/08, financed by the Aragón Regional Government. The authors also acknowledge support from RESEL (the Spanish Ministry of the Environment). N. Lana-Renault was the recipient of a research contract (Juan de la Cierva programme) and J. Latron the recipient of a research contract (Ramón y Cajal programme), both funded by the Spanish Ministry of Sciences and Innovation.Peer Reviewe
Geomorphic process signatures reshaping sub‐humid Mediterranean badlands: 1. Methodological development based on high‐resolution topography
High‐resolution topography data sets have improved the spatial and temporal scales at which we are able to investigate the landscape through the analysis of landform attributes and the computation of topographic changes. Yet, to date, there have been only limited attempts to infer key geomorphic processes in terms of contributions to shaping the landscape. Highly erodible landscapes such as badlands provide an ideal demonstration of such an approach owing to the rapid changes observed over a relatively short time frame. In this technical note we present the Mapping Geomorphic Processes in the Environment (MaGPiE): a new algorithm that allows mapping of geomorphic process signatures through analysis of repeat high‐resolution topography data sets. The method is demonstrated in an experimental badland located in the southern central Pyrenees. MaGPiE is a geographic information system (GIS)‐based algorithm that uses as input: (a) terrain attributes (i.e. Slope, Roughness and Concentrated Runoff Index) extracted from digital elevation models (DEMs), and (b) a map of topographic changes (DEM of difference, DoD). Initial results demonstrate that MaGPiE allows the magnitude and the spatial distribution of the main geomorphic processes reshaping badlands to be inferred for the first time
Rainfall kinematics energy effect on physical properties dynamics and crusting of a clayey bare soil
[ES] El abandono de cultivos causa en ocasiones un deterioro progresivo del suelo. El contexto climático
Mediterráneo, por su régimen estacional de precipitaciones, favorece el encostramiento en suelos arcillosos
descubiertos durante ciertas tormentas. El objetivo de este trabajo es diferenciar que factores distinguen dichas
tormentas críticas, por medio de realizar series de simulaciones de lluvia en campo y laboratorio, combinando
diferentes características de la lluvia y condiciones superficiales de un suelo arcilloso. La información hidrológica
y de la dinámica de la rugosidad superficial, asimilada al coeficiente de rugosidad hidráulica de
Manning en dos trabajos, permitió relacionar la agresividad de la escorrentía con las condiciones experimentales.
Los resultados indican un incremento de erosividad de la escorrentía relacionado con el descenso de la
rugosidad superficial y el encostramiento del suelo. Esto puede justificar la aparición de erosión intensa en
suelos arcillosos descubiertos durante determinadas tormentas, capaces de generar pequeños barrancos y
modelar cárcavas.[EN] Field abandonment on the rural landscape some times is associated to progressive soil degradation. T h e
Mediterranean climatic setting, because of its irregular precipitation regime, makes de clayey bare soil prone to the
crusting within certain storms. Nevertheless, it has not been clearly defined yet what conditions differentiates the
said critical storms; this represents the main objective of this work. For this reason some rainfall simulation sets
were performed in the field and laboratory, over a clayey bare soil, combining different rainfall characteristics and
surface soil conditions. The measurements of hydrological responses as well as surface random roughness dynamics,
that has been linked to Manning’s hydraulic roughness coefficient through two sets of relationships proposed
in the studies of Gilley and Finkner (1991) and Mwendera and Feyen (1992), allowed to estimate the runoff erosivity
or drag force in relationships with the experimental soil physical conditions and rainfall characteristics. T h e
results point to a large increase in drag, hence in erosive power of overland flow, reaching values of between 2 and
6 times, within storms mainly associated to dry soil conditions, which are prone to the surface random roughness
reduction and crusting development. These results can justify intense erosion and ephemeral gullies occurrence in
clayey bare soils within-storm, as well as bring some support to the knowledge about progressive badland formation
and development.Los autores expresan su agradecimiento a los
doctores Paolo Bazzoffi y Sergio Pellegrini por
facilitar el acceso a la “Stazione Sperimentale de
Sta Elisabetta”, asimismo agradecen a Luigi
Gabellini el apoyo técnico durante la fase experimental
desarrollada en el campo y a la doctora
Marta Yánez por su colaboración durante algunas
de las simulaciones realizadas en el laboratorio.
Este trabajo ha sido realizado en el marco de los
proyectos: MWISED (EU-ENV4-CT97_687),
HIDROESCALA (REN2000-1709-C04-02 GLO),
TRANSMIN (PPQ2001-2100-C04-01) y PROHISEM
(REN2001-2268-C02-01/HID).Peer reviewe
Uncertainty in the evaluation of sediment yield from badland areas: Suspended sediment transport estimated in the Araguás catchment (central Spanish Pyrenees)
Badlands are important in terms of sediment yield, particularly in mountain areas having subhumid and humid climatic conditions. Various studies concerning erosion and hydrological processes have demonstrated that suspended sediment transport is probably the main process in sediment export from badland areas. In the Araguás catchment (central Pyrenees) there is a statistically significant positive linear relationship between maximum discharge and the maximum suspended sediment concentration (SSC). The high frequency of hyper-concentrated fluxes of SSC (>500g·l-1) recorded at two gauging stations close to badland areas in the Pyrenees (Araguás) and the Alps (Draix) indicates that these fluxes are not uncommon, and suggests that they may transport relatively large suspended particles, especially during extreme floods. In a study involving sampling during two moderate floods (August 2006 and February 2007) in the Araguás catchment it was observed that the mean suspended sediment particle size was significantly greater during the highest SSC conditions. The results showed the great heterogeneity of particle sizes that can affect suspended sediment transport, which is usually estimated from concentration determined from turbidity values obtained using infrared devices and associated with the corresponding discharge value. Infrared turbidimeters have problems in detecting particles with a diameter (D)>0.1mm, although discharge can be evaluated with relative high accuracy. The combination of these factors suggests that the evaluation of sediment yield from badland areas using turbidity values involves significant uncertainty. If most suspended sediment is transported during moderate-high floods, which carry large quantities of suspended particles having D. >0.1. mm, then the sediment yield will be underestimated. The uncertainty can be calculated by determining the percentage and mean diameter of particles not detected, and the specific weight of the material. However, the uncertainty is not linear because of the exponential relationship between increasing diameter and the volume/mass, and consequently the error will increase with the growth in the suspended concentration. In this study the physical factors associated with uncertainty in the estimation of sediment yield were investigated, and quantitative estimates of the errors involved are provided. © 2012 Elsevier B.V.This study was supported by funding from the Spanish “Plan Nacional” projects CETSUS (CGL2007-66644-C04-01/HID), PROBASE (CGL2006-11619/HID) and HIDROCAES (CGL2011-27574-C02-01). The Spanish Environmental Ministry (RESEL) provided specific funding for development and maintenance of the experimental plots and catchments. E. Nadal-Romero was the recipient of a research contract from the Spanish Ministry of Science and Innovation (Programme Juan de la Cierva).Peer reviewe
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