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