The transport of wood material in rivers has been the subject of various studies in recent years. Most research has focused on the ecological and geomorphologic role of wood, its recruitment processes and spatial distribution in streams. In this study, we focused on wood transport dynamics, and we have developed a numerical model to simulate wood transport coupled with a two-dimensional (2D) hydrodynamic model. For this purpose, wood drag forces were incorporated as additional source terms into the shallow water equations, which are solved together with wood transport by using the finite volume method. This new tool has been implemented as a computational module into ?Iber?, a 2D hydraulic simulation software. The new module analyzes the initial motion threshold of wood based on the balance of forces involved in the wood?s movement, and computes the position and velocity of differently shaped logs using a kinematic approach. The method also considers the interaction between the logs themselves and between the logs and the channel walls or boundaries. Flume experiments were used in a straight channel with obstructions to validate the model?s capacity to accurately reproduce the movement of floating logs
Marti-Cardona B, López-Martínez C, Dolz-Ripolles J (2012) Local texture stationarity indicator for filtering DoÑana wetlands SAR images., IGARSS pp. 4903-4906 IEEE
ASTER and Landsat images were used for mapping the water surface temperature in the Sobrón, Mequinenza and Ribarroja reservoirs in the Ebro River, Spain. The spatially continuous information in these maps reveals the impact of the reservoir on the river natural thermal gradient in two different periods of the year. It also evidences the thermal impact intensity and extent of the refrigeration flow discharge from a nuclear power plant located on the river bank.
The high spatial resolution images of the Ribarroja reservoir, acquired by the airborne hyperspectral TASI sensor, show spatial patterns which complemented the in-situ point measurements and contributed valuable data for validating the three-dimensional thermo-hydrodynamic model of the reservoir.
Marti-Cardona B, López-Martínez C, Dolz-Ripolles J (2009) Analysis of ASAR/Envisat Polarimetric Backscattering Characteristics of Doñana National Park Wetlands., IGARSS (3) pp. 721-724 IEEE
Marti-Cardona B, López-Martínez C, Dolz-Ripollés J (2014) Local Isotropy Indicator for SAR Image Filtering: Application to Envisat/ASAR Images of the Doñana Wetland (November 2014), IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 8 (4) pp. 1614-1622 IEEE
This paper explores a geometrical and computationally simple operator, named Ds, for local isotropy assessment on SAR images. It is assumed that isotropic intensity distributions in natural areas, either textured or nontextured, correspond to a single cover class. Ds is used to measure isotropy in processing neighborhoods and decide if they can be considered as belonging to a unique cover class. The speckle statistical properties are used to determine suitable Ds thresholds for discriminating heterogeneous targets from isotropic cover types at different window sizes. An assessment of Ds as an edge detector showed sensitivities similar to those of the ratio edge operator for straight, sharp boundaries, centered in the processing window, but significantly better sensitivity for detecting heterogeneities during the window expansion in multiresolution filtering. Furthermore, Ds presents the advantage versus the ratio edge coefficient of being rotationally invariant, and its computation indicates the direction of the main intensity gradient in the processing window. The Ds operator is used in a multiresolution fashion for filtering ASAR scenes of the Doñana wetland. The intensities in isotropic areas are averaged in order to flatten fluctuations within cover types and facilitate a subsequent land cover classification. The results show high degree of smoothing within textured cover classes, plus effective spatial adaptation to gradients and irregular boundaries, substantiating the usefulness of this operator for filtering SAR data of natural areas with the purpose of classification.
We used Landsat 8 thermal images to study the longitudinal
patterns of surface water temperature in the
Mequinenza reservoir, Spain, in 2016. We also estimated
its thermal impact on the river by comparing
upstream and downstream temperatures.
Los humedales de alta montaña conocidos como bofedales constituyen un hábitat indispensable para numerosas especies, entre las
que se encuentran los camélidos. En las últimas décadas se ha observado la recesión de algunos bofedales y lagunas andinas. En la
cuenca del rio Locumba, Perú, se ha postulado que esta recesión puede estar ligada al consumo de los recursos hídricos para usos
agrícolas y mineros. El estudio que aquí se presenta utiliza imágenes satelitales para determinar la superficie de agua en las
principales lagunas naturales, así como el área ocupada por los bofedales y la superficie agrícola,desde la década de los 70 hasta la
actualidad. La tarea incluye además el cómputo de la evapotranspiración real en las áreas cultivadas de la cuenca a partir de dos
imágenes recientes correspondientes a los períodos seco y húmedo. La teledetección aporta de este modo una serie histórica de
datos espaciales cuantitativos de gran valor para determinar la variación de cubiertas naturales e investigar sus causas.
Doñana National Park wetlands are located in southwest Spain, on the right bank of the Guadalquivir River, near the Atlantic Ocean coast. The wetlands dry out completely every summer and progressively flood again throughout the fall and winter seasons. Given the flatness of Doñana?s topography, the wind drag action can induce the flooding or emergence of extensive areas, detectable in remote sensing images. Envisat/ASAR scenes acquired before and during strong and persistent wind episodes enabled the spatial delineation of the wind-induced water displacement. A two-dimensional hydrodynamic model of Doñana wetlands was built in 2006 with the aim to predict the effect of proposed hydrologic restoration actions within Doñana?s basin. In this work, on-site wind records and concurrent ASAR scenes are used for the calibration of the wind-drag modeling by assessing different formulations. Results show a good adjustment between the modeled and observed wind drag effect. Displacements of up to 2 km in the wind direction are satisfactorily reproduced by the hydrodynamic model, while including an atmospheric stability parameter led to no significant improvement of the results. Such evidence will contribute to a more accurate simulation of hypothetic or design scenarios, when no information is available for the atmospheric stability assessment.
ASTER images were used for mapping the water surface temperature in the Mequinenza and the Ribarroja
reservoirs, on the Ebro River. The spatially continuous information of these maps reveals the impact of the reservoir on
the river?s natural thermal gradient in two different periods of the year. The high spatial resolution images of the Ribarroja
reservoir, acquired by the airborne hyperspectral TASI sensor,
Pillco Zolá Ramiro, Bengtsson Lars, Berndtsson Ronny, Marti-Cardona Belen, Satgé Frederic, Timouk Franck, Bonnet Marie-Paule, Mollericon Luis, Gamarra Cesar, Pasapera José (2018) Modeling Lake Titicaca Daily and Monthly Evaporation, HYDROLOGY AND EARTH SYSTEM SCIENCES
COPERNICUS GESELLSCHAFT MBH
Lake Titicaca is an important water ecosystem of South America. Due to uncertainties in estimating the evaporation losses from the lake, surface water storage calculations are uncertain. In this paper, we try to improve evaporation loss estimations by comparing different methods to calculate daily and monthly evaporation from Lake Titicaca. These were: water balance, heat balance, mass transfer method, and the Penman equation. The evaporation was computed at daily time step and compared with estimated evaporation using mean monthly meteorological observations. We found that the most reliable method of determining the annual lake evaporation is using the heat balance approach. To estimate the monthly lake evaporation using heat balance, the heat storage changes must be known in advance. Since convection from the surface layer is intense during nights resulting in a well-mixed top layer every morning, it is possible to determine the change of heat storage from the measured morning surface temperature. The mean annual lake evaporation was found to be 1700mm. Monthly evaporation computed using daily data and monthly means resulted in minor differences.
Thermal images of water bodies often show a radiance gradient perpendicular to the banks. This effect is frequently
due to mixed land and water thermal pixels. In the case of the Landsat images, radiance mixing can also
affect pure water pixels due the cubic convolution resampling of the native thermal measurements. Some authors
recommended a general-purpose margin of two thermal pixels to the banks or a minimum river width of three
pixels, to avoid near bank effects in water temperature retrievals. Given the relatively course spatial resolution of
satellite thermal sensors, the three pixel margin severely restricts their application to temperature mapping in
many rivers. This study proposes a new algorithm to enhance the retrieval of stream surface temperature using
Landsat 8 thermal data, although it is also applicable to Landsat 7 and Landsat 5. The aim is not to perform a
subpixel radiance unmixing but to refine the selection of unmixed, reliable pixels for temperature mapping. For
this purpose, the spatial arrangement of native Landsat thermal pixels is approximated, and pure water pixels in
the downscaled thermal band are selected accordingly. The least-favourable cubic convolution near-bank radiance
mixing is simulated on image basis. Only pure thermal water pixels unaffected by the simulated worstcase
resampling are selected. The algorithm allowed retrieving water surface temperature in reaches down to
120m wide, clearly improving the existing three pixel, i.e. 300m for Landsat 8, recommendation. The enhancing
algorithm was applied to a reach in the Ebro River reach, Spain. It provided spatially distributed temperatures in
narrow parts, upstream and downstream of a wide reservoir, offering new insight of the overall impact of the
reservoir over the river thermal regime.
Pillco Zolá Ramiro, Bengtsson Lars, Berndtsson Ronny, Marti-Cardona Belen, Satgé Frederic, Timouk Franck, Bonnet Marie-Paule, Mollericon Luis, Gamarra Cesar, Pasapera José (2019) Modelling Lake Titicaca's daily and monthly evaporation, Hydrology and Earth System Sciences 23 (2) pp. 657-668
Lake Titicaca is a crucial water resource in the
central part of the Andean mountain range, and it is one
of the lakes most affected by climate warming. Since surface
evaporation explains most of the lake?s water losses,
reliable estimates are paramount to the prediction of global
warming impacts on Lake Titicaca and to the region?s water
resource planning and adaptation to climate change. Evaporation
estimates were done in the past at monthly time
steps and using the four methods as follows: water balance,
heat balance, and the mass transfer and Penman?s equations.
The obtained annual evaporation values showed significant
dispersion. This study used new, daily frequency hydrometeorological
measurements. Evaporation losses were calculated
following the mentioned methods using both daily
records and their monthly averages to assess the impact of
higher temporal resolution data in the evaporation estimates.
Changes in the lake heat storage needed for the heat balance
method were estimated based on the morning water surface
temperature, because convection during nights results in a
well-mixed top layer every morning over a constant temperature
depth. We found that the most reliable method for determining
the annual lake evaporation was the heat balance
approach, although the Penman equation allows for an easier
implementation based on generally available meteorological
parameters. The mean annual lake evaporation was found
to be 1700mmyearÉ¹. This value is considered an upper
limit of the annual evaporation, since the main study period
was abnormally warm. The obtained upper limit lowers by
200mmyearÉ¹, the highest evaporation estimation obtained
previously, thus reducing the uncertainty in the actual value.
Regarding the evaporation estimates using daily and monthly
averages, these resulted in minor differences for all methodologies.