By combining the complementary relationship of evaporation with the coupled long‐term water‐energy balance of Porporato et al. (2004) in a Budyko‐type framework, one can, from atmospheric measurements alone, derive important ecosystem characteristics, such as the mean effective relative soil moisture and the maximum soil water storage, as well as predict changes in the rooting depth of vegetation as a response to climate variations.
Abstract The paper demonstrates that the wind stress curl as an external vorticity source plays an important role in shaping large scale shallow lake circulations. The analysis of purpose-oriented simultaneous wind and current measurements data from the Hungarian part of Lake Neusiedl reasonably fits well the internal boundary layer development theory over the lake surface. A 2-D vorticity formulation of wind-induced flows is used to demonstrate mathematically the IBL-related large scale circulation generation mechanism well reflected in the measured data. Further validation of the findings is carried out by means of simple 2-D numerical flow modelling, in which details on the flow pattern besides the measurement sites could be also revealed. Wind-induced lake circulations linked to IBL development shows a novelty to be implemented in up-to-date numerical flow models.
Natural shallow-flow domains have irregular boundaries which can strongly influence the interior flow field. Here, the nonlinear shallow water equations are solved on adaptive quadtree grids that can approximate any two-dimensional boundary topology and are easy to enrich or coarsen. A special indexing system matches the quadtree structure to conventional finite volume notation. Grid adaptation is controlled by a cell circulation parameter. Simulations of standard test flows are in close agreement with analytical and other numerical data. The sample application of wind-induced circulation in Lake Balaton, Hungary, demonstrates the ability of the model to deal with a complicated shallow-flow geometry.
This paper describes the in-situ implementation of a recently developed bedload transport estimation method, called Acoustic Mapping Velocimetry (AMV). The method combines components and processing protocols from acoustic and image-based methods to provide velocity maps of bedforms migrating in the riverbed. The AMV implementation is illustrated with repeated Multibeam Echo Sounder (MBES) mappings that are acquired along longitudinal swaths over the entire transect of the study river sections. The paper exemplifies AMV implementation case studies leading to the estimation of bedload transport rates in two large sand-bed rivers: the Ohio and Mississippi rivers, in the USA. The analysis associated with these case studies emphasizes the importance of linking the characteristics of the bedform dynamics with the selection of the spatio-temporal parameters used during data acquisition for AMV processing (e.g., required length of the measurement section, and the effect of the time lag between the repeated surveys) for accurate quantification of bedform dynamics. The role of superimposed secondary small bedforms migrating over the large primary ones, in terms of their contribution to the sediment transport, is also discussed. The paper demonstrates the applicability of this novel technique, as a complement or stand-alone method for quantifying bedload transport in large sand-bed rivers, an area where the implementation of conventional methods is difficult and inadequate while the emerging measurement alternatives are not widely recognized yet.
Abstract Trends in monthly evapotranspiration (ET) rates across three watersheds covering the Central Valley in California were calculated by the latest calibration‐free version of the complementary relationship of evaporation for 1979–2015. While a recent study concluded that ET rates of the irrigated fields in the Central Valley were declining in 1981–2007, here an ET trend of about 2.6 ± 12 mm per decade was found over the same period in spite of a drop in precipitation (−22 ± 30 mm per decade) and ET rates (−9.5 ± 10 mm per decade) for the rest of the watersheds, none of them statistically significant. After 2007, the precipitation decline accelerated causing a sharp drop in both irrigated and nonirrigated ET rates across the watersheds. Observations from the California Irrigation Management Information System support the present findings: Under increasing air temperatures, both dew point temperature and relative humidity values increased (at a statistically significant rate) during 1983–2007, while they reversed afterwards, in agreement with the estimated sharp irrigation ET trend decline for the remainder of the study period. Actual (in this case over irrigated fields) and reference ET rates complement each other, that is, they express opposite tendencies, as was demonstrated with California Irrigation Management Information System data, yielding a statistically significant plot‐scale irrigation ET rate increase of 31 to 41 (±17) millimeters per decade for 1983–2007 in accordance with a similar drop in reference ET rates of −28 to −50 (±16) millimeters per decade, depending on whether published monthly or daily values (aggregated to monthly ones after leaving out spurious measurements) were employed.
Waves induced by ship movement might be harmful for the habitat in the littoral zone of rivers due to the temporally increasing bed shear stress, the high-energy breaking waves and the consequently related detachment of benthic animals. In order to understand the complex hydrodynamic phenomena resulting from littoral waves, we present the testing of a novel methodology that incorporates field observations and numerical tools. The study is performed at a section of the Danube River in Hungary and analyzes the influence of different ship types. The field methods consist of parallel acoustic measurements (using Acoustic Doppler Velocimetry (ADV)) conducted at the riverbed and Large Scale Particle Image Velocimetry (LSPIV) of the water surface. ADV measurements provided near-bed flow velocities based on which the wave induced currents and local bed shear stress could be estimated. The LSPIV was able to quantify the dynamics of the breaking waves along the bank. Furthermore, computational fluid dynamics (CFD) modeling was successfully applied to simulate the propagation and the breaking of littoral waves. The used techniques complement each other well and their joint application provides an adequate tool to support the improvement of riverine habitats.
Spatially and temporally distributed in-situ wave data is difficult or expensive to collect, however, such a dataset is important for understanding wave propagation and validating numerical models.Here we explored an alternative to array of underwater pressure gauges, consisting of cheap and easy-to-install ultrasonic wave gauges mounted on tripods above the water surface, measuring the downward distance, equipped with telecommunication modules and solar panels.In a pilot application, these wave gauges were deployed in a shallow lake, and their data was compared to those collected simultaneously with an underwater, upward looking echosounder.The presented network proved to be able to provide an accurate picture of the sea state at a fraction of the cost of a "professional" instrumentation.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)