The identification of the moment when direct flow ends and baseflow begins is one of the biggest challenges of hydrological cycle modeling. The objectives of this research were: to characterize the recession curves (RC) and to separate the components of the hydrograph in a compact model. The RC were extracted from time series in three subwatersheds in Mexico. An expo-linear model was adapted and fitted to the master recession curves to find the transition point of the hydrograph and separate the baseflow. The model discriminated the RC in two decreasing ratios: one linear associated to the direct flow, and one exponential linked to the baseflow. The transition point between these two flows was obtained analytically by equaling both ratios. The derivation of a model parameter allowed to find the maximum points in the hydrometric time series, which were the criterion to separate the baseflow. The application of this model is recommended in the analysis of RC with different magnitudes from the flexibility and attachment to the fundaments of exhaustion of a reservoir.
Traditional depth-averaged morphodynamic models for turbidity currents usually focus on the propagation of currents after plunging. However, owing to the unsteady characteristic of the plunge point locations and the tough conditions of field measurement within the plunge zone in a reservoir, it is difficult in practice to directly provide upstream boundary conditions for these models. A one-dimensional (1D) morphodynamic model coupling open-channel flow and turbidity current in a reservoir was proposed to simulate the whole processes of turbidity current evolution, from formation and propagation to recession. The 1D governing equations adopted are applicable to open-channel flows and turbidity currents over a mobile bed with irregular cross-section geometry. The coupled solution is obtained by a two-step calculation mode which alternates the calculations of open-channel flow and turbidity current, and a plunge criterion is used to determine the location of the upstream boundary for the turbidity current, and to specify the corresponding boundary conditions. This calculation mode leads to consecutive predictions of the hydrodynamic and morphological factors, from the open-channel reach to the turbidity current reach. Turbidity current events in two laboratory experiments with different set-ups were used to test the capabilities of the proposed model, with the effect of free-surface gradient also being investigated. A field-scale application of the coupled model was conducted to simulate two turbidity current events occurring in the Sanmenxia Reservoir, and the method for calculating the limiting height of aspiration was adopted to estimate the outflow discharge after the turbidity currents arrived in front of the dam. The predicted plunge locations and arrival times at different cross-sections were in agreement with the measurements. Moreover, the calculated interface evolution processes and the sediment delivery ratios also agreed generally with the observed results. Therefore, the 1D morphodynamic model proposed herein can help to select the design capacity of the outlets, and optimize the procedure for sediment release in reservoirs.
Stabilisation of banks is a very important, but often disregarded stage of setting a newly built water structure in operation. The descibed type of stabilisation creates in-time appropriate bank reinforcement (here, regardless the dam) that may prevent creation and development of subsequent abrasive or erosive damage. Here are presented first experiences with the stabilisation use of so called ''earth armour'' in an interaction with a root system of suitable woody plants on an operational experimental surface. This surface is the endangered, at present already very abraded shore of the Bílovec irrigation reservoir in South Moravia. and Stabilizace břehů je velmi důležitou, mnohdy však podceňovanou součástí uvedení nově budovaného vodního díla do provozu. Právě včasná stabilizace, tedy realizace vhodného opevnění břehů (nemluvíme zde o hrázi) může zabránit vzniku a rozvoji následného abrazního, či erozního poškození. Příspěvek prezentuje první zkušenosti se stabilizačním využitím tzv. ''zemní armatury'' za spolupůsobení kořenového systému vhodných dřevin na provozované experimentální ploše. Touto plochou je ohrožené a dnes již silně abradované pobřeží závlahové nádrže Bílovec na jižní Moravě.
This study introduces the possibility theory, the foundations of which were laid by Zadeh (1978), using the fuzzy sets theory, and it clarifies its basic concepts and principles. The study was aimed to verify methodological procedures of the possibility theory in current water management tasks. The case study examined possibilities of simultaneous occurrence of several causal factors of hydrological situations, and their impacts on water sources in changed climatic conditions. The second task was focused on the assessment of effects of climatic change on the storage function of the Šance reservoir in the Odra River catchment. In the end, problems open up for further research are outlined. and Studie uvádí do problematiky teorie možnosti, jejíž základy položil Zadeh (1978) s využitím teorie fuzzy množin, a objasňuje její základní pojmy a principy. Cílem studie bylo ověřit metodické postupy teorie možnosti na aktuálních vodohospodářských úlohách. V případové studii se zkoumaly možnosti současného nastání několika příčinných faktorů hydrologických situací a jejich dopady na vodní zdroje ve změněných klimatických podmínkách. Ve druhé úloze byly posuzovány dopady klimatické změny na zásobní funkci nádrže Šance v povodí Odry. V závěru se uvádějí problémy otevřené pro další výzkum.
The Joaquín Costa reservoir contains a mixed fish assemblage of native and exotic species. Feeding habits and feeding relationships of species in the fish assemblage were analysed over a one year cycle. Differences in diet composition were found both between species and within species among seasons. Food overlap and trophic similarity among species also showed seasonal variations. Cluster analysis differentiated four groups of predominant diet: (1) macroinvertebrates (trout and largemouth bass), (2) detritus (nase), (3) cladoceran crustaceans and (4) an omnivorous feeding regime, with large seasonal variations in food habits. Food of fish species included in groups 3 and 4 (roach, white bream, barbel, common and mirror carp) varied seasonally. Using graphical models of feeding strategies, similarity indexes, cluster and multivariate analyses based on the relative importance of food categories in the diet of the species, we illustrate that the fish assemblage showed food resource partitioning according to food habits and foraging habitats within the reservoir.
Dissolved organic carbon (DOC) transported by rivers represents an important link between carbon pools of terrestrial and oceanic ecosystems. However, it is unclear how frequent DOC must be sampled to obtain reasonable load estimates. Here, we used continuous records of the specific UV absorption coefficient (SAC) and discharge from a headwater stream at the Ore Mountains (Germany) to calculate load errors depending on DOC sampling frequency. SAC was used as a proxy for DOC. The results show that the load was underestimated by 13-19% with monthly, 10-13% with bi-weekly and 7-9% with weekly DOC samplings, respectively. We conclude that collecting additional data from high discharge events decrease the error significantly.
The construction of dams is a significant environmental issue due to its impacts on native fish populations and riparian animals and habitats. The response of otters Lutra lutra Linnaeus, 1758 to such disturbances was evaluated using the Aguieira reservoir (Central Portugal) and its associated tributaries as a model. Visiting rates suggested the presence of resident otters, both in the reservoir and in two of the tributaries. There was a significant negative influence of water level and precipitation in the number of spraints found around the reservoir. Nevertheless, marking behaviour was positively related to substrate and negatively related to vegetation cover, though these variables explained only a small amount of variation in otter signs. In the tributaries, although precipitation also negatively affected the number of otter signs found, the availability of rocks in the riverbed and the presence of refuge had a positive influence in marking behaviour. Prey composition and abundance differed between reservoir and tributaries, but the main otter prey in both systems was the pumpkinseed, which is very abundant in the reservoir. Results demonstrate that otters regularly use the Aguieira reservoir, which provides a good prey base, and the associated tributaries, which provide shelter.