Soil erosion decreases soil fertility of the uplands and causes siltation of lakes and reservoirs; the lakes and reservoirs in tropical monsoonal African highlands are especially affected by sedimentation. Efforts in reducing loads by designing management practices are hampered by lack of quantitative data on the relationship of erosion in the watersheds and sediment accumulation on flood plains, lakes and reservoirs. The objective of this study is to develop a prototype quantitative method for estimating sediment budget for tropical monsoon lakes with limited observational data. Four watersheds in the Lake Tana basin were selected for this study. The Parameter Efficient Distributed (PED) model that has shown to perform well in the Ethiopian highlands is used to overcome the data limitations and recreate the missing sediment fluxes. PED model parameters are calibrated using daily discharge data and the occasionally collected sediment concentration when establishing the sediment rating curves for the major rivers. The calibrated model parameters are then used to predict the sediment budget for the 1994–2009 period. Sediment retained in the lake is determined from two bathymetric surveys taken 20 years apart whereas the sediment leaving the lake is calculated based on measured discharge and observed sediment concentrations. Results show that annually on average 34 t/ha/year of sediment is removed from the gauged part of the Lake Tana watersheds. Depending on the up-scaling method from the gauged to the ungauged part, 21 to 32 t/ha/year (equivalent to 24–38 Mt/year) is transported from the upland watersheds of which 46% to 65% is retained in the flood plains and 93% to 96% is trapped on the flood plains and in the lake. Thus, only 4–7% of all sediment produced in the watersheds leaves the Lake Tana Basin.
Daily emigrations of non-native age 0 and age 1 potamodromous (fluvial) rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta
were investigated in two Missouri River tributaries, USA over the period 1998-2002. The patterns of emigration for both age 0 and age 1 fish of both species were highly variable, sometimes showing bimodal (spring and fall) emigrations and other times less well defined patterns. Peak timing of age 0 emigration was also highly variable among years (up to 5 months) and more
variable than the timing of age 1 emigrations (more than two months). Emigrations were preferentially associated with increasing photoperiod before June 22, with water temperatures from 7.5 to 12.5 °C, and often followed sudden increases in stream discharge. More emigrations were associated with the new moon phase as opposed to the full moon phase. In an analysis of models of emigration (2 rivers × 2 species × 2 ages/species
× 31 model combinations for five categorical variables – year, temperature, discharge, moon phase, and photoperiod) using the information-theoretic approach, none of the models were especially effective at explaining emigrations; for the 16 models (i.e. the two with the lowest AIC per river, species and age), no corresponding multiple linear regression model explained more than 41 % of the emigration, and most other models explained considerably less. Results of this study suggest that emigrations of both brown and rainbow trout as part of their fluvial life histories are potentially influenced by a variety of environmental factors, and can be expected to show considerable variation yearly based on the complex, poorly defined genetic origins of the fish and the highly variable climatic conditions associated with the Missouri River Basin.
The experimental basins in the Jizera Mountains were established at the beginning of the 1980th as a result of the forest devastation due to acid rain and repercussions of following human activities during its disposal with the aim to gain data for the quantification of runoff conditions changes in a changing environment. Seven small catchments with an area from 1.87 km2 to 10.6 km2 are situated in the spring regions in an elevation from 700 m a.s.l. to 1100 m a.s.l. in the catchments of the Černá Nisa, Kamenice, Jizerka and Směda streams. The long-term average annual temperature in the elevation of 780 m a.s.l. is +4.4°C, the long-term annual precipitation sum fluctuates between 1300 mm and 1800 mm. The Jizera Mountains are known for numerous intensive rainfalls in the summer period. The administrator of the experimental basins is the Czech Hydrometeorological Institute (CHMI), Department of Hydrological Research, Experimental Base Jablonec nad Nisou, which performs all operative activities and basic processing of data. In the basins, the monitored elements are water stages and discharges in rivers, surface water quality, rainfall, snow depth and snow water equivalent and climatological parameters. The following contribution gives an overview of information obtained from the hydrological research in the period 1981 - 2004. and Příspěvek se zabývá přehledem poznatků z hydrologického výzkumu v období let 1982-2005 v experimentálních povodích Českého hydrometeorologického ústavu (ČHMÚ) v imisně poškozené oblasti Jizerských hor. Základnu tvoří 7 malých povodí s rozlohou od 1,87 km2 do 10,6 km2 celkové plochy 37 km2 . Všechna povodí leží ve vrcholové části Jizerských hor v Chráněné krajinné oblasti Jizerské hory, na rozvodí řek Labe a Odry. Nadmořská výška povodí se pohybuje mezi 700 až 1100 m. Správcem povodí je Oddělení hydrologického výzkumu, pracoviště Jablonec nad Nisou. Zpočátku byly práce zaměřeny převážně na získání co největšího počtu informací o srážkách, sněhu, množství a jakosti povrchové vody. Po roce 1995 byl monitoring rozšířen na více parametrů hydrologické bilance, sledování klimatických prvků a složek hydrologického procesu. Následně byl upřesňován jejich režim i jejich prostorové rozložení. Byla studována problematika rozdílnosti akumulace a odtávání sněhu na mýtině a v lese a odtoková a kvalitativní odezva na srážkovou činnost a tání sněhu. Za pomoci hydrologických a chemických modelů byly hledány odhady změn jejich závislosti na změně vegetačního pokryvu.
The effect of water temperature and flow on the migration of fish was observed using weekly inspections of a fishpass on the lowland section of the River Elbe (Střekov, Czech Republic) from spring to fall 2003 and 2004. The effect was examined separately for immature (up to 2 years old) and adult fish and also the most abundant species (roach Rutilus rutilus, bleak Alburnus alburnus, chub Squalius cephalus, gudgeon Gobio gobio). More than 13 thousand fish from 23 species were recorded in the fishpass during both years. The highest levels of fish occurrence in the fishpass were observed during the spring spawning migrations of adults (April-May) as well as during the late summer and fall migrations of adult and immature fish (September-November). While the total number of both fish age categories was significantly related to the interaction of water temperature and flow, however, responses of individual species and age categories differed from each other. The numbers of adult bleak, chub and gudgeon increased with higher temperature. The maximum numbers of adult bleak migrated at medium values of temperature (15-20 °C) and flow (140-270 m3 s–1). The abundances of adult chub and adult plus immature gudgeon were higher with higher flow. The numbers of immature bleak and chub decreased with increasing flow. The numbers of adult and immature roach were influenced only by water flow with maximal numbers migrating under medium values of flow. Generally, we observed that immature fish and small- and middle-sized species required lower values of water flow than adult fish or large species to facilitate their movement. The exception was gudgeon, which required higher values of flow for its migration, a feature that could be related to its bottom dwelling nature or rheophily.
This research was focused on the relationship between river discharge and organism drift. It was carried out for three years in a small heavily modified river in Saxony (Germany). The amount and species composition of drifting invertebrates were observed, depending on discharge and flow velocity. A station was installed where the flow velocity was continually measured and drifting organisms were caught with nets. An inventory of the aquatic community (benthic invertebrates) was taken to determine the species living in the river at the research station. The highest drift density measured was 578 organisms per m3 at a flow velocity of 0.90 m s-1 , the mainly drifting organisms were Chironomidae. Different organisms groups started drifting at different flow velocities. Heavy impacts, such as dredging the river and flood waves, affected the aquatic ecosystems and severely changed the aquatic community regarding the number and the diversity. Some of the aquatic invertebrates such as the Anthothecata completely disappeared after dredging. It was found that many different terrestrial organisms were part of the drift. The typical family of soil biota Collembola represented the largest share.
The aim of the paper is to analyse a possible teleconnection of AO (Artic Oscillation), SO (Southern Oscillation), PDO (Pacific Decade Oscillation), NAO (North Atlantic Oscillation) and QBO (Quasi Biennial Oscillation) phenomena with long-term streamflow fluctuation in Hron River basin (Central Slovakia). The spectral analysis shows that for the series of AO, NAO, SO, and PDO indexes we can identify the ca 2.4-; 3.6-; 7.8-; 14-; 21-;30- and 36-yr cycles. The coincident cycles were found in the monthly discharge time series from the Hron basin (period 1931-2000) using combined periodogram method. As these periods were found in almost all discharge series analysed within very different geographical zones, it can be considered as the general regularity on the earth. The regularity is related to general oceanic and atmospheric circulation, part of which are also the SO, AO, PDO and NAO phenomena. and Cieľom predloženej štúdie je analýza možných telekonekcií Arktickej oscilácie (AO), Južnej oscilácie (SO), Tichomorskej dekádnej oscilácie (PDO), Severoatlantickej oscilácie (NAO) a Kvázi dvojročnej oscilácie (QBO) s viacročnými cyklami priemerných ročných prietokov v povodí rieky Hron (stredné Slovensko). Spektrálnou analýzou časových radov AO, NAO, SO, a PDO indexov boli nájdené nasledujúce viacročné cykly kolísania indexov: ca 2,4; 3,6; 7,8; 14; 21; 30 a 36 rokov. Metódou kombinovaného periodogramu boli nájdené zhodné cykly kolísania viacročných suchých a mokrých období i v mesačných prietokových radoch z povodia Hrona (1930-2000). Keďže tieto periódy boli nájdené vo všetkých prietokových radoch z rôznych geografických zón, môžu byť považované za všeobecný jav na Zemi. Toto pravidelné opakovanie mokrých a suchých období súvisí so všeobecnou cirkuláciou oceánov a atmosféry, súčasťou ktorých sú i SO, AO, PDO, NAO a QBO javy.
This paper is aimed at differences in designs of spiral case and impeller of mixed flow pump with regard to suppression of Y-Q characteristic curves instability, pressure pulsations and especially to achieving necessary delivery head. The differences between new and old conception will be explained. The reasons of these differences with regard to flow in pump interior, hydraulic losses, static pressures and velocities will be explained as well.
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.