Abstract:Tile drainage water temperatures and discharge rates were measured in five highland watersheds of which most are underlain by acid crystalline rock. One of them, Dehtáře in the Bohemo-Moravian highland (Czech Republic), was studied in greater detail. The aim was to evaluate water temperature monitoring as a means of determining the source and pathway of drainage runoff during high-flow events. Rapid increase in drainage discharge was accompanied by rapid change in water temperature. In winter, the rising limb of the hydrograph was accompanied by a decrease in temperature, and the falling limb was associated with a corresponding temperature increase. In summer, the trends were reversed. These data suggest that the water temperature changes are caused by the fastest component of drainage runoff, water from a precipitation event or snowmelt, which can be separated from the remainder of the hydrograph. Measurements of hydraulic conductivity, soil moisture content, soil temperature, and groundwater table level indicate that the major portion of the event water causing this effect infiltrates in the watershed recharge zone where soils are permeable, enters the weathered bedrock, flows preferentially and rapidly down the slope along disjoint fissures in the bedrock, finally emerging as ascending springs, and is, for the most part, intercepted by the tile drainage systems.
Abstract:The changes in water quality caused by grassing of arable land followed by the reduction in the use of fertilisers after 1989 are demonstrated on an example of two tile-drained subcatchments in spring areas in the Šumava Mountains. The original water quality monitoring was performed in the mid-1980s, at the time when the area was used as tile-drained arable land.
Changes in land use and runoff characteristics in Otava river basin and its two subcatchment (Volšovka and Vydra) were examined. The goal was to find out how water retention have responded to changes in landscape management in Šumava mountains and foothills since the year 1970. There were two basic levels of changing land use -(a) conversion of arable land with varying intensity at different management of intensive and extensive grassland, (b) deforestation of large areas of indigenous mostly spruce monocultures and their transfer to the shrub and herbaceous vegetation covering the surface with a discontinuous vegetation. Water retention in Šumava mountains is locally reduced due to vulnerability of monoculture spruce forests by natural disasters (windstorms), diseases and pests. A positive effect of current agricultural management in the Šumava foothills on the reduction of direct runoff during intense rainfall was confirmed.Key words: land use, water retention, direct runoff, runoff CN, ŠumavaAbstrakt: Článek řeší změnu využití území a odtokových charakteristik v povodí řeky Otavy a jeho dvou subpovodích (povodí řeky Volšovky a Vydry). Cílem práce bylo zjistit, jak se změnila retence vody v krajině společně se změnou využití území v horských partiích a podhůří Šumavy od roku 1970. Změna využití území probíhala dvěma hlavními směry -(a) Převod orné půdy s různou intenzitou hospodaření na různě intenzivní či extenzivní louky a pastviny, (b) Odlesňování rozsáhlých ploch původních většinou smrkových monokultur a jejich převod na křovinatou a bylinnou vegetaci s nesouvislým pokryvem povrchu. V horských polohách Šumavy je retence vody místy snižována v důsledku zranitelnosti smrkových monokulturních lesů přírodními katastrofami (vichřice), nemocemi a škůdci. V podhůří Šumavy byl prokázán pozitivní vliv současného managementu krajiny na snižování přímého odtoku při intenzivních srážkách.
In order to evaluate the proportion of old and new water in drainage runoff, we recorded air temperature, drainage discharge, drainage runoff temperature, soil temperature, precipitation totals, and temperature. The results of separation by temperature were compared with the results of chemical separation using the stable isotopes δ 18O and δ 2H measured in causal precipitation and monitored in drainage runoff. Separation was determined based on precipitation temperature in 18 rainfall–runoff events and on soil temperature in 20 rainfall–runoff events, with no significant difference between results of separation of drainage runoff based on temperature and that based on isotopes. Separation of runoff based on temperature is feasible only for simple isolated rainfall–runoff events as opposed to those involving multiple rainfalls. Time to peak discharge was identified as a viable factor to determine whether to employ separation based on soil temperature or on precipitation temperature. Time to peak discharge showed a strong correlation with the intensity of precipitation. The results suggest that, conditional on analysis of a larger dataset, isotope separation of drainage runoff and, possibly, runoff in watercourses may potentially be replaced with more economical and technically simple measurement of soil and precipitation/air temperature.
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