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Retention potential in river headstream areas

Congress: 2008
Author(s): Jan Kocum, Bohumír Janský
Charles University in Prague Faculty of Science Department of Physical Geography and Geoecology Albertov 6, 128 43 Prague 2, Czech Republic phone: +420 720 303 030, +420 221 951 350 fax: +420 221 951 367 email: kocum1@natur.cuni.cz

Keyword(s): retention potential, peatbogs hydrological function, flood protection, headstream area, ultrasound water level gauge, peak flow, drought
Article:
AbstractIn context of catastrophic floods and extreme droughts in recent years there is an urgent need of solving of flood protection questions and measures leading to discharge increase in dry periods, not using just classical engineering methods but also untraditional practices. There is a new strategy focusing on gradual increase of river catchment retention capacity including the realization of measures as runoff retardation and water retention increase in headstream areas. To increase water retention in Vltava River headstream area (southwestern Czech Republic), the source area of a number of catastrophic flood events in recent years, the detailed analysis of peatbogs hydrological function and qualified reference of measures being implemented at present by the Bohemian Forest National Park Management in connection with former ameliorative channels (made during communist regime) dyking need to be done. The peatbogs influence on runoff conditions is being assessed by detailed comparison of hydrological regimes in two subcatchments with very different peatland proportion. We can reason about the peatbog influence on hydrological process also with respect to its affecting of water quality, respectively to ionic structure of water in periods of high or low discharges. Very favourable conditions for realization of this project currently bear on existence of several water measure profiles with long time series and on using modern equipment and methods including a number of automatic ultrasound water level gauges and shuttle precipitation gauges. Our department can also go upon results of bog pools detailed research that has been carried out in recent years. Thorough analyses of extreme runoff ascending and descending phases carried in profiles closing several subcatchments with different geographical conditions show higher amount of peak flows and their shorter reaction to causal amount of precipitation in the case of highly peaty areas, therefore more distinct runoff variability of streams draining peatland localities. As well, detailed analysis of snow conditions in the study catchment as an important component of rainfall-runoff process is carried out by means of aerial photographic surveying for monitoring of snow cover thickness and of hydrometers for water value determinations. The problem of the peatbogs hydrological function has not been so far fully solved despite a number of domestic and foreign projects and broad debates among experts. It depends on a number of factors considering the type of a peatland, its health state, its rate of anthropogenic impact, etc. In addition to considering the renewal respectively dyking of former channels draining peatbogs we should consider also evaluation of possible former accumulative reservoirs (used for wood floating in former times) restoration which could function for example as dry (green) polders. Using complex system of hydrological models such as rainfall-runoff and routing models with semi-distributed approach we could be able to simulate the runoff process in the source area and to assess the effectiveness of these small accumulation reservoirs. By implementation of these unforceable measures realized in river headstream areas we could contribute to reduction of peak flows and to increase of water resources during extreme droughts in future.
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