The role of the water movement and retention during extreme runoff formation was demonstrated in the Modrý Důl catchment (Krkonoše Mts., Czech Republic). A cyclone, which moved from Hungary to Poland, caused an extreme rainfall (120 mm) and subsequent extreme runoff in August, 2002. The precipitation, discharge, air and soil temperatures, tensiometric pressure, and soil moisture were recorded. The maximum retention capacity of the catchment was evaluated (70 mm). Depending on the actual retention capacity and the precipitation amount, two situations were recorded: (1) the precipitation amount lower than the actual retention capacity where the precipitation was fully absorbed in the catchment and the discharge in to the stream was not influenced by rain, (2) the precipitation amount higher than the actual retention capacity where the precipitation caused a saturation excess of the soil profile, generating extreme outflow into the stream. Neither the soil cover in the catchment or fluvial deposits along the Modrý potok stream were able to retain the extreme rain and inhibit the catastrophic flood.

Abstract:The purpose of the pilot project Senotín (1993Senotín ( -2000 was to prove the methods of revitalization of sub-mountain headwater area (0.38 km 2 ) in the Novobystřická Vysočina Highland (610-725 m a. s. l.) in the CzechRepublic. This area was tile-drained and ploughed in 1985. Seven underground clay shields newly constructed in 1995 stopped the function of the tile drainage. Four balks prevented the surface and subsurface runoff. These adaptations improved water retention capacity of the whole catchment, which is demonstrated using an example of runoff formation in the revitalized area. A typical storm rain (total 15 mm, duration 5.6 h, max. intensity 4 mm/20 min) and the consequent runoff was analysed, including the role of the soil in the runoff retardation and water retention. The runoff started in two hours since the rain beginning. The retention reached 98% of the rain total. The runoff lasted for 85 h. The concave-upward shape of the falling hydrograph limb indicates that the maximum retention capacity of the studied catchment is high.