Influence of drainage system maintenance on storm runoff from a reforested, waterlogged mountain catchment

Abstract

The maintenance of a drainage system in a waterlogged mountain catchment impacted by earlier harvesting operations was assessed on the basis of a hydrological analysis (hydrological balance, three linear reservoirs method). To restore pre-harvest hydrological conditions, the water-saturated localities were experimentally drained both by restoration of existing ditches and digging of additional open ditches. The rainwater retention of the soil was illustrated by two comparable storm flow events occurring before and after the draining treatment. Pedohydrological analysis revealed the important involvement of static retention in capillary pores in the rainfall-runoff process during rainstorm events. Restoration and addition of the drainage system yield more favourable generation and better proportioned distribution of storm flow discharge. There would be no danger of water depletion in the catchment during dry periods in connection with the draining treatment. In comparison with the state before drainage system maintenance, the static retention after draining treatment became greater than zero. Both the dynamic retention (detention) and static retention helped balancing storm flows in terms of flood and drought control. The successive drop of the raised water table level following drainage system maintenance resulted in changes of actual retention and subsequent runoff. The drainage procedure proved its positive influence on reforestation and the environment, as no negative impact on soil and stream hydrology was found.