Abstract
Subsurface drainage is a common water management practice in rural areas whose soil has poor permeability and where the groundwater table is periodically high. In addition, drainage systems are used to prevent waterlogging and flooding. The aim of this study was to investigate the influence of drained clay water retention properties on flood risk reduction. Field research was conducted at the Lidzbark Warmiński experimental site (Poland). Three case studies were considered: early spring, spring, and late autumn/early winter. In the first case, soil moisture was found to be close to the saturated water content. Snow melting and even light rainfall had caused an immediate reaction from the drainage system. In the second case, soil moisture decreased steadily, so the soil water retention capacity increased. The response time between precipitation and outflow was four days. In the third case, melting snow and further precipitation during the days that followed caused a rapid increase in drainage outflow (after 24 h). Two values were introduced: the precipitation retention rate (prr) and drainage outflow factor (df). In all cases, the prr value was in the range 32–34%; the df oscillated around 29% in the first and second cases, and reached a value of 68% in the third case.
Highlights
Over the last 50 years, heavy precipitation events have been increasing in frequency in most extra-tropical regions, on a continental and global scale
This is due to increased annual rainfall in many regions, where daily rainfall can exceed the 95th percentile. This corresponds to the significant increase that has been observed in the amount of water vapor present in warm atmospheres
Conclusions first phaseofofthe theearly earlyspring springperiod, period, when when rainfall of of snow, thethe In In thethe first phase rainfallcaused causedintense intensemelting melting snow, groundwater table was over a dozen centimeters below the surface, and the soil moisture was close groundwater table was over a dozen centimeters below the surface, and the soil moisture was to the saturated content
Summary
Over the last 50 years, heavy precipitation events have been increasing in frequency in most extra-tropical regions, on a continental and global scale. This is due to increased annual rainfall in many regions, where daily rainfall can exceed the 95th percentile. Floods caused by rainfall are characterized by vehemence Their range and course depend on the nature and duration of rain, soil moisture during precipitation, landform, and land cover. Snowmelt floods are caused by the rapid melting of snow cover, which is often accompanied by warming, rainfall, and soil impermeability, which in turn increases the outflow rate
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