Pegelabfall

Pegelabfall is a term used in hydrology to describe the decline of a water level at a gauge site after a peak, typically following rainfall or flood events. The word combines Pegel (gauge or water level) and Abfall (fall). In practice, Pegelabfall can refer to either the absolute drop from the peak to subsequent levels or to the rate at which the level decreases, often expressed as dH/dt in meters per hour or centimeters per hour.

Measurement and calculation: Data come from river or stage gauges that continuously record water level. From the hydrograph, one identifies the maximum level, the time to peak, and the subsequent decline. The Pegelabfall can be quantified as a difference (Pegelmax minus current level) or as a rate of decline over a chosen interval.

Applications: Pegelabfall informs flood risk assessment and management, supports calibration of hydrological models, and helps operators judge how quickly a flood wave dissipates. It is used alongside peak level, duration, and total runoff to interpret flood dynamics and residual risk.

Factors: The size and speed of Pegelabfall depend on rainfall cessation, catchment saturation, soil infiltration, groundwater contribution, river cross-section, backwater effects, reservoir releases, and snowmelt.

Limitations: Gauge placement, backwater from confluences or structures, and network-scale effects can affect Pegelabfall. As such, it is best used together with the full hydrograph and other indicators.

See also Pegel, Hochwasser, Hydrograph.