Sissevool

Sissevool is a hydrological term used in Estonian to denote inflow—the volume of water entering a lake, reservoir, or aquifer from external sources. The concept is central to the hydrological water balance, which tracks the inputs and outputs of a water body over time. Inflow sources typically include surface inflows from rivers and streams crossing into the water body, groundwater seepage or leakage into the subsurface, and surface runoff from the surrounding catchment that reaches the water body. Direct precipitation onto the water surface is sometimes treated as part of inflow in some models, but is often handled separately as precipitation.

In practice, inflow is measured with stream gauges and groundwater observations, or estimated by hydrological models that integrate rainfall, catchment characteristics, and upstream conditions. Accurate estimates of inflow are important for reservoir operation, flood forecasting, ecological management, and water resource planning. In Estonia and other regions, national hydrological services publish inflow data for lakes and reservoirs to support these applications.

Sissevool is contrasted with outflow (väljavool), which represents the water leaving the body through rivers, drains, or evaporation to the atmosphere. Together, inflow and outflow determine changes in storage and the overall health of aquatic systems. See also hydrology, water balance, inflow, and outflow.