THE IMPACT OF URBANIZATION ON STORMWATER RUNOFF IN THE VĖŽIŲ STREAM CATCHMENT, KLAIPĖDA DISTRICT

Abstract

This thesis examines the impact of urbanization on surface water runoff generated during heavy rainfall events. The relevance of the topic is driven by the observed effects of climate change, which lead to increasingly frequent and intense heavy rainfall. The investigated area is located in Klaipėda District, where field measurements were conducted in July and August 2025. The Vėžiai stream catchment is unevenly urbanized; overall, impervious surfaces account for 11.5% of the territory, according to LiDAR data from January 2025. Within the analyzed area, five sub-catchments were delineated, and the total catchment area is approximately 8 km². At selected monitoring points, flow velocity and water level measurements were performed in order to determine stream discharge. In addition, data published on the Meteo.lt and Geoportal.lt portals were used. The collected data were processed using CloudCompare and ArcGIS Pro software. Sub-catchments were delineated using the ArcHydro extension, while changes in runoff were evaluated using the HEC-HMS (Hydrologic Modeling System). Graphical visualization of the data was prepared using Microsoft Excel. Based on the collected water level measurements, it was determined that the velocity of the flood wave increases with increasing precipitation amounts. Peak water levels strongly depend on the degree of soil water saturation. Flow velocity measurements indicate that channel condition as well as the water level at the receiving channel have a significant influence on flow velocity. Analysis of precipitation data collected during the measurements and published by the Lithuanian Hydrometeorological Service shows that, under changing extents of impervious surfaces, surface runoff inflow to the channel also changes, along with variations in peak water level values.