MODELLING FETCH-LIMITED WAVES IN COASTAL BASINS AND LAKES

Coastal risk studies often focus on estuarine regions where storm surges interact with river flows (e.g., Maskell et al., 2013) or areas exposed to swell and wind-driven wave growth, where the probability of wave-storm surge concurrence is high (e.g., Maskell, 2019). However, in fetch-limited coastal basins and large lakes, fetch-limited waves can pose significant risks. This study investigates such waves in two contrasting regions: (1) Beauly and Moray Firth, semi-enclosed coastal basins in Scotland (UK), and (2) Lake Tanganyika, the world’s longest freshwater lake in Africa. Beauly and Moray Firth exhibit short fetch lengths (8 km and 11 km, respectively) with potential for strong extratropical cyclone winds, while Lake Tanganyika features long fetches (up to 400 km at Uvira, DR Congo) under moderate seasonal wind conditions. Fetch-limited wave growth was modeled using JONSWAP and a fully spectral wave model (TOMAWAC).Maximum wave heights were estimated using Carter's (1982) method and JONSWAP. In Beauly and Moray Firth, peak wave heights of 1.47 m and 1.73 m, respectively, were predicted for extreme wind conditions. The spectral wave model showed slightly lower heights, with a maximum of 1.28 m and 1.3 m for west and northeast winds. On Lake Tanganyika, JONSWAP predicted significant wave heights of up to 2.19 m at Kalundu Port under strong winds from the south-southeast. Spectral modeling confirmed rapid wave growth within 4 hours of 20 m/s winds but highlighted that extreme winds are rare, with gusts up to 30 m/s occurring annually.The results demonstrate that JONSWAP provides useful insights into fetch-limited wave potential but should be supplemented with spectral modeling to account for depth-limited dynamics and wave spectrum adjustments. Both regions face risks from fetch-limited wave generation, which could lead to flooding or, in Lake Tanganyika’s case, hazards for navigation and port operations. Understanding fetch-limited basin responses to wind is essential, especially under future climate-induced changes in regional wind patterns.