Abstract:
The importance of analysing peak water levels and rainfall patterns lies in its
ability to enhance flood risk management and preparedness. Understanding
the relationship between rainfall and flooding trends helps identify high-risk
areas, guide infrastructure planning, and inform early warning systems,
ultimately mitigating the impact of future flood events and protecting
communities and resources. The objective of the present study was to
investigate a recent anomaly in flood patterns observed in areas located
within the Nilwala River Basin (NRB), southern province, Sri Lanka.
Although the area typically experiences monsoon-related flooding, an
unusual persistent flooding condition was reported recently. The NRB
consists of main four gaging stations (GS) named, Thalgahagoda,
Panadugama, Pitabeddara, and Urawa. Water levels (WL, m) and rainfall
(RF, mm) data were collected from each GS of September, October,
November, and December in three consecutive years (2021,2022, and 2023).
Data were analyzed using one-way ANOVA and DMRT to investigate the
differences of WL and RF among stations and correlation analysis was
conducted to investigate the relationship between RF and flooding patterns.
In 2023, all stations recorded their highest peak WLs, with Thalgahagoda
(1.69±0.47), Panadugama (5.35±0.99), Pitabeddara (1.84 ±0.68), and Urawa
(1.17±0.51) showing significant increases from previous years (P=0 at all
GSs), indicating a potential rise in flood intensity. Results showed no
statistically significant differences in RF amounts across years at
Thalgahagoda, Panadugama, Pitabeddara, and Urawa stations (P=0.14,
P=0.32, P=0.76, and P= 0.62 respectively), with mean rainfall values varying
slightly. This suggests that although rainfall did not vary significantly yearon-
year, increased rainfall in certain areas may contribute to the elevated
flood levels observed. Overall, the results highlight a weaker correlation
between rising water levels during flood events and consistent rainfall
patterns, emphasizing the need for enhanced flood management strategies
and investigation of potential contributing factors, particularly in high-risk
areas like Thalgahagoda and Panadugama.
