Assessment of rainwater runoff using the Rational Method and its applications - Applied to rural case studies in Ockelbo, Sweden, affected by the extreme rain event in Gävleborg county of August 2021
Typ
Examensarbete för masterexamen
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2022
Författare
Dristig, Annie
Välikangas, Elin
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The aim of this master thesis is to investigate different applications of the Rational
Method (RM), applied to manually calculate rainwater runoff and estimate
culvert pipe dimensions at two rural case study areas affected by the extreme rainfall
in Gävleborg county in August 2021. This rain event is in Sweden referred to
as Gävleregnet. Each case study consisted of a culvert pipe transporting a creek
through a country road. The dimensioning flows from the forested catchment areas
were calculated by the RM and three of its applications; the version of Svenskt
Vatten (SV-RM), the Swedish Transport Administration (STA-RM) and Flödesappen.
All of these except the latter, which is a digital modelling tool, were combined
with the Time-area Method (T-A), and their calculations were based on two rain
scenarios; the Worst Case of Intensity (WCI) and the Worst Case of Return Period
(WCRP). All four applications of the RM utilized Colebrook’s method to determine
the suitable pipe dimensions needed to manage the dimensioning flows. Furthermore,
the catchment areas and calculations for RM, SV-RM and STA-RM were
estimated manually in Excel and GIS. A field visit was also conducted to retrieve
deepened information of the case study areas. The results of the areal parameters
were compared between the digital calculation in Flödesappen and the manual
methods. The influence of some parameters on the peak flow was investigated in a
Sensitivity Analysis (SA) for each method and rain scenario.
Overall, the results showed that the WCRP was the actual worst of the two scenarios,
for both case studies, where the highest peak flows were generated by the two
methods that considered a climate factor (SV-RM and STA-RM). The results from
the SA show that the most affected flow is generated by the change of the catchment
area in the WCRP scenario for SV-RM and STA-RM.
Beskrivning
Ämne/nyckelord
Rational Method , Time-area method , Culvert pipe , Runoff , Swedish Transport Administration , Svenskt Vatten , Gävleregnet , Extreme rain event , Rural , Catchment area