Modeling of overland flow at Overvikfeltet, Trondheim

Abstract

This thesis looks at what factors influence the hydrology of a catchment, and modeling how low impact development can be used to mitigate the effects of urbanization in a catchment through the use of PCSWMM. The catchment used for modeling in this thesis is the Overvik area in Trondheim. This area is currently an agricultural area, but plans are made for development, increasing the amount of impervious areas and thus increasing the runoff coefficient. Downstream of the catchment is a culvert dimensioned for the runoff pre-development, so the peak runoff to this culvert cannot increase post-development. Three models were created for the catchment, one for the pre-development situation, one for the planned post-development situation and one using low impact development. All models are simulated using the same weather events in order to see how the runoff changes between the models. Rainfall events used in the simulation are 1-year measured data from 2011 and design storms based on the IDF-curve for Trondheim with return periods of 2, 20 and 200 years. Simulation results show that LID controls work well for smaller rainfall events, with reductions in LID total runoff by 22 % and 9 % for the 1-year model and 2-year design storm compared to post-development. For 20- and 200-year design storms the total runoff reduction is 4 % and 2 % respectively. The same results are found in the peak runoffs, where 2-year reduction is 20 % while 20- and 200-year reductions are both 12 %. The calculated storage needed to maintain the pre-development peak runoff in the LID model is 1 062 m3 for the 200-year design storm.