Evaluation of the feasibility of solutions to flash flooding in the municipality of Tirana (Albania)

Abstract

In the
recent years, several cases of flash floods have been reported in the
Municipality of Tirana, causing important material damage in the region. One of
the most devastating events occurred in December 2017, which flooded the City
Park area (West of the Municipality of Tirana). This area is strategical
because it includes relevant centers of economic development, such as
commercial and industrial areas, that are located nearby a main road connection
between the Port of Durres, the Tirana International Airport and Tirana
itself.  To mitigate the flood risk at
this location, several hydraulic engineering concepts have been developed.
However, the suitability of the concepts is limited by two main constraints:
budget constraints and spatial constraints. With the aim to develop a flood
protection system that is financially and spatially feasible, a system that
combines dikes and flood walls is proposed. The industrial and commercial areas
of the City Park are very close to the river. Hence, due to the spatial
constraint, flood walls are used to protect these areas. Dikes are implemented
in the river boundaries were agricultural and green land uses are found. Grass
covers are implemented on the dike slopes to compensate the impact provoked by
the water retaining structures in the local environment. The grass enhances the
local visual amenity. Furthermore, bike paths are implemented on the dike
crests and contiguous to the flood walls to improve the livability of the
area.  In order to adapt further to the
budget, the dimensions of the structures to be built are reduced by dredging
the river beds, what increases the section of the river to convey water. A
granular filter is placed on the river bed in order to reduce the soil erosion.
Moreover, in order to reduce the financial and visual impact of the dikes,
temporary structures of one meter height will be placed on the crest of the
dikes in case a 100-year flood event occurs. A Cost-Benefit Analysis (CBA) of
the proposed solution has been carried out to evaluate the feasibility of the
alternative. The resultant BC ratio of the solution is 0.84, which is close to
what is considered feasible (BC > 1). However, this ratio is sensitive to
the discount rate. According to the falling tendency of this rate in Albania in
the recent years, as shown by the information published by the Central Bank of
Albania, the rate is expected to fall from 1.25% to 1% in the close future. This
drop would make the project feasible (BC = 1.05 > 1).