Design & assessing the flood risk management paradigm shift: an interdisciplinary study of Vlissingen, the Netherlands

Figures & data

Figure 1. The location of Vlissingen (Netherlands) in the maritime system.

Figure 2. Synthetic storm surge for Vlissingen using the still water level (SWL) from HydraNL (10,000 year RP and 2100 climate change scenario W+) (elaboration: A. Diaz).

Table 1. The qualitative CBA for the Vlissings Model.

Spatial interventions	Costs	Benefits	Effects	Risks
Raising 3 million m^2 of boulevard surface	- Addition of 9 million m^3 sand (environmental cost sand mining) - Public space reconstruction		Full protection against storms 1:30.000 in 2100 in scenario W+ spatial connection to hinterland more lost	Spatial degradation
Demolition and reconstruction of the historic urban front	- Demolition of 1 million m^2 building surface - Reconstruction of double the amount of existing m^2 building surface	Increase of gross (new - old) floor area	Loss of historical seafront of the city Increase tourist accommodations capacity	Spatial fragmentation, loss of legibility of the seafront

Figure 3. Spatial design strategy: the Vlissings Model; plan and prototypical section (elaboration: A. Bortolotti).

Figure 4. Spatial design strategy: the Spuikom Model; plan and prototypical section (elaboration: A. Bortolotti).

Figure 5. The results of the D&A framework - general overview: Maximum water depth map (a-c) and the corresponding total flood damage map (d-f) under extreme sea level at 1/10,000 p.Y in 2100 fora) Baseline strategy, b) Vilissings Model and c) Spuikom Model (elaboration: A.Bortolotti, A.Diaz,Q.Ke)

Table 2. The qualitative CBA for the Spuikom Model.

Spatial interventions	Costs	Benefits	Effects	Risks
Redesign/reconstruction of the Spuikom as a floodable park/green area	Reservoir of 2 m (= 186,000 m^3 capacity) 15,400 m^3 excavated earth for digging out 4400 m^2 of filled water reservoir (= 22,000 m^3 capacity) raising the basin’s embankments 8,500 m^3 extra earth volume for heightening 680 m perimeter of existing water planting of trees and plants	Increase real-estate value	Protection of green space from urban development improvement urban quality/functionality revenue from ecosystem services	Working of the system on the long term, too much water, too little water maintenance disturbance
New buildings	Building costs	- Revenue m3 Gross floor area - Additional urban functions	Economic carry capacity coherent urban densification
Street re-design and reprofiling	Construction costs of public space movable barriers	Reduction of costs related to rainwater stress	Adaptation to pluvial flooding legible public space as part of the new flood defense and rain water adaptation strategy spatial functionality ecosystems/biodiversity better integrated	Working of the system on the long term, too much water, too little water

Table 3. Summary of flood economic damage, the number of total fatalities, and affected people, EDA and benefit for different strategies.

Strategy	Baseline	Vlissings Model	Spuikom Model
Present value (PV) of damage *	[78.5-103]	0	[12.4–16.5]
Total fatality [person]	2	0	0
Total affected people [person]	805	0	42
value of a life	10 million
Investment to avoid one affected person	0.5million
EAD [euro/year]**	[5010–5255]	0	[334-375]
Benefit [euro/year]		[5010–5255]	[4676–4880]

* The discount rate to convert 2011 price to PV is [4%, 7%] with mean value of 5.5%; **The given return period of flooding is 10,000 years.

Table 4. The summary and comparative table of qualitative evaluation of each strategy.

Strategy	Baseline	Vlissings Model	Spuikom Model
Total interventions’ investment qualitative conclusion	There is no investment	Investments are public for the dike (single purpose flood defense) and private for the lot owners and developers of the new buildings	Investments are public for the area development (multiple purpose flood defense/ecosystem/urban quality) and private for the lot owners and developers of the new buildings
Total interventions’ revenue qualitative conclusion	There is no revenue	The revenue is located with private developers of the historical front’s demolishment & reconstruction	The revenue is societal because of the qualitative and functional improvement of the Spuikom area which is beneficial to the (qualitative in already good condition) district and thus general increase real estate value, the development of 4 new buildings in revenue for the developers of these
Total interventions’ effects qualitative conclusion	More risk over time	Lowering of flood probability so decrease of risk, loss of spatial connection and historical seafront, increase of tourist accommodation capacity	Lowering of the flood consequences so decrease of risk, adaptation to pluvial flooding, protection and qualitative improvement of the whole urban area in relation to functionality, nature, legibility, history
Total interventions’ risk qualitative conclusion	No risk	Spatial degradation, fragmentation, loss of legibility of the seafront	Working of the system on the long term, too much water, too little water
Qualitative conclusion of the damage assessment	The situation will become very unsafe with high casualties, affected people and high damage on the larger scale	The situation will become risk free with no casualties, affected people and damage	The new situation will reduce the damage on the large scale and have some damage and affected people on the project scale