Table 2. Stormwater collector scenarios. Scenario analysis is related to changes in operation of the stormwater collectors. The model operator (stakeholder) has the option of selecting two variables related to the sewerage system (capacity and direct runoff), as well as the sensitivity of beach users to changes in water quality (turbidity and runoff). Because this sensitivity is currently unknown, only the two extremes are shown in the table: none and high (both to bacteria and turbidity). The two extremes demonstrate the maximum possible difference to both the non-market and market value of the beaches for each scenario. The approximate cost of constructing the stormwater collectors for each scenario is included for comparison. It should also be noted that the number of turbid days is the same for both the “current” and “planned” scenarios because although increasing stormwater collector capacity does not affect “low” turbidity, it does affect “high” turbidity (although only by a small degree).

Stormwater Collector Scenarios
Units and details No collectors (simulated) Current Current with improved runoff (simulated) Planned (simulated) Planned with improved runoff (simulated)
Sewerage system Capacity stormwater collectors (Gigaliter) 0 0.52 0.52 1.5 1.5
Runoff direct to coastal water (%)
100 50 0 50 0
Bacteria Number of days in the year in which limits are exceeded during the bathing season†
7.17 3.88 2.58 3.63 1.42
Turbidity Number of "turbid" days during the bathing season† 19.21 15.75 11.29 15.75 8.08
Number of "high turbidity" days during the bathing season†
1.29 0.75 0.58 0.71 0.42
Beach user sensitivity Beach user sensitivity to bacteria and turbidity
none high none high none high none high none high
Beach users Visitors per year (millions)
6.36 4.85 6.36 5.26 6.36 5.41 6.36 5.33 6.36 5.69
Non-market value Travel cost evaluation per year (€ millions)
16.03 12.22 16.03 13.25 16.03 13.64 16.03 13.43 16.03 14.33
Market value Revenue from bars and restaurants per year (€millions)
29.36 29.32 29.36 29.33 29.36 29.33 29.36 29.33 29.36 29.34
Cost stormwater collectors Approximate construction costs per scenario (€millions) 0 150 150 450 450
† The bathing season is from May until September, inclusive. The value for number of days is calculated from the annual average of a 5-year forecast period.