1.6 Resulting flood risks on the national and provincial level
Table 1-5 and Figures 1-9 – 1-12 show, at the national and district levels, the economic losses and affected people in absolute numbers, as well as in percentages of the total population and total capital stock.
1.7 Projection of future flood risk
The information from the SSP (Shared Socio-Economic Pathway) scenarios developed for the Intergovernmental Panel on Climate Change (IPCC) is used to determine the projections of exposed asset values. According to the SSP projections, the flood risk in Afghanistan will increase substantially, as more of the population will be exposed to flooding, and more and more valuable assets are accumulating. In Figures 1-13 and 1-14, the expected annual people affected by flooding, and the expected annual damages from flooding in Afghanistan until the year 2050 are displayed. Note that these figures are based on the future climate scenario simulated by the NorESM GCM (as described in section 1.3.3).
1.8 Measures for resilient reconstruction and risk reduction
1.8.1 Introduction
If the level of flood risk is not acceptable, flood risk reduction is necessary. Several measures can be taken to reduce flood risks, from measures that focus on load reduction (e.g., upstream measures), prevention with dikes, reduction of consequences, or compensation through insurance; see Figure 1-15 for an overview.
Following the definition of risk as a function of probabilities and consequences of a set of scenarios, two types of interventions can be distinguished: those that reduce the probability of flooding (prevention) or those that reduce the consequences (mitigation).
• Prevention measures reduce the probability of flooding. They include reducing the loads on a flood defense (e.g., room for rivers or foreshores for wave reduction) or increasing the strength of the flood defense (dike reinforcement).
• Mitigation measures reduce the consequences of failure of a flood defense. Examples of mitigation measures include: adaptation of existing or new buildings, the construction of internal compartment dikes to limit the flooded area, and emergency and evacuation plans. A special category of measures concerns insurance or government compensation as it will not reduce the damage from flooding, but instead leads to compensation or redistribution after damage has occurred.
• Several frameworks have been developed for managing flood risks and evaluating portfolios of flood risk reduction measures. Many of these frameworks attempt to combine the different risk reduction measures and the various actors involved. Eventually, all the different interventions can also be expressed by means of their contributions to the reduction of flooding probability or flooding consequences, and thus be evaluated for risk reduction and cost-effectiveness.
• For example, the 「multilayer safety」 approach (depicted in Figure 1-16) distinguishes prevention as a first layer, land use planning as a second layer, and emergency management as a third layer.
1.8.2 Types of flood prevention measures
Flood defenses are generally a useful measure to prevent flooding of low-lying areas. A flood defense is a hydraulic structure with the primary objective to provide protection against flooding along the coast, rivers, lakes, and other waterways. Different types of flood defenses exist. The most important ones are:
• A dike (levee) is a water retaining structure consisting of soil, with a sufficient elevation and strength to be able to retain the water under extreme circumstances.
• A dam is another type of water retaining structure which separates two water bodies.
• A flood wall is a water retaining structure which generally consists of concrete, and sometimes steel. Due to the high horizontal forces on the flood wall, a solid foundation is necessary.
• Temporary flood defenses are used during periods of high water levels to strengthen dikes or other vulnerable objects. Examples of temporary flood defenses are sandbags, synthetic-bellow barriers, or box barriers that are filled with water for the purpose of stability, and various types of beams and stop logs.
• Hydraulic structures, such as sluices, siphons, and pumping stations arestructures that can also be a part of a flood defense system.
1.9 Flood risk, erosion, and cost-benefit analysis for focus areas
1.9.1 Introduction on Cost-Benefit Analysis
A Cost-Benefit Analysis (CBA) on flood risk reduction measures is conducted to select the most economically feasible measures. In a CBA the costs, i.e., the investments of a set of measures, is compared with the reduction in flood damages from the proposed measures. When benefits outweigh the costs, a flood risk reduction measure is deemed economically viable. For the examples that are described in this report, we have chosen measures that are effective for frequent flood events (i.e., those with a relative short return period of 1 in 20 years), which are associated with less extensive flooding in order to limit complexity of the designs of the flood risk reduction measures.
The CBA is based on an analysis over a period of 20 years, and assumes an average economic growth of 7 percent, which is the average economic growth over the past 10 years in Afghanistan, as calculated from the world development index database from the World Bank. The result of the cost benefit analysis is presented as the internal rate of return (IRR) on investments in flood risk reduction, based on initial investments (costs) and avoided damages (benefits). Normally a project is considered economically viable when the IRR is equal or higher to the market interest rate.
In order to conduct a CBA for flood risk reduction measures, vulnerability, or potential damages from flood events with specific return periods, need to be determined. In the design for flood risk reduction measures, the new protection level and resulting reduction in potential flood risk is calculated. Estimates of reductions in flood damages are based on the developed hydrological and hydraulic flood hazard estimates (see sections 1.3 and 1.4), and the results from the flood damage FIAT model (section 1.5) that have been developed within the project. The risk reduction and the investment costs and service life of the risk reduction measures are subsequently compared in the CBA. The annual reduction in flood risk is discounted over the timeframe of the project in order to determine the IRR (see above). When IRR reaches a predetermined value a project is deemed economically viable.
1.9.2 Unit costs
Unit costs for specific flood protection designs are commonly calculated on the basis of total direct construction costs based on material cost and labor and adding surcharges for specific activities, such as planning, detailed designs, supervision, implementation risks, and so on.
For this study the distinction is made between simple and complex construction based on the following characteristics:
• Simple constructions (small earthworks, small masonry structures, mass concrete, rural environment)• Complex constructions (gabion structures, reinforced concrete structures, large earthworks, urban environment)Besides flood protection measures such as dams and dikes, the potential reduction of flood damages through adjustments in buildings is assessed. The flood proofing of residential buildings is assumed to be done by either:
• Cement plaster of unfired brick houses; or• Construction of a concrete protection wall around the dwellings.The cost-benefit analysis and economic rationale for risk reduction measures is illustrated in two study areas:
1. Kabul city flood risk.2. Amu Darya (Panj Aumur) flood risk.For these case studies, typical risk reduction measures are proposed based on a cost calculation.
1.9.3 Kabul city case study
1.9.3.1 Model runs for stochastic events
A hydrodynamic model was set up to simulate flooding in the Kabul area. Stochastic events were simulated for the Kabul and Paghman rivers for return periods of 5, 10, 20, 50, 100, 250, 500 and 1,000 years.
The maximum water depth for a 10-year event resulting from the model is shown in Figure 1-17. First flooding occurs near the confluence of Kabul and Paghman rivers and in the old town located in District 1.
Figure 1-18 displays the maximum water depth modelled for a 1,000-year event. The flood plain extent is much wider compared to the 10-year event; especially the area near the confluence of Kabul and Paghman rivers is heavily flooded.
The modelled maximum water depths are input for the flood risk analysis for Kabul city.
1.9.3.2 Impact and flood risk assessment for Kabul
Two options for flood risk management in the Kabul city center are evaluated:
(i) flood wall strengthening and
(ii) retrofitting of residential buildings through flood proofing. The reconstruction cost for buildings was estimated to be $160/m2. The maximum damage for commercial property was set to $133/m2.
The analysis was carried out for three different situations:
• S1: Baseline scenario—situation as currently implemented• S2: Dike strengthening—increasing the bank level by 1 meter• S3: Retrofitting—Dry-proofing of residential buildings in the most affected part of District 1, North of Maiwand Street.1.9.3.3 Risk reduction measures
Dike strengthening
The embankment level is set at 1,800.5 meters, which is an average of 1 meter above the current level of the river bank protection. The model simulations indicate a flood defense with that level prevents flooding of the old town area up to and including a 50-year event. Figure 1-19 and Figure 1-20 show the resulting maximum water depth for a 10-year event and a 1,000-year event. Dike strengthening prevents flooding of the old town for the 10-year event (compare Figure 1-19 with Figure 1-17), but has a minor effect for the 1,000-year event (compare Figure 1-20 with Figure 1-18).
Table 1-6 shows the results of the baseline situation (no measures) S1, compared to the outcomes of measures for S2 and S3. It can be seen that strategy S2 can lead to a significant decrease of flood damages for both residential and commercial buildings. For flood events less frequent than 1 in 100 years, the effect of the embankment is limited.
Retrofitting buildings
The reduction in flood losses after retrofitting residential buildings is less significant for events up to 1 in 100 years, but still has an effect for floods with lower return periods.
1.9.3.4 Cost estimate for risk reduction measures
Flood wall strengthening
Increasing the flood retaining wall within Kabul by 0.5–1 meter over a length of about 600 meters in order to avoid a flood event with a 1 in 50 frequency results in a total cost including flood wall, concrete, and road work of US$398,549. The resulting IRR would be 138 percent, indicating a very positive economic return for investments for flood prevention in Kabul city at this particular location.
Retrofitting buildings
Flood proofing can be achieved by construction of a small concrete/stone wall around a housing compound, or plastering of the lower part of residential buildings (especially mud brick houses) with water proofed cement plaster. Both measures are assumed to have similar costs per protected house.
The cost-benefit analysis is conducted for all houses in Kabul that are exposed to a 1 in 50 years flooding area (with a combined surface of 94,234 m2 residential houses). Total costs for flood proofing of the residential houses are based on the surface of the exposed residential housing to flooding. Implementation of flood proofing results in avoided annual damages of US$341,000. This gives an IRR of 10 percent. The construction of a flood wall, with an IRR of 138 percent, indicates the latter is a far better flood risk reduction measure.
1.9.4 Panj Amur case study
1.9.4.1 Introduction
In order to gain insight into the possibility and economic rationale for the construction of flood risk prevention, a case study was conducted in the Panj Amur catchment area. Based on the risk maps, several areas with significant damages were selected. The areas and the geographic representation of the damages are presented in Figure 1-21, Figure 1-22, and Figure 1-23. The estimated actual damages for different return periods and consequential values of the expected annual damages (EAD) are presented in Table 1-7.
1.9.4.2 Cost benefit of risk reduction measures
Kunduz agricultural area
From the flood hazard maps it has been estimated that for the protection of the agricultural lands in Kunduz (Figure 1-21) approximately 35 km of dike are required. Construction of a simple earth dike would cost about US$3.2 million. This measure, assuming a protection level up to and including the 1 in 20 years flood level, would result in benefits of annual reduced damages of about US$301,000. The IRR of the reduction in annual damages, assuming a lifespan of 20 years of the investment and economic growth of 7 percent, would be 14 percent, showing a significant return of the investment in flood reduction measures.
Puli KhumriFrom
the map of the Puli Khumri area (Figure 1-22) it can be estimated that a protective embankment of 22 km (2 sides of 11 km each) would be required. Assuming that the embankment will require a stone protection, the construction costs would be US$990,000.
Assuming a protection level up to and including the 1 in 20 years flood level, benefits would result in annual reduced damages of US$223,000. The IRR of the reduction in annual damages, assuming a lifespan of 20 years of the investment and economic growth of 7 percent, would be 29 percent.
Fayzabad
From the map of the Fayazabad area, (Figure 1-23) it can be estimated that a protective embankment of 6 km (2 sides of 3 km each) would be required. As the proposed embankment is in an urban environment, it is assumed that a more complex construction4 in reinforced concrete would be required. Construction costs would be US$1.3 million.
Assuming a protection level up to and including the 1 in 20 years flood level, benefits would result in annual reduced damages of US$112,500. The IRR of the reduction in annual damages, assuming a lifespan of 20 years of the investment and economic growth of 7 percent, would be 12 percent.
1.9.5 Conclusions from Kabul and Panj Amur case studies
From the calculated flood damages and possible solutions for flood prevention measures, it is clear that urban environments have much higher flood damages. Therefore, as a risk reduction option flood prevention measures have much higher benefits (through avoided damages) in urban areas than in rural areas, including a higher internal rate of return (IRR). The case study of Kabul indicates that there are substantial damages (US$14 million) in a relatively small area (600 m long wall flood). Although the total damages in the rural Panj Amur cases are similar (around US$9 million) the stretches of dike that need reinforcement are longer (up to 35 km length). Nevertheless, flood risk reductions seem economically feasible in all case studies.
The study from Kabul shows that prevention measures are not required along the full length of the proposed embankments, and that flood proofing of houses has a much lower IRR than construction of a flood retaining wall.
Further recommendations include the following:
• For any flood prevention projects, detailed information on local costs (including transport, labor, etc.) is essential to inform the level of protection and type of implementation that would be economically justified.• More information on topography, hydraulic characteristics, subsoil, etc. would better determine the required design of the local flood prevention measures, improving the estimates for costs of construction and materials.The results presented above provide an initial basis for informed decision making on planning and implementing flood protection measures in Afghanistan, based on a financial cost-benefit analysis. A more extended analysis, including indirect costs because of business interruption and other co-benefits of flood projection, such as prevention of injury, ecological impacts, and so on, could allow a social cost benefit analysis.