The green infrastructure valuation toolkit user guide

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Building natural value for sustainable economic development: the green infrastructure valuation toolkit user guide These are promoted by the Environment Agency as a cost-effective approach to coastal defence. ASSESSING THE BENEFITS Measuring the impact of green infrastructure on improved water management and reduced flood requires detailed knowledge of: the hydrology of an area existing water infrastructure the area and permeability of surfaces (natural and built) climatic conditions. For most schemes, detailed appraisal by the Environment Agency and statutory drainage authorities - water companies and local authorities - will be needed. This toolkit provides a guide to assess the type and potential level of benefits likely to be achievable. The evidence highlighted above shows that the potential benefits are significant. For example, reinstatement of catchment ecosystems can improve water quality and attenuate river flows, reducing flood risk. Reduced flood risk can reduce losses from property damage - avoided loss - and reduce insurance premiums. Green infrastructure can also substitute for more costly hard engineering/flood prevention solutions. QUANTIFYING Quantifying and valuing water management benefits accurately requires detailed modelling of water catchments, including surface water sewer systems. Major flood risk management schemes Bespoke appraisal by the Environment Agency will usually be required, where natural drainage options will be considered alongside other flood risk management interventions. The Environment Agency uses a number of ‘Outcome Measures (OM)’ 28 to assess schemes, including: OM1: Economic benefits OM2: Households at risk OM3: Deprived households at risk Other output measures include: nationally important wildlife sites UK Biodiversity Action Plan habitats flood warning contingency planning inappropriate development long-term policies and action plans. SUDS schemes An indication of the scale of benefit can be derived from their capacity, measured in cubic metres (m 3 ). An indirect valuation (see below) can then be made, comparing the scheme to the cost of creating equivalent capacity via a hard engineering solution. Green space Partial estimates of the water management value can be made using data for evaporation, transpiration and interception of rainwater for different land cover types. This effectively estimates reduced surface water run off - where this run off would otherwise enter the sewer network, there are resulting cost reductions in treatment and provision of the sewer capacity. Water companies recognise the benefit of reducing surface water flows into their combined sewers and offer reduced tariffs to customers who implement sustainable drainage schemes. All these valuation approaches will significantly underestimate the cumulative impact of local green infrastructure schemes. Reducing surface water run off will reduce failure of combined sewer overflows (CSO) and overtopping of flood defences in extreme flows - this is where there are significant cost savings through avoided infrastructure costs and avoided cost of property damage. MONETISING Three valuation tools are included in the toolkit. Tool 2.1 – Energy and CO2 emissions savings from reduced volume of stormwater entering combined sewers -!- This tool is only appropriate in urban areas with a combined sewer network. This tool is designed to help assess the impact of vegetation on the amount of rainfall entering combined sewers. It uses Forestry Commission values for evapotranspiration and interception for different land cover - coniferous trees, deciduous trees, grassland. It does not take account of water retention within soils, which is highly dependent on soil types and their storage capacity - which itself varies according to how much water they are already holding. 28
Building natural value for sustainable economic development: the green infrastructure valuation toolkit user guide Reductions in surface water entering combined sewers lower operational costs for water treatment, including energy consumption - water companies use an average of 645 kWh/megalitre of wastewater treated. Tool 2.2 - Savings in wastewater treatment costs to domestic and commercial water customers This tool uses published water industry figures for surface water drainage charges to assess cost savings to residential and commercial customers who are not draining rain water into combined sewers. Where property holders – residential and commercial – avoid discharging surface water from their property into the combined sewer network, water companies provide a discount to wastewater bills. For domestic properties in north-west England, the discount is £35.33 per year 29 . For commercial properties the discount varies with ‘chargeable area’ - the area of the premises, discounting and permeable areas - in bands. For example: • for a site of 0.15-0.3 hectares, the discount is £918 per year • for a site of 2.5-5 hectares the discount is £15,313 per year. Potential: tool 2.3 - Avoided infrastructure costs This tool is designed to help assess cost savings from managing stormwater with SUDS and avoiding the need for hard engineering solutions. SUDS can bring savings by reducing or avoiding the need for investment in new storage and treatment capacity, and also avoids ongoing operating costs. TOOLS AVAILABLE IN THE CALCULATOR Tools Data input Tool basis Tool 2.1: Energy and CO2 emissions savings from reduced volume of stormwater entering combined sewers [ Functional] Estimates the energy savings associated with the impact of vegetation on reducing the amount of stormwater entering combined sewers. Tool 2.2: Savings in wastewater treatment costs to domestic and commercial water customers [ Functional] Uses published water industry figures for surface water drainage charges, to estimate the actual cost savings to residential and commercial customers who are not draining rainwater into combined sewers. Land use - coniferous trees, deciduous trees, grassland. Average rainfall (or 800mm pa default) Water treatment costs (energy and other inputs) Number of domestic properties avoiding discharging to combined sewers. Area of commercial property. Application of Forestry Commission data on the use of water by trees and other land cover to estimate reduction in surface water to sewers. Water company information on site area charges for surface water drainage. Tool 2.3: Avoided costs of traditional water drainage infrastructure [Quantification and monetisation require further research] Estimates cost saving from managing stormwater through SUDS rather than through traditional engineering solutions. Requires average cost data for construction of new rainwater storage tank capacity 29
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The green infrastructure valuation toolkit user guide

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