FlexAdapt. Development of flexible adaptation concepts for the urban drainage of the future.

Funding:

Federal Ministry of Agriculture, Forestry, Environment and Water Management, BMLFUW (Austria)

Partner:

• Graz University of Technology - Institute of Urban Water Management and Hydraulic Engineering
• University of Natural Resources and Life Sciences, Vienna - Institute of Sanitary Engineering, Industrial Water Management and Water Protection

Duration: 08/2016 - 12/2018

Project objectives:

Municipal water management faces a variety of challenges. Ageing infrastructure systems with an increasing need for refurbishment, potential climate change impacts, challenges posed by shrinking or rapidly growing municipalities or growing concerns about pollution from (micro)pollutants are coming up against increasingly tight municipal budgets.

One of the core tasks of urban water management infrastructure is the safe drainage and, in some cases, treatment of stormwater runoff. Various methods are possible for this, such as discharge to wastewater treatment plants in combined systems or decentralised precipitation water treatment on site through infiltration or discharge into a nearby body of water. Under certain circumstances, it may also be necessary to pre-treat the precipitation runoff in order to preserve water quality.

In the case of new buildings or as soon as existing systems have to be extensively renovated, the question arises as to which of the available technical systems are best suited to fulfil these tasks now and in the future. In times of uncertain future developments, for example in the population (and thus in land utilisation) or in the climate, there is often a call for the most flexible processes possible. In this context, decentralised solutions are increasingly being proposed as the method of choice for the future. The core idea is to avoid investments in expensive grid-bound infrastructure and thus be able to react more flexibly to different future conditions. A further advantage is seen in the fact that decentralised methods, such as on-site infiltration, shift the urban water cycle towards a natural water balance and these methods therefore also have ecological advantages, such as increased groundwater recharge, an improvement in the microclimate or a reduction in rapid surface runoff.

However, well-founded decision-making should not be based on these obvious factors alone, but should be carried out as objectively as possible, taking into account a wide range of influencing factors. Examples of influences to be taken into account are the condition and age of existing systems (channels, infiltration systems, pre-treatment), population density, sensitivity of groundwater bodies and water bodies including any previous pollution, existing organisational structures for maintenance and operation of the systems, expected population development and changes in land use or possible climatic changes. It is also necessary to consider the consequences of a system change, even in a transition period that may last several decades. These can be of a technical, organisational or financial nature. At the same time, it is also important for network operators to plan ahead, as they are often contractually obliged to take over discharges in the long term, for example, and a transition must not only take place technically, but also organisationally and financially (e.g. in the fee structure).

Decision-making is therefore extremely complex. The situation of small and medium-sized municipalities in rural areas must be explicitly considered. These differ from the larger cities in several respects, in particular in the drainage method - (modified) mixed/separate system -, in the building density and type of development and thus the space available for alternative solutions, as well as in the pollution of rainwater runoff. Furthermore, smaller municipalities are also confronted with other institutional and economic constraints. For example, the financial situation of many smaller municipalities is still strained, which means that the sewerage and water charges collected are not used for their intended purpose. Additional challenges include strong population growth in both directions, strong growth in the "bacon belts" around the larger cities with a corresponding need to adapt the infrastructure, but also strong declines in rural areas with the associated loss of revenue.

In a joint research project, the three sister institutes for urban water management at the University of Innsbruck, BOKU Vienna and TU Graz aim to investigate sustainable solutions for rainwater treatment in Austria from a technical-operational, environmental, organisational, financial and social perspective and to make recommendations for sustainable development. The following research questions will be analysed:

• What should the stormwater disposal of the future look like depending on different boundary conditions? Under what conditions should decentralised solutions be preferred to existing centralised processes?
• Under what conditions (e.g. pending need for renovation, age of existing infrastructure, existing need for adaptation, predicted municipal development) does it make sense to actively pursue the transition to an alternative concept? How can the transition from piped infrastructure to decentralised stormwater treatment be prepared?
• How do specific problems of small and medium-sized municipalities (e.g. sharp population decline in rural municipalities, population growth in the "bacon belts") influence the optimal solution?
• What economies of scale exist in terms of construction and operation? (e.g. comparison of decentralised rainwater infiltration at property level versus rainwater ponds at municipal or district level)
• What other changes are to be expected, e.g. with regard to future requirements for the treatment of stormwater runoff, and to what extent should these already be taken into account in planning?
• What consequences can the increased use of alternative drainage concepts have (e.g. changes in groundwater levels)? How can this be countered?
• How can alternative drainage concepts be financed? Who is responsible for construction and maintenance (public or private)? How should the fee structure be changed?
• What are the requirements for the maintenance and upkeep of alternative drainage concepts? Can these be covered by existing organisational resources (regulations, training courses, etc.) or are new activities required here too? How can inter-municipal co-operation in the maintenance of the systems be promoted?

The result of the project consists of direct instructions and advice for wastewater associations, municipalities, planners and experts. In detail, these are

• Concrete instructions in the form of a guideline / final report
• Catalogue of possible precipitation water treatment methods including an assessment with regard to financial and technical expenditure in construction and operation as well as feasibility, taking into account local boundary conditions
• Evaluation of various options for stormwater treatment in terms of hydraulic and material performance
• Recommendations and decision-making aids for the choice of stormwater treatment method, taking into account future developments such as population, climate and environmental requirements

Contact:

University of Innsbruck
Dr Manfred Kleidorfer
Technikerstrasse 13
6020 Innsbruck
manfred.kleidorfer@uibk.ac.at