CHALLENGES

İzmir is a city of 4.4 million inhabitants, spectacularly located on the Gulf of İzmir at the west coast of Anatolia, Turkey. The city was founded near various natural springs, on the waterfront and with multiple streams coming from the hills: a blessing, but sometimes a burden. Especially because İzmir is a very densely urbanized area nowadays, and almost fully paved. Waterways have been covered and rivers channelized to quickly discharge the water, but they have limited capacity. Moreover, the soils of İzmir are generally compacted and infiltrate poorly, resulting in a fast runoff – also from the upstream hinterland. All together, these conditions result in a high risk of flash floods during heavy rainfall such as in January 2021.

VISION

In this quickscan we used a holistic basin approach to find ways to rebalance the water system of İzmir. This approach aims to provide integrated solutions at multiple scales, from upstream to downstream. An essential principle is to not only prepare for extreme weather events but to improve the everyday living environment and microclimate as well. The key to the complex water management challenge of İzmir can be found in a combination of upstream storage, detention and retention, and optimizing the discharge system. The city should be ‘softened’ by reducing the amount of paved surfaces. Moreover, utilizing the natural processes should become a priority as part of a long-term plan, taking inspiration from the historical and natural situation.

CATCHMENT SYSTEM FUNCTIONING

In our study we focused on two exemplary catchment area’s: Bostanli and Poligon. For both cases, three subareas are distinguished: the upstream rural area, the middle area (city on the hills) and the lower area (city in the floodplain). In the upstream areas, many small natural streams come together and form wider streams that run towards the city. These streams are denaturalized in downstream urban areas. As culverts under bridges are relatively small, they become bottlenecks for water drainage during extreme weather events. Other challenges in the middle and upstream areas are erosion in case of bare slopes and fast surface run-off due to intensively paved surfaces in the neighbourhoods. Challenges for the city in the floodplain are the additional water flows from higher areas and the drainage challenges due to rising water levels in the channels. In case of high tides the situation can become even more problematic.

BOSTANLI

Within the Bostanli case study area we zoomed into different locations as potential pilot projects. For the upstream areas that cope with fast run-off and erosion, potential interventions could be the implementation of contour trenches, improving the system of check dams and to take measures against erosion such as gabions or terracing. Another proposal to be researched in further detail is to invest in a reservoir strategy, with a sequence of small reservoirs or a big new reservoir.

Midstream, currently channelized streams should be widened and regreened. These can become green corridors with new recreational routes along them. On a smaller scale, networks of bioswales, parks with infiltration/storage ponds and wadi’s can be developed. The focus of downstream areas should be on draining as much water and as quickly as possible. To achieve this, profiles of current channels can be widened, culverts enlarged and bridges raised. This decreases the amount of obstacles causing a bottleneck and helps to lower waterlevels while maintaining discharge capacity. Channels can be turned into green corridors with attractive edges and bike routes that can be used during the dry season.

POLIGON

In many ways, the Poligon catchment area copes with similar challenges as Bostanli. The scope of the suggested interventions can be distinguished in the same three areas: upstream, midstream and downstream. For the upstream areas, the goal is to hold and store as much water as possible. This can be done by making adjustments in current land use. For example, by improving the soil, by applying contour trenches or by reforestation. More technical measures would be to improve the current water storage infrastructure, by creating more and bigger reservoirs and/or dams.

In the midstream areas – ‘City on the hill’ – the focus should be on slowing down the water and to reduce outflow to lower areas. The designs of green-blue public spaces in these areas, especially in new urban developments, should be optimized by creating terraces, urban parks, wadi’s and bioretention areas. Technical measures to achieve this could include cisterns, pervious pavement with underlying storage and detention ponds. In our pilot project downstream we suggest to replace parking spaces into one building to create space for a green boulevard, combining water retention with recreational opportunities.

CONCLUDING RECOMMENDATIONS

Improving resilience in İzmir's water system will be a long-term process. It will require coordination across departments, the engagement of the private sector and residents, and significant investments. Nevertheless, it should be seen as a great opportunity to improve the city’s living environment while improving the city’s water system.

This quickscan has shown the potential of an integrated approach for İzmir’s water related challenges. In the most promising locations pilot projects are identified for a more detailed study. Next steps should include the development of preliminary designs, a technical and financial feasibility study and more detailed hydrological modeling. Parallel to this, the process of an integrated waterplan and a citizen engagement program should be initiated. This should include an awareness campaign to engage private landowners to collaboratively capture as much water as possible in up- and midstream areas.

With the contribution of former colleagues Josje Hoefsloot and Yuka Yoshida.