Impact assessment, analysis with GIS, flood control, urban development, geodesign, SDGs.
During a course "Advanced digital landscape analysis with GIS" (winter-spring 2021) at SLU, I have participated in a Geodesign workshop (together with the GeodesignHub), where together with other students we discussed and developed several strategies for the development of a coastal town Lomma in Sweden. After the group work at the Geodesign workshop we individually did impact assessments of the final designs. My individual impact assesment is found below.
Geodesign week
Report: Flood resilience
Report: Flood resilience
This report presents a short impact assessment (of how many planned housing areas are going to be under the presure of flooding in the future) that I did for two designs from the Geodesign week: group 4&5 design and the negotiated design. I decided to take the common design from group 4 and 5 as I belive it was more reasonable in more aspects than the design of my group alone. Even though generally I believe that our design (4&5) was more reasonable in terms of flood measures than the negotiated, I was surprised and disappointed to find out in the impact assessment that our designs were similar in terms of developing housing largely to the north of the Looma center, which I personally belive might be not the best strategy. I describe my reasoning in the end of the report.
Calculating Sea level rise in 2050 and 2121
Considering the given data of estimated levels of sea level rise in best and worst scenarios for 2121, and observed high and average levels of storm surge and wave effect, as well as the yearly post glacial rebound (+1mm per year), I have calculated the total rise of sea level during storms. So, this would help me to map areas that can be covered by water, even though not all the time, but as we do not want to build houses, for instance, on places that might be flooded a couple of times per year, it it a useful result.
Moreover, as we were asked to do impact assessment of the two designs from the Geodesign week for 2050, I estimated the sea level rise for that year too. I decided to take the worst case scenario, as I believe that it is better to estimate for worst to plan a bit more long-term. Moreover, it gives a perspecitive of the direction water would spread in the upcoming years in case the best case scenario happen to be the true scenario. Table below shows the calculations that became the basis for the bath tub analysis.
Considering the given data of estimated levels of sea level rise in best and worst scenarios for 2121, and observed high and average levels of storm surge and wave effect, as well as the yearly post glacial rebound (+1mm per year), I have calculated the total rise of sea level during storms. So, this would help me to map areas that can be covered by water, even though not all the time, but as we do not want to build houses, for instance, on places that might be flooded a couple of times per year, it it a useful result.
Moreover, as we were asked to do impact assessment of the two designs from the Geodesign week for 2050, I estimated the sea level rise for that year too. I decided to take the worst case scenario, as I believe that it is better to estimate for worst to plan a bit more long-term. Moreover, it gives a perspecitive of the direction water would spread in the upcoming years in case the best case scenario happen to be the true scenario. Table below shows the calculations that became the basis for the bath tub analysis.
I did bath tub models for every case. then, I reclassified each file (that is in raster format the same as DEM) into 1 (minimum value - up to the “Total” value from the table above (so, the maximum area that will be covered by water sometimes during a year)) and 0 - area above the total sea level rise. I also did the classification into 1 - sea level rise, 2 - storm surge, 3 - wave effect, 0 - not flooded, and created separate files. However, this classification was not helpful and in any way descripritive when doing the final analysis of the housing flooded in 2050, so I have decided to use the binary classification instead.
Afterwards, I could transform the raster files into vector, which is necessary to be able to sort out the flooded areas that are not connected to the sea (as in reality, flooding created by the sea level rise comes from the sea, however the bath tub model shows all areas in land below the estimated sela level as “flooded”, which does not correspond to the reality.
I manually selected polygons for the sea and the river that is connected to the sea from the Hydrography file. I created a separate layer with the selected features. then I did “select by location” for all three flood models to intersect with the sea and the river. This helped me to get rid of the flooded areas not connected to the sea or the river.
Afterwards, I could transform the raster files into vector, which is necessary to be able to sort out the flooded areas that are not connected to the sea (as in reality, flooding created by the sea level rise comes from the sea, however the bath tub model shows all areas in land below the estimated sela level as “flooded”, which does not correspond to the reality.
I manually selected polygons for the sea and the river that is connected to the sea from the Hydrography file. I created a separate layer with the selected features. then I did “select by location” for all three flood models to intersect with the sea and the river. This helped me to get rid of the flooded areas not connected to the sea or the river.
Impact Assessment (ArcGIS process)
I decided to use the results of the sea level rise models for 2121 as well to show perspective and the predicted direction of water. I created separate layers of Low density housing (LDH) and High density housing (HDH) for each design. Then I chose to do “Intersect” between the flood model 2050 and the LDH+HDH for each design to see the difference. I created maps with flood models for 2121 (best and worst cases) and 2050, sea and the river (as the current areas covered with water), housing flooded in 2050 and the housing (LDH and HDH) are visible.
I decided to use the results of the sea level rise models for 2121 as well to show perspective and the predicted direction of water. I created separate layers of Low density housing (LDH) and High density housing (HDH) for each design. Then I chose to do “Intersect” between the flood model 2050 and the LDH+HDH for each design to see the difference. I created maps with flood models for 2121 (best and worst cases) and 2050, sea and the river (as the current areas covered with water), housing flooded in 2050 and the housing (LDH and HDH) are visible.
Discussion
The results of the impact assessment are quite similar for both designs. I think that it is vital to set right priorities at the start of the geodesign process. Moreover, a support and advice from experts from a variety of fields that represent the compexity of the place and its challenges is important for the effectivennes and success of the negotiated solutions.
I think that we missed from the start (both in groups and during the negotiation of the final design) to determine what is the primary focus of our solution and what aspects are determining our strategy. In the case of Lomma, I think population growth, predicted sea level rise and the exisitng character of the town were the most important. But then we need to face questions, like “what is our strategy for flood preparadness and mitigation?” and “what specific part of the exsiting character of the place we want to preserve?” and “what features we expect to introduce in the future for a sustainable city?”. I believe that we also need to study the tendency of the spread of the flood not only up to the year we are planning for, but beyond as well. For instance, by knowing that the water flows inland in 2050, leaving out a little piece of land (at the coast and north from the Loomma center), we could decide to leave it as a natural barrier. Natural barriers (permeable surface elevated above sea level and covered with dense vegetations) are considered to be one of the important flood protection solutions (1). However, at some point water will cover this land as well, but the natural barrier might give us more time to prepare for the next stages of the flood spread. Moreover, it is obvious that water is flowing to the north of Lomma. I belive that we need a combination of constructing flood protection (walls, barriers) and letting the water flow inland by directing its flow to specified areas away from exisitng settlements (2). So, by considering a more long term scenarios (worst case to see a “bigger picture” of the tendency of the flood spread) we can avoid developing cities in the areas that are going to be under a high pressure of flood. This way we avoid solving bigger problems at the point the flood comes by planing cities away from the pressure zones. We also might save resources byb mot building in the pressure zones and resources for the flood protection when it reaches the newly built settlements.
By desgining cities and flood protection only for the predicted sea level rise in 2050 and not considering 100-150 years form now, we create permanent solutions to temporary problems. Sea level rise is not a temporary problem, but the specific estimate for sea level rise in a certain year is a “temporary” stage of the problem.
The results of the impact assessment are quite similar for both designs. I think that it is vital to set right priorities at the start of the geodesign process. Moreover, a support and advice from experts from a variety of fields that represent the compexity of the place and its challenges is important for the effectivennes and success of the negotiated solutions.
I think that we missed from the start (both in groups and during the negotiation of the final design) to determine what is the primary focus of our solution and what aspects are determining our strategy. In the case of Lomma, I think population growth, predicted sea level rise and the exisitng character of the town were the most important. But then we need to face questions, like “what is our strategy for flood preparadness and mitigation?” and “what specific part of the exsiting character of the place we want to preserve?” and “what features we expect to introduce in the future for a sustainable city?”. I believe that we also need to study the tendency of the spread of the flood not only up to the year we are planning for, but beyond as well. For instance, by knowing that the water flows inland in 2050, leaving out a little piece of land (at the coast and north from the Loomma center), we could decide to leave it as a natural barrier. Natural barriers (permeable surface elevated above sea level and covered with dense vegetations) are considered to be one of the important flood protection solutions (1). However, at some point water will cover this land as well, but the natural barrier might give us more time to prepare for the next stages of the flood spread. Moreover, it is obvious that water is flowing to the north of Lomma. I belive that we need a combination of constructing flood protection (walls, barriers) and letting the water flow inland by directing its flow to specified areas away from exisitng settlements (2). So, by considering a more long term scenarios (worst case to see a “bigger picture” of the tendency of the flood spread) we can avoid developing cities in the areas that are going to be under a high pressure of flood. This way we avoid solving bigger problems at the point the flood comes by planing cities away from the pressure zones. We also might save resources byb mot building in the pressure zones and resources for the flood protection when it reaches the newly built settlements.
By desgining cities and flood protection only for the predicted sea level rise in 2050 and not considering 100-150 years form now, we create permanent solutions to temporary problems. Sea level rise is not a temporary problem, but the specific estimate for sea level rise in a certain year is a “temporary” stage of the problem.
I like the idea of following the flow of the water, as we can not only build walls, “as we will end up living behind 10m walls” (2) that also need maintenance. The water reservours created as a consequence can be imagined as future nature reserves and places for recreation. However welcomg sea water on land poses multiple challenges including loss of land, habitat and soil quality, preparadness for unexpectancy of how water spreads further into the land, dealing with multple land interests (the water is going to flood areas that are currently used for agriculture, provate businesses, etc).
So, to create a good housing strategy we need to simultaneously design solutions for the compexity of accompanying environmental, social and econimical challenges. At the moment I belive that both the negotiated and the group designs have good thoughts, but to reach a better realistic solution, they should be compared, combined in certain aspects, adjusted according to the advice of experts in climate change, enineering, economics, sociology and culture to name a few.
1. Sea Level Rise: Risk and Resilience in Coastal Cities (2016). Climate Institute. https://climate.org/sea-level-rise-risk-and-resilience-in-coastal-cities/
2. The Dutch Have Solutions to Rising Seas. The World Is Watching (2017). The New York Times. https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-change-rotterdam.html
So, to create a good housing strategy we need to simultaneously design solutions for the compexity of accompanying environmental, social and econimical challenges. At the moment I belive that both the negotiated and the group designs have good thoughts, but to reach a better realistic solution, they should be compared, combined in certain aspects, adjusted according to the advice of experts in climate change, enineering, economics, sociology and culture to name a few.
1. Sea Level Rise: Risk and Resilience in Coastal Cities (2016). Climate Institute. https://climate.org/sea-level-rise-risk-and-resilience-in-coastal-cities/
2. The Dutch Have Solutions to Rising Seas. The World Is Watching (2017). The New York Times. https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-change-rotterdam.html
Flow chart of the analysis in ArcGIS
Conference at International Geodesign Collaboration (ESRI) - june 2021
After the course I helped our course leader to adapt and develop the outcomes of the workshop for a conferece at International Geodesign Collaboration organised by ESRY (june 2021). Particularly, I was part of developing missing strategies for 2035 and 2050, conducting analysis agains the SDGs and working in ArcGIs to prepare a map of tree cover density for various scenarios.
The municipality of Lomma is looking for options to address growing population while taking into considerations various challenges like expected flooding caused by the sea level rise, preserving character of the town and valuable agricultural land surrounding it.
Prerecorded presentation of the project: https://www.youtube.com/watch?v=HIO6rrvwbbg
PDF of the presentation: https://b52a2f9e-824b-440e-8d87-00e7c850671a.filesusr.com/ugd/f24d78_c2f11d90124f42e593e6ef4d82cdbe0d.pdf
More about the International Geodesign Collaboration: https://www.igc-geodesign.org/igc-overview