Safety and risk streaming through the city - Halden municipality
When the municipality of Halden began to review its area planning, they saw a need for more knowledge about safety and risk along two streams running through the center of the city; Remmenbekken and Schultzebekken.
The municipality has already experienced floods and landslides, and large parts of the area of the two streams are below the marine limit. NGI was engaged in conducting an initial investigation and in surveying safety and risks associated with natural hazards such as:
- flooding
- landslides and debris flows
- quick clay slides
NGI was provided with information about the municipality's drainage network and input about areas planned for new developments near the streams, which were included for assessment.
An area of concern was if these new developments could lead to a higher risk of run-off downstream in case of extreme rainfall or run-off.
Picture showing a path which has been diminished by erosion. The ravine appears as a flood plain.
NGI has conducted several types of investigations
- hydrological analysis and modeling of flood and surface water
- GIS analyses and assessments based on available data
- surveys along both streams to identify critical points
- assessment of historical events
- assessment of the effects of climate change
The assessments were submitted as a report, and associated maps were adapted for use in municipal area planning. The most detailed type of map possible was produced for each natural hazard, given the available material and scope of the fieldwork.
The hazard maps show areas of potential danger and where it was impossible to calculate probability. The hazard maps show where the various natural hazards can occur and how likely they are to occur.
Maps produced
- hazard map - flooding
- areas of concern - landslides
- areas of concern - quick clay slides
- consequence map - landslides
- consequence map - quick clay slides
- total consideration zones for all natural hazards
Use of the maps
- define consideration zones with associated provisions in the municipal area planning
- prioritize further surveys to safeguard residents in connection with emergency preparedness and comprehensive risk and vulnerability analysis following the Civil Protection Act
- prioritize areas for development, for example, by avoiding development in areas of potential danger or prioritizing regions involving least risk
- identify the need for further and more detailed investigations in continued planning work (regulation plans and building issues)
NGI welcomes many municipalities, such as Halden, to take precautionary measures by mapping safety and risk associated with natural hazards in challenging areas. The Planning and Building Act requires that municipal plans show important considerations and restrictions for land use.
By assessing safety and risk associated with natural hazards, the municipality possesses the necessary knowledge to avoid development in hazardous areas, secure existing buildings against natural hazards, initiate other measures to prevent damage from natural hazards, and improve preparedness related to natural hazards and extreme weather. The fact that the municipality is aware of challenging natural hazards is of prime importance in making decisions that recognize climate change.
Carl Bonnevie Harbitz
Expert Adviser Climate Adaptation and Hydrodynamics carl.bonnevie.harbitz@ngi.no+47 922 39 636