WATER RUNOFF MAPPING
Flow mapping helps identify suitable locations for sediment trapping and other edge-of-field mitigations. By using Topographic Wetness Index (TWI) modeling, landowners can determine optimal sites for wetlands, sediment traps, dams, and bunds.
What is TWI?
Topographic Wetness Index (TWI) measures an area’s likelihood of accumulating and retaining water based on its slope and contributing upslope area. It highlights wet or poorly drained areas, making it a valuable tool for siting edge-of-field mitigations such as bunds and wetlands.
How TWI Supports Landowners
TWI modeling provides an estimate of water accumulation areas and volumes, aiding in catchment and farm planning. While ground-truthing is necessary, this tool can help landowners explore options for additional farm actions that enhance environmental outcomes.
Accessing TWI Data
TLC has KML files available for use in GIS or Google Earth, allowing landowners to visualise suitable mitigation sites. Contact your TLC catchment coordinator to learn more about accessing and applying this information. To find out who your TLC catchment coordinator is, head to your catchment page.
TOPOGRAPHIC WETNESS INDEX - MANGAMAHAKI
Choosing The Right Mitigation Approach
Edge-of-field mitigations should align with the specific outcomes each catchment is seeking. In New Zealand, there has been a tendency to promote single-solution approaches, such as focusing solely on constructed wetlands or detention bunds. While these can be effective, TLC emphasises a broader perspective, ensuring that mitigation strategies suit the unique needs of each landscape and farming system.
Examples of edge of field mitigations, from large detention bunds, large wetlands through to in-line or off-line sediment traps.