1. David Mulla Professor and W. E. Larson Chair in Soil and Water Resources and Shannon Wing, Joel Nelson, Jake Galzki, Wenyu Wang Dept. Soil, Water & Climate University of Minnesota
19. 0 300m 3m Area: 1.995 ha 30m Area: 2.34 ha 30m Area: 3.89 ha 30m Area: 5.92 ha
20. Manually digitized area comparison between 30m DEM and 3m LiDAR datasets Digitizing from 30m DEM results in 144% overestimation in ravine area relative to 3m LiDAR Ravine 30m DEM Area 3m LiDAR Area Area Difference 30m - 3m Percent Change ID (m 2 ) (m 2 ) (m 2 ) (%) 3 38069 17033 21036 123 4 31562 13197 18365 139 5 26130 5189 20941 404 6 134098 78646 55452 71 7 28271 15022 13249 88 8 9941 4051 5890 145 9 27641 9880 17761 180 10 403664 259619 144045 55 11 37484 38900 17535 88 Average 144 Standard Deviation 105
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22. Ravines (blue) or their center lines (green) are defined using GIS terrain attributes such as profile curvature, slope steepness, and catchment area. Upland contributing areas are in light green
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24. Pearson Correlation Coefficients: Ravine vs Upland Contributing Area Features Ravine Feature Upland Contributing Area Channel Length Max CTI in Upland Contributing Area Max SPI in Upland Contributing Area Area 0.81 0.82 0.6 0.69 Volume 0.78 0.78 0.55 0.66 Perimeter 0.72 0.76 0.61 0.61
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28. Minnesota River Ravines and Bluffs *Ravine and bluff areas are expressed as a percent of the total area of ravines or bluffs. Total area of ravines is roughly 80 times greater than total area of bluffs Watershed Area (km 2 ) Ravines (%)* Bluffs (%)* Le Sueur 2881 2.9 41.8 Blue Earth 4015 3.6 26.6 Cottonwood 3400 5.9 8.9 Watonwan 2273 1.3 4.6 Chippewa 5371 5.2 0.4 Redwood 1826 2.1 0.8 Hawk-Yellow 5373 7.5 6.3 Lac Qui Parle 2841 5.6 5.5 Lower 4714 22.9 3.4 Middle 3490 14.4 1.7 Upper 5341 28.6 0
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Editor's Notes
At this scale, the difference between the 2 resolutions is not as visible
As we scale in, the coarseness starts to rear its ugly head…
Even closer, this is a somewhat conservative (area-wise) hand-digitized ravine boundary for a ravine on the Cobb
But as you can see, with the LiDAR, it is clearly an overestimation of the area
These are the areas for comparison. The 30m was digitized from the DEM, the 3m was digitized from the LiDAR
The coarse resolution makes it difficult to define the ravine boundary. What follows are 3 examples of how this ravine boundary might be delineated from conservative to generous…
3 possible boundaries are illustrated: area 23,400 m^2 – The most conservative
38,900 m^2
Area = 59,214 m^2
Noting the variance between the 30m areas…
The 3m LiDAR shows a much more accurate boundary
And results in an area which is (most likely) closest to truth. When compared with the orthoquad, the black boundary shown here is almost exactly aligned.
![Wikipedia’s Definition of a Ravine ,[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)