Identifying and characterizing ravines with gis terrain attributes for precision conservation

Ravines are a source of sediment loading into surface waters of the Minnesota River Basin (MRB). Ravines formed as the natural product of a landscape adjusting to disequilibrium in the main channel of the MRB caused by a massive glacial flood 11, 500 yr ago that lowered the base level of the river channel. Precision conservation techniques are needed to locate and correct ravines that contribute large amounts of sediment. This study uses a geographic information system (GIS) to identify the location of all ravines in the MRB and quantify their spatial distribution, area extent, and connectivity to the mainstem MRB. An analysis of test ravines with 3-m light detection and ranging (LiDAR) digital elevation model (DEM) was conducted to quantify uncertainty in ravine aerial extent estimates. Ravines could be located with an accuracy of 90% using a GIS algorithm involving slope steepness, flow accumulation, and standard deviation of aspect. Calculations from the GIS algorithm to delineate ravines show that ravines compose a total of 197, 830, 000 m2 (0.45%) of the basin landscape. Watersheds and agroecoregions along the main channel of the MRB had a greater incidence of ravines than in other locations due to their proximity to the lower base level of the main channel. Statistical and GIS-based analyses of ravine morphometrics showed that the elevation change from ravine to the main channel of the MRB was strongly correlated with ravine volume (r = 0.64) and relief (r = 0.8); both are characteristics that lead to greater sediment loading from ravines. Thus, ravines located near the main channel tended to be larger and steeper than ravines located farther from the channel. With the techniques developed in this study, conservationists can identify, for the first time, all ravines in the MRB and quantify features that are strongly related to sediment loading, such as volume, area, and relief.