Detecting Channel Riparian Vegetation Response to Best-Management-Practices Implementation in Ephemeral Streams With the Use of Spot High-Resolution Visible Imagery

Kendall Vande Kamp, Matthew Rigge, Nels H. Troelstrup Jr., Alexander J. Smart, Bruce Wylie

Abstract


Heavily grazed riparian areas are commonly subject to channel incision, a lower water table, and reduced vegetation, resulting
in sediment delivery above normal regimes. Riparian and in-channel vegetation functions as a roughness element and dissipates
flow energy, maintaining stable channel geometry. Ash Creek, a tributary of the Bad River in western South Dakota contains a
high proportion of incised channels, remnants of historically high grazing pressure. Best management practices (BMP), including
off-stream watering sources and cross fencing, were implemented throughout the Bad River watershed during an Environmental
Protection Agency (EPA) 319 effort to address high sediment loads. We monitored prairie cordgrass (Spartina pectinata Link)
establishment within stream channels for 16 yr following BMP implementation. Photos were used to group stream reaches
(n¼103) subjectively into three classes; absent (estimated ,5% cover; n¼64), present (estimated 5–40% cover; n¼23), and
dense (estimated .40% cover; n¼16) based on the relative amount of prairie cordgrass during 2010 assessments of ephemeral
channels. Reaches containing drainage areas of 0.54 to 692 ha were delineated with the use of 2010 National Agriculture
Imagery Program (NAIP) imagery. Normalized difference vegetation index (NDVI) values were extracted from 5 to 39 sample
points proportional to reach length using a series of Satellite Pour l’Observation de la Terre (SPOT) satellite imagery.
Normalized NDVI (nNDVI) of 2 152 sample points were determined from pre- and post-BMP images. Mean nNDVI values for
each reach ranged from 0.33 to 1.77. ANOVA revealed significant increase in nNDVI in locations classified as present prairie
cordgrass cover following BMP implementation. Establishment of prairie cordgrass following BMP implementation was
successfully detected remotely. Riparian vegetation such as prairie cordgrass adds channel roughness that reduces the flow
energy responsible for channel degradation.

Key Words: channel morphology, Conservation Effects Assessment Project (CEAP), northern mixed-grass prairie, prairie
cordgrass, remote sensing


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