Module 7:

Assignment

Use the geomorphic change detection add-in to ArcMap to become familiar with quantitative analysis of channel geometry changes.

The goal of this assignment is to:

1) Get experience working with topographic datasets

2) Recognize and identify specific mechanisms of geomorphic change

Tasks

1. Using the Freshie Dataset, create a GCD (Geomorphic Change Detection) Project

   • 1.B.1: Add three of the five years loaded as surveys-- DONE (Added 3 of the 5)

   • 1.B.2: Two change detections (threshold @ 80% probability) for two of the epochs-- DONE (2003-2004 and 2004-2005)

   • 1.B.3: A budget segregation with at least two examples each of the following mechanisms of change identified:

     • Bank Erosion-- DONE

     • Channel Bed Lowering (degradation/incision)-- DONE

     • Channel Bed Rising (aggradation)-- DONE

     • Bar Development-- DONE

**Note-- I used the same years as Joe did for his instructional videos, but I completed my own interpretations for this assignment while including the ones he presented in his demonstration video.

Study Site- River Freshie, Highlands of Scotland

Methods

1. Aerial survey DEMs of the study site of the River Freshie from 2003, 2004, and 2005 were loaded and analyzed using the Geomorphic Change Detection (GCD) ArcMap Add-in. A new GCD project was created for this analysis. The error surfaces were calculated that represented the uncertainty of the elevations displayed in the DEMs.

2. Change detection raster's with a threshold of 80% probability were generated from the aerial survey DEMs for two epochs. The two analyze epochs are:

   1. 1 year time period from 2003 - 2004.

   2. 1 year time period from 2004 - 2005.

3. Next, a budget segregation was completed for each of the epochs through identification of areas of bank erosion, channel bed lowering (degradation), channel bed rising (aggradation), and bar development from interpretation of the 2003 to 2004 change detection raster and the 2004 to 2005 change detection raster.

2003-2004 Topographic Change

2004-2005 Topographic Change

Topographic Change Detection Results

Areas of bank erosion, channel bed lowering (degradation), channel bed rising (aggradation), and bar development were identified through interpretation of the change detection raster in each of the two epochs analyzed. Discussion of the interpretation of each mechanism and results are presented below.

Bank Erosion

Bank erosion is the detachment of grains from the bank meaning the stream bank is being worn away. This usually happens through increases in discharge. Bank erosion will be apparent when comparing the DEMs of different years by the identification of dark red slivers along channel edges. . Areas of channel bank erosion were identified in each of the two epochs. The volumetric loss from identified bank erosion for the two epochs is shown below. Grey = total predicted change and red = bank erosion.

The identified bank erosion in 2003-2004 comparison ranges from 10 cm to 125 cm loss. Comparatively, the identified bank erosion from 2004-2005 ranges from 30 cm to 130 cm loss.

Channel Bed Lowering (Degradation/Incision)

Channel bed lowering is the vertical adjustment of the channel to a lower elevation. A destabilized bed and increased erosion commonly initiated by a reduction in the available bed material typically leads to channel bed lowering. Degradation is visible in the change detection DEMs by extensive erosion occurring in the channel bed itself which will be colored red. Areas of channel bed lowering were identified in each of the two epochs. The volumetric loss from identified channel bed lowering is shown below. Grey = total predicted change and red = degradation.

The identified degradation in 2003-2004 comparison ranges from 10 cm to 65 cm loss. Comparatively, the identified bank erosion from 2004-2005 ranges from 28 cm to 120 cm loss.

Channel Bed Rising (Aggradation)

Channel bed rising is the vertical adjustment of the channel to a higher elevation. This will result in an increase in sediment accumulation on the bed of the river. Channel aggradation is visible in the change detection DEMs displayed in the light blue color. Areas of channel bed rising were identified in each of the two epochs. The volumetric addition from identified channel bed rising is shown below. Grey = total predicted change and blue = aggradation.

The identified aggradation from 2003-2004 ranges from 5 cm to 55 cm addition. Comparatively, the identified aggradation from 2004-2005 ranges from 15 cm to 75 cm.

Bar Development

Bar development occurs when there is sufficient bed deposition to result in a lateral shift in the channel at lower flows. Bar development can be detected as higher depths of deposition compared to what is seen when channel bed rising occurs and results in the area no longer being part of the low flow of the channel bed. Bars reflect sediment supply conditions, and can show where the sediment supply rate is greater than the transport capacity. On the change detection DEMs, the areas in darker blue were determined to designate bar development. Areas of bar development were identified in each of the two epochs. The volumetric addition from identified bar development is shown below.

Bar development from 2003-2004 ranges from 8 cm to 88 cm addition. Comparatively, bar development ranges from 20 cm to 225 cm addition.

Summary

With the use of the Geomorphic Change Detection Software (GCD) in ArcMap, topographic change detection and a sediment budget segregation was completed for two different epochs for the Freshie River located in the Highlands of Scotland. Bank erosion, channel bed lowering (degradation), channel bed rising (aggradation), and bar development were identified from 2003-2004 and 2004-2005.

2003-2004 Overall Topographic Change

2004-2005 Overall Topographic Change