Quantifying Debris Flood Deposits in an Alaskan Fjord Using Multitemporal Digital Elevation Models.

Matthew Balazs,Gabriel Wolken,Anupma Prakash

doi:10.3390/s21061966

Abstract

Six DEMs over a 10-year period were used to estimate flood-related sedimentation in the Japanese Creek drainage located in Seward, Alaska. We analyze two existing LiDAR DEMs and one GNSS-derived DEM along with three additional DEMs that we generated using differential Global Navigation Satellite System (dGNSS) and Structure from Motion (SfM) techniques. Uncertainties in each DEM were accounted for, and a DEMs of Difference (DoD) technique was used to quantify the amount and pattern of sediment introduced, redistributed, or exiting the system. Through correlating the changes in sediment budget with rainfall data and flood events, the study demonstrates that the major flood events in 2006 and 2012—the 7th and 5th highest precipitation events on record—resulted in an increased sedimentation in the drainage as a whole. At a minimum the 2006 and 2012 events increased the sediment in the lower reaches by 70,100 and 53,900 cubic meters, respectively. The study shows that the DoD method and using multiple technologies to create DEMs is effective in quantifying the volumetric change and general spatial patterns of sediment redistribution between the acquisition of DEMs.

Highlights

Alluvial fans in recently deglaciated areas of the world, like the fjords of South-CentralAlaska, are dynamic areas where the forces of water and gravity are actively at work and continuously reshape the landscape
The resulting Digital elevation models (DEMs) of Difference (DoD) show how both the quantity and patterns of sediment deposition and erosion has changed from year to year
The normal regime of these reaches of the alluvial fan are erosional and transitional, and the sediment volumes are back near the 2006 levels with having only an additional ~1200 cubic meters of sediment. This is important because it is this area which has the least capacity to hold sediment and it is closest to the apex which is of concern as the channel could avulse into the surrounding neighborhood if the channel was filled to the top of the levee

Summary

Introduction

Alluvial fans in recently deglaciated areas of the world, like the fjords of South-CentralAlaska, are dynamic areas where the forces of water and gravity are actively at work and continuously reshape the landscape. In cities located within fjords, the active river channel cannot be allowed to avulse as it would flood the developed areas of the fan and bring in unwanted sediment. To mitigate this from happening city planners incorporate various measures such as constructing levees, spillways, or diversionary tunnels to contain and direct the flow of water and the distribution of sediment [6,7]. These protective measures remain useful only as long as they have the capacity to hold and divert enough water and sediment. City managers and engineers must actively monitor and manage these protective areas

Results

Discussion

Conclusion