BayCEER Workshop 2015

Phases of Sediment Production in Upper Franconia derived by High-Resolution DTM

P 4.1 in Digging DATA, molding models: On the pursuit of patterns and correlations

Introduction

The Trebgast Valley with its small stream Trebgast is situated northwest of Bayreuth. Here, many specific relief features prove a long-term human impact on local geomorphology, which in turn had an effect on subsequent landscape development and soil erosion.

Material and Methods

 

We use a multi-methodical approach combining Digital Terrain Models (DTM), Sedimentology, soil survey and Historical Maps. A DTM detects structures beneath wooded areas that are not visible in ordinary satellite images. The maps are georeferenced and processed in a GIS-application. These results are cross-checked by geomorphic field studies.

Results

There is evidence of phases of morphodynamic activity and stability:

Firstly, there are relictic plough horizons on linchets that are covered by forests since 1852 at least. Neither previous agricultural land use nor the transition time between farming and reforestation led to their erosion. Moreover, the distribution of these structures indicate the extend of the medieval farming area.

Secondly, there are paleomeanders of the Trebgast that fell dry 160 years ago due to human channelization of the main stream. These former channels are coinciding with former field boundaries mentioned in historical maps. As they are still visible in DTM, subsequent accumulation of overbank fines was not high enough to fill and bury them.

Thirdly, there are sharply modeled field structures and field boundaries in farming areas. Their presence indicates a low rate of soil erosion in Modern Times.

 

Fourthly, compared to 1852 the area of woodland and buildings increased by +25% and + 560%, respectively. The summation of these two categories yields the area which is no longer suitable for agriculture. This adds up to nearly one half of the study are.

Conclusions

 

As a result, we are able to detect different phases of geomorphic activity caused by land use, hydraulic measures and reforestation.

Keywords: Digital Terrain Model, Historical Maps, Sedimentology, Soil Erosion, Upper Franconia