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In Press Article IN PRESS ARTICLE Remote Predictive Mapping 5. Using a Lidar Derived DEM to Test the Influence of Variable Overburden Thickness and Bedrock on Drainage and Basin Morphology Tim L. Webster, John C. Gosse, Ian Spooner, and J. Brendan Murphy DOI: http://www.dx.doi.org/10.12789/geocanj.2014.41.033 To appear in: Geoscience Canada Received: April 2012 Accepted as revised: July 2013 First published on the web: January 2014 Articles ‘In Press’ are peer-reviewed, accepted articles that have undergone layout in journal format, subsequent proof-editing by the author(s) and are ready for publication. The article in this form is the version of record. The article will be removed from this page and paginated once it is published as part of an issue. The date the article is first made available online as either “Accepted” or “In Press” will be carried forward to the published article. The article has been assigned a doi number that is finalized and citable. The doi number will be consistent with the article through to issue publishing and will be activated in CrossRef when the paper has been published in a Geoscience Canada issue. GEOSCIENCE CANADA Volume 41 2014 1 SERIES 4Department of Earth Sciences l'érosion linéaire de multiples petits (5 Saint Francis Xavier University km2) bassins versants dans l'Est du Antigonish, Nova Scotia, B2G 2W5 Canada. Le site d'étude a été choisi parce que sa géologie est homogène et SUMMARY que son pendage est parallèle à la sur- A 4–m lidar digital elevation model face du sol, qu’il est tectoniquement (DEM) provides sufficient resolution stable, qu’il a subi des changements to examine the impact of variable till similaires du niveau de base d’érosion, cover on the incision history of multi- de même qu’ une histoire glaciaire sim- ple small (5 km2) catchments in eastern ilaire, avec une épaisseur de mort-ter- Canada. The study site was selected rain variable, d’une couverture mince à because it has homogeneous bedrock l'ouest jusqu'à une couverture épaisse à Remote Predictive geology that dips parallel to the land l'est. La morphométrie du bassin a été Mapping 5. surface, is tectonically stable, has comparée à celle de bassins de taille undergone common base level semblable aux épaisseurs de till vari- Using a Lidar Derived DEM changes, and has a common ice history, ables. Les bassins aux couvertures de to Test the Influence of with variable overburden thickness, till plus épaisses sont plus larges et Variable Overburden from thin cover in the west to thick montrent des différences hyp- cover in the east. Basin morphometrics sométriques comparé à ceux aux cou- Thickness and Bedrock on were compared for similar-size basins vertures minces. Deux bassins Drainage and Basin that have variable till cover thicknesses. représentant les termes extrêmes de l'é- Basins with thicker till cover are wider paisseur du till ont été mesurées quant Morphology and show differences in hypsometries au débit du courant et à la chimie de compared to those where till cover is l'eau. Les till épais (>1 m) sur la Tim L. Webster1, John C. Gosse2, thin. Two basins representing end moitié est du mont Nord retardent l'in- Ian Spooner3, and J. Brendan members of till thickness were meas- filtration, ce qui favorise l'écoulement Murphy4 ured for stream discharge and water en surface et accélèrent l’érosion chemistry. Thick till (> 1 m) on the linéaire par rapport aux zones cou- 1Applied Geomatics Research Group eastern half of North Mountain vertes de couches de till plus minces. Nova Scotia Community College retards infiltration sufficiently to pro- On s’attend donc à ce que l'épaisseur 50 Elliot Rd. Lawrencetown, NS, Canada, mote overland flow and accelerate inci- de la couche de till et sa continuité B0S 1M0 sion relative to areas with thinner till. agissent comme une entrave à la stabil- Email, [email protected] Till thickness and continuity therefore ité et puissent aussi retarder les effets are expected to impede the achieve- de la loi de puissance de l’écoulement 2Department of Earth Sciences ment of steadiness and may also delay dans les grands bassins récepteurs Dalhousie University stream power law relationships in larg- jusqu'à ce que la couverture de till a été Edzell Castle Circle er catchments until till cover has been effectivement érodée. Halifax, NS, Canada, B3H 4R2 effectively eroded. INTRODUCTION 3Geology Department SOMMAIRE Understanding the relationships Acadia University Un modèle altimétrique numérique between stream incision and factors Wolfville, NS, Canada, B4P 2R6 (MAN) par lidar 4 m offre une résolu- related to fluvial erosion such as rock- tion suffisante pour étudier l'impact uplift, climate, base level changes, and des divers dépôts de till sur l'histoire de bedrock resistance to erosion (e.g. Seidl Geoscience Canada, v. 41, http://dx.doi.org/10.12789/geocanj.2014.41.033 © 2014 GAC/AGC® 2 et al. 1994; Gíslason et al. 1996; Stock groundwater interaction on discharge which have uniform resistance to ero- and Montgomery 1999; Kirby and (Tague and Grant 2004). At the scale sion (Figure 1), (ii) the area is tectoni- Whipple 2001; Stock et al. 2005) is of basin areas of tens of square kilo- cally inactive, (iii) the Bay of Fundy important for the analysis of landscape metres and larger, factors such as over- provides a uniform base level for all evolution (e.g. Pazzaglia 1993, 2003; burden thickness and the fracture den- streams, (iv) there is a clear distinction Kooi and Beaumont 1996; Dietrich et sity of bedrock can strongly influence in till cover thickness over the eastern al. 2003). The mechanics of river inci- infiltration rates and affect peak annual and western portions of the study area, sion have been studied by Whipple et stream discharge. and (v) the age of deglaciation and al. (2000), Whipple and Tucker (2002) Although the effect of DEM subsequent fluvial erosion is well docu- and related to rock strength by Sklar resolution on measuring different mented and uniform throughout the and Dietrich (2001). The availability of hydrologic and geomorphic properties area. The local effects of the variable high resolution (4 m) Light Detection has been examined (e.g. Wolock and till cover on basin morphology and the and Ranging (lidar) DEMs can facili- Price 1994; Zhang and Montgomery interaction of surface and groundwater tate quantitative analysis of incision 1994; Gao 1997; Zang et al. 1999; on net discharge and stream power and basin morphometrics at sufficient- Walker and Willgoose 1999), most of were evaluated. This study benefited ly small scales to allow the examination these studies have focused on the dif- from previous work related to validat- of factors controlling stream evolution. ferent effects of grid cell size interpo- ing the accuracy of the lidar DEM Fluvial processes in glaciated terrain lated from similar source data from (Webster 2005), and individual points are complex because glaciers and photogrammetry rather than advances (Webster and Dias 2006), mapping the streams may sequentially occupy the in data acquisition technologies such as basalt flow units (Webster et al. 2006a), same valleys but each can uniquely laser altimetry. In this study, the high- and relating the stream incision depth contribute to erosion, making the rela- resolution of the lidar (Light Detection to the basaltic flow units (Webster et tive influence of glacial and fluvial and Ranging) DEM allows detailed al. 2006b). The objectives of this paper processes on valley size difficult to dis- analysis of basin morphometrics to are to examine the morphology of sev- tinguish. In addition to glacial process- assess the local effects of variable eral drainage basins derived from a es shaping the landscape glacial till overburden thickness within a region. high resolution lidar DEM to better deposits can influence the permeability Lidar is a remote sensing technique understand landscape evolution of a of basin sediments and can affect used to derive precise elevation meas- section of North Mountain of the Bay drainage characteristics, such as over urements of the earth’s surface (Ritchie of Fundy area in Nova Scotia. The land flow and infiltration of precipita- 1995; Flood and Gutelius 1997; Wehr effects of variable overburden thick- tion. Brocklehurst and Whipple (2002, and Lohr 1999). It has been used in a ness, rock type and drainage character- 2004) and Montgomery (2002) use limited number of geoscience applica- istics are evaluated with respect to morphometric analysis including hyp- tions, including the analysis of river landscape evolution. Drill core data of sometry and valley cross-sections to networks (Kraus and Pfeifer 1998; the NMB volcanic flow units were differentiate large catchments affected Gomes Pereira and Wicherson 1999; examined and fracture density meas- by alpine glacial processes from others Stock et al. 2005), the generation of ured to test the influence of bedrock that were affected only by fluvial river floodplain cross-sections (Charl- fractures on erosion and drainage with- processes. They concluded that ton et al. 2003), the investigation of in each drainage basin. In addition, although glaciers widen and deepen landslides (McKean and Roering 2004), stream discharge and water chemistry valleys, significant relief enhancements and the mapping of tectonic fault were measured in two basins of similar are limited to large alpine glaciers. scarps (Harding and Berghoff 2000; size to determine the contribution of Studies applying the stream power law Haugerud et al. 2003), and bedrock overburden to stream discharge. often use the contributing drainage contacts (Webster et al. 2006a). Web- area as a surrogate parameter for ster et al. (2006a) used lidar data along PHYSIOGRAPHY AND AGE OF THE stream discharge, which in addition to with field observations to revise the LANDSCAPE the local channel slope, controls the bedrock geology and map three indi- The study area is situated along a 20- stream’s ability to incise the underlying vidual volcanic flow units within the km section of North Mountain, main- bed (e.g.
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