A simplified GIS-based model for Large Wood recruitment and connectivity in mountain basins

A simplified GIS-based model for Large Wood

recruitment and connectivity in mountain basins

Franceschi Silvia, Antonello Andrea, Lucía Ana, Cavalli Marco, Crema Stefano,

Comiti Francesco, Giustino Tonon

EGU Vienna 14 April 2015

INTRODUCTION

● practically all the basins in the Alps have been impacted by humans since ancient times

● forests were regularly and heavily harvested mainly for timber and firewood production and eliminated to create pastures, livestock and agriculture

INTRODUCTION

● in the 20th century we assisted at the decline of the rural and forest economy and the depopulation of upland areas: forest become old, shrubs and trees encroach abandoned crop and pasture lands

● between 1880 and 2000, the average increase of woodland in Switzerland has been 21.6%

● vegetation influence erosion, input, transport and deposition of sediment and wood in streams

INTRODUCTION

INTRODUCTION

● GIS-based tool for predicting the magnitude of LW transport during flood events at any given section within a river basin

● two main processes related to wood debris:

– LW recruitment from hillslopes

– LW transport/propagation along the network

JGRASSTOOLS: workflow

SHALSTABmodel

Channelwidening

Slopeinstability

EXTREME EVENTS

INPUTS AND PROCESSES OUTPUTSLEGEND

JGRASSTOOLS: workflow

SHALSTABmodel

Unstable slopes connectedto fluvial network

CONNECTIVITYmodel

Channelwidening

Slopeinstability

EXTREME EVENTS

INPUTS AND PROCESSES OUTPUTSLEGEND

JGRASSTOOLS: workflow

SHALSTABmodel

Unstable slopes connectedto fluvial network

CONNECTIVITYmodel

AREAS THAT PROVIDES LW

Channelwidening

Slopeinstability

EXTREME EVENTS

INPUTS AND PROCESSES OUTPUTSLEGEND

JGRASSTOOLS: workflow

SHALSTABmodel

Unstable slopes connectedto fluvial network

CONNECTIVITYmodel

AREAS THAT PROVIDES LW

TREE HEIGHT ANDFOREST STAND VOLUME

CHM and semi-empirical model

Channelwidening

Slopeinstability

EXTREME EVENTS

INPUTS AND PROCESSES OUTPUTSLEGEND

Volume and dimensionsof available LW

JGRASSTOOLS: workflow

SHALSTABmodel

Unstable slopes connectedto fluvial network

CONNECTIVITYmodel

AREAS THAT PROVIDES LW

TREE HEIGHT ANDFOREST STAND VOLUME

CHM and semi-empirical model

CRITICAL SECTIONS AND LW VOLUME

Channelwidening

Slopeinstability

EXTREME EVENTS

INPUTS AND PROCESSES OUTPUTSLEGEND

Volume and dimensionsof available LW

LW propagationField data

monitoring LW transport

JGRASSTOOLS: workflow

JGRASSTOOLS: input

● digital models of the terrain and vegetation: DTM, DSM, FSV

● DTM derived geomorphology attributes: TCA, slope, connectivity, watershed delineation

● extension of the bankfull area: area covered by water during standard flow conditions

● position and dimensions of bridges and dams: field survey or available cadaster

● superficial geology: rock and deposits (erodible)

JGRASSTOOLS: input & output

clogging sectionscumulated volume

TotalContributingArea

ExtractNetwork

FlowDirections

GEOMORPHOLOGY

DSM

FSV

DTM

INPUT

BANKFULLPOLY

Shalstab

DownSlopeConnectivity

Slope

SuperficialGeology

CheckDams

Bridges

OUTPUT

LW ALGORITHMS

source of logs

MapCalculator

JGRASSTOOLS: network attributes

● creates the vector of the network with hierarchical attributes based on an input raster network

● Input:

– network raster layer– map of flow directions– map of TCA

● Output:

– vector layer of network split at each confluence– attributes: strahler, hack, pfafstetter enumeration

JGRASSTOOLS: network attributes

PfafstetterStrahler Hack

JGRASSTOOLS: bankfull width

● extracts the bankfull width for each section of the stream and adds it as attribute

● different origin of input data:

– network inside the bankfull polygon– network tangent to the bankfull polygon– network do not intersect the bankfull polygon

JGRASSTOOLS: bankfull width

network inside polygon

network tangent polygon

network outside polygon

JGRASSTOOLS: bankfull width

● Input:

– bankfull polygon layer– vector of the network– maximum distance between network and bankfull

● Output:

– vector layer of network with width as attribute

– vector layer of the bankfull sections– vector layer with the problematic sections

JGRASSTOOLS: bankful width

JGRASSTOOLS: bankful width

JGRASSTOOLS: bridges + dams width

● corrects the bankful width where a bridge or a check dam is located

● Input:

– vector of the network– vector layer of the bridges– vector layer of the check dams

● Output:

– vector layer of network with corrected width as attribute

– vector layer with the problematic bridges (no width)

JGRASSTOOLS: area providing LW

● calculates the possible areas along the channel network where there is the possibility for the water during extreme events to erode and recruit material from outside the river

● the extent is calculated following a power law where new width is a function of the bankfull width and channel slope, parameters of the power law should be derived from field observations (input parameters)

● if available, widening would be limited by the presence of rock

newWidth=width+k⋅slopen

JGRASSTOOLS: area providing LW

JGRASSTOOLS: area providing LW

rock

deposits

JGRASSTOOLS: LW from hillslopes

● calculates the median vegetation height and total timber volume of the vegetation coming from the hillsopes

● steps for the evaluation of LW from hillslopes

Unstable ConnectedAreas

SubBasins

TSV

Shalstab

DownSlopeConnectivity

h_vegVegetation Parameters

JGRASSTOOLS: LW from hillslopes

JGRASSTOOLS: LW from hillslopes

JGRASSTOOLS: propagation

● identifies the critical section for the transit of LW in the given stream network

● based on the comparison between the length of the logs and channel width

JGRASSTOOLS: propagation

JGRASSTOOLS: propagation

criticalnon critical

● improve the propagation algorithm to consider also the height of the water in the river

● connect the results of the elaboration of LiDAR data for the evaluation of the position, the height and the diameter of the logs

FUTURE PLANS

USEFUL LINKShttp://www.jgrasstools.org

http://bit.ly/stage_downloads

Franceschi [email protected]

EGU Vienna 14 April 2015

THANKS FOR THE ATTENTION!