National Research
Council of ItalyResearch Institute for Geo-
Hydrological Protection
Durham, 15/09/2015
Index of Sediment Connectivity:
applications and future perspectives
CONNECTEUR - COST Action ES1306
3rd WG Meeting
Marco [email protected]
Durham, UK – 15/09/15 – Index of Sediment Connectivity
Outline of the presentation
• Index of sediment connectivity
• Tools
• Applications of the index at catchment scale
• Applications and testing of the index at regional
scale
• Recent IC developments
• Final considerations and perspectives
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Durham, UK – 15/09/15 – Index of Sediment Connectivity
Borselli L., Cassi P., Torri D., 2008. Prolegomena to sediment and flow connectivity in the
landscape: a GIS and field numerical assessment. Catena, 75(3), 268-277.
Cavalli M., Trevisani S., Comiti F., Marchi L., 2013. Geomorphometric assessment of spatial
sediment connectivity in small alpine catchments. Geomorphology, 188, 31-41.
dn
up
D
DlogIC 10
Index of sediment connectivity
3
Geomorphometric approach for the assessment of sediment connectivity
The connectivity index (IC) is
computed using two
components:
Upslope component Dup
potential for downward routing
due to upslope area, mean slope
and impedance factor.
Downslope component Ddn
flow path length that a particle
has to travel to arrive to the
nearest target or sink.
Durham, UK – 15/09/15 – Index of Sediment Connectivity
slope S (m/m) (steepest descent direction)
S < 0.005 => S = 0.005 to avoid ∞ in the downslope component
equation
S > 1 => S = 1 to limit the bias due to very high values of IC on steep
slopes (e.g. rocky outcrop)
Flow direction: algorithm D∞ (Tarboton, 1997)
Slope (S) and flow direction
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Tarboton, 1997. A New Method for the Determination of Flow Directions and Contributing Areas in Grid Digital Elevation Models, Water
Resources Research, 33(2): 309-319.
Durham, UK – 15/09/15 – Index of Sediment Connectivity
MEAN
MOVING WINDOW
DTM LIDARSmoothed
DTM
RESIDUAL
TOPOGRAPHY
ROUGHNESS
INDEX
DIFFERNCE
MOVING WINDOW
STANDARD DEV.
MOVING WINDOW
The roughness value on each cell corresponds
to the topographic variability over the
investigated area (DTM resolution – moving
window size)
Roughness Index
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Durham, UK – 15/09/15 – Index of Sediment Connectivity
The standardization of roughness value was introduced for three reasons:
(i) to have the same range of variation as for S factor in order to weight them
equally in the model (0 – 1);
(ii) to remove the bias due to high RI values in steep areas;
(iii) to provide comparable values with USLE C-factor and therefore with the
original model.
The use of a roughness index as weighting factor has several advantages:
• the weight is estimated objectively;
• it avoids the use of tabled data;
• it allows the model to be applied straightforwardly (only DTM as an input).
)(1
RIMAX
RIW
Weighting factor (W)
Lower limit = 0.001
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Durham, UK – 15/09/15 – Index of Sediment Connectivity
• Running under ArcGIS version 10.1 (with SP1!) and 10.2.
• It requires the installation of TauDEM 5.1 http://hydrology.usu.edu/taudem/taudem5/downloads.html
Tools
Input working
DirectoryPits removed
DTM raster
Input DTM
cell size
Weighting
factor raster
Output Index of
Connectivity
raster
ArcGIS implementation
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Durham, UK – 15/09/15 – Index of Sediment Connectivity
• It avoids the use of commercial GIS;
• It implements the “Sink” function.
Tools
Open-source implementation (SedInConnect 2.0)
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http://www.sedalp.eu/download/tools.shtml
http://connecteur.info/indices/
Durham, UK – 15/09/15 – Index of Sediment Connectivity
Application at catchment scale
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Durham, UK – 15/09/15 – Index of Sediment Connectivity
Applications at catchment scale
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IC to
outlet
IC to
channel
network
D’Haen et al. (2013)
Messenzehl et al. (2014) Brardinoni et al. (2015)
Durham, UK – 15/09/15 – Index of Sediment Connectivity
1096 km2 area – LiDAR DTM with 2.5 m resolution
Application at regional scale
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Venosta Valley (Eastern Italian Alps) is a typical inner-
Alpine dry valley, dominated by metamorphic lithologies
Durham, UK – 15/09/15 – Index of Sediment Connectivity
IC to the outlet
• slight increase in IC values with decreasing
resolution;
• more evident for the application of IC with
regard to the Adige River;
• simplification of the flow paths due to increased
cell size leads to an increase of IC values.
IC vs. DTM resolution
IC to the Adige
River
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Durham, UK – 15/09/15 – Index of Sediment Connectivity
• different pattern when different impedance factors are used;
• overall lower IC values with Manning’s n.
Manning’s n vs. topographic roughness
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Durham, UK – 15/09/15 – Index of Sediment Connectivity
IC vs. catchment size
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Target: catchment outlet (fan apex) Target: main channel
When analyzing separately Dup and Ddn:
• no relationship is observed between Dup and catchment area;
• data show a positive correlation between Ddn and catchment area.
Durham, UK – 15/09/15 – Index of Sediment Connectivity
Recent index developments
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Sediment Connectivity Index Channel width Model Stream Power Model
in collaboration with S. Keesstra and F. Comiti
Structural connectivity Functional connectivity
Durham, UK – 15/09/15 – Index of Sediment Connectivity
Recent index developments
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in collaboration with Z. Kalantari and C. Cantone
Flood hazard along roads
Statistical modelling approach based on the identification
of the Physical Catchment Descriptors (PCDs) (Kalantari
et al., 2014) applied to 10 catchments in Western Sweden
affected by a flood event in August 2004.
Kalantari, Z., Nickman, A., Lyon, S. W., Olofsson, B. and Folkeson, L. (2014) ‘A method for
mapping flood hazard along roads’, Journal of Environmental Management, 133pp. 69–77.
doi: 10.1016/j.jenvman.2013.11.03
Durham, UK – 15/09/15 – Index of Sediment Connectivity
• IC has proved very promising for a rapid spatial characterization of sediment
dynamics both at catchment and regional scales;
• An integrated approach, encompassing sediment sources mapping and
connectivity assessment, can improve hazard and risk assessment;
• Quality and resolution of DEM has a strong effect on IC results;
• Being a topography-based index, IC is focused on structural aspects of
connectivity. Future development should also consider process-based connectivity
and incorporate temporal variability;
• Indices need models to a certain degree; are there models that might need indices
as parameters?
Final considerations and perspectives
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Tutto bene?
From static to dynamic
Durham, UK – 15/09/15 – Index of Sediment Connectivity 18
Thank you for your
attention!
Marco Cavalli