Propose a new aggregated index of connectivity

Modelling structural and functional flow and sediment connectivity in a Mediterranean catchment by using a new aggregated index Division 3: Soil Use and Management C3.2: Soil and Water Conservation C3.2.5: Soil erosion modelling: Global Alliance Tuesday (Aug, 14)

Manuel López-Vicente, Nahed Ben-Salem Dept. of Soil and Water, Soil Management and Global Change Group, Experimental Station of Aula Dei, EEAD-CSIC. Zaragoza, Spain.

Modelling flow & sediment connectivity with AIC

López-Vicente & Ben-Salem

INTRODUCTION  The term ‘Hydrologic connectivity’ (HC) is used in different disciplines to refer to water‐mediated transfer of matter, energy, and/or organisms within or between elements of the hydrologic cycle (Pringle, 2001; Bracken et al., 2013).  Over the last decade, HC has emerged as a significant conceptual framework within which to address the spatial and temporal variability in runoff and sediment transport (Parsons et al., 2015).  Flow and sediment connectivity (FSC) is a concept implicit in the approach using the SDR (sediment delivery ratio) because low ratios imply a lack of (structural and/or functional) connectivity.  HC in large catchments is influenced by natural and human-induced heterogeneities and dynamic processes, and thus the accurate assessment of HC is a complex task.

1 López-Vicente M, Ben-Salem N. Science of the Total Environment, under review (STOTEN-D-18-05511R1).



INTRODUCTION Several approaches (tools) have been published in the literature to assess FSC: - Flow and sediment connectivity index (IC) by Borselli et al. (2008) & revised versions

- Network Index by Lane et al. (2009) - Relative Surface Connection (RSC) function by Antoine et al. (2009) - Reaney et al.’s (2014) Connectivity of Runoff Model, 2D version

- Sediment cascades using graph theory by Heckmann and Schwanghart (2013) and Cossart and Fressard (2017)

Dimensionless [-∞, +∞]

W is the “landscape-impedance weighting factor” W = C-RUSLE factor (vegetation and management)




INTRODUCTION Several approaches (tools) have been published in the literature to assess FSC: - Flow and sediment connectivity index (IC) by Borselli et al. (2008) & revised versions

• None of these studies have combined residual topography, soil permeability, the C-factors and rainfall erosivity, and their temporal changes, to model structural and functional connectivity at catchment scale. • We hypothesise that the use of a new aggregated index of FSC (AIC) will improve the assessment of the actual processes of connectivity at large catchment scale where multiple heterogeneities appear.

Related to the W weighting factor: - Residual topography (roughness index) - Density of the drainage network - Gross soil erosion - Rainfall erosivity

- Wildfire severity 3

López-Vicente M, Ben-Salem N. Science of the Total Environment, under review (STOTEN-D-18-05511R1).


OBJECTIVE

TASK 1

TASK 2

TASK 3


• Improve the prediction ability of Borselli’s index (IC) to simulate structural and functional flow and sediment connectivity (FSC) at catchment scale.

OBJECTIVE & TASKS

• Propose a new aggregated index of connectivity (AIC) and test it in a Mediterranean Basin at average and monthly (96 months) scales. • Evaluate the spatial changes of FSC with IC and AIC in the different land uses and geomorphic features. • Validate the temporal dynamic of FSC near the outlet by using river flow values.




NEW INDEX - AIC 𝐴𝐼𝐶𝑘 = log10

𝐷𝑢𝑝 ,𝑘 𝑅𝑡 · 𝑅𝑇 · 𝐶𝑡 · 𝐾𝑃 · 𝑆 · = log10 𝑑𝑖 𝐷𝑑𝑛 ,𝑘 𝑛 𝑘=𝑖 𝐴𝑊𝐶 𝑖

𝐴𝑊𝐶𝑖 = 𝑅𝑡𝑖 · 𝑅𝑇𝑖 · 𝐶𝑡𝑖 · 𝐾𝑃𝑖 · 𝑆𝑖

𝐴𝑘

AWC is the “aggregated landscape-impedance weighting factor at catchment scale”

R: rainfall erosivity

RT: residual topography

C: vegetation & practices

Kp: soil permeability

S: slope gradient

Easy-to-obtain factors

Rainfall erosivity (RUSLE2; 2017)

If t = average year  Structural (AICST) If t = specific period  Functional (AICFN)




STUDY AREA Vero River Basin • 380 km2 • Tributary of the Ebro River • NE Spain • Semi-arid (S) to sub-humid (N) • The Vero River is not regulated by any dam and thus the stream flow at the outlet reflects the natural hydrological response of the entire catchment 6 López-Vicente M, Ben-Salem N. Science of the Total Environment, under review (STOTEN-D-18-05511R1).



DATA ACQUISITION & PRE-PROCESSING




TEMPORAL CHANGES Interpolation:

- Average year


- 96 months




TEMPORAL CHANGES TEMPORAL CHANGES Interpolation:19 land uses:

- Average year- Cropland: 40%


- 96 months - Forest: 57%

Maps of C-factors




TEMPORAL CHANGES TEMPORAL CHANGES Interpolation:19 land uses: - Map of Lithology

- Average year- Cropland: 40%- Map of Soil types


- 96 months - Forest: 57% - 24 soil profiles: Map of Maps of

Soil water retention

C-factors

capacity




TEMPORAL CHANGES TEMPORAL CHANGES Interpolation:19 land uses: - Map of Lithology

- Average year- Cropland: 40%- Map of Soil types


- 96 months - Forest: 57% - 24 soil profiles: Map of Maps of

Soil water retention

C-factors

capacity

Spatial resolution: 5 x 5 m LiDAR-derived DEM Target of the simulation: Vero river




RESULTS:

IC

Range: 15.2

AIC

STRUCTURAL CONNECTIVITY

Non-normal

Range: 19.7 (>30%)

Almost-normal




RESULTS:

Cropland

Forest

with low soil water retention capacity

with high soil water retention capacity

IC

AIC

IC

STRUCTURAL CONNECTIVITY

AIC




RESULTS: FUNCTIONAL CONNECTIVITY

AIC-catchment vs. AIC-river (R2 = 0.9971) AIC-catchment vs. AIC-outlet (R2 = 0.9901)

Range: -20.102 and -11.292 (SD = 2.573)

Highest values of AICFN in September 2010, September 2014 and August 2015  Heavy rainfall Lowest values of AICFN in January, February 2012 and December 2016  Low rainfall (R = 0 mm in S)





SIMULATION of the 96-month test period: Sep’2009 – Aug’2017



















Main land uses Near river High C Low Kp

DISCUSSION & FURTHER RESEARCH

Far river Low C High Kp





Main geomorphic elements -14.077 -14.098

No significant differences

-14.181 -13.298 -7.172

Significant differences

-3.552 13 López-Vicente M, Ben-Salem N. Science of the Total Environment, under review (STOTEN-D-18-05511R1).



Validation of FLOW connectivity with the Vero river flow near the outlet r = 0.217  96 months

When Q > 2 m3 / s (14% of all days): r = 0.348  highest runoff yields in the hillslopes


Marked seasonality in water (Q) and sediment load (SY). Most Q occurred in winter and spring, and most of the sediment was transported during summer and autumn 14

López-Vicente M, Ben-Salem N. Science of the Total Environment, under review (STOTEN-D-18-05511R1).



CONCLUSIONS  The new aggregated index of runoff and sediment connectivity (AIC) successfully generated the maps of structural and functional connectivity in a large and heterogeneous catchment.  The incorporated inputs allowed generating more realistic maps of structural connectivity than the well known Borselli’s index.  The histogram obtained with the new index followed a normal distribution, which is characteristic of natural random variables.  Modelling testing with the river flow values suggested different runoff and sediment responses of the catchment over the year.  Further research is required to split the runoff and sediment connectivity processes and modelling testing with independent field- and model-based results.


Thank you for your attention! Questions?

Contact: [email protected] [email protected] Personal website: https://digital.csic.es/cris/rp/rp03203

Modelling structural and functional flow and sediment connectivity in a Mediterranean catchment by using a new aggregated index Manuel López-Vicente, Nahed Ben-Salem Dept. of Soil and Water, Soil Management and Global Change Group, Experimental Station of Aula Dei, EEAD-CSIC. Zaragoza, SPAIN.

Follow me at: @MLopezVicente López-Vicente M, Ben-Salem N. Computing structural and functional flow and sediment connectivity with a new aggregated index: A case study in a large Mediterranean catchment. Science of the Total Environment, under review (STOTEN-D-18-05511R1).

Propose a new aggregated index of connectivity

Propose a new aggregated index of connectivity

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