Modelling soil erosion and runoff for a super typhoon event using PCRaster

Figures & data

Figure 1. Location of the study site. Alimit River Sub-watershed is situated in the northern portion of the Island of Luzon, Ifugao Province, Philippines.

Figure 2. Mechanics of soil erosion relating to sediment concentration and fluxes (Rose & Freebairn, 1985). The symbol e represents rate of rainfall detachment; d, rate of deposition; and r, rate of entrainment of sediment.

Figure 3. Location of tipping-bucket rain gauge and water-level recorder overlain on the DEM of Alimit River Sub-watershed.

Figure 4. Input maps required by the model: (a) land use/ land cover map, (b) NDVI map, (c) Manning's n map, and (d) saturated hydraulic conductivity (Ksat) map.

Table 1. Manning's n and saturated hydraulic conductivity value for various land uses.

Land use	Manning's n	Saturated hydraulic conductivity (mm/hr)
Forest	0.1	100.8
Brush	0.12	42.0
Grass	0.035	100.8
Sparse grass	0.03	33.0
Bare	0.025	0.6
River	0.04	0.0
Terrace	0.06	6.0
Trail	0.025	0.6
Urban	0.02	0.6

Table 2. Spatial characteristics of raster data used in modelling.

Parameters	Value
Data type	Raster
Number of columns	437
Number of rows	402
Reference system	Universal Transverse Mercator Projection, Zone 51, Northern Hemisphere
Reference units	Meters
Minimum X	291,335.0000000
Maximum X	313,185.0000000
Minimum Y	1,863,665.0000000
Maximum Y	1,883,765.0000000
X resolution	50
Y resolution	50

Table 3. Land use categories and their area coverage for Alimit River Sub-watershed.

Land use	Area (hectares)	Per cent of total
Forest	16,940	66.5
Brush	3,239	12.7
Grass	1,086	4.3
Sparse grass	1,622	6.4
Bare	1,310	5.1
River	1,048	4.1
Terrace	159	0.6
Urban areas	77	0.3

Table 4. Rainstorm events utilized in the modelling of soil erosion and runoff.

Event no.	Start (date)	End (date)	Rainstorm duration (hours)	Rainfall depth (mm)	Maximum intensity (mm/hr)
1	05/29/2015	05/29/2015	1.25	54	135
	14:00:00	18:49:55
2	08/30/2015	08/31/2015	4	36	54
	14:50:00	06:29:55
3	10/17/2016	10/20/2015	31	145	28
	14:20:00	06:19:55

Figure 5. Correlation analysis between the measured and predicted streamflow.

Figure 6. Correlation analysis of measured and predicted sediment mass.

Figure 7. Sediment mass and predicted streamflow of Alimit River, October 18–19, 2015, Barangay Alimit, Mayoyao Municipality.

Table 5. Summary table of rainfall and estimated runoff and eroded sediments for Alimit River Sub-watershed.

Event no	Total rainfall volume (m^3)	Estimated total surface runoff volume (m^3)	Estimated total eroded sediments (kg)
1	13,732,000	102,000	13,218,000
2	9,249,000	473,000	33,366,000
3	37,051,000	3,037,000	429,762,000

Figure 8. Screengrab of timeseries videos being played on a media player software: (a) Runoff timeseries video for rainstorm event 3 and (b) Sediment mass timeseries video for rainstorm event 3.

Rose, C. W. , & Freebairn, D. M. (1985). A new mathematical model of soil erosion and deposition processes with applications to field data. In E. Swaify , S. A. Moldenhauer , & A. Lo (Eds.), Soil erosion and conservation (pp. 549–557). Iowa: Soil Conservation Society of America.

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