a spatial information technology approach for the mapping and quantification of gully erosion...

A spatial information technology approach for the

mapping and quantification of gully erosion

University of Lleida, Spain

José A. Martínez-Casasnovas

Content

1. Introduction.– Spatial information technologies for gully erosion

analysis.– The gully erosion problem in the study area.– Objectives.

2. Materials and methods.

3. Results.

4. Conclusions.

1. Introduction

• A lot of research works on Gully Erosion Mapping have been based on Remote Sensing techniques, and particularly on airphoto interpretation.

• Satellite images may also offer interesting possibilities provided that gullies affect areas wide enough to be covered by the resolution of the images.

Landsat 5 TM Image Walls Activity Map

• At detailed scale, Photogrammetry has also been used to map the volumetric changes in gullies, sediment production and gully erosion rates.

1957

1993

The convergenceand extension ofPhotogrammetry,Digital Imaging Technologyand GIS have contributed to the use of multi-temporal DEM to computesedimemt production by gully erosion.

• In this context, the present work shows the methods and results of a research to compute Gully Erosion Rates using Spatial Information Technologies:

The Channel Incision Rate

The Sediment Production Rate

The Gully Walls Retreat Rate

España

Cataluña

Penedès– Suffers serious gully erosion problems– Gully erosion is favoured by the cropping of vineyards

The research was carried out in thePENEDÈS Vineyard Region (NE Spain)

Contouring and terracing

1957

1957

Elimination of traditional conservation measures

1993

• Particularly important has been the period after the advent of mechanization (1950’s).

1993

• The area has suffered a substantial transformation.

• At present, the problems are so grave that even afect to urban areas, that were built-up in the neighbour of gullies.

Alt Penedès Rierussa Catchment

25 km2

Martorell

Piera

Sant Sadurníd’Anoia

Sierra

Pre

litora

l

Sierr

a Lito

ral

Study Area

SpainCatalonia

LithologyMARLS, Sandstones, Conglomerates

Rainfall471 - 670 mm/yearAutumn & Spring> 100 mm h-1 in short periods

L’Anoia

2. Materials and methods

1957 Situation 1993 Situation

Aerial Photographs1957, 1:30000

Aerial Photographs1986, 1:30000

Orthophoto 1993

DEM

Gullied area 1957 DEM Gullied area 1993

Changes:Retreat of gully walls

Changes: Channel Incision & Sediment Production

Gully Walls Retreat / Channel Incision / Sediment Production

Photo-interpretation Restitution Photo-interpretationGeo-referenciation

Construction of the 1957 DEMPhotogrammetric Restitution of Contours (10 m interval)

Filtering Spatial Interpolation

Sediment Production Rate (SPR)

1993 DEM 1957 DEM

-

GR2 x ED x Bd

A x TSPR =

Bulk density(1.735 Mg m-3)

Time of the studied period (years)Surface of the gullied area (ha)

Grid resolution (m)

Elevation differences (ED)

=

3. Results

1. Gully area extent and Rate of gully walls retreat

Overlaying (UNION) of Gully Area Extent Maps

Overlay

1957

1993

Contingence matrix: UNION of Gully Areas

Year 1993 (ha)

Gullied areas

Non-gullied areas

565

1770

Year 1957 (ha)

Gullied areas Non-gullied areas

Areas without changes

Year 1993 (ha)

Gullied areas 77

Non-gullied areas

565

1770

Year 1957 (ha)

Gullied areas Non-gullied areas

Contingence matrix: UNION of Gully Areas

1957 1993

Gully Retreat

Year 1993 (ha)

Gullied areas 77

Non-gullied areas 39

565

1770

Year 1957 (ha)

Gullied areas Non-gullied areas

New parcel

1957 1993

Contingence matrix: UNION of Gully Areas

Gully Filling

Year 1993 (ha)

Gullied areas 77 642

Non-gullied areas 39

565

1770 1809

Total (Year 1957) 604 1848 2451

Year 1957 (ha)

Gullied areas Non-gullied areas Total (Year 1993)

Contingence matrix: UNION of Gully Areas

Retreat rate

(Rierusa Catchment)

2.1 ha year-1

Gully Retreat Rate

Linear Retreat Rate 0.2 m year-1

Retreat rate

(m2 / 1000 m2 of catchment)

0.9 ‰ year-1

When did the acceleration of gully erosion processes start ?

1957 1993

77 ha in 36 years

Let’s apply back this rate considering that

at present there are ~ 640 ha of gullies

~ 1650

From XVI century = Massive plantation of Vineyards under theprotection of temporary contracts till the end of vineyards’ life.(Balcells 1980)

Altitude difference (m)(1993 - 1957)

Areas withloss of materials

Areas withgain of materials

2. Channel Incision and Sediment Production Rates

0.8 m year-1

0.15 - 0.35 m year-1

2. Channel Incision and Sediment Production Rates

Topographic changes 1957-1993 - Profile 1

0.0

50.0

100.0

150.0

200.0

250.0

0 25 50 75 100125150175200225250275300325350375400425

Distance (m)

Alt

itu

de

(m

)

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

5.0

10.0

Alt

itu

de

dif

fere

nc

es

(m

)

1957 1993 Difference

Sediment Production Rate

Rate in the Gully-eroded Areas

1322 +/- 142 Mg ha-1 year-1

Rate with respect the

total catchment area

331 +/- 35 Mg ha-1 year-1

Comparison with respect other research areas

SE France (Bufalo and Nahon 1992)

190 Mg ha-1 year-1

Barasona basin (NE Spain)(Penella 1997)

375 Mg ha-1 year-1

Only account foroverland flow

erosion processes

Mass Movements

Penedès, Spain

1322 Mg ha-1 year-1

Channel Incision

Overland flowNew Zealand

(DeRose et al. 1998)

1550 - 2480 Mg ha-1 year-1

4. Conclusions

• The present work confirms the conclusions of other researchers who state that sediment production by gully erosion is very far from negligible

(around 1.300 Mg ha-1 year-1 are a lot of tons).

• In comparison with other methods of measuring sediment production, the proposed method computes a rate that is one order of magnitude higher.

Mass Movements

Channel Incision

Overland flow

• The reason is that it integrates the losses due to:

• In the Penedès region, the research confirmed the acceleration of erosion since the late Middle Ages because of the massive deforestation and plantation of vineyards, and in the recent past since the advent of mechanization.

• At present, we are working on a multi-temporal study centered at the head of the gully system, using 1:5.000 aerial photographs.

• This will serve to compute gully erosion rates at very detailed scale from high resolution DEMs.