Ulrik Mårtensson Lund University Sweden. Methodology

Transcription

1 Ulrik Mårtensson Lund University Sweden Department of Earth and Ecosystems Science Lund University GIS Centre Centre for Middle East Studies Methodology Geomorphological applications Field work - GPS Remote sensing Geographical Information Systems (GIS) 1

2 Example of jobs and activities University teacher and consultant in GIS, RS and geomorphology Tunisia - Soil and water conservation, salinity, vegetation, socioeconomy Pakistan Water Resource Management Viet Nam and Thailand CSMP Nigeria & Kenya Land resource management (soil erosion) Ghana Country at a Glance Ghana & Uganda BPEIS BPEIS Synthesis report Swedish national GIS implementation programme Physical Planning in Egypt data quality assessment IRBM Lake Victoria GIS implementation in Sri Lanka and Uganda Universities LAO PDR GIS in Agriculture and forest research Tunisia & Lebanon Remote sensing for land degradation mapping Tanzania Remote sensing and GIS for studies of the relationship HIV/AIDS and agriculture Syria Remote sensing for forest fire area estimations Palestine accessibility to helth services Croatia mapping sea grass beds and coastal environment Mass movements (wasting) 2

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4 gbvfffff Fluvial Processes Davis conceptual model for landscape development is still very often referred to in textbooks Sub-picture E name several characteristic landforms on a developed floodplain 4

5 The drainage basin Important area unit! Principle the same from meter scale to 1000 km scale Different systems for classifying stream order 5

6 Runoff = P I E Horton overland flow occur when P>I+E Saturated overland flow when the soil is saturated by water Once motion has been initiated it can be maintained by a lower flow velocity 6

7 Erosion processes Rain drop erosion Sheet erosion Rill erosion Gully erosion Inter rill erosion Transport by: Saltation Suspension Rain splash Sheet wash Rill Gully a) Orchard terrass Station "A" Station "B" b) Station "C" Set-up of an erosion measurement station using erosion pins, normally planted in groups of five at different locations on the slopes 7

8 Stony surface typical for a desert/semi arid climate Stone or desert pavement due to small particles transported away, courser materials left behind Intense rainfall combined with lack of natural vegetation on the stony slopes leads to severe erosion, infrastructure rupture, cultivated soils disappear 8

9 Gully development starts with a rupture in vegetation that leads to the forming of a depression eventually ending as a Gully. Note that the erosion starts down stream and work its way up-stream Gullies in agriculture lands in central Tunisia. Feather-like pattern spreading upslope. Contour bonds build to prevent spreading 9

10 Huge gully developing on flat cultivated ground at one single rain fall event Distance between trees in orchard 24 m Badland formation 10

11 USLE is used all over the world to estimate mean annual erosion intensity Critiziced of many but still good to demonstrate impact from different factors Standard erosion plot that may be used to calibrate USLE to new environments Width 7 m Fenced Erosion plot Length 23 m Sediment collection ditch Evacuation tube Width 0.4 m Water collection tank (2 x 2 x 2 m) 11

12 A B C D Soil sampling sites (three per plot (A - D) Test plot Metal sheet border of the plot preventing runoff from entering from outside areas Four test plots with different treatment Runoff concentration and subdivision Concrete surface to eliminate unwanted sedimentation before collection 50% 50% Sampling from each plot only 25 % of the total run off 25% to be sampled 75% of total to be spilled Combined Erosion Model (case from Nigeria National soil erosion modelling ) Rainfall Erosivity Drainage Density Geology and Soils Soil Erodibility Depression Soils Slope Length (constant) Topography Watercourse Topography Slope Angle Land Cover Land Use & Vegetation Rubber Band Development Soil Management Input data from existing sources and satellite image interpretation, combined with field data collection MUSLE Modelling Wind Direction Soil Erodibility Universal soil loss equation Water Processes Eolian Processes Land Cover Wind Speed E R K L S C P Combined Erosion Modelling Soil Management Fetch Soil Erosion Intensity Soil Degradation Trend 12

13 Rainfall erosivity index The R-factor Soil map from satellite image The K-factor 13

14 Digital elevation model The L and S-factors Vegetation maps from 1975 and 1995 The C and P-factors 14

15 Big variation in vegetation cover North West East South GIS Geographical Information System 15

16 Geology Land Use & R Topography and Soils K L S C Vegetation P Drainage Density Depression Soils Watercourse Topography Rubber Band Development Rainfall Erosivity Soil Erodibility Slope Length (constant) Slope Angle Land Cover Soil Management MUSLE End result, brightere tone = higher estimated Modelling erosion rate Used to prioritise actions, but needs field verification for actual planning Soil Erodibility D Water Processes Eolian Processes Land Cover Wi Combined Erosion Modelling Soil Management Soil Soil Erosion Degradation Intensity Trend Sediment transport in a river Suspension and saltation important 16

17 Lag time important, e.g. inondations Depend on basin shape Pattern usedd to classify and may give information about rock type and tectonics Flow velocity influenced by friction with river banks and bottom. Concept of Talweg, note meandering even in a straight channel (fig 12)! 17

18 Concept of meandering important to understand development of the flood plain and its major shapes Braided river sign of too heavy sediment load. Very often glacier melt water and also associated with formation of alluvial fans 18

19 Headward erosion could lead to River capture and completely change the hydrology of an area see Niger/Benue example Alternate scouring and deposition depending on current regime. Dynamic environment with shifting depth and drifting material forming e.g. sand banks. 19

20 Meander Levée Oxbow lake Backswamp Yazoo stream Terraces indicate tectonic up lift or sea level shift (Base level shift) Extreme case in very soft rock Grand Canyon Frozen meanders 20

21 Base level local could be a lake Base level global ocean water level Knick points see also Gully development The dead of a river when it meets the ocean (or a local lake) Delta growing sediment from river exceeds erosion from waves and currents Delta soils often very fertile, historical importance 21

22 Delta shapes: A. Nile, slow sedimentation, lots deposited on the delta, less at the mouth, strong long shore current B. Good sediment supply to mouth, limited erosion except in extreme events C. Only one channel survive, strong erosion D. Inland delta due to very heavy tidal effects 22

23 Ulrik s comment to text figure 1: Vegetation binds soil on the slope. In arid climate stone pavement develops due to lack of vegetation Ephermal streams are also braided streams. Illustration is also an alluvial fan Playa extremely flat, fine clay soil particles, quick sand and qiuck clay, extremely slippery and fragile when wet 23

24 Satellite images - a good way to collect info Here a lake formed on the playa after a one day heavy rain it is the position in the landscape that would be a permanent lake in a temperate climate zone Two weeks after an innondation flamingos, 300 km from the closest known resort Before After 24

25 Decrease in ground water level on the Gammouda plain April December Station 1 Station 2 Station Irrigation in hot areas high risk of salinisation Pumping groundwater High evaporation Salty groundwater intrusion 25

26 Weathering is an important process active in all environments but most prominent in tropical climates 26

27 Depending on rock resistance, weathering is affecting also arid landscapes Referring back to similar graph for running water but density differences are bigger so transport requires higher wind speed 27

28 Same modes of transportation as running water Erosion by wind 28

29 45 million tons to Amazonas every year Wind erosion a global process Present in all climates, particualrly on cultivated fields, these iamges is from just outside Lund 29

30 Dune classification done according to wind direction(s) and availability of sand Elements in an arid landscape Mountain ranges Alluvial fans/bajada Playa 30

31 Alluvial fan High mountains where India is pushing against Asia In Pakistan it is very dry and water availaility is an issue. In the mountains suitable land for cultivation is also a problem. Traditionall issigation use surface water, and the alluvial fans are a good way to profit from the water. 31

32 Analysis of satellite recordings demonstrate a strong increase of vegetation Seasonal variation could be strong Soil and water conservation Check dam Orchard terrace Contour bond Tabia and Yessour Re-plantation of vegetation Shelter belt plantation or mechanical Perennial crops 32

33 Set-up of an erosion measurement station using erosion pins, normally planted in groups of five at different locations on the slopes a) Orchard terrass Station "A" Station "B" b) Station "C"

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36 Dry year wet year Desertification??? 36

37 THE FUTURE??? Overexploitation of the land leads to erosion, irrigation to salinisation, but at the same time on short-term basis the crop yield increases and thus revenue for farmers. Should WE tell them to not do that? Long term solutions return to animal husbandry? 37

38 Water harvesting??? Coastal processes Mechanical waves (Tsunami) Tide water waves (Pororoka in Amazone) Wind generated waves Sea vindvåg Swell dyning Wind speed Fetch the distance Duration the time Wavelength Wave height = wavelength (distance between two wave peaks) = frequency (number of cycles passing a fixed point per unit time) 38

39 Currents Wind generated Salinity differences Temperature Near shore circulation cell wave generated Some numbers Sea Short and relatively steep, h/λ = 0.03 Ocean h = 2-5 m, extreme 10-15, λ = m The Baltic h = m Max measured 9 m Swell λ increase and h decrease, crest regularised, smaller waves are eaten by bigger due to interference λ = 300 m, up to 750 m 39

40 Breakers Deep water wave Circular movement of water molecules Diameter h at surface; 0.043h at depth = ½ wave length; 0.002h at depth = wave length Bottom contact from about depth < ½ wave length Spilling breaker Plunging breaker Surging breaker Depends on steepness (h/ λ) and the slope of the ocean bottom Spilling breaker summer waves that normally build on the beach Plunging breaker winter waves that erode the beach collapsing wave disturb the forward motion under the crest => outward net transport and deposition of sand bars Surging breaker last brake on the beach it self => long shore drift and sorting on the beach 40

41 Near shore circulation system Wave refraction due to bottom contact of waves Sand bars 41

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43 follow link to LUMA-GIS 43

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