Reversing the Catastrophic landslide as agent for regeneration
Student: Haifan Chen Supervisor: Dr Sareh Moosavi Master of Landscape Architecture Melbourne School of Design University of Melbourne Nov. 2017
Acknowledgement This book would not be possible without the support and guidance from many academics at Melbourne School of Design, Faculty of Architecture Building and Planning, University of Melbourne. Including my thesis supervisor Dr Sareh Moosavi, for her constant advice and inspiration throughout the entire progress. Dr Margaret Grose’s encouragement and support on researching of landslide and ecological solutions. Dr Siqing Chen and Mr Christopher Newman’s technical support on GIS and Mr Elliot Summers’ hands-on assistance with Rhino modelling. In addition, very special thanks go to Marc Christen and the whole RAMMS team from WSL Institute for Snow and Avalanche Research SLF of Switzerland. Their generous provision of the RAMMS (Rapid Mass Movement Simulation) software licence and online support have granted me the essential stepping stone for this thesis. Their unique contribution has allowed me to deeply engage with the science behind landslide and debris flow, eventually complete this project with the original intention.
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INTRODUCTION an event triggered thesis city of Mocoa - site map site context affected neighbourhood the interplaying narrative
HYPOTHESIS + SCOPE thesis hypothesis theoretical framework mapping the scope
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MITIGATING SHALLOW LANDSLIDE
contents
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mapping of shallow landslide dynamics of plant colonization plant and slope gradient plant adaptations responsive schedule for reforestation reforestation x drones visualising plant colonization
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SIMULATION + DESIGN 39 41 43 44 45 47 49 51 53 55
RAMMS program constructing the digital terrain simulating the existing initial simulation findings meandering river vs debris flow initial terrain manipulation testing manipulated terrain proposed terrain manipulation simulating diversion and detention simulating riparian zone
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AFTERMATH AS CATALYST 59 69 73 75 77 85 87 89
final proposed terrains proposed intervention site designing with the aftermath recycle and rebuild ecological public spaces a multifunctional terrain site visualisation unfolding future stories
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INTRODUCTION
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image: https://www.pri.org/stories/2017-04-01/death-toll-southern-colombias-huge-mudslides-rising-fast
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NOT AN APRIL FOOLS’ DAY JOKE
IMAGE: http://www.nationalgeographic.com.au/nature/mudslide-in-colombia-sweeps-through-town-heavy-rains-may-portend-el-nio.aspx
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THE EVENT THAT TRIGGERED THIS THESIS On the midnight of April 1st, 2017, a major landslide has occurred in the Colombian city of Mocoa, destroying seventeen neighbourhoods (barrios) and killed at least 263 people with more than 300 still listed as missing.
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Site Location City of Mocoa is located Southwest of Colombia near the Andes range with a population of approx. 44,000. The sea surface temperature rise off the coast of Colombia, Ecuador and Peru have been higher than normal and constantly in utuation. This has contributed to the increase of the evaporation rate, and leading to greater moisture in coastal atmospheres, and ultimately greater precipitation.
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SOUTH PACIFIC OCEAN
MOCOA
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The Andes Range
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COCA PLANT DEFORESTATION PRECIPITATION Up to 129.3 mm of rainfall was measured in the area around Mocoa during a period of only three hours compared to 270mm of average monthly rainfall in Mocoa. This sudden increase in precipitation combined with the high level of rainfall over the last ten days triggered a wide range of landslides in the hillslopes of the catchments of the surrounding ďŹ ve rivers and eventually reached the urbanised neighbourhood.
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In the 1980s there plantations, but they conspicuous when surveillance came alon growers adapted farming plots smaller the satellite images a nibbling at and hollo frontier.
Over the last decades, decades deforestation has been extensive across the resource-rich region due to the expansion of livestock breeding, coca plantations, mining, and logging
SHALLOW LANDSLIDE Shallow landslides and soil loss in the upper part of stream catchments lead to high sediment yields downstream. The land mass that obstructed the water sources generated a damming and clogging of the rivers, which created the ultimate destruction.
TATION
The Interplaying Narrative
combined causes of both natural and man-made factors contributed to the formation of the landslide
e were giant y became too satellite-based ng. So the coca and started than a pixel in and constantly owing out that
DISPLACEMENT A large percentage of Mocoa’s residents are people fleeing violence from Colombia's five-decade-long civil war. The majority of these displaced residents generally have nowhere else go and can only construct their homes in high-risk areas.
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HYPOTHESIS + SCOPE
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image: https://www.theguardian.com
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IMAGE: http://miputumayo.com.co/2017/04/01/no-fue-una-avalancha-fue-una-avenida-torrencial/
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THESIS HYPOTHESIS How can landscape architects regenerate sites with the aftermath of landslides? Landscape Architecture x Earth Sicence.... and what’s my role?
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debris flows
sediment transportation
terrain manipulation
ECOLOGICAL responsive landscape
LANDSLIDE ECOLOGY
SCIENTIFIC DYNAMICS OF LANDSLIDE
Nbs
d
primary succession
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Analytical + Theoretical Framework multiscalar
site speciďŹ city
mitigation
prevention
riparian + terrestrial
disturbance + regeneration
SOCIAL DISASTER MANAGEMENT
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Overall Scope The three approaches illustrated here will create the basic framework for the research, testing and design process. They are aimed to provide a consolidated strategy to mitigate landslide within both short and long term, ultimately transforming the site to be more adaptive and resilient to future events with the similar extent.
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MITIGATING SHALLOW LANDSLIDE
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image: https://www.reuters.com/article/us-colombia-landslide
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Dynamics of Plant Colonization
TIME
COLONIZATION ZONE
PLANT GROUP
For Mocoa’s disturbed site, research shows a few major plant groups can colonize and adapt well to the disturbed regions. They disperse and grow on different elevation of the affected slopes over time.
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FERNS
GRASSES
Ferns dominate landslides in both temperate and tropical regions. They adapt to landslide sites with rapid spore dispersal and vegetative reproduction. Ferns can also withstand great uctuations in temperature and moisture, and tolerance of a wide range of substrates.
Grasses can colonize almost all microsites of a landslide, and dominate the region for several years following disturbance. Some grasses can produce hundres of seeds on a single plant and have accessories to aid in wind dispersal.
SHRUBS
TREES
Shrubs becomes dominant on landslide disturbed areas after several years of herbaceous dominance. Apart from within the disturbed areas, they can also be established and widely spread near the edges next to the undisturbed regions.
Trees can colonize landslides at all stages of succession. Seedlings of trees may be dispersed across the site in the ďŹ rst years following the disturbance and dominate after 5-10 years in both tropical and temperate regions.
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Plant Colonization and Slope Gradient
SLOPE GRADIENT (DEGREE)
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0
Lichen
Bryophyte
Forbs
Grass
Fern
Shrub
Tree Fern
Tree
PLANT SIZE (INCREMENTAL) Plant groups colonizing on landslides according to the gradient of the slopes. This chart provides the basic knowledge of a re-vegetation strategy which can be implemented to treat the deforestation and shallow landslides. (Data source: “Landslide Ecology”, Walker L, 2013)
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rhenia ru par fa Hy
Amelan ch
Sp or
Cyathea ar
rea bo
Cornus sto
Cyathea bro
nii w
ra nife lo
alnifolia ier
us Ciss sicyo i
s de
indicu olus s ob
Pterid ium uilinum aq
Trema mi cr
tha an
Ble c tula Lutea Be
spicant um hn
steep slope
high light
extreme temp
nutrient stress
water stress
Plant Group and Adaptations In order to establish and survive in the landslide areas, particular plant groups / species displayed abilities to tolerate conditions such as water and nutrient stress, extreme temperature, exposure to high level of sun light and steep terrain. The above diagram have chosen a number of plants that are likely to perform well and dominate different zones of the Mocoa landslide areas.
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Responsive Schedule for Reforestation TREES
Trees can colonize at all stages of succession, particular species (eg. #20) can grow on bare and rocky debris sites. They can also be planted strategically next to the remnant patches in order to increase biodiversity.
SHRUBS Shrubs can be planted early for immediate colonization, however, most shrubs are late colonists due to their growth speed, and they can replace herbaceous dominance (grasses and forbs) after several years.
FORBS
Some forb species, especially vines play vital roles in terms of slope stabilisation during early stages. They can colonize the site without any vertical structure and they can grow on remnant stems or on new colonists (such as tree fern trucks).
GRASSES
Grasses tend to dominate landslide sites with their rapid colonization. Their morphological and physiological adaptation abilities allow them to grow well in the early stage of the disturbance. Protection from tree ferns will further increase their chance to thrive, and their extensive and fine roots can contribute significantly to soil stabilisation.
FERNS
Tree ferns as important pioneer plants due to their rapid growing speed and they can colonize a wide range of sites as they can disperse offspring widely. A range of smaller ferns can be introduced in the following stage, and they can quickly adapt due to their small size and short reproduction time.
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formation of landslide disturbed surface
19. Trema micrantha 20. Nothofagus dombeyi 21. Weinmannia trichosperma
Based on Mocoa’s post-event site condition, a responsive schedule for reforestation with groups of endemic plants has been designed according to various their characteristics and the transformation of the site overtime.
17. Amelanchier alnifolia 18. Cornus stolonifera
15. Cissus sicyoides 16.Jacquemontia capitata
8. Sporobolus indicus 9. Hyparrhenia rufa 10. Andropogon gerardii 11.. Andropogon gracilis 12. Andropogon hallii 13. Chusquea grandiflora 14. Chusquea ibiramae
1. Cyathea arborea 2. Cyathea brownii 3. Cyathea crinita 4. Blechnum spicant 5. Pteridium aquilinum 6. Pityrogramma calomelanos 7. Dicranopteris flexuosa
stabilised slope (matured landslide site)
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Reforestation x Drones
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IDENTIFY & ANALYSIS
Using the scanned result to identify multiple target zones according to slope angle, gradient, and substrate profile in order to generate a specific mapping for re-vegetation.
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AERIAL SURVEY
Utilising drones fitted with LiDAR and Multispectral sensors to scan the high slopes with possible deforestation and shallow landslides. Photogrammetry can be used to generate a collection of point coloud for a high precision 3D model of the terrain.
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CONTROLLED PLANTING
The planting drones will then take off and plant the seeds to specif regions according to the re-vegetation plan. Multiple drones can be used for complex planting schedules which may involve different species on different landslide microsites.
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LOADING SEEDS
Germinated seeds of different plant groups and species are loaded to planting drones which are equipped with guidance and control software to be coordinated by the re-vegetation plan and customised ight trajectories.
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SPORE RAIN
Spore rain form Cyathea arborea can distribute 700 spores / m2. Spores from the parent plant can reach as far as 30m
ZOOCHORY
Animals such as birds and bats can also assist with seed dispersal on site, and tree ferns provides essential habitat for them
ERECT RHIZOME
Trunks of tree ferns can act as substrate for forest seedings to germinate, and increase diversity on site.
Myiodynastes hemichrysus
Cyathea arborea
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Colonization of Ferns
Dicranopteris exuosa
RHIZOME & ROOTS FERN THICKETS
Scrambling ferns can establish quickly on landslide sites and form thickets and stabilise soil
Rhizomes within the Bracken fern contribute to vigorous reproduction, and the extensive and ďŹ ne root system in the Gleicheniaceae family allows them to adapt to harsh substrate Pteridium aquilinum
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Colonisation of Grasses
Chusquea ibiramae
Chusquea meyeriana
BAMBOOS
Chusquea spp. are proven to be a frequent colonist of landslide sites in tropical America, and Colombia has the second highest woody bamboo diversity in Latin America, hence great potential to introduce bamboos in the disturbed sites.
Chusquea pinifolia
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SEED DISPERSAL
Grasses can produce hundres of seeds on a single plant, and in some species, the hairy spikelets can assist seed disperal by travelling further with wind
ROOT SYSTEM
Grass’ extensive, fine root system help soil stabilisation, and improve water and nutrient uptake. This is why they can adapt well on unstable, dry and nutrient-poor sites
COLONIZATION ZONES
Grass normally colonize slip face and chute during early stage, which is useful to establish the first layer of protection over bare substrate
Andropogon gerardii
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SIMULATION + DESIGN
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image: http://www.itv.com/news/2017-04-03/colombia-landslide-desperate-search-for-survivors/
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Simulation and Iterative Design This thesis project is intend to design and engage with the site and employ an evidence based approach to support the design outcome. The key is to first understand the dynamics of landslide and debris flow. This was achieved by utilising a specialised program called Rapid Mass Movement Simulation developed by a group of Earth scientists in Switzerland to simulate debris flow with Mocoa’s digital site model
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Institute for Snow and Avalanche Research
Swiss Federal Institute for Forest, Snow & Landscape Research
RAMMS Rapid Mass Movement Simulation
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USGS DATA
import to arcGIS
Constructing the Digital Terrain A set of steps have been taken to construct Mocoa’s digital terrain in order to initiate the simulation with RAMMS 41
CONTOUR MAP
reprojection
convert to raster
DEM
convert to ascii
ASCII GRID
export to RAMMS
3D TERRAIN
ready for simulation
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Simulating the Existing The first simulation ran within a selected region where shallow landslide has triggered debris flow during the actual event. The initial release areas were imported from GIS data and terrain surface parameters have been set according to the site condition. The run time was set to 1,000s to examine how far the debris flow can reach within this timeframe. (The colour bar represents flow height, ranges from 0m - 9.28m)
initial release areas
t=5s
t=100s
t=200s
t=300s
t=400s
t=500s
t=600s
t=700s
DEBRIS FLOW COVERAGE REGION X Extent (m): -1925730.6 to -1920840.6 Y Extent (m): 3558055.9 to 3566855.9 Z Extent (m): 666.6 - 1876.2 Coverage Area: 43.065km2 t=800s
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t=900s
t=1000s
Initial Simulation Findings The first simulation indicates a close relationship between flow height, velocity and pressure
MAX FLOW VELOCITY
MAX FLOW HEIGHT
MAX FLOW PRESSURE
Vmax = 9.35m/s
Hmax = 1.99m
Pmax = 174.78kPa
High velocity debris flow concentrated on higher / steep slopes Velocity decreases dramatically after existing the valley
Max flow height mainly accumulated in deep valleys (water channels) Clear indication of the formation of debris dams
Creating higher stress on the Tension Zone of Convex Slopes Leads to larger and more severe debris flow and slide
high velocity region
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cut bank (erosion) higher ow velocity
UPPER STREAM
point bar (sedimentation) lower ow velocity
drop of velocity
Simulation Result : Max Velocity
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Simulation Result : Max Flow Height
Cut Bank Point Bar
LOWER STREAM
Meandering River vs Debris Flow Meandering River Meanders normally develop in alluvial plains of lower reaches. The shape of meander changes through time due to the constant erosion along cut banks (outside edge of the turn) and sediment deposition along point bars (inside edge of the turn)
ou te r
ed
ge
in ne r
ed
ge
Relationship of Velocity and Height When debris ow reaches the turning point of the channel, its velocity starts to change. Taking the observation from the uvial sediment transport behaviour, the simulation indicates similar result where the debris accumulates towards the inner edge of the turn (lower velocity) and widely spread over the outer edge.
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Initial Terrain Manipulation
MANIPULATED TERRAIN
ORIGINAL TERRAIN
Manipulating the original contour in Rhino and converting the new model into ASCII grid, re-importing the model into RAMMS. A 6m high mound has been created at the bottleneck area of the valley and tested the difference.
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Testing Manipulated Terrain
Result indicates that the mound can absorb certain amount of debris, diverting the ow direction and also decrease the velocity further. Total volume of debris towards the lower stream has also decreased. (Inidcated by the ďŹ nal image at the time of 1000 seconds after initial release)
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t=5s
t=200s
t=300s
t=600s
t=700s
t=800s
t=400s
t=500s
t=900s
t=1000s
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Simulating Flow Diversion and Detention The results below indicates this terrain is effective in terms of diverting, accumulating and detaining terrestrial debris. Notice that at around 200s after initial release, the movement of the ow reaches its kinetic threshold, and no longer further spreading. However, given that majority of debris was own down via Mocoa’s main river channels, further investigation was made on the detention part of the new landform, to determine its effectiveness when applied to the riparian zone. initial release areas
t=0s
t=5s
kinetic threshold
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t=150s
t=200s
t=500s
t=750s
t=50s
t=100s
t=250s
t=300s
t=1000s
t=1800s
diversion + accumulaton
detention
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Simulating Riparian Zone with Manipulated Terrain This subsequent simulation proves that the new terrain is affective in terms of delaying and detaining certain amount of debris. The berms and depressions can be strategically shaped and placed along the river bank in order to increase sediment accumulation and reduce the impact of debris ow River Channel
t=30s
delayed ow
t=240s
t=600s
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t=60s
breakage
t=300s
t=900s
t=120s
t=360s
t=1200s
t=180s
sedimentation
detained debris
t=480s
t=1800s
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AFTERMATH AS CATALYST
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image:https://mundo.sputniknews.com/trend/america_latina_colombia_alud/
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FINAL PROPOSED TERRAINS Based on all previous simulations, three major terrains have been developed with different intentions. Prevention: to block and divert debris ow Detention: a series of ridges and depressions act as detention ponds and entrapment zones. Cohabitation: manipulated landform with gentle scale and gradient in order to suit urbanised areas and human programs Combining them together according to different site conditions will create a hybrid strategy in order to minimise the impact of debris ow.
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COHABITATION
10m 10m 10m 10m
ARRAY OF SECTONS
The new base terrain can be further manipulated towards the more urbanised zones. Scale and gradient of the ridges are more gentle in order to fascilitate programming and human cohabitation, while still maintains a certain level of preventative function.
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River Mulato
River Mocoa
Barrio Miraflores
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Barrio Pablo VI
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River Sangoyaco
Barrio San Miguel
Barrio Floresta
Barrio los Prados
Barrio Modelo
Extent of Event Proposed Sites for Intervention
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DESIGNING WITH THE AFTERMATH How to utilise the boulders, tree trunks and clay debris available on site 73
IMAGE: https://www.lapatilla.com/site/2017/04/14/conďŹ rman-321-fallecidos-por-avalancha-en-mocoa/
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Recycle and Rebuild TREE TRUNKS
Vegetated debris can be used to reconstruct and stabilise slopes
GABIONS AS BY
local residents are produce gabion c crushed rocks are t make gabions
BOULDERS ON SITE
Utilise rocks and boulders brought by the debris flow
WOOD CHIPS
Shredded tree truncks to be utilised further
CRUSHED LOCALLY
Boulders and trunks are collected, sorted and crushed to produce raw materials for further processing
CLAY DEBRIS
Extensive amount of clay debris accumulated in the urban area can be utilised for brick making
PULVERISED ROCK MATERIAL
Finely crushed rocks will be fed into the pug mill
TEMPORARY ROAD
Those bricks can be used as a temporary paving solution for neighbourhoods with affected road network
BRICK MAKING
Locally sourced and recycled ingredients are mixed togther with water, passed into a de-airing chamber, then compacted, and extruded out as bricks.
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VEGETATED TERRAMESH
Soil sprayed onto the gabions and transforming into a form of environmentally sensitive river bank protection
INSTALLATION
Communities will also participate with the installation of gabions in order to improve slope stabilisation
YPRODUCT
e engaged to cages. Coarsely then ďŹ lled in to
ORGANIC MULCH
Applied on riparian areas to fascilitate plant establishment
LIGHT WEIGHT FILL
Wood chips used as the primary base material for reshaping the slopes
REBUILDING HOMES
Houses that are damaged during the event can also be repaired or reconstructed with those bricks.
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TERRACED FLOWER PATCH WITH GABIONS
The terrain along the slopes can be further manipulated for a terraced formation. As water and nutrient tend to funnel down and accumulate in the deposition zone, this space can be used by the community for the production of cut flowers. In addition, detention ponds can be formed in order to store rain water for irrigatio, controlling storm run-off and decrease flood damage. Flower patches with native species can be applied to generate economical benefit and further stablilise the soil. Detention Pond Community Flower Patch
Terraced Landform Recycled Rock Gabions
RIVER SANGOYACO
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RIPARIAN PARK WITH VEGETATIVE RIPRAP
While acting as a protective buffer for debris flow and flash flooding, the manipulated slope can also provide a recreational space by the river. Tree trunks from the landslide can be recycled and re-used to build timber board walks and decking in order to create direct access to the river front. A layer of vegetated rock and boulder armouring the bank, increasing bank stability and establishing riparian growth as well as habitat diversity.
Bioswale
Recycled Timber Boardwalk
Debris Flow Prevention Mound
Vegetated Recreational Space
Vegetative Riprap
RIVER MULATO
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PLAY SPACE WITH ROCK VANES
Mounds with various curvature and dimension offers a natural play spaces for the local residents. Boulders and tree truncks from the landslide are being used as playing instruments. Excessive amount of debris can be filtered and washed to fill up the pits within the slopes to create additional sand pits. In addition, Rock vanes are constructed along the bank to redirect flows, further increase the length of riparian edge, and also diversity of flow depth, velocity and substrate.
Crawling Hole
Sand Pit
Recycled Timber Sleepers Boulder as Playing structure Playing Mound Riparian Rock Vanes
RIVER SANGOYACO
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A MULTIFUNCTIONAL TERRAIN The new terrain with berms and depression generates multiple new functions to the riparian slopes. Normally they act as access route to the river and bioswale to filtrate and cleanse water run off. However, during the event of a major landslide, the alternate landform can affect and transform the flow of water and debris from the river channel. The depressed areas acting as catchments for deposited load such as boulders and rocks, minimise the impact and overflowing sediments reaching the urbanised neighbourhood.
BARRIO MODELO
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N
SCALE - 1:200
Extensive Vegetation for Soil Stabilisation
Bioswale
Recycled Timber Boardwalk
WATER LEVEL DURING DEBRIS FLOW
RIVER MULATO Deposited Boulders and Rocks
Debris Flow Prevention Mound
Vegetated Recreational Space
Recycled Timber River Decking
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Unfolding Future Stories Despite the event and tragic loss, people of Mocoa are still deeply attached to their homes. All the designed interventions are aimed to work with the existing site and maintaining that sense of place. The city’s transformation will take time, but hopefully during that period, negative connotations associated with landslide can be lifted. Spiritually, the reconstructed spaces with all the remnant materials will act as a reminder of the event, telling stories of what has happened, and what may still happen for generations to come.
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Online Resources “ANOMALÍA DE LA PRECIPITACIÓN DECADAL” ideam.gov.co, Accessed 02 Aug, 2017, http://www.ideam.gov.co/web/tiempo-y-clima/precipitacion-mensual-por-ano “Colombia - Potentially Affected Zones by the Mudflow in Mocoa” , humdata.org, Accessed 22 July 2017, https://data.humdata.org/dataset/potentially-affected-zones-by-the-mudflow-in-mocoa-colombia-situation-as-of-10-april-2 017 "Disaster foretold" leaves hundreds dead in Colombia, many of them kids” cbsnews.com, Accessed 29 Jul 2017, https://www.cbsnews.com/news/colombia-landslide-disaster-foretold-warnings-mocoa-flooding-mudslide/ “En Mocoa, en la noche de la tragedia, llovió lo que en 10 días”, eltiempo.com, Accessed 27 Jul 2017, http://www.eltiempo.com/vida/medio-ambiente/causas-ambientales-de-la-tragedia-en-mocoa-74356 “How deforestation of the Amazon is after the Mocoa landslide”, Univision.com, Accessed 30 Jul 2017, http://www.univision.com/noticias/planeta/como-la-deforestacion-del-amazonas-esta-tras-el-deslave-de-mocoa “Mocoa Event 2017: The new STEP TRAMM landslide and debris flows model applied to the Mocoa event (31st March 2017), Colombia – STEP TRAMM “ step.ethz.ch, Accessed 07 Aug 2017, http://www.step.ethz.ch/step-tramm/mocoa-event-2017.html ”Neglect and drug trade led to Colombian landslide disaster,” newscientist.com, Accessed 29 Jul 2017, https://www.newscientist.com/article/2126870-neglect-and-drug-trade-led-to-colombian-landslide-disaster/ Petley, Dave. “Mocoa: the cause of the tragic debris flow in Colombia,” (blog). Posted 04 April, 2017. Accessed 20 July, 2017. http://blogs.agu.org/landslideblog/2017/04/04/mocoa-1/ Petley, Dave. “Mocoa debris flow: analyses of the event” (blog). Posted 05 April, 2017. Accessed 20 July, 2017. http://blogs.agu.org/landslideblog/2017/04/05/mocoa-debris-flow-2/ "Resilient Design: Landslides." ASLA.ORG. Accessed August 12, 2017. https://www.asla.org/landslides.aspx
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