SAND DUNE CONTROL FOR THE COMMUNITY OF TULOR - BETER
MA ENVIRONMENTAL ARCHITECTURE 2019/20
INTRODUCTION This proposal is provided following a site visit to the community of Tulor - Beter in northern Chile where leaders requested design proposals to mitigate the encroaching sand dunes into Tulor from the northwestern direction. This sand dune expansion has a direct impact on agricultural activities as it blocks irrigation canals and causes distress on crops and soils.
Location of sand dunes at Tulor
CONTEXT SAND DUNE EXPANSION The dunes have been progressing on a yearly basis and are currently at the northern edge of the settlement. The shift of northern edge contour indicates the sand dune movement towards the settlement from 2005 to 2019.
Google Earth image from 2005
2005 contour line 2019 contour line
Google Earth image from 2019
Contour lines showing dune progression
Sand covering canals in northern Tulor
Community leader at a location with extensive sand encroachment
CONTEXT
ENVIRONMENTAL ANALYSIS NDVI (Normalized Difference Vegetation Index) According to NDVI analysis, we can see that from 1975 to 2019, the density of vegetation in the region has decreased over time.
N
D
VI
an
al
ys
is
From 1975 to 1986, the amount of high density vegetation (greater than or equal to 0.4) was significantly higher than from 2005 to 2011. By 2015, the vegetation density was at a minimum. From 2015 to 2019, the density of vegetation increased. This is likely due to the El Nino phenomenon that occured in the region in 2015.
NDVI Analysis at Tulor
CONTEXT WIND PATTERNS Wind originates from the north-west direction bringing in eroded sand to the northern part of Tulor. Due to the topography and existing isolated trees in this northern region, the accumulation of dunes is higher where the wind comes in contact with objects along its path.
Hill
Source of irrigation canal
Bas
in
Are by s as not and affec t dun es ed
Hil
l
Nor
thw
est
Dun
Dun
e
slop
e
Wo
Wo
odl and
In July 1957, winds of 100km per hour were recorded, with gusts of up to 150 kilometres per hour in San Pedro de Atacama (10km from Tulor). Winds of this force can carry both medium and coarse sand.1
odl and
e
The plan to the left indicates areas with higher levels of erosion, and where sand dunes have likely infiltrated canals. The location of canals, as well as sections covered in sand must be verified on site for accuracy. 1 Robert J. Dingman, ‘Geology and Ground-Water Resources of the Northern Part of the Salar de Atacama, Antofagasta Province, Chile’, Geological Survey Bulletin, .1219, (1967), (p. 5)
Areas with Higher Wind Impact 1. Most areas in the north of Tulor are highlands so the wind can have less intensity; however, this place is a basin so the wind will increase here. 2. A positive pressure area due to the slope towards the northwest, in which the wind and ultraviolet rays are relatively strong. 3.Duetotheterrain,windwillincreasehere.(Similartoasmall-scalecanyon) 4. The woods here weaken the wind and change its direction.
Plan showing impact of objects on sand dispersion
Topographical sections
5. The original irrigation canal is located at a lower terrain, far away from the plant community boundary. Thus it would be difficult to use for the future expansion of vegetation.
6. As the terrain steps down from north to south, the wind blocking effect becomes weaker, and so the wind becomes stronger in this direction. At the same time the positive presure zone appears here, so the direction of the wind changes due to the terrain. 7. Although the distance between the plant boundary and the irrigation canal is relatively close, the irrigation canal is located at a low terrain, thus the original irrigation canal is difficult to irrigate plants without the help of artificial instruments. (Although the local plants are drought-tolerant, they still need water for irrigation in the first few months after planting) 8.Otherareasaffectedbysanddunesbecauseofwinddirectionandterrain. 9. Compared with the northwest of Tulor, this area gets less affectedby sand dunes, due to the angle of the boundary and the angle of the wind.
Tamarugo Tree
Native vegetation is well adapted to the unique conditions of the Atacama Desert. Tamarugo and Algarrobo trees are native species of Prosopis that are common in the region, and are well adapted to survive in the salty soil conditions and with little water requirements. These are used as a source of fodder, fuel, food, and wood in the region.
Prosopis Tamarugo Phil. is a leguminous tree endemic to the region that is used as source of wood and fodder for livestock. It’s average height is 15m and can live up to 400 years.
The humidity of the region allows for low lying shrubs to thrive. Examples of these are Rica Rica, Brea, and Copa. These are often used in the construction when dried for roof Agricultural crops are cultivated on a small scale for both food and fodder production. After mining and tourism activities, agriculture is a major source of revenue in the region. Local species of wheat, and corn, are commonly grown. Another common crop cultivated is Alfalfa which is primaly used as fodder.
Rica rica shrub
Alfalfa
1.2
The Tamarugo has very outstanding water requirements as it needs irrigation during the first 6 months of its life, and once established survival rates range from 80% - 90%.
11.5%
.4 4.5%
Its roductivity is linked to age, plant spacing, depth and quality of groundwater.
Chanar Trees in farm at Tulor
6.5%
.2
24.0%
The tamarugo’s double root system allows it to tap groundwater from existing aquifers at 2m - 40m. Additionally, the foliage structure of the plant allows it to absorb moisture from the atmosphere, as well as exude moisture to the soil.2 2 Mario a. habit, Prosopis Tamarugo: Fodder Tree for Arid Zone (2020) <http:// www.fao.org/3/ad320e/AD320E00.htm#TOC> [accessed 2 April 2020].
Tamarugo Trees
.2
.3 7.0% .3 7.5%
15% .5 3.5 % Moisture
Source: FAO
DEPTH IN METERS
VEGETATION
HEIGHT IN METERS
CONTEXT
CONTEXT WATER Surface Water Resources The San Pedro and Villama Rivers supply the Tulor-Beter communities with water.However, a decrease in flow from the San Pedro River has resulted in a reliance on the Villama River.
Tulor
Ground Water Resources There are two separate aquifer systems in the San Pedro area. A survey3 performed in 1967 identified the following: An unconfined upper aquifer with depths from surface to 16 meters below ground. This aquifer is recharged by the San Pedro and Villama Rivers, from flood waters from surrounding highlands and from upward leakage from the artesian aquifer.
Salar de Atacama
A confined artesian aquifer that is recharged almost entirely by infiltration and subterranean flow of the rainfall from the Puna de Atacama east of Tulor towards the Argentine border.
Canal Northern contour line (2019) Water resources in the Tulor region Source: Lithium Triangle Studio 2018/2019
0
500m
1000m
* Northern contour was adjusted to QGIS imagery.
Water Infrastructure 3 Robert J. Dingman, ‘Geology and Ground-Water Resources of the Northern Part of the Salar de Atacama, Antofagasta Province, Chile’, Geological Survey Bulletin, .1219, (1967), (p.39)
Water for agriculture has traditionally been directed through a system of canals supplied by the rivers in the region. However, the expanding dunes now cover several sections of the canals, especially in the northern region.The plan above indicates areas where sand dunes have likely infiltrated canals. These locations must be verified on site for accuracy.
PROPOSAL
STRAW CHECKERBOARD
Installing straw checkerboard barriers Such straw barriers are installed in a grid system to prevent further movement of sand, and to promote the growth of vegetation in the future.
PRIMARY STABILIZATION (Mechanical)
SAND DUNE CONTROL
VEGETATION
Planting of native vegetation Native vegetation like Tamarugo trees are to be planted, both to act as a barrier against sand and to locate underground water.
SECONDARY STABILIZATION (Biological)
WATER INFRASTRUCTURE
Clean existing canals Clean out existing canals where sand has accumulated, particularly along the northern edge of the settlement. Identify areas for potential canal and road expansion as work extends beyond the northern edge.
PROPOSAL The control of sand dunes will follow the guidelines of the Food and Agriculture Organisation of the United Nations4 method of approach outlined below. PRIMARY STABILIZATION This is aimed at immediately reducing the progression of sand dunes through mechanical stabilization, to allow enough time for natural and planted vegetation to become established. The stabilization technique we propose here is the installation of a 1 meter x 1 meter straw checkerboard using dried alfalfa and other such shrubs local to the region. SECONDARY STABILIZATION This involves biological fixation and soil regeneration through the planting of the Tamarugo Tree. The process involves nursery development of trees, transplanting and management until establishment has been reached. EXPANSION Identify and mark out areas for road and canal expansion to ensure allow for maintenance once the trees are established and afforestation is achieved. 4 FAO, Combating Sand Encroachment in Drylands (2020) < http://www.fao.org/3/a-i7363e. pdf> [accessed 7 April 2020]
Install 1m x 1m x 20 cm straw checkeboard grid using alfala Plant tamarugo trees spaced minimum 10m x 10m square or 15m x 15m triangular Plant scattered individual trees further north to determine underground water availability, and areas for potential expansion Leave room for a road with buffer space for maintenance purposes once trees are established
PROPOSAL
Ground water detection Newly planted trees can transfer groundwater indirectly from the ground to the ground, alleviating the local drought problem. The groundwater is absorbed by the plant roots and transferred to the aerial part of the plant, the canopy. (Plants need water to grow.) During the growth of plants, the leaves fall, the fruit (which contains water), and part of the water is transferred to the ground for use by local animals and plants. Since fallen leaves and fallen fruits are organic matter, they can provide nutrients for other plants and food for animals.
When there is groundwater that can be used by plants in the area, plants can survive; conversely, when there is no available groundwater, plants cannot survive.
Wind Reduce wind force through multiple windbreak
When the tree survives, it means that there is fresh water available to plants around the tree. Other plants can be planted around this surviving tree to achieve the purpose of expanding the plant community.
PROPOSAL TAMARUGO TREE PLANTING
STRAW CHECKERBOARD A 1 meter by 1 meter grid of straw is proposed as a barrier to prevent further dispersal of sand by wind. For the installation, straw made of alfalfa is pushed into the ground using a shovel in a grid. 10-20 cm of the straw is left above ground, to prevent the movement of sand. This technique can reduce sand flux by up to 99.5%.5 It is also a suitable approach for improving the quality of the soil. The application of this straw checkeboard grid is proposed to begin in locations with the highest wind impact as shown in the wind analysis.
Planting Process Rock to hold down plastic
Step 1: Lay alfalfa on the ground in a vertical line
Plastic cover
Step 2: Using a shovel, vertically penetrate alfalfa into the ground
5mm perforations on plastic cover around the pot Planting hole
Watering bag for min. 6 months where access to water canals is limited
10 - 20 cm
Step 3: Push a mound of sand around the base
80 cm
Step 4: Lay alfalfa on the ground in a horizontal line
20 cm
40 cm
20 cm Pot - 30 cm x 12 cm
60 cm 15 cm
Unfertilized Soil 5 GuoYu Qiu, ‘Principles of sand dune fixation with straw checkerboard technology and its effects on the environment’, Journal of Arid Environments, 56.3, (2004),.
Mixture of soil and manure
Step 5: Using a shovel, vertically penetrate alfalfa into the ground to form the grid
Step 6: Push a mound of sand around the base Planting Stage
Drip irrigation up to 6 months
Established Tree
PROPOSAL DETAIL PLAN This detail plan shows a sample on how to progressively introduce the straw checkerboard grid, trees, and infrastructure, starting from the northern edge of Tulor and progressing further north as necessary.
PROPOSAL MAINTENANCE AND EXPANSION - Plant vegetation species that are found in association with tamarugo such as fortuna, brea, carob, etc. These should be in areas where trees have survived. - The straw checkerboard grid requires replacement every 3 to 5 years. - Herding in the area can help to sustain the trees because of the animal manure. - Existing water canals can be expanded at locations identified by the community. - Plan for a maintenance road as expansion continues further north of the sand dune.
Ayse Melis Goksan Morgan Liu Hongru Yvette Njoki Waweru