Landslides are a serious threat especially to areas that are densely populated such as Hong Kong and that have fault lines such as California. The Philippines, especially mountainous areas, are also prone to landslides especially because the trees that used to prevent such disasters have been avariciously cut down.
Landslides are very common. Japan is the hardest hit country by landslides, costing their country $4 billion annually in losses. The US, Italy and India follow Japan with an annual cost of $1 to $2 billion annually. “Landslide disasters are also common in developing countries and economical losses sometimes equal or exceed their gross national products.” (Popescu and Sasahara)
It is interesting to note that Japan, one of the most technologically advanced countries is also the hardest hit by landslides. This might lead us to think that the use of IT to detect, prevent and minimize landslides is futile and is simply a waste of time, money and resources. However, I would beg to differ. I believe that IT can help mitigate the negative effects of this natural disaster. In this paper, I will discuss several technologies that can be used to help prevent and detect landslides. Although the beneficiary of this technology would be the general public, particularly the residents and property owners of landslide prone areas, I will focus on a particular stakeholder which would be the National Disaster Coordinating Council. I will discuss how various technologies can help this government unit and what the role of IT is in landslide prevention and mitigation.
When typhoon Ondoy hit, it caused severe flooding and landslides. Many people began pointing the finger at the National Disaster Coordinating Council (NDCC). They believed that NDCC is ill equipped to face natural disasters. Rather than being proactive, we wait like sitting ducks for calamities to hit. Once the unthinkable has happened, that’s the only time we’ll act, the epitome of too little too late.
To be fair to NDCC, we also need to consider that NDCC’s main objective is for rescue, succor and relief, not prevention. There is a pending bill in Congress that will form a unit dedicated to disaster mitigation and management. While a separate agency is yet to be formed, I believe it rests in NDCC’s shoulders to prevent natural disasters and warn the public in advance. Although it is not their mandate, I believe the sheer necessity for calamity prevention obliges NDCC to come up with preventive measures as well.
Under NDCC are the regional, provincial, city, municipal and barangay coordinating councils. They are tasked to protect the public through an “integrated, multi-sectoral and community based approach and strategies for the protection and preservation of life, property and environment.” (NDCC)
The NDCC and the National Calamity and Preparedness Plan promote self-reliance by encouraging self-help and mutual assistance. Each unit is mandated to use their own resources before they ask for assistance from nearby barangays or higher authority. The NDCC and each unit below it will have the following units: Damage Assessment and Needs Analysis, Emergency Management Information Service Unit, Vulnerability Risk Reduction Management Unit, Plans and Operations Unit and a Resource Unit.
Each unit should be equipped and ready to respond to the following: Communication Transportation Service and Early Warning Service, Health Service, Auxiliary Fire and Police Service, Relief and Rehabilitation Service, Public Information Service, Rescue, Evacuation and Engineering Service.
Despite the focus on rescue and relief, I believe prevention will help not only NDCC but the general public as well. If we can warn people in advance of impending danger, we will be able to save lives and property. Clearing and rehabilitating areas that were affected by landslides are very costly. NDCC would have to clear the debris and rebuild the infrastructure. On top of this, lives were lost, homes were ruined, livelihoods were destroyed and local businesses were disrupted. NDCC would then have to relocate the victims, and provide them with food and shelter. The ripple effects of landslides reach far and wide, and are indeed very costly. Instead of using all that money for succor, why not use that money for prevention which in the long run will save us time, money and misery.
There are various technologies we can use to prevent landslides. Some may be less advanced but nevertheless effective. A method known as soft engineering or bioengineering uses plants to stabilize eroding slopes. This can be particularly useful particularly in areas that have been deforested.
In inundated soils, drainage can be used to lessen slope instability. Drains decrease pore pressure and increase soil strength. “Surface water is diverted from unstable slopes by ditches and pipes. Drainage of the shallow groundwater is usually achieved by networks of trench drains.” (Popescu and Sasahara) We can also utilize retaining structures such as gravity retaining walls and gabion walls. A summary of methods we can use is summarized in Table 1 (from Popescu and Sasahara):
Table 1
1. MODIFICATION OF SLOPE GEOMETRY
1.1. Removing material from the area driving the
landslide (with possible substitution by
lightweight fill)
1.2. Adding material to the area maintaining stability
(counterweight berm or fill)
1.3. Reducing general slope angle
2. DRAINAGE
2.1. Surface drains to divert water from flowing
onto the slide area (collecting ditches and
pipes)
2.2. Shallow or deep trench drains filled with
free-draining geomaterials (coarse granular fills
and geosynthetics)
2.3. Buttress counterforts of coarse-grained
materials (hydrological effect)
2.4. Vertical (small diameter) boreholes with
pumping or self draining
2.5. Vertical (large diameter) wells with
gravity draining
2.6. Subhorizontal or subvertical boreholes
2.7. Drainage tunnels, galleries or adits
2.8. Vacuum dewatering
2.9. Drainage by siphoning
2.10. Electroosmotic dewatering
2.11. Vegetation planting (hydrological effect)
3. RETAINING STRUCTURES
3.1. Gravity retaining walls
3.2. Crib-block walls
3.3. Gabion walls
3.4. Passive piles, piers and caissons
3.5. Cast-in situ reinforced concrete walls
3.6. Reinforced earth retaining structures with strip/
sheet - polymer/metallic reinforcement elements
3.7. Buttress counterforts of coarse-grained material
(mechanical effect)
3.8. Retention nets for rock slope faces
3.9. Rockfall attenuation or stopping systems
(rocktrap ditches, benches,fences and walls)
3.10. Protective rock/concrete blocks against erosion
4. INTERNAL SLOPE REINFORCEMENT
4.1. Rock bolts
4.2. Micropiles
4.3. Soil nailing
4.4. Anchors (prestressed or not)
4.5. Grouting
4.6. Stone or lime/cement columns
4.7. Heat treatment
4.8. Freezing
4.9. Electroosmotic anchors
4.10. Vegetation planting (root strength
mechanical effect)
As we can see from these examples, different technologies such as sensors and wireless systems can help in the early detection of landslides. Despite extensive prevention methods, landslides are inevitable. Therefore, early detection and warning systems are important as well. However, prevention and early detection of such disasters are difficult due to wiring and power supply issues. Nevertheless, Crossbow’s wireless sensor mesh network has provided a solution to this problem. In a project in China, Crossbow drilled several holes in a landslide prone mountain. “Water level sensors and tilt sensors were placed in each hole to predict the possibility of a landslide. Sensors in each hole sampled at 3-10 minute intervals. Each sensor was interfaced to Crossbow's IRIS Mote platform through the MDA300 data acquisition board. These sensor readings were transmitted via the mesh network to the Stargate base station. The Stargate would then relay the data to a central location through the Hong Kong GSM mobile phone network. The IRIS Motes were powered by regular AA batteries and the Stargate was powered by a rechargeable battery and solar cell. The sampling rate was adjusted depending on the weather conditions to monitor the underground water level and the mountain's movement at each layer.” (Crossbow Solutions Blog)
The IRIS Mote platform is a module used for enabling wireless sensor networks. It “enables the development of custom sensor applications and is specifically optimized for low-power, battery-operated networks. It is based on the open-source TinyOS operating system and provides reliable, ad-hoc mesh networking, over the air programming capabilities, cross development tools, server middleware for enterprise network integration and client user interface for analysis and configuration.” (IRIS Datasheet) It is used for indoor monitoring and security, high speed sensor data (such as video and vibration) and large scale sensor networks. Its features include:• “2.4 GHz IEEE 802.15.4, Tiny
Wireless Measurement System
• Designed Specifically for Deeply
Embedded Sensor Networks
• 250 kbps, High Data Rate Radio
• Wireless Communications with
Every Node as Router Capability
• Expansion Connector for Light,
Temperature, RH, Barometric
Pressure, Acceleration/Seismic,
Acoustic, Magnetic and other
Crossbow Sensor Boards
• Up to three times improved radio
range and twice the program
memory over previous MICA Motes
• Outdoor line-of-sight tests have
yielded ranges as far as 500
meters between nodes without
amplification
• IEEE 802.15.4 compliant RF
transceiver
• 2.4 to 2.48 GHz, a globally
compatible ISM band
• Direct sequence spread spectrum
radio which is resistant to RF
interference and provides inherent
data security
• 250 kbps data rate
• Supported by MoteWorks™ wireless
sensor network platform for reliable,
ad-hoc mesh networking
• Plug and play with Crossbow’s
sensor boards, data acquisition
boards, gateways, and software”
(IRIS Datasheet)
The MDA300 is a data acquisition board which includes a temperature and humidity sensor. Because of its easy access micro-terminals and multi-function direct user interface, it is used in various applications such as environmental data collection, agricultural monitoring, nursery management and HVAC control.
The MDA300 utilizes Crossbow’s MoteView software which is “designed to be the primary interface between a user and a deployed network of wireless sensors. MoteView provides an intuitive user interface to database management along with sensor data visualization and analysis tools. Sensor data can be logged to a database residing on a host PC, or to a database running autonomously on a Stargate gateway.” (MDA300 Datasheet)
The Stargate baste station “allows the aggregation of sensor network data onto a PC or other computer platform. Any IRIS Mote can function as a base station when it is connected to a standard PC interface or gateway board.” (MDA300 Datasheet)
They were able to predict landslides because the water level would usually rise first. The tilt sensors that were positioned in different locations would detect the changing angles in the slope’s layers. Early detection would enable authorities to evacuate the area or take preventive measures.
“If a landslide is coming, the water level would typically rise first and the tilt sensors placed at the different depths would be able to report the changing angles in the slope's layers to warn about the impending disaster thus giving authorities time to vacate the area or take preventive measures. The ability to use a wireless sensor network in these scenarios could ensure the safety of many lives and homes. This monitoring solution can be applied to bridges, structures, machinery, etc. Sensors can be embedded at different support joints, truss systems, columns, stress areas, etc. and be interfaced to the Mote platforms to enable the wireless collection and transmission of data.” (Crossbow Solutions)
We already have the infrastructure to transmit the data gathered by the sensors. We can use the existing GSM mobile phone networks of private Telecommunications companies such as Globe and Smart.
In India, students of Amrita Vishwa Vidyapeetham University used Crossbow’s MICAz Mote platform to detect landslides. Wireless panels that read moisture, vibration and movement of the soil were placed 15 meters underground at different points, which were then attached to Crossbow’s MICAz platform, a wireless transmission device. It converted the analog values into digital values, which were sent to the base stations. Experts monitored the data in real time and any abnormal behavior would trigger an alarm.
A sensor column which is about 5-6 meters long, contains several sets of geophysical sensors which are distributed inside the column. It is buried in the earth and the data that they gather are retrieved via lower layer wireless sensor nodes attached to the sensor columns. “The lower layer wireless sensor nodes were wirelessly connected to a hierarchy of upper level wireless nodes that would forward the data on to a Gateway. The data was then sent via a directional Wi-Fi link to a Field Data Management Center (FMC). The data was then forwarded over a satellite link to the Data Management Center (DMC) which has sophisticated landslide data processing and modeling capability, located at Amrita University, Amritapuri campus which is situated approximately 252 kilometers away from the deployment field.” (Crossbow Solutions)
The NDCC should have an IT unit that will monitor landslides as well. We can use the same setup that the students of Amrita University used. I believe that each region, province, city or municipality should have a landslide monitoring unit, depending on its geography, topography and population density. For example, urban areas can be monitored by regional units but mountainous areas should have a provincial or even a municipal unit to monitor any activity. The local unit should have a base station and whatever data they receive can also be accessed by the NDCC. If any abnormal behavior is detected, an alarm would be triggered at both the local unit and NDCC. Each unit should have the equipment I mentioned above such as sensor columns, IRIS Mote platform, MDA300 and a base station. Needless to say, the units should have intranet and internet connections. Apart from the usual modes of communication such as e-mail, telephone and mobile phone, they should also be equipped with an instant messaging system like Yahoo! messenger that will allow the IT department and the local unit to communicate with other units and the NDCC. This way, they can easily share the data that they have.
Each IT unit should have a monitoring unit that will constantly keep an eye on the data that is fed by the sensors. Any abnormal behavior, even if it is not enough to trigger the alarm, should be reported and investigated. The IT unit should be vigilant and well organized. Once a red flag is raised, the responsibility of evacuation and warning the public will rest on the local unit. The IT department will function more as a support and monitoring unit. Their main task is to detect landslides and make sure that the equipment is maintained properly. However, they may also be given other tasks in times of emergency which will be given by their local unit or NDCC.
The structure of the IT units will be similar to how the NDCC is formed wherein the local units will first utilize whatever resources they have. If it is not enough, that’s the time that they will call on other units or higher authority for help.
Reference:
Mihail E. Popescu (Illinois Institute of Technology, USA), Katsuo Sasahara (Kochi University, Japan). Engineering Measures for Landslide Disaster Mitigation. Last accessed: November 4, 2009. www.geoengineer.org/Lanslides-Popescu.pdf
Crossbow Solutions Blog. Landslide Detection for Mountainous Regions. Last accessed: November 4, 2009. www.amrita.edu/news/media/Crossbow Solutions.pdf
Crossbow Solutions. IRIS Datasheet. Last accessed: November 4, 2009. www.xbow.com/Products/productdetails.aspx?sid=264
Crossbow Solutions. MDA300 Datasheet. Last accessed: November 4, 2009. www.xbow.com/Products/productdetails.aspx?sid=178
NDCC. History of Disaster Management in the Philippines. Last accessed: November 4, 2009. http://ndcc.gov.ph/home/index.php?option=com_content&task=view&id=14&Itemid=28
NDCC. About NDCC. Last accessed: November 4, 2009. http://ndcc.gov.ph/home/index.php?option=com_content&task=view&id=12&Itemid=26
The Manila Times. Disaster Mitigation. Last accessed: November 4, 2009. http://ndcc.gov.ph/home/index.php?option=com_content&task=view&id=12&Itemid=26
