Disaster Mitigation and Vulnerability Reduction: Perspectives On The Prospects For Vetiver Grass Technology (VGT)

James Smyle, Natural Resources Specialist, Regional Unit For Technical Assistance , World Bank , San José, Costa Rica

Paper presented at the Second International Vetiver Conference, Thailand, January 2000

Abstract

On October 24 1998, Atlantic Tropical Storm Mitch was upgraded to a hurricane that developed into one of the strongest and most damaging storms to ever hit the Caribbean and Central America. At its height on October 26 and 27, the hurricane had sustained winds of 290+ kph and dumped heavy rains over Central America. Although the winds diminished as Hurricane Mitch travelled inland over Honduras on October 30, the storm continued to produce torrential rains, reaching rates of more than 100 mm per hour. Catastrophic floods and landslides occurred throughout the region. When it was over, some 9,200 people had died; almost 270,000 homes were lost; 21,325 miles of roads and 335 bridges were destroyed. Immediately after the storm, some 2,000,000 Central Americans were pushed out of their homes. Agricultural losses were staggering. Mitch's impacts on watersheds, human lives, and the economies of the affected countries will be felt for at least some 8 to 10 years...assuming that another storm of such magnitude does not return. International experts in disaster mitigation and vulnerability reduction rushed to Central America to assist in diagnosing what had happened and what needed to be done. Perhaps, not surprisingly, the majority of their recommendations consisted of things which natural resource and civil engineering professionals have been recommending on a daily basis as being "good practice"; many being things for which the VGT system is very well-suited. Disasters, like Hurricane Mitch, do not tell us much that is new. But they do focus our minds on what we should be paying attention to in carrying out our professional responsibilities. This paper attempts to pass on some of the lessons learned by one natural resources professional, particularly on where and how the VGT system should play a role in disaster mitigation and vulnerability reduction, as both a bystander and participant in the post-Mitch emergency and reconstruction efforts.

This paper is entitled “perspectives” as it only represents the perceptions of the author based on experiences coming from involvement with the emergency and subsequent reconstruction programs following Hurricane Mitch. It is not a scientific review. However, in writing the paper it was apparent to the author that an effort is required to look systematically at what we know and do not know about the limits to the applications of the vetiver system, particularly as they may relate to design standards. For applications such as those discussed here -- VGT for disaster mitigation and vulnerability reduction -- we are looking to see how VGT might perform in extreme events. Inherently then we are talking about limits to the application, and we simply have not yet adequately defined these. Both systematization and synthesis of what we already know, as well as further research, are required.

I. INTRODUCTION

The region of Central America occupies an area comparable in size to Thailand. Its 32 million inhabitants live within the 7 nations of which the region is comprised: Guatemala, Belize, El Salvador, Honduras, Nicaragua, Costa Rica and Panama. In general, the countries have mountainous interiors surrounded by coastal plains. On the path to urbanization, the population is still predominantly rural and poor. Agriculture remains the main source of livelihood, employment and, generally, the dominant economic sector.

In the last days of October 1998 Hurricane Mitch, the most intense storm in the Atlantic Basin in the past 200 years and the most destructive hurricane in the history of the western hemisphere (1), battered the Caribbean coast and parts of Honduras, Nicaragua, El Salvador, and Guatemala. From October 27, 1998, to November 1, 1998, it dumped from 300 to 1900 mm of rain on large areas of the four countries. The storm produced sustained wind speeds of 290+ kilometers hr-1 and rainfall intensities of more than 100 mm hr-1. The main destruction resulted from the intense rainfall. The storm's arrival at the end of the rainy season guaranteed maximum damage. In the weeks prior to its arrival, there had been significant rainfall. Soils tended to be at or near their water-holding capacity. The spring/summer crops were at the point of harvest and the summer/fall cropping cycle was beginning.

Summary Of Hurricane Damage

Severe flooding and landslides were widespread throughout the region. More than 9,000 people were killed. Over 2,000,000 people were left homeless. Much of the transportation and communications infrastructure of Honduras and Nicaragua was devastated. Towers and bridges were destroyed and roads were lost to landsliding or washed away by floods. In Nicaragua, the rain-saturated southern slopes of the Volcano Casitas gave way and mudslides reached the town of Posoltega, almost 10 miles away. In nearby communities some 1,900 people were killed due to mudslides. In Tegucigalpa, the mountainous capital city of Honduras, a landslide blocked the main channel of the principal river. When the dammed river finally broke through, the flood peak washed away entire neighborhoods. The raging current undercut city hillsides, bringing other neighborhoods crashing into the floodwaters.

The dimension of damage to the region was (and is) huge. The Central American commercial corridor, about 90 percent dependant on road transport, was blocked; intra-regional commerce came almost to a halt. The indirect economic losses ran into the hundreds of millions of US dollars. Of the estimated US$6 billion in direct and indirect losses, about 50 percent were from the agricultural sector. Flooding, landsliding and sediment inundation primarily affected banana, melon, pineapple, coffee, basic grain and other subsistence crops, and sugar cane; shrimp farms in Honduras were particularly hard hit. Literally tens of thousands of hectares of the region's best agricultural lands were damaged or destroyed; washed away, carried away by landslides, or inundated under deep layers of rock or coarse or sandy sediments.

Table 1. Human Losses

Country Killed Injured Missing Suffered Losses Evacuated
Belize n.a. n.a. n.a. n.a. 75,000
Costa Rica 4 n.a 3 16,500 5,500
El Salvador 240 n.a 19 84,316 49,000
Guatemala 268 280 121 105,000 104,016
Honduras 5,657 12,275 8,058 617,831 2,100,721
Nicaragua 3,045 287 970 368,261 867,752
Panama 2 n.a. n.a 8,408 602
Total 9,216 12,842 9,171 1,200,316 3,202,591
Equivalent in Thailand 1 17,510 24,400 17,425 2,280,600 6,084,923

(Source: CEPAL)

1 Thailand and Central America have roughly the same land area (Central America is 5% larger), with Thailand's population being some 90% greater.

The deposition of massive amounts of sediments within river courses has caused radical changes in fluvial morphology and hydrology of many catchments. The hydraulic capacity of the river systems have been drastically reduced. In a substantial number of areas, it is unclear where the current (and future) channels of major rivers are located. In the steep upper watersheds, slope instabilities were activated due to soil saturation. Risks of future flooding and landsliding have greatly increased. This year's rainy season, wetter than normal, resulted in widespread flooding in the cities of the Caribbean coastal plains and landsliding has continued.

Table 2. Economic Losses

Item Damaged or Economic Losses
  Destroyed (US$ millions)
  No. Direct Indirect Total
Social   552 247 799
Homes 268,007 436 155 591
Public Buildings 1 1,704 116 92 208
Infrastructure   657 589 1,246
Roads / Bridges 34,550 km / 335 528 542 1,070
Power Generation Facilities / Power Grid 12 / n.a. 29 30 59
Water & Sanitation Systems 319 75 16 91
Irrigation Systems 15 25 1 26
Productive   1,824 2,083 3,907
Agriculture, Forestry, Fisheries 70% 1,702 1,245 2,947
Industry   33 575 608
Commerce & Tourism   89 263 352
Environment   67 ... 67
TOTAL 3,100 2,918 6,018

1 schools, clinics, hospitals, etc. (Source: CEPAL)

Viewpoint Of Disaster Specialists

As the true picture of the impacts began to emerge, an explanation was sought to explain what happened and why the impacts were so severe. In addition to the understanding that the disaster was the result of a natural phenomena of extreme magnitude, much attention was focused on the potential role that deforestation and hillslope farming in upper watersheds had played in "causing" or worsening the impacts of the devastating floods. In a real sense, this became the most high profile issue in the months following. The media focused on how "...it seems that Hurricane Mitch has been far more deadly than it need to have been, just because the forests were no longer there" (2). Government and foreign donor agencies publicly agreed that "the effects of Hurricane Mitch have been increased...in particular [by] the deforestation of forests and wetlands that act as "buffer" systems diminishing the surface run-off in the case of such intense rains as those experienced during Mitch" and that "flooding was aggravated by a lack of adequate watershed management" (3).

In parallel to this more public analysis, international experts in disaster mitigation and vulnerability reduction were assisting to diagnose what had happened and what needed to be done. Radar imagery of flooded areas, overlain on geologic maps, showed that Mitch flooded those areas which are underlain by Quaternary sediments, i.e., those soils formed in areas naturally subject to flooding. Damage assessments increasingly tended to place less emphasis on upper watersheds and deforestation per se and more on the broader issues of:

What Was Potentially Avoidable ?

Following these conclusions, flowed a long series of recommendations of how to avoid, mitigate, and reduce impacts from future disasters. To those working in areas related to natural resource management, civil engineering or rural development, not surprisingly, the majority of their recommendations consisted of things which have been recommended on an almost daily basis as being "good practice". Indeed, most were basic elements of watershed management and have been a part of the development agenda for decades. Unfortunately, they are also basic elements that tend to be ignored.

We know that good watershed management requires consideration of the many issues that fundamentally influence how humans use natural resources: political, socio-economic, institutional, scientific, technical, community, legislative, regulatory framework, economic incentives, etc., – and as such, is extremely complex. However, despite the complexity, in each of these areas one eventually has to come down to: (i) getting the objectives right and, (ii) ensuring that you have appropriate and affordable tools in order to achieve those objectives.

In the specific case of Hurricane Mitch, the lessons learned seemed to point out four main "objectives" that should have been pursued prior to the hurricane in order to have reduced or avoided the much of the human tragedy and economic losses. At the risk of oversimplifying, these were:

Minimize encroachment into flood plains and other elements of the natural drainage patterns, and areas subject to mass movements of earth – Urban, commercial and industrial encroachment into these areas resulted in the greatest losses of human life and of high value infrastructure and environmental contamination (toxic and hazardous substances washed into rivers).

Ensure proper design and construction of transport network – In Honduras, access and transport were returned to pre-1900 conditions. The majority of road and bridge damage and losses were ascribed to poor design, shoddy construction, and inattention to stabilization during the construction phase.

Ensure the adequate protection and proper maintenance of key roads and access points – Lifeline roads and critical access link points were destroyed, leaving large populations isolated and endangered and the country's and affected region's economic activities were brought almost to a halt.

Assist rural households to adequately protect their production systems and housing sites – The main economic losses took place in valley agriculture and were a direct result of massive flooding. In the uplands, the main economic impacts were in coffee; thousands of hectares of coffee plantations were lost to landsliding. Large indirect losses occurred due to loss of market access roads, forcing producers to leave crops in the field. Smallholder subsistence agriculturalists (the majority of farmers) were extremely hard hit by landsliding, flood torrents carrying away their best streamside lands, extreme soil losses from torrential rains, and loss of crops in the field. These latter's losses barely enter into the official loss figures. Even with tens of thousands of poor households losing almost everything (house, land, crops), having very little to lose, their losses figured very little in the macro calculations.

The Aftermath. What Needs To Be Done ?

According to the disaster specialists the issue now is not "reconstruction", rather it is "development in the new context created by the last disaster". From a watershed management perspective, the main challenges in this "new context" seem to involve:

II. Where does vetiver grass technology fit in ?

If the challenge is to bring about development in the new context left after Hurricane Mitch while ensuring that the hundreds of millions of dollars of official aid transfers coming into the region are used to best advantage, then certainly VGT has a role to play. This fact is underscored by VGT having been specifically identified as a key technology for post-Mitch construction by the World Bank, the US Army Corps of Engineers, the Interamerican Development Bank, the United States Agency For International Development, CARE International, Chiquita Brands and Tela Railroad Company among others. Also, Mitch finally began to create interest in VGT among the Costa Rican, Nicaraguan, and the Honduran Ministries of Transport. In El Salvador, the work by NOBS Anti-erosion had already ensured that their country's transport and infrastructure ministry was aware of VGT and seeing it applied. In addition, to promote the use of VGT in post-Mitch construction, the World Bank provided the Regional Unit for Technical Assistance and the Latin American Vetiver Network a "knowledge management grant". The grant's purpose was to educate key actors and decision-makers in the post-Mitch construction (government, donors, and private sector) as to the potential, the benefits and the means to go about incorporating vetiver grass technology as a low cost, proven, bio-engineering approach for infrastructure and watershed stabilization.

All that is good. But there is also very limited experience in Central America with the use of VGT, relative to the size of the job ahead. Also, misuse or overselling of VGT can not only result in discrediting the approach, it can also put at risk human lives and high dollar investments. Recently, in a workshop on watershed management in Honduras, an experienced field man spoke up, saying: "We need to systematize our approaches...I am tired of being told 'use vetiver grass' when my problem is something like an actively cutting gully which is 5 meter deep and 30 meter wide gully". From this perspective, a brief review of for what VGT might be good, and possibly not so good is in order.

For What Might VGT Be Good?

What are the uses and limits for VGT? A number of aspects are worth noting:

For What Might VGT Not Be So Good?

Within the uses and limits described above, for what might VGT not be so good? Three particular aspects appear to merit mention:

Pre-Mitch: Where Might VGT Have Reduced Damage ?

As mentioned above, there appear to have been four main "objectives", which had they been more effectively pursued prior to the hurricane, might have reduced or avoided human tragedy and economic losses. What role might VGT play such that future disasters are less disastrous?

Minimizing encroachment into vulnerable areas. Under Central American conditions it is clear that these areas will continue to be encroached upon for a significant span of time yet to come. The main impacts (loss of human life and economic losses) occur in urban and peri-urban areas. The use of zoning does not seem to be a very effective option as neither enforcement of laws and statutes nor insurance (which most businesses and individuals lack) discourages building in vulnerable areas. Indeed, many of the areas hit hardest by Mitch were identified as "vulnerable" and "high risk" in land use plans and zoning ordinances one or more times, since the 1950s. Such areas need to be put under some economically or socially useful activity which, if wiped out in a flood or landslide, does not cause undue economic loss or human suffering.

In urban areas, these risk zones can be converted by the city or turned over to neighborhood associations for recreation areas, city parks, sports fields, community gardens, etc. The utility of VGT in these areas would be to protect these areas from the "normal" hazards and maintain their useful life between the more extreme events, through: stabilizing river banks and natural drainages, protecting roads and footpaths, redirecting runoff from upper slopes, stabilizing hillslopes and fill areas, etc. In addition, the concept of 'social fencing' acts as a deterrent in most Central American societies, i.e., if one can demarcate land (and maintain the demarcation), thus establishing usufruct, this becomes a mild to moderate deterrent to encroachment. Vetiver barriers make excellent boundary markers and are much less expensive to put up and maintain than real fences. "Regular" maintenance, such as twice yearly pruning, would serve to demonstrate continued interest and "will".

Table 3. Some possible applications of VGT in reducing future damage.

 

  Stabilize soils & slopes Trap sediments Reduce runoff velocity Divert flow Enhance infiltration Protect structure / soil interface Demarcate areas
Minimizing encroachment into vulnerable areas ~ ~ ~   ~ ~
Proper design and construction of transport network X X X X   X  
Adequate protection and maintenance of key roads and access points X/~ ~ ~ ~ ~ X  
Adequate protection of production systems & housing sites X X X X ~ X  

'X' = could have a primary/ significant role. '~' = could have a useful secondary/tertiary or very localized role.

Proper design and construction of transport network and adequate protection and proper maintenance of key roads and access points. These two points are substantially the same, the main difference being one of strategy and intensity. In general, proper design and construction require that stabilization of roadsides, roadcuts, fill banks, drainage, etc. etc. be taken into account. Without going into details (as there is a whole section in the conference on these aspects), we know that vetiver works well and is low cost. The experience in El Salvador shows this – over 300 km of vetiver hedges were established before Mitch hit to protect roads and other high value infrastructure, the only failure was in one location where it was discovered that the building contractor had not compacted a fill slope to design specifications. As did the experience in Puerto Rico with Hurricane George, where, Mr. Eduardo Mas of the US Natural Resource Conservation Service was reported to have remarked: "The storms were terrible. [Afterward there were] Landslides, roads destroyed, agricultural lands washed away; but, where there were vetiver barriers, everything seemed normal”.

Road maintenance is always a problem as there is generally little or no budget provided for this activity. Under such circumstances, vetiver is a good alternative. As Mr. William Ibarra, a division chief in El Salvador's Ministry of Public Works, explained to the attendees at the World Bank-sponsored Vetiver Bioengineering Workshop: "We never have budget for road maintenance" therefore his strategy is "to lose fingers, not the hand" by building into the construction phase protection measures which are going to give him long term, very low maintenance protection in critical areas. He counts vetiver as one of those approaches.

In terms of ensuring adequate protection of lifeline roads and critical access link points, this involves expecting disasters to occur and identifying and taking incremental measures to protect key roads and access points. Simply stated, these would be the points where the greatest attention and intensity should be given to see that VGT is used for stabilization and protection. However, given the criticality of these points, VGT would need to be part of an overall package which included hard as well as soft approaches.

Adequately protecting production systems and housing sites. With the main economic losses having occurred in valley agriculture as a direct result of massive flooding, there is little that VGT could be expected to have done to lessen impacts. In the uplands, where thousands of hectares of coffee plantation were lost to landsliding, VGT might have reduced some small percentage of losses. Many of the landslides were deep, tens of hectares shearing off and dropping into the valleys or plantations being wiped out by fast moving debris and mud flows from upslope.

Smallholder subsistence agriculturalists would be the greatest beneficiary of VGT. Damage surveys noted that virtually all the farms using recommended soil and water conservation techniques (especially, vetiver grass contour barriers, rock terraces, "green mulch" [1] and crop residue management, and an indigenous agroforestry system [2]) survived Mitch with little damage, while neighboring farms using conventional practices suffered devastating landslides that destroyed homes and degraded fields.

Simeon Gomez, a hillside farmer in Los Espabeles, Honduras who went through Hurricane Mitch said it best: "On my field with vetiver grass contours the hillside remained perfectly in place. The fields without grass contours have had their crops and soil washed away".

Vetiver hedges could also have be somewhat useful in protecting home sites on sloping lands and near minor drainages, especially from undercutting of walls by runoff, and perhaps diverting flows away from the house and reducing sediment damage to interiors.

Post-Mitch: Where Might VGT Be Applied In The Aftermath ?

The incorporation of VGT in development efforts might reasonably be expected to assist in dealing with the conditions left behind in many of the watersheds severely impacted by Hurricane Mitch. At the same time, it would also be reducing future vulnerability and risk. Application of VGT can be utilized for treating the following situations:

Mass wasting. Many of these are deep slides whose continued instabilities derive from zones below the depth at which vetiver's root system could affect stabilization, or from huge masses of material still in movement from gravity, or from unstable materials of texture classes (large stones, boulders, etc.) for which VGT is unsuited. On the other hand, VGT could play an important, low cost role in reducing the risk that these instabilities would trigger. Among the particular applications for VGT here are in: (i) reducing erosion and undercutting of the toe slopes, which generate upslope sliding – establish contour vetiver barriers along the bases of the debris slopes, especially where they contact river channels; (ii) halting and diverting run-on from upslope which would increase soil moisture and increase risk that slides or shears would be triggered due to increased pore water pressures – establish cross-slope and herringbone pattern vetiver hedges upslope; (iii) stabilizing the shallow unconsolidated and unstable shallow debris slopes; and (iv) stabilizing the soil surface of both the newly exposed areas as well as the debris slopes such that revegetation (natural regeneration or planting) might occur.

Table 4. Some possible applications of VGT in vulnerability reduction.

  Stabilize soils & slopes Trap sediments Reduce runoff velocity Divert flow Enhance infiltration Protect structure / soil interface Demarcate areas
Mass wasting X / ~ ~     ~    
Shallow slips         ~    
Sediment storage in stream system ~ ~          
"Where's the stream channel?"       ~      
Sediment inundation X X X        
Not all future risk can be avoided in new construction X / ~ X / ~ X / ~ X / ~   X  
Danger zones and encroachment ~   ~ ~   ~ ~

'X' = could have a primary/ significant role. '~' = could have a useful secondary/tertiary or very localized role.

Shallow slips. VGT could play a larger role in achieving complete stabilization of shallow slips in: (i) stopping further landsliding and shearing by stabilizing the heads and sides of slide zones; (ii) stabilizing unconsolidated and unstable shallow debris slopes; (iii) stabilizing the soil surface of both the newly exposed areas as well as the debris slopes such that revegetation (natural regeneration or planting) might occur; and (iv) halting and diverting run-on from upslope to avoid further cutting, shearing, or soil saturation.

Sediment storage in stream system. The sheer volume of the sediments involved are such that VGT might only play a very localized role in such things as: (i) trapping sediments to reduce siltation of lowland irrigation and drainage canal systems (e.g., in banana plantations); (ii) stabilizing and trapping sediments desposited primarily in ephemeral drainages and first-order streams, and (iii) stabilizing sediments in streamside zones for reclamation as agricultural lands.

"Where's the stream channel?" VGT could play a modest role in attempting to influence where the future channel might eventually develop. River training works with gabions and concrete walls are extremely expensive and often a complete waste of money. Vetiver diversion hedges at key points would be much lower cost and in the smaller stream systems (first and second order streams) could be at least as effective as hard structure in 'suggesting' where the channel might develop. Where hard structures are required, it would be recommendable to protect them from undercutting by establishing vetiver hedges along all of points of contact between the structure and the soil.

Sediment inundation. In these areas the challenge is to stabilize the soil surface so that the sites can either be reclaimed for agricultural use (e.g., through over-seeding with leguminous cover crops or pasture grasses) or revegetated. VGT is an ideal system for this use.

Not all future risk can be avoided in new construction. As previously mentioned, bridges must cross the rivers, roads have to go through the mountains, and some homes will be built in unsuitable areas. In these endeavors, VGT should not be perceived as allowing these to be carried out in newer, even riskier or more vulnerable areas. The appropriate role of VGT here is to extend the design life and safety margin where risk is unavoidable.

Danger zones and encroachment. See Minimizing encroachment into vulnerable areas, above.

Post-Mitch: Where Is VGT Being Applied In The Aftermath ?

Will these "recommendations and promotions" result in concrete actions on the ground? Will VGT be applied as a key technology in the aftermath of Mitch? It remains to be seen. At this point there is simply not enough material in the region to meet the potential demand. The region will have to see a tremendous effort in propagating planting material over the next couple of years if the potential is to be realized. It is now a year later and only CARE and Chiquita Brands have made any significant investments in vetiver propagation.

III. Conclusions

VGT can play a key role in disaster mitigation and vulnerability reduction. However, we should not get too carried away on defining the potential for its impact. The purpose and role of VGT in disaster mitigation and vulnerability reduction is to protect and conserve, not nature, but our interventions within nature and our attempts to manage nature for our own ends. Extreme events like Hurricane Mitch create conditions which simply overwhelm our works and our fabricated systems. As such, VGT is not and cannot be a substitute for appropriate siting of infrastructure, for avoiding encroachment into flood plains and other vulnerable areas, for halting watershed and soil degradation, in short, for overall good natural resource management and land stewardship, for common sense, and for quality designs and construction.Having said that, VGT can be integrated into our systems in order to make them 'more resistant' to disaster and 'more efficient' at surviving them. It can extend their useful lives between extreme events and increase their margins of safety. The success of VGT in protecting roads and infrastructure in El Salvador and in saving farmer's fields in Honduras during Hurricane Mitch proves this to be true. And, we know it can do so at such a reduced cost that should allow for its much broader application.Finally, too often we forget, until a disaster comes along to remind us, that it is not enough that we build or design for average conditions. Engineers remember this instinctively. Natural resource professionals often do not, especially those working with the rural poor. We accept soil and crop management systems and unprotected feeder roads because we understand the farmer's and poor community's logic and time horizon; an economic calculus that does not necessarily pay attention to the medium and long terms. But what happens when the 5-year event overwhelms the pineapple, sugar cane and fallowed strip hedgerows? and the 10-year event the tree hedgerow? and the 25 year event closes the only access road for a year or more? Or, as in the case of Mitch, an even more extreme event forces tens of thousands of rural households off the land and into urban areas whose economies cannot absorb them? While we may not know with precision the limits of VGT, we do know that for many applications no other hedgerow or soil stabilization plant has proven more effective. As appropriate, VGT should always be included as an option in farming systems and bioengineering applications where hedgerows or soil and slope stabilizing plantings are called for. Certainly, for the next few years in Central America we are assured that all natural resource management, civil engineering, rural and urban development professionals will be re-evaluating what constitutes "good practice" and comparing it against what they saw happen with their own eyes when Mitch hit. If we can get enough planting material produced and distributed and enough good technicians trained, maybe the next time around VGT success stories will be too numerous to tell.

Bibliography

  1. United States Geological Survey. 1999. Hurricane Mitch - USGS Briefing Notes.
  2. BBC. 1998. The curse of cut trees. Ben Brown, Special Correspondent. November 17, 1998
  3. CEPREDENAC. 1999. The Impact Of Hurricane Mitch In The Central American Region. Report #14 February 2, 1999.
  4. Interamerican Development Bank. 1999. Reducing Vulnerability To Natural Hazards: Lessons Learned From Hurricane Mitch. A Strategy Paper On Environmental Management. IADB.
  5. PADCO. 1999. Rebuilding Shelter After Natural Disasters: Three Decades of USAID Experience in Latin America and the Caribbean. April 1999.
  6. Hengchaovanich, D. 1998. Vetiver Grass for S1ope Stabilization and Erosion Control (with particular reference to engineering applications). APT Consult Co. Ltd., Bangkok, Thailand.
  7. Bracken, Nevil and Paul Truong. 2000. Application of Vetiver Grass Technology in the Stabilisation of Road Infrastructure in the Wet Tropical Region of Australia. Presented at the Second International Vetiver Conference, Thailand, January 2000
  8. Xia Hanping, Ao Huixiu, Liu Shizhong, He Daoquan. 1998. Application Of Vetiver Eco-Engineering For The Prevention Of Highway Slippage In South China. Presented at: International Conference on Vetiver Bio-Engineering Technology for Erosion and Sediment Control and Civil Construction Stabilisation, Nanchang, China.
  9. Paul Truong, Paul. 1999. Report on the Impact of Vetiver Grass Technology. at the Ground and Water Bioengineering Conference, Manila, Philippines, April 1999. The Vetiver Network.
  10. Vetiver Newsletter #17. 1997. Jano Labat: A Champion of Vetiver in Zimbabwe, Africa.
  11. Rodríguez, Oscar S. 1999. Live Barriers Associated With Vegetative Covers for Erosion Control and Environmental Protection: Research Findings and Recommendations For Venezuela. Paper presented: Bioengineering Workshop for Post-Mitch Construction. May 1999. San Salvador, El Salvador.
  12. Thurow, Thomas and James E. Smith, Jr. 1998. Assessment of Soil and Water Conservation Methods Applied to the Cultivated Steeplands of Southern Honduras. Soil Management CRSP Technical Bulletin 98-2, April 1998.
  13. USDA/ARS. 1991. Vetiver Barriers Pond Water. Vetiver Newsletter #7. November 1991.
  14. Paul A. Dalton, Rod J. Smith and Paul N.V. Truong. 1997. Hydraulic Characteristics of Vetiver Hedges: An Engineering Design Approach to Flood Mitigation on a Cropped Flood Plain.

Footnotes

[1] A cover cropping technique: leguminous cover crop is not incorporated into the soil, rather it is : (i) slashed and the main crop is planted with a minimum till approach either before or after the cover crop is slashed, or (ii) the agricultural crop is planted (usually maize, in this case) and the cover crop planted into the field some weeks after the main crop comes up.

[2] The "Quesungual" system is indigenous to the sloping lands in the humid subtropics of southern Honduras: small holder system (<2 ha); natural regeneration (150 to 500 trees/ha); pruning of trees at 1.5 to 2 m; residues and weeds slashed and left as mulch; associated with bean, corn, sorghum; use of 65 kg urea/ha with grain crops beans climb or are hung on pruned trees; fields are not burned to promote regeneration of trees for next year. From farmer's perspective: reduced labor and costs; conserves soil moisture; fuelwood and mulch from tree prunings; trees provide support to bean crop and for harvested corn.