Using Bioengineering to Stabilize Landslide-Prone Hillsides
One of the major challenges in building hill roads is stabilizing hill slopes with appropriate and costeffective interventions. The Mizoram State Roads Project employed innovative bioengineering techniques that used the abundantly available local bamboo to stabilize the hill slopes at a fraction of the cost of conventional methods that use concrete structures for the purpose.
Bioengineering is the use of vegetation, mostly shrubs and grasses, either alone or in conjunction with stone and concrete protection works such as retaining walls etc. to enhance the stability of slopes. It benefits both road building agencies and users alike as it not only provides one of the best, and cheapest, ways to protect the road and its users from landslides, but also retains the hillside’s productivity, unlike stone and cement works on which no vegetation can grow. A slope treated with bioengineering measures can therefore retain its forests, water bodies, farmlands and orchards while also covering up any unsightly scars that result from road widening activities. These environmentfriendly measures also reduce the carbon footprint of roads.
Bioengineering techniques are now being implemented under the World Bank supported Himachal Pradesh State Roads Project.
The Mizoram State Roads Project sought, amongother objectives, to improve connectivitybetween Aizwal, the state capital, and Lunglei,its second largest town, by upgrading, widening andimproving the old road between these two majortowns. Connectivity is crucial for a distant hill state suchas Mizoram which, like the other northeastern states, isgeographically isolated from the mainland. However, longand difficult transportation routes over predominantlymountainous terrain have long hampered trade anddevelopment. As a result, Mizoram conducts virtually notrade with the mainland or with neighboring countries.The drawing of new borders following the partition ofIndia in 1947, with the loss of access to the port ofChittagong, dealt a major blow to the region’s economy.It particularly isolated the state’s southern region andthe town of Lunglei, situated near the Myanmar andBangladesh borders.
While the new road would bring enormous benefits to the people, environmental and social assessmentshighlighted a number of challenges in projectimplementation:
Stabilizing hill slopes
The soft rock and immature geology of the projectarea, together with the region’s heavy rainfall, wouldrequire the stabilization of hill slopes both aboveand below the road. Over 100 such landslide-pronelocations were identified all along the 164 kmproject corridor.
Disposing of debris
Cutting the hillside to widen a road invariablygenerates debris. Disposing of this debris in thehilly areas is a challenging task as loose debriscan potentially cause landsides, lead to unsightlyscarring, and cause the hill slopes where it isdumped to lose their productivity. Although theroad’s technical design had reduced the generation of debris by 40 percent - by filling the valley portionswith the debris - about 0.7 million cu.m. of debris wouldstill need to be disposed of.
The region is part of the Indo-Burma biodiversityhotspot. Roadside slopes support a rich variety ofnative flora including many medicinal plants. Parts of thecorridor also support wildlife, including the endangeredChinese pangolin. Project activities would thereforeneed to be conducted in a manner that protected thearea’s rich flora and fauna.
Maintaining the productivity of hill slopes
A fairly large proportion of Mizoram’s people usehill slopes for agriculture where they still follow thetraditional practice of ‘jhum’, or shifting cultivation, a‘slash and burn’ method of cultivation that requires largetracts of land. The productivity of these slopes wouldtherefore need to be retained and any land acquisition for project work or the disposal of debris would needto be done in close consultation with the local people.This was especially so in Mizoram as, under Mizo tribalcustom, a significant part of the land is jointly ownedand administered by the community.
Meeting community needs
Considering the adverse impacts that road improvementactivities could have on local communities and theirlivelihoods, the environment management plan (EMP)included extensive community consultations. Theseconsultations covered a broad range of issues, such asidentifying exclusion zones for construction activitiesto safeguard biodiversity patches, identifying measuresto prevent deforestation and protect water bodies,and identifying prudent alternative road alignmentsand debris disposal sites to minimize impacts oncommunities and natural resources. Communities werealso involved in project construction, and contractorswere made responsible for involving them.
Using locally available bamboo to terrace the hillslopes for cultivation is a well-known and ageoldpractice in Mizoram. Bringing in significanttechnical know-how from the Rural Access Project(RAP) in Bhutan, the World Bank team introduced thenew concept of using this bamboo to bind and stabilizethe hill slopes on both the hill and valley side of theroad, as well as on debris disposal sites. This combinedthe traditional techniques long employed by the localpeople with new ideas about how to expand their use.
In Bhutan, the RAP project used pine logs to createcrib walls and other bioengineering measuresto protect the slopes. In Mizoram, given thelocal people’s traditional know-how and ease inhandling bamboo, the World Bank team adaptedthe techniques employed in Bhutan to suit localconditions by using the abundantly availablebamboo.
Using local materials and labour
Bamboo terracing, bamboo crib walls and bambooknitting were developed to suit the requirementsof each slope as well as for debris disposal sites.The Mizoram State Public Works Department(PWD), the project implementing authority, as wellas World Bank staff and the supervision consultantstogether devised their own method of bamboomatting, working out as they went along the exactdimensions that were suitable for a particular slope.
Implementation was assigned to local villagecouncils. The local people had retained thetraditional skills of working with bamboo; they also knew where to collect the raw material from as theyknew where the bamboo forests were located. Thenew bioengineering techniques were demonstrated tothem on small trial patches. Drawings/sketches weremade of the various types of work needed at a particularsite. Given their familiarity with the materials, the locallabourers employed in the trial patches adapted thesemethods to suit particular conditions. They were thentaken to other sites along the route to demonstratethese new methods to local groups working near theirown villages.
Despite these efforts, however, many bioengineeringmeasures could not be effectively implemented in theinitial years of project implementation. The contractorswho were from outside the northeastern region lackedthe local bioengineering skills and were unable to take local communities into confidence. They also placeda higher priority on achieving construction targetsand, with a stake in maximizing the constructed area,resorted to using conventional civil constructiontechniques such as retaining walls, stone pitching, etc toprotect the slopes. This led to long delays as the stonesfor building the masonry works had to be importedfrom Silchar in Assam and skilled masons were in shortsupply in the state. As a result, many slopes identifiedfor stabilization could not be covered before the onsetof the 2004 monsoon season, leading to several slopefailures and road damages.
Subsequently, the Mizoram PWD took special initiativesjointly with the World Bank and the supervisionconsultants to address the damage caused. A concertedeffort was made, led by the Executive Engineer(Environment) of the Mizoram PWD, to reach out tolocal communities, improve understanding and benefitfrom local knowledge and skills. It was also ensured thatthe project benefited local livelihoods and enhancedcommunity assets.
The flowering of the bamboo in 2005-06 provided anopportunity to use the dying bamboo for constructionpurposes. (This is a cyclic ecological phenomenon that occurs every 48 years in a particular species of bambooin Manipur and Mizoram; the price of bamboo falls atthis time and a great deal of bamboo is traditionallyextracted for construction purposes.) With thebamboo becoming abundantly and cheaply available, thebioengineering works proposed for the slopes wereredesigned to make the maximum use of this resource.
Planting useful shrubs and grasses
The abundantly available bamboo seeds were thenplanted over the bamboo structures to complete theprocess of slope stabilization quickly and cheaply overlarge areas. Project staff also ensured that local species of vegetation were planted on the bioengineered sites,including fruiting trees and shrubs as well as speciesof grasses which are used by the local people to makebrooms etc. In fact, different grasses were used in theAizawl and Lunglei areas to keep the local ecologyintact. Special care was also taken to provide chutedrains to avoid erosion when the saplings were youngand their roots shallow. The quick-growing local floraensured that the slopes became green very soon.
In 2007, when the highest rainfall in the region in tenyears was recorded, causing severe damages to roadworks, the pilot bioengineering works remained stablewith minimal damage.
Since resources were scarce, using the abundantlyavailable local bamboo to stabilize the hill slopesproved to be the most appropriate and costeffectiveintervention, leading to a ‘win-win’ situation:
The bioengineering works were very labor-intensiveand required little capital investment. The involvementof local skills, labor and materials resulted in considerablecost savings. Bioengineering measures for slopeprotection were implemented on 105 sites, coveringan area of about 140,000 sq. m., at a total estimatedcost of about US$90,000. (Costs ranged from US$40 toUS$100 per sq. m. depending on the type of slope andthe nature of the treatment). By contrast, the estimatedcost of conventional civil works would have been aboutUS$650,000 to US$1million for the same area.
The bioengineering measures were also quickerto implement than conventional civil construction techniques. This was especially important inMizoram which has a short construction season ofjust 6 to 7 months when it does not rain.
The bioengineering works also helped retain theproductivity of the hill slopes whereas masonryworks would not have done so. This was of majorimportance to local communities, given thatagriculture is the predominant land use along theproject corridor. Where the bioengineering workshave been completed, communities have been ableto resume their traditional ‘jhum’ cultivation.
Rural livelihoods created
While stone masonry and cement concreteprotection works would have required skilledmasons from outside the state, generating veryminimal local employment, the bioengineeringmeasures involved local labour and generatedsubstantial local employment in the short term for the residents of about 20 villages. An estimated 130,000man days of employment were generated. This alsoenabled local communities to develop their village areas,led to strong community ownership, and encouragedthe local people to take responsibility for safeguardingthe structures over the long term.
Labour shortage solved
Using local labour to stabilize the hill slopes also didaway with the need to deploy labour gangs at numeroussites along the project corridor. This was especiallyimportant in Mizoram as mobilizing labour from outsidethe state was difficult.
Carbon emissions reduced
An indirect benefit was that the carbon emissionsassociated with cement concrete construction weresignificantly reduced. The plants used for the bioprotectionworks will also help absorb more carbon.
Spreading the Innovation
Building on the successful experience gained fromthis project, the World Bank team introducedthe concept of bioengineering in the HimachalPradesh State Roads Project as a fundamental part ofthe project’s environmental management plan.
Based on the experience gained in Mizoram, as well as thetechnical specifications and training materials preparedfor the Mizoram project, a comprehensive manual wasprepared. This detailed about 12 to 14 bioengineeringtechniques as well as the various types of grasses,shrubs and trees that can be used in Himachal Pradeshdepending on the temperature, rainfall, altitude, and soilconditions prevailing at different locations in the state.The Himachal Pradesh PWD as well as the state’s Roadand Infrastructure Development Corporation havenow incorporated these practices into their regular operations.