ENGINEERING


Hydraulic Characteristics Of Vetiver Hedges:
An Engineering Design Approach To Flood Mitigation On A Cropped Flood Plain.

P.A. Dalton, R.J. Smith and P.N.V. Truong
University of Southern Queensland and Queensland Department of Primary Industries, AUSTRALIA

Although the Vetiver system has been used worldwide, few studies described the hydraulic characteristics of Vetiver hedges quantitatively. This paper describes the effectiveness of the Vetiver system in a quantitative hydraulic manner beyond the well documented anecdotal evidence.

The hydraulic characteristics of Vetiver hedges were first determined in a testing flume. From the data collected an empirical hydraulic relationship was developed between the depths and discharge. This relationship was used to calculate the maximum Vetiver grass hedge spacing required to control soil erosion on a flood plain.

From the model of flow through Vetiver hedges, design hedge spacing were selected for a field site in Queensland. The various catchment and farm characteristics were considered before a hedge spacing of 91.5m was selected for the site. Six rows of Vetiver totaling over 3,000 m were planted on the contour at this spacing.

Flood discharges and depths and sediment movement are being monitored at this site to validate the above theory and quantification of Vetiver on the flood plain and to monitor the effectiveness of the hedges. Early results from a small flow over the site show that the hedges reduce significantly the depth and therefore energy of flow through the hedges. At a low depression. 7.25 tonnes of sediment was trapped.


Vetiver In A Southern African Context
Anthony Tantum Specialized Soil Stabilization CC, P.O. Box 167, Howick, 3290, South Africa

Vetiver grass has been promoted and researched extensively in Southern Africa with considerable success. As a consequence it is being used in a range of applications including; combating of soil erosion, in farming and forestry, commercial planting for generation of essential oil, slope stability on engineering sites, and most significantly as stabilization hedges on slimes dams in the gold and diamond industry.

South Africa has numerous very large slimes dams which represent a by-product of deep level gold mining. These dams consist of an extremely sterile, highly acidic rock flour which becomes encrusted with salts in the near surface layers. Aside from being hostile to plant growth, the slimes dams present severe dust, aesthetic, and acid mine drainage environmental problems. These dams are also located in harsh climatic conditions including low rainfall and temperatures which range from -5 C in winter to plus 30 C in the summer. Trial survival planting has shown that Vetiver represents an ideal plant material for stabilization of gold mine and slimes dams. Vetiver has survived successfully for nearly 4 years on slimes dams in Welkom with minimal maintenance. Its use as a stabilization medium is now accepted by the Gold Mining Industry, and aside from the above, other commercial aspects (e.g. mulching, thatch grass, weaving material) applications are being widely considered in the new South Africa.

Slope Stabilization: Vetiver Application In Bio-Engineering Aspect
Karn Trisophon and M.R. Samjamjaras Rajanee, Department of Land Development, Thailand.

Tremendous earth work during the construction of Noppamaetaneedol and Noppapol Phumisiri Pagoda at Intanon summit has caused substantial change in the relief on the construction site. Falling earthwork had formed a steeper slope which was stable enough to sustain itself during the dry season. But in the rainy season, infiltrated water which was contributed by subsurface flow had gradually increased pore pressure and subsequently overcame shear stress of the soil. This caused slope failure. In order to reduce pore pressure, strips of gravel pit were built so as to induce inflow from the excess moisture content of the soil. The excess water was then drained into concrete dikes next to each pit. Even though most of the excess water was drained out, what was left was enough to make the portion of slope adjacent to the dikes become unstable. To remove this problem a row of vetiver was planted on the outer bank of each dike. Vetiver's outstanding root system had two roles. The first was to mesh up and mechanically add stability to the slope. The second role was to suck up the excess water and dissipate it via evapotranspiration process.


An Assessment Of Strength Properties Of Vetiver Grass Roots In Relation To Slope Stabilization
Diti Hengchaovanich and Nimal Santha, Nilaweera Erocon Sdn Bhd, Kuala Lumpur, Mala Ysia.

It is well reported that the root properties of vetiver grass can help reduce soil erosion and enhance slope stability when properly planted on soil slopes. In general the root properties can be subdivided into root strength properties and root morphological parameters. Some previous studies on vetiver plant have elaborated the root morphological parameters qualitatively. However, the strength properties of vetiver roots, which also play a significant role in terms of erosion control and slope stabilization, have not yet been understood adequately. Vetiver is considered as a very deep-rooted penetrating grass variety which develops a fibrous profusely grown root system. The root penetration is mainly vertical and sometimes up to 3.6 m deep depending on the soil conditions. When a root penetrate across a potential shear surface in a soil profile the distortion of the shear zone develops tension in the root; the component of this tension tangential to the shear zone directly resist shear, while the normal component increases the confining pressure on the shear plane. Therefore, it is essential to understand about the root tensile properties in the process of evaluating a plant species as a component of slope stabilization.

This paper intends to discuss about root tensile strength of vetiver grass and its contribution to soil strength increase by means of experiments on root tensile strength determinations and root permeated soil shearing, which is a part of an ongoing research work specially design to assess both root strength properties and root morphological parameters in relation to slope stability and erosion control. Unbranched sections of vetiver roots in different diameter classes up to about the average maximum root diameter (3.5 mm) were tested in order to determine the tensile strength. The results were compared with the root tensile strengths of other tree species which were obtained from previous studies, and the effect of root diameter on the tensile strength of vetiver roots was established. To obtain the contribution of root tensile strength to the shear strength of soil, large scale direct shear tests were performed in 0.5 x 0.5 x 0.5 m3 root permeated soil blocks along with root free soil blocks with same soil properties. The difference between the shear strength values of root permeated and root free soils, the shear strength increase due to the presence of roots, were then analyzed with the root area ratio, root diameter, root orientation and eventually with the root tensile strength to elaborate the significance of root tensile strength of vetiver grass and its influence in soil strength increase.


Calibration Of Rusle With Vetiver Grass As Life Sediment Filter In The Hills Of Puerto Rico.
Luis R. Perez-Alegria, Ph.D.,P.E. and Luz Cruz MSc (C). Agricultural Engineering Department, University of Puerto Rico, Maya guez, Puerto Rico.

Vetiver is being evaluated and considered, along with other conservation practices, as a viable alternative for erosion control and reforestation of large clear areas. Research to calibrate the performance of vetiver as a live sediment filter is in progress; the Revised Universal Soil Loss Equation (RUSLE) is being used as the prediction model in very steep slopes subject to several management practices including denuded areas.

Vetiver barriers have been planted at 30 foot intervals in a 100 percent slope planted in an intercrop of pigeon pea and celery in the town of Jayuya, Puerto Rico. A sediment collection equipment was designed, built and installed before and after each vetiver barrier. Sediment accumulation behind the barrier is measured after every rain event with surveying equipment. The farmer has collaborated in all aspects of the work from planning. contouring, planting to data collection.

The result of this experimental work will be used to develop guidelines for use of vetiver in the hills of Puerto Rico and other tropical islands with similar ecosystems and under agriculture and in construction sites and along road banks to reduce the high level of sediment yields from most agricultural watersheds in tropical environments.


Root Characteristics And Root Distribution Studies Of Some Vetiver Grass (Vetiveria zizanioides L, Nash And Vetiveria Nemoralis A. Camus) In Thailand By Using P-3z Tracer Technique
J Mahisarakul, P. Snitwongse and R. Payamanonta1
Nuclear Research in Agriculture Section, Di vision of Agricultural Chemistry,
Department of Agriculture, Bangkok, Thailand and 1the Office of the Royal
Doitung Development Projects, Maesai, Chiangrai, THAILAND.

The Root performances at different growth stages of some local vetiver grass was conducted at different experimental sites within the Royal Doi Tung project area. Soil injection technique with P-32 at various distances and depths of a vetiver plant hill was used. Radio activity of P-32 was monitored from the leaves at growth stages to evaluate rooting characteristics and pattern of root system.

Under field trial for studying root characteristics at Doi Tung Vetiver Crass Research and Development Centre, 2 vetiver grasses originated from Surat Thanee (Vetiveria zizanioides L, Nash) and Pimai (Vetiveria memoralis A. Camus) were studied. It was observed that at 1 and 2 1/2 month after planting of a Slip of vetiver grass, roots of both vetiver plants were found at 150 and 250 cm depths respectively. However, more root density was found at the depth 30 -100 cm. At 9.6 months growth stage of both vetiver plants, roots were found at soil depth 400 cm. and the highest root density was at the depth of 150, 250 and 350 cm. respectively. It was also found the roots of both vetiver grasses at the depth of 500 cm. when observation was made at 25 months old.

Vetiver grass, Viangchai, from Chiangrai was grown at side slope for the purpose of soil erosion control. Root systems was not extensive due to inadequate nutrients which was shown by the handed growth of vetiver plants. However, roots penetrating were as deep as 400 cm. when the plants were 17.6 months old. The results of root density were vague.

Vetiver grass from tissue culture from Surat-Thanee and Hua Ka Kaengere were used to study root distribution at field trial. It can be concluded that on the average root development of vetiver grass studies of Surat-Thanee would distribute horizontally from the plant hill 60 cm. (soil depth 80-90 cm.) at the age of 6 months. At 8 -10 months old the distribution was between 80-140 cm. (30-120 cm. depth) respectively. The root could spread in between 70-100 cm. apart from the testing at the depth of 150 cm. It could be observed that at 180 cm. depth, the root could distribute to the distant of 80 cm. away from the testing hill. For Hua Ka Kaeng the root distribution was not as good as that at Surat-Thanee. The root could spread uniformly between 40-60 cm. on average away from the testing grass (6 -10 months old).


The Introduction, Early Results And Potential Uses Of VGHR In Mediterranean Regions.
Troglia M., Yoon P.K., Tasias J., Rodriguez J.N., and Frutos D.T. Techa grind S.L, Italy.

The establishment and growth of VGHR were tested in the hostile, aerial and edaphic environment of Murcia, Spain. The climatic condition consists of hot summer, cold winter with sub-zero temperatures, low precipitation and negative water balance over more than half a year. The soil is calcareous, mostly clayey. Hilly topography is common with serious erosion rates of more than 5000 Tm/km2 per annum.

The experimental sites were in El Chopillo with 300 plants and in Lorca with 32,498 plants on 5 trials testing soil protection and moisture conservation under different conditions. Despite cold winter with frost, trials established by container plants, from December 1994, had overall transplanting success of 95.9%.

Harvesting of plant tops in El Chopillo, produced 55 tiller and 1033 gm/plants after 14 months. In San Julian, the Malaysian and American Cultivar produced 304 and 377 gm/plant with 45 and 79 tillers respectively after 9 months.

Excavation showed that the root system in El Chopillo had reached a depth of 2.6 m. In San Julian, the Malaysian and American Vetiver had produced roots reaching down to 2.1 m. and 1.7 m. respectively. In all cases, the major root masses were at the top 0.5 m. In a 45% slope of 11 meter height, 2 blocks of 20 meters were planted with VGHR at 1 metre vertical interval in January 1995. The in-between block, left unplanted as control, suffered severe erosion by September 1995 despite the low rainfall. Significant soil had been trapped by the VGHRs.

Sub-zero temperatures in winter killed exposed tops but the buried crowns survived. In early spring, new tillers were formed, followed by good and vigorous growth in Summer and Autumn. The plant's response to the seasonal weather condition suggests 4 distinct phases:

Frost injury and dormancy
Awakening and tillering
Rapid growth and biomass production
Slow growth or sustenance period.

The tropical Vetiver Grass adapted well to the weather conditions and appeared to behave like a temperate plant. This, and the good growth and root system suggest potential uses for Vetiver in the Mediterranean Regions. It also suggests that Vetiver could be established in the highlands of the tropics and the subtropics.