CONSTRUCTION TECHNIQUES AND MANAGEMENT OF
ECO-ENGINEERING SOLUTION FOR RECTIFICATION OF
RIVERBANKS
SAA 4064 PROJEK SARJANA MUDA
SINOPSIS
SYAHERMAN BIN JOHAR
AA990522
810118-05-5061
4 SAW
SUPERVISOR
PROF. DR. NORAIENI HJ MOKHTAR
PANELS
EN. ZULKIFLEE IBRAHIM
PROF. DR. ALEJENDRO CARMELENGO
PN. PONSELVI JEVARAGAGAM
Fakulti Kejuruteraan Awam
Universiti Teknologi Malaysia
CONSTRUCTION TECHNIQUES AND MANAGEMENT OF ECOENGINEERING SOLUTION FOR RECTIFICATION OF RIVER
BANKS.
Noraieni Hj. Mokhtar, PhD1 , Syaherman Johar ,Bsc2
1
Faculty of Civil Engineering, Universiti Teknologi Malaysia
2
Faculty of Civil Engineering, Universiti Teknologi Malaysia
Abstract: River banks erosion can present serious problems to river engineers,
environmental managers and farmers through loss of agricultural land, danger to
riparian and floodplain structures, increase downstream sedimentation, and
occasional riverine boundary disputes. Design and construction details are vitally
important to successful control of erosion and sediment. Nowadays, the
technology for erosion and sediment control is well developed. The problem is to
apply the technology correctly and thereby control the problem at its source.
Improper design and installed often results in problems more severe than those
that were to be avoided.
Keywords: design and construction, river bank, erosion.
1. INTRODUCTION
Vegetation is one of methods used to control erosion for rectification and stabilization of
river bank. Experience the numerous rivers indicates that vegetation is ineffective in
protecting river banks from erosion except at the water surface-bank interface. Grasses
and shrubs help protect banks against erosion from wave action, surface velocities, and
small variations in flow elevation in the vicinity of the water surface. Vegetation is the
most cost-effective form of erosion control. It is also self-healing and attractive. Since
vegetation prevents erosion, it is a more desirable control measure than straw bale dikes,
silt fences, and sediment traps and basins. Vegetation reduces erosion by absorbing the
impact of rain drops, reducing the velocity of runoff, reducing runoff volumes by
increasing water percolation into the soil, binding soil with roots and protecting soil from
the wind.
2. SITE PREPARATION
Construction practices, such as extensive clearing and earth moving, procedure large
areas of exposed soil with a high potential for erosion. Grading creates cut and fill areas
that have soil conditions substantially different from the original ones. Cut slopes are
typically stripped down to the subsoil or parent material (rock). The exposed slope is
often hard, rocky, and low in fertility. Initial plant regrowth on such slopes will probably
be scraggly and thin. Fill areas generally contain a mixture of topsoil, subsoil, rock and
anything else that had to be disposed of. A common fill material may be the grading
spoils from the other construction projects. Thus, a fill area may contain the right types of
soil for plant growth, but they are often mixed up or inverted or may not have originated
at the site. The unpredictable soil composition and potential for differential compaction
and settling make fill areas particularly susceptible to erosion.
Before a disturbed site is revegetated, the earth should be shaped and roughened to create
a favorable environment for plants to grow in. it is a common practice to grade slopes
until they have a hard, smooth surface. Such slopes give false give a false impression of
“finished grading” and a job well done. Seedling roots have a difficult time penetrating
these surfaces. A light rain or wind can easily carry away the seeds.
3. FIELD WORK
3.1 SEEDING
The key factor of seeding is to get the seeds evenly distributed and in contact with the
soil. Best results are obtained when seeds are covered with shallow layer of soil to a
depth of ¼ to ½ inch (0.6 to 1.3 cm). It should not have a soil cover greater than 1 inch
(2.5 cm). Seeding can be done by hand, by machine (seed drill), by hydraulic jet, or by
aircraft. The steepness of slope and size of area determine the proper equipment to use.
Hand broadcast seeding is effectively seeded at small, gently sloping or flat areas. Breast
seeders (“belly-grinders”) are inexpensive. Seed can be covered by lightly raking the soil
or by dragging a chain over the surface. The seed may become covered naturally on a
rough, loose seedbed. Hydraulic seeding and mulching (hydroseeding) is the most
efficient means for seeding steep slopes. It is a one-step process for spraying a slurry of
seed, fertilizer, wood fiber mulch, and water. The critical factor in hydroseeding is the
ability of the fiber to adhere to the soil and hold the seed in place during rainfall and
wind. Seed drills are commonly used in agriculture. They can be used only on flat or
gently sloping sites. Because seed drills plat seeds at the proper depth, they provide the
best stands of grass. In addition, when seed is drilled, seed and fertilizer rates may be cut
in half.
3.2 FERTILIZER
Fertilizer is essential to the establishment of vegetation, particularly on cut slopes. The
amount and composition of fertilizer to use depends on local soil conditions. As was
stated earlier, it is preferable to use plants that can survive without repeated fertilization.
Fertilizing is costly, and on most sites you cannot count on having someone there to do it
year after year. Excessive fertilizer can cause water pollution. However, on sites with
sandy or coarse-grained soils, such as decomposed granite, reapplication of fertilizer may
be necessary for continued plant cover.
3.3 MULCHING
Application of mulch protects a disturbed site from erosive forces until plants are large
enough to do the job. Mulch materials include straw, wood fiber, wood chips, bark, fabric
or plastic mats, soil and gravel.
3.3.1 Straw Mulch
Straw mulch is highly effective at absorbing raindrop impact and moderating the
climate on the soil surface. Straw mulch should not be applied too heavily. Soil
should be visible through the straw mat. Straw can be applied either by hand or by
blower. It is difficult to apply straw uphill or under windy conditions. Straw must
be anchored to keep it from blowing away. Common methods of holding straw in
place includes crimping, disking, rolling or punching it into the soil, covering it
with netting and spraying with a chemical or fiber binder. Those methods are
commonly accomplished with commercial machine called sheepsfoot roller.
3.3.2
Wood Fiber Mulch
Wood fiber mulch consists of fine wood fibers to which a green dye added to
make the mulch visible on the ground when it is being applied. It is easy to apply
with a hydroseeder. Instead, wood fiber mulch does not by itself provide much
erosion protection. This is because it does no have enough mass to absorb the
energy of raindrops and flowing water. Typically, wood fiber is applied
hydraulically which is wood fiber, seed, fertilizer, and water are combined in a
tank and applied together as a slurry.
3.3.3
Nettings
Heavy-weight netting materials such as jute (woven fibers) and excelsior can be
effective mulches. Not only do these dense nettings hold soil in place but also
absorb water and hold moisture near the soil surface. It must be so applied that is
in complete contact with soil so it can be protected from erosion. Netting should
be anchored to the soil with No. 11 gauge wire staples at least 6 inch long. On
very hard rocky soils, the netting can be anchored by using large nails and
washers. However, the materials may need a high cost.
4. TEST AND RESULT
4.1
Test Procedures
Mulches were tested on 0.6- by 1.2 meter boxes of soil inclined at 5:1 and 2:1 slopes
(horizontal to vertical ratio). Rainfall was simulated by using 3-mm-diameter drops
falling 4.5 meter at the range of 152 mm/hour for periods of 2 to 6 hour. The soil boxes
were designed to allow rapid drainage if water moved through the top 15 cm of soil. Soil
washed from each box was collected, dried and weighed. Eight soils were used in the
tests which is taken from construction sites (Table 1.0)
4.2
Test Results
Figure 1.0 shows the rate of erosion from each of the soil types when no protection was
used. Soil loss was greater from all soil types when inclined at 2:1 than at 5:1. the most
erodible soils were those with high percentages of fine sand and silt including the three
loam soils. The uncemented fine sand did not erode initially, but it would liquefy when
saturated and down downslope. On, the 2:1 slope, this liquefied sand flowed rapidly and
thus produced very high erosion rate. The least erodible soils were the coarse, gravelly,
decomposed granite and the soil with the highest clay content.
Table 1.0 : Textures and particle size percentages of soils used in mulch
Texture
uncemented fine sand
very gravelly coarse sand
gravelly sandy loam
sandy clay loam
loam
loam
loam
clay loam
Name
Arnold
Decomposed granite
Cieneba
Dibble
Los Osos
Yolo
Auburn-Sobrante
Altamont
Clay
2
3
9
21
17
22
21
29
Silt
3
4
9
18
48
45
43
45
Sand
95
41
49
61
35
33
36
26
Gravel
0
52
33
0
0
0
0
0
Figure 1.0 : Erosion rater from unprotected soil surfaces inclined at 5:1 and 2:1 slopes.
4. CONCLUSIONS
The conclusions that can be drawn from this study are as follows:
1. Vegetation using straw mulch provided much greater protection on all soils, but
particularly on the uncemented fine sand, the decomposed granite, and the clay
loam.
2. The wood fiber mulch, though less effective than straw, did offer some protection.
3. When an erosion control treatment is to be selected, it is necessary to consider
both short and long-term effectiveness.
4. Hydraulic seeding and mulching with wood fiber does provide adequate erosion
protection if plants are established, but its pregermanation effectiveness is low to
moderate.
5. Jute netting and jute over straw are highly effective but very costly treatments and
they are best for small sites and critical areas.
5. REFERENCES
1. Association of Bay Area Governments, Manual of Standards for Erosion and
Sedimentation Control Measures, ABAG, Oakland, Calif., 1981.
2. R. P. Beasley, Erosion and Sedimentation Pollution Control, The Iowa State
University Press, Ames, Iowa, 1972.
3. F. W. Bennett and R. L. Donahue, Methods of Quickly Vegetating Soils of Low
Productivity, Construction Activities, U. S. Environmental Protection Agency,
Washington D. C., 1975.
4. Dr. Farber, “Recommended Planting Time For Vegetative Stabilization of
Construction Sites,” Technical Memorandum No. 51, in San Francisco Bay Area
Environmental Management Plan, Appendix J, Association of Bay Area
Government, Oakland, Calif., 1981.
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