Individual Training
Ecological Engineering Purification System
Ecological Engineering Techniques For
Lake Restoration In Japan
(Oct. 29th, 2001—Apr. 27th, 2002)
By Hu Xiao Zhen
(China)
Advisor: Nakamura Keigo
River Environment Group
Public Works Research Institute
Tsukuba International Center, JICA
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Contents
Acknowledgement ............................................................................................................ 5
1. Introduction .................................................................................................................. 6
1.1 Lakes and its function in Japan ................................................................................. 6
1.2 Lake pollution in Japan .............................................................................................. 7
1.3 Efforts toward protecting lakes in Japan .................................................................. 8
1.3.1 Laws and regulations ........................................................................................... 8
1.3.2 Pollution control ................................................................................................... 9
1.3.3 Restoration measures ......................................................................................... 10
1.4 Ecological engineering and its development ........................................................... 10
2. Artificial Floating Island (AFI) Method ......................................................................12
2.1 Features and Function .............................................................................................. 12
2.1.1 AFI and its development .................................................................................... 12
2.1.2 Function .............................................................................................................. 12
2.1.3 Suitable installation places................................................................................ 13
2.2 Structure of AFI......................................................................................................... 13
2.2.1 Structural classification ..................................................................................... 13
2.2.2 Vegetation base ................................................................................................... 16
2.3 Points for AFI Design and Installation.................................................................... 17
2.3.1 AFI plan process ................................................................................................. 17
2.3.2 Structure design ................................................................................................. 17
2.3.3 External force calculation .................................................................................. 19
2.3.4 Fixing design ....................................................................................................... 20
2.4 Cost ............................................................................................................................. 21
2.5 Monitoring and Maintenance ................................................................................... 21
2.5.1 Monitoring ........................................................................................................... 21
2.5.2 Maintenance........................................................................................................ 21
2.6 Application case in Lake Kasumikaura ................................................................... 21
2.6.1 Introduction ........................................................................................................ 21
2.6.2 effects ................................................................................................................... 22
2.7 AFI case in Lake Jonuma ......................................................................................... 23
3. Attached Lagoon and Artificial Lagoon Method .........................................................26
3.1 Features and Function .............................................................................................. 26
3.2 Application case in Lake Biwa ................................................................................. 26
3.2.1 Introduction ........................................................................................................ 26
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3.2.2 Operation............................................................................................................. 27
3.3 Artificial lagoon case in Lake Kasumikaura ........................................................... 27
3.3.1 Introduction ........................................................................................................ 27
3.3.2 Effects .................................................................................................................. 29
3.3.3 Some Key Points from AL case .......................................................................... 29
4. Constructed Wetland Purification Method .................................................................31
4.1 Features and advantages.......................................................................................... 31
4.1.1 Introduction ........................................................................................................ 31
4.1.2 Advantage............................................................................................................ 31
4.1.3 Types .................................................................................................................... 31
4.2 Design criteria for constructed wetland .................................................................. 33
4.2.1 FWS Wetland ...................................................................................................... 33
4.2.2 SF Wetland .......................................................................................................... 34
4.3 Compact wetland and its advantages ...................................................................... 35
4.3.1 Features and advantageous ............................................................................... 35
4.3.2 Structure ............................................................................................................. 35
4.3.3 Effects .................................................................................................................. 37
4.4 Operation and maintenance ..................................................................................... 37
4.5 Bio-park in Lake Kasumikaura ............................................................................... 37
4.5.1 Introduction ........................................................................................................ 37
4.5.2 Layout .................................................................................................................. 38
4.5.3 Effects .................................................................................................................. 39
5. Lake Littoral Restoration Method ..............................................................................40
5.1 Introduction ............................................................................................................... 40
5.2 Restoration key points .............................................................................................. 41
5.2.1 Understanding of geomorphology of shoreline ................................................. 41
5.2.2 Succession of the shoreline vegetation .............................................................. 41
5.2.3 Relation between wave strength and erosion ................................................... 41
5.3 Restoration model ..................................................................................................... 42
5.4 Application case in Lake Biwa ................................................................................. 43
5.5 Application case in Lake Kasumikaura ................................................................... 44
5.6 Application case in Lake Shinji ................................................................................ 45
5.7 The littoral zone naturalization case in Lake Constance....................................... 46
5.8 Application Case in Lake Suwa................................................................................ 47
6.Others ...........................................................................................................................49
6.1 Vegetable purification case by a private organization ............................................ 49
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6.1.1 Installation .......................................................................................................... 49
6.1.2 Vegetable species ................................................................................................ 49
6.1.3 Cost ...................................................................................................................... 50
6.1.4 Effects .................................................................................................................. 50
7. Summary .....................................................................................................................52
Reference .........................................................................................................................53
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Acknowledgement
During the 6 months’ individual training for Ecological Engineering Purification
System organized by JICA, I have not only read a lot of books in theory, but also have
visited many studying tour places for practical experience, as well as attend two times
academic conferences and a lot of meetings. I am very grateful to the Japan
Government, JICA, the Ministry of Land, Infrastructure, and Transport and the Public
Works Research Institute for providing me with such a good training chance and I
believe that the training is both fruitful and useful.
This report is a summary of my training course, prepared based on the knowledge
and information obtained during training. Nakamura Keigo san, who is my instructor
for the training and can speak excellent English, has given a lot of materials and
helpful instructions to me. He is also very kind to arrange all the studying tour for me.
Here I’d like to take this opportunity to express my sincere gratitude to him for his
instruction and assistance. I also want to give my thanks to Muraoka san, Hayashida
san, and Denda san, who are very kind and show me their labs and explain their
research to me. Special thanks to Yoshida san, Hashimura san, Hinuma san and
Sawabe san, who are so warmhearted and patient and really helped me a lot not only
in my training but also everyday life. Also many thanks to the group leader Sago san,
team leader Ozawa san, and Ito san. And I also give my thanks to all the colleagues in
our group, staying with them, I really feel at home and learned a lot about Japan.
Finally, thanks are given to all the staff in TBIC, PWRI and NILIM who have
worked hard to create a good living and study condition for us and help us have a
pleasant stay in Japan. Especially my Program Office-Nishigada san, who has paid
much attention on my training, helped a lot for my studying schedule and buying
books.
The training does not only give me a chance to studying advanced technology in
Japan, but also give a chance to make friends with Japanese people and all the
participates from the other countries. I will remember this nice experience in Japan
forever.
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1. Introduction
1.1 Lakes and its function in Japan
The numbers of lakes in Japan, including the artificial ones with a diameter
greater than 100m, is approximately 11600. According to results from Japanese
Environmental Agency in 1984, there are 1120 lakes with water surface area large
than 0.1km2 and a watershed area large than 1km2. Approximately 80% of these lakes
are man-made by dams constructed after the Second World War for water supply and
irrigation reservoirs. However, natural lakes hold 90% of the total water volume of all
lakes in Japan. (1)
Table1-1 Number of Lakes dams in Japan
Lake Type
Number
Natural Lakes
197 (17.6%)
Dams
763 (68.1%)
Ponds
160 (14.3%)
sum
1120
Source: Japan Environmental Agency (1984)
Total volume 106m3
117435 (89.4%)
13521 (10.3%)
346 (0.3%)
131302
Lakes and rivers are of vital importance in Japan. They service as drinking water
source, provide water for agriculture and industry, produce products from fish to reed,
help prevent floods, reduce level of pollutants, and are an important link to natural
world, giving recreational opportunities and “breathing space”. Besides, they provide
important social and ecological functions while storing water and supporting
significant aquatic biodiversity.
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Figure 1-1 Main functions of lakes in Japan (1)
Data by The Japanese Prefectures' Association on the Promotion of Environmentally Sound
Management of Lakes ("National Lake Association")
1.2 Lake pollution in Japan
Lake environment in Japan changed greatly with rapid economic growth. Land
reclamation in lakes was prevalent among many parts of Japan in and around the
1950s for increased food production, which caused lake shrinkage and dramatic change
of lakeshore ecosystems. Furthermore, the level of transparency in lakes tended to drop
during the 1950s and 60s. In the 1970s, red tide and water bloom symbols of
deteriorating water quality - appeared in many lakes throughout the county.
At present, the main environmental problems in lakes in Japan are similar as that
exist in the world's lakes, they are 1) Eutrophication, 2) Sedimentation, 3) Water Level
Reductions, 4) Toxic Waste Pollution, 5) Disturbance of Ecosystem. Eutrophication is
occurring in an overwhelming number of Japanese lakes and reservoirs, and water
bloom or red tide cause such problems as foul smelling of drinking water, fisheries
damage and loss of landscape beauty. Sedimentation has become a problem in some
dam reservoirs but hardly causes a problem in natural lakes. Aoki Lake is an example
of water level reduction (in this case, 21 m) due to water being taken for power
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generation. Toxic waste pollution is at level that can be ignored. Furthermore, there
are some lakes disturbing their ecosystem, because exotic species of fish are being
introduced to them for sports fishing. (2)
Figure1-2
Lake eutrophication status in Japan (1)
1.3 Efforts toward protecting lakes in Japan
1.3.1 Laws and regulations
Many countries have codified laws promoting environmental protection. These
laws provide a statutory framework for the regulation of industrial and domestic
discharges to water-bodies. The Water Pollution Control Law in Japan has established
standards for wastewater from factories and establishments, and 300,000 factories and
establishments involved in some 600 types of work across the country are applicable. In
the case of water areas that environmental quality standards are difficult to apply,
effluent standards can be applied in an even suffer form by regulations enacted by
prefectural bodies(e.g. Lake Kasumigaura Eutrophication Prevention Ordinance). To
promote water quality in designated lakes, the Law Concerning Special Measures for
Conservation of Lake Water Quality (Clean Lakes Law) was enacted in 1984 with the
aim of providing integrated and planned protection measures for entire basin areas
(the source of pollution outbreaks) of lakes. Some positive measures to deal with basin
and in-lake problems were initiated through water quality conservation plans based on
the Clean Lakes Law as well as eutrophication prevention measures introduced by
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local autonomy bodies. (2)
1.3.2 Pollution control
(1) Point source control measures
a. Sewerage System Installation.
This measure is taken in watershed areas of natural lakes with large populations
almost without exception. The expansion population rate of Kasumikaura Lake's
sewerage system has increased from 10.9 percent in 1980 to 33.4 percent in 1992. (2)
b. Small-scale wastewater facilities for rural communities with low-density
population districts.
And in places where there are no sewerage systems, it is desirable to install
integral type of septic tank treatment system for domestic wastewater rural sewerage
systems. (2)
(2) Non-point source control measures
a. Agriculture pollution control.
In order to curb agricultural pollution load, farmers are educated on the
appropriate use of fertilizers and enhancement of water circulation putting back into
water supplying canals from drainage canals. Examples of these works can be observed
in catchment areas of Lake Abashiri, Kamafusa, Kasumigaura, Kahoku-gata, Mikata,
Nojiri, Nakanoumi and Lake Shinji. (2)
b. Livestock pollution control.
To help installation of livestock excrement treatment facilities. And to give
guidance on manuring arable land with livestock excrement. Examples of these works
can be observed in catchment areas of Abashiri, Kamafusa, Kasumigaura, Toyano-gata,
Kahokugata, Shibayama-gata, Nakanoumi, Shinji and Kojima Lakes/Reservoirs. (2)
(3) In-lake cleaning measures (2)
In-lake cleaning measures mainly includes:
a. Diversion
b. Water Conveyance (Dilution)
c. Promotion of Aeration and Water Circulation
d. Collection of Water Weeds, Water Bloom and Red Tide
e. Dredging
f. Aquaculture management
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g. Ecosystem conservation
1.3.3 Restoration measures
Presently, lake restoration measures mainly include biomanipulation aiming at
accelerate the recovery of a lake’s ecosystem and lake littoral zone rehabilitation. The
Reed Colonies Conservation Ordinance for Lake Biwa has required that existing
colonies (only 120 ha in 1990 compared to 280 ha in 1953) be maintained and that new
colonies be introduced (Ohkubo, 2000). (2)
Figure 1-3 Conservation Measures by Prefectural Governments (2)
1.4 Ecological engineering and its development
The construction of conventional water pollution control facilities are of higher
energy prices and high labor costs, these systems also have become significant cost
items for the communities, especially for small communities which operate them. The
high cost of some conventional treatment processes has produced economic pressures
and has caused researches and engineers to search for creative, cost-effective, and
environmental sound ways to control water pollution.
One technical approach is ecological engineering. Ecotechnology and ecological
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engineering are not developed until recent years. Uhlmann(1983), Straskraba(1984),
and Straskraba and Gnauck(1985) have defined ecological engineering as the use of
technological means for ecosystem management, based upon deep ecological
understanding, to minimizing the costs of measures and their harm to the environment.
J. Mitsch and S. E. Jørgensen define ecological engineering and ecotechnology as the
design of human society with its natural environment for the benefit of both（Mitsch,
1988.”）
(3)
Ecological engineering combines basic and applied science for the restoration,
design and construction of ecosystems. The goals of ecological engineering and
ecotechnology are:
(1) The restoration of ecosystems that have been substantially disturbed by human
impacts such as environmental pollution, climate change or land disturbance.
(2) The development of new sustainable ecosystems that have both human and
ecological value.
(3) Identification and protection of the life-support value of existing ecosystems.
Ecological
engineering
provides
approaches
for
conserving
our
natural
environment while at the same time adapting to and sometimes solving intractable
environmental pollution problems. Due to its outstanding features, ecological
engineering has been the most favorable methods frequently used in developed
countries like the United States and Europe. Recently it has gained widespread
interest in many countries like Japan, Australia and the South Eastern Countries.
In this report, some successful, applicable and developed ecological engineering
measures that have been recognized as effective means for solving non-point pollution
of lakes in Japan will be discussed here.
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2. Artificial Floating Island (AFI) Method
2.1 Features and Function
2.1.1 AFI and its development
The Artificial Floating Island (AFI) is a floating structure on which aquatic
vegetation such as reed grows. The main purpose is to create habitats, purify water,
improve landscape, and preserve lakeshore by wave absorption. AFI technology was
originally developed as fish spawning reef in 1950’s. It is kind of new ecological method
and didn’t attract much attention until 1995 on the 6th ILEC Conference. After that
there is a big increase of AFI application case in Japan and also other countries, such
as Germany, and U.S.A. And recently it is widely recognized as Eco-technology, and
installed at many lakes and ponds in Japan, investigation revealed that about 15
companies laid artificial floating islands, and the number of those so far is
approximately 2,000 reaching 24,000m2. (4)
2.1.2 Function
There are many functions of AFI concerning water environment management such
as water purification, habitat for wild life, and improvement of lake shore scenery
listed as follows: (26)
(1) To create habitat for fish and birds
AFI can support growth of aquatic plant and thus create a habitat and offer shelter
for birds, insects, and other bio-organisms. It also provides “spawning bed” for fish. As
a result, the ecological diversity is intended to restore and improve after construction of
AFI.
(2) To purify water
The growth of aquatic plants densely on the AFI and the micro-organisms attached
in the AFI help purify water a lot. Besides, the AFI can inhibit growth of phytoplankton
due to that it occupies water surface and form a “shadowing effects”.
(3) To break wave and protect littoral zone
The AFI is designed to dissipate wave and can help stabilize and protect littoral
zone through reducing wave impacts and erosion, and thus advantageous to the
recovery and growth of vegetation in the littoral zone.
(4) To improve landscape
The growth of different plants on floating island form a favorable landscape.
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plant
bird
Creating Habitat
Function of AFI
fish
Purifying water
insect
Wave breaking
Improving landscape
Figure2-1
Function of AFI
(8)
2.1.3 Suitable installation places
The AFI creates artificial nearshore mini-ecosystem through utilization of water
surface instead of occupying the shoreline space. Since the AFI uses floating platforms
to support vegetation, it can move up and down with the fluctuation of water level, and
also can be move from place to place. Due to its unique features, it is suitable for the
following places: (8)
(1) It is effective structure for the dam lakes with violent fluctuations in the
water level;
(2) It is suitable for the lakes and marshes involving difficult in the recovery of
vegetation zone due to the waves,
(3) It is also possible for the ponds and marshes requiring accents in the
landscapes, shores requiring the spawning site for fish and habitat for birds.
2.2 Structure of AFI
2.2.1 Structural classification
The AFI is composed of the vegetation base-AFI platform and the fixing
system-anchor. According to its platform structure, the AFI is classified into two types,
the dry type and the wet type. See table2-1. The Wet type with frame is the most
frequently used type until now, sharing about 70% or more, dry type shares 20%, and
wet type without frame shares about 10%. (10)
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Table2-1
Type of the AFI
type
characteristics
Wet type:
Mat-with-frame
type
Plant
can
contacts
directly with water and
performs good water
purification effects.
Mat-without
frame type
Floating log type
Dry type:
Waste tire
other type
Box type
and
Plant cannot contact
with water. It Scarcely
bring water purification
effect, but possible to
plant arbors and garden
trees.
Floater
and
vegetation-base
separating type
Vegetation base: usually inundated by water.
Dominant plant: emergent plant, such as reed, cattail,
etc.
Advantages: habitat for bird resting and fish spawning,
water purification, etc.
Vegetation base: up-part emergent out of water
Dominant plant: hydrophyte plant
Advantages: habitat for birds resting, natural landscape
Vegetation base: contacts with water
Dominant plant: water-resisting plant such ad willow
Advantages: habitat for birds, ducks
To use wasted tire and pet bottle for plant growing.
Easily making with low cost.
Vegetation base: doesn’t contact with water
Dominant plant: terrestrial tree and grass
Advantages: Habitat for bird resting and fish spawning,
good landscape, wave-broken
Vegetation base: doesn’t contact with water
Dominant plants: emergent plant such as reed, cattail
Advantages: habitat for birds, duck, aquatic animals
AFI just after installation in lake Kasumikaura
The most popular used type. FRP, stainless steel+foam polystyrene, PVC, concrete, etc are used as
support for the growth of the plant. Stainless steel is utilized as frame.
Figure2-2 Wet and with frame type AFI (4)
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Vegetation base
180mm
Floater
netting
2000mm
To use coconut fibers skillfully sewn together without frame, It gives a soft impression to the
landscape due to absence of frame.
Figure2-3 Wet and without frame type AFI
bolt
log
To combine logs or plastics to be a raft shape, and plant vegetation on it.
Figure2-4 Floating log type
Tire filled with
foam as floater
Netting
Figure2-5 Tire type (10)
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Vegetation base
raft
filled with foam
Concrete box
as floater
To fill the foaming material in the box structure. Soil cover the structure supporting growth
of the terrestrial plants.
Figure2-6 Box type (8)
Vegetation base
Support structure
Ecotone slope for wildlife
Floater
The floater is separated from vegetation base and
installed underneath the vegetation base.
Figure2-7 Floater and vegetation base separate Type
(8)
2.2.2 Vegetation base
Coconut palm fibers are most often used as the vegetation base. Other than those
in coco palm fibers, vegetation bases are often made of special foam polyurethane,
fishing nets, foam polyurethane beads, and the combination of these materials in many
cases.
2.2.3 Size and configuration
As the sizes, one side of a unit range from about 1 to 5 meters, but many of them
have a side ranging 2 to 3 meters, transportability, workability, and durability being
taken into account. The most popular configuration is four-sided.
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2.3 Points for AFI Design and Installation
2.3.1 AFI plan process
The process for conducting an AFI plan is showed as follows: (8)
On-site survey
(water quality, wave, plant, and bio-organism, etc.)
Purpose for installation of the AFI
Data collection and analyze for meet the aim
To decide the concept of the AFI
Deciding AFI type
( wave, stability, strength calculation, anchoring)
design)
Cost comprehensive assessment
Construction
Structure
design
Maintenance and monitoring
Figure 2-8 AFI design and installation process
2.3.2 Structure design
There are 5 keypoints that should be taken in good consideration including
stability, durability, landscape, cost-effectiveness, and easily-construction in structure
design of the AFI.
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
Stability: To maintain stable and avoid destruction from strong wave, wind
and conflict between units.

Durability: To choose adaptable materials for frame and floater, and design the
reasonable structure to make the AFI durable.

Landscape: To fit the landscape of the AFI with the surrounding landscape.

Economically: to reduce the cost for the AFI and make cost-effective.

Construction: The connection of the units considerate easily construction,
move, maintenance, etc. factors.
To decide concept for AFI
To check:

Durability

Landscape

Economically

Construction

stability
Natural and economical conditions

To set the target

Necessary condition to meet the target

To decide the basic type
To decide the structure

To decide the float structure(floatage, and
material)

Weigh load of AFI

To decide the fixing (anchor, rope)
Design calculation
To check
To decide the structure
Figure 2-9 The structural design of AFI (8)
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2.3.3 External force calculation
In the design step of AFI, the calculation of external force including wave force,
wind force, water flow force is necessary and important for stability of the AFI. (8)
(1) wind force
The wind force is calculated according to the following formation:
P1 = 1/2xPa xVa2 xCa xG xAl
Pa: air density (kgf.s2/m4)
Va: wind velocity (m/s)
Ca: force-resistant coefficient
G: atmospheric-response coefficient
A1: projection area of the AFI on the water surface (m2)
(2) wave force calculation
The wave force is calculated according to the following formation:
P2= 1/2 xPw xU2 xCw xA2
Pw: water density (kgf.s2/m4)
U: water particulate moving velocity (m/s)
Cw: water-resistant coefficient
A2: projection area of the AFI under water surface (m2)
(3) Water flow force calculation
The water flow force is calculated according to the following formation:
P3=1/2 xPw xV2 xCw xA2
Pw: water density (kgf.s2/m4)
V: water velocity (m/s)
Cw: water-resistant coefficien
A2: projection area of the AFI under water surface (m2)
(4) Total external force
The total external force is:
P = P1 + P2 + P3
With the total external force, it is possible to check the intensity of the rope
connecting float with anchor, the intensity of anchor against external force, the
intensity of the floater against the force and the intensity of the rope connecting units.
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2.3.4 Fixing design
There are 3 methods for fixing of AFI: gravity type, anchor type, and pole type. See
figures. (8)
Counter floater
Counter floater
Weight
Anchor
Figure2-10 Gravity type fixing
Figure2-11
Anchor type fixing
Counter floater
pole
Figure2-13
Pole type fixing
Table2- 2 Fixing type and its characteristics (8)
Items
Water depth
Gravity type
Possible in every depth
Geology
Displacement with water
level
landscape
No influence
Horizontal
displacement
Exposure of anchor in
the low level season
Economically
Heavier the weight,
much cost of both
material
and
construction
large size machine, and
complex construction
Construction
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Anchor type
Water
deeper,
requirement higher
influence
Horizontal
displacement
Anchor is fixed under
water without exposure
Material is expensive,
but construction is less
expensive than gravity
type
Less large machine and
less
complex
than
gravity
Pole type
Water
deeper,
pole
longer
influence
Vertical movement
Exposure of poles don’t
do good to landscape,
but it may offer resting
places for birds.
Shallow places, cost is
less than gravity and
anchor type
Large machine and
difficult construction
2.4 Cost
Cost of AFI varies a lot from different structures of the AFI. Among all types of AFI,
the box type is the most expensive one and cost about 250-500 thousand yen/m2, while
the wet-with-frame type is less expensive with cost of 50-100 thousand yen/m2.
Generally, the cost of AFI is high and will exceed 100 thousand yen/m2. However,
sometime, if use recycled material such as tire, the cost of AFI less than 10 thousand
yen/m2 becomes possible. (8)
2.5 Monitoring and Maintenance
2.5.1 Monitoring
After the installation of the AFI, it is necessary to conduct 3-5 years’ monitoring for
mastering the change of surrounding environment and evaluating effects of the AFI.
Monitoring items including biological survey, water quality, wavebroken effects, etc.
2.5.2 Maintenance
Maintenance mainly includes:
(1) Check, repair and emergency measures: To examine the connecting part
between different units, fixing rope, anchor, vegetation base, etc so that to keep
in good condition. To repair the destroyed parts.
(2) Plant management: To remove the undesired and invaded species away from
the AFI, to keep the desired and designed landscape. To mow at some interval
and irrigate and fertilize.
2.6 Application case in Lake Kasumikaura
2.6.1 Introduction
The AFI case at Tsuchiura Port in Lake Kasumigaura was installed in March,
1993, by the Ministry of Construction. It belongs to the wet-with-frame type. It has a
length of about 91.5m and a width of 9m, consisting of 40 segments.
Each segment has an area of 20.25m2, with each side of 4.5X4.5m. The segment is
made of steel frame with polystyrene. Sponge was filled into the frame for supporting
aquatic plants. And on the sponge, there are many 10cm cuts for planting of plants. (9)
The purpose of this AFI is (1) create better landscape and habitat (2) To purify
water, and (3) To protect lakeshore.
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Figure2-14
AFI at Tsuchiura Port in Lake Kasumigaura (26)
Another AFI also installed at Aso town in Lake Kasumikaura. It aims at wave
dissipating and protecting vegetation in the littoral zone.
Figure2-15
Wavebroken AFI in Lake Kasumikaura (26)
2.6.2 effects
On Figure2-15 case, research carried out vegetation restoration by using AFI as a
breakwater. This AFI was designed to break water 50% and reduces wave height to 40
cm, which is critical wave height for vegetation growth. As a result of our experiment,
vegetation area has expanded 3.4% a year.
The AFI installed in Kasumikaura proved AFI really effective in creating habitats
for small fish and prawn, in increasing the biodiversity on and underneath the AFI, in
purifying water quality surrounding AFI, and in dissipating wave’s erosion at the
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littoral vegetation. (11)
2.7 AFI case in Lake Jonuma
On 11st, April, we visited the Tatebayashi City where there is floating island under
construction on Lake Jonuma which is one part of Tsuruuta River flowing through
Tatebayashi Park. Sato san who is from the Seniya Oceanic Service Company and have
engaged in AFI work for about 8 years explained the main structure and installation
points of AFI for us.
(1) Aim of AFI on the river
One of the main purposes for installation the AFI is to purify water quality of the
river which is polluted by non-point pollution from paddy field and surrounding areas.
The other one is to provide habitat for birds and other animals, and also improve the
landscape of the river for the river is inside the Tatebayashi park. The AFI is installed
on two different sites in the Jonuma City, see the pictures in the following, Figure 2-16
shows the newly finished AFI and Figure 2-17 shows the under constructing AFI
started one week ago.
(2) Structure
The AFI installed in the 2 sites both belongs to the wet without frame type—mat
without frame type. The structure of the unit see Figures.
Coco fiber
floater
Edge rope
Begitotion mot
netting
Figure 2-15 Structure of the vegetation base (6)
The unit is primarily composed of (1) the vegetation base which is made of coconut
fiber imported from Indonesia. After the mat is arranged on the water, the coconut can
absorb water and this keep plant untouched with water. (2) the Begitotion Mot made
from polyplopirene fiber, which will provide growth of the rhizome of plant, which may
provide support for the plant even after 3 or 4 year’s when the coconut fiber decayed
- 23 -
away. (3) the floater, which is made of polyetirene foam provides sufficient floating
ability for units. (4) netting covering outside of the unit encloses the different parts of
unit and make it a integrate.
Each unit has an area of 4m2 with each side of 2mX2m. Moreover, the AFI
installed on two sites has 25 units with an total area of 100m2 separatively.
(2) plants on the AFI
The primary plants on the AFI are reed, cattail, etc, which are all taken from the
nearby river side. See photo. To taken plant from near area of AFI is critical so as to
make sure the plant is native and adapt to local environment.
The plantation on the unit is very easy, see photo. Firstly, making some cuts on the
netting, and then put the plant root into holes. In this case, 16 cuts are made in each
unit for 16 pieces of plant root. Sometimes after installation, the plant may be eaten by
bird or other organisms.
(3) connecting of the units
Rope made from polyetirene with diameter of 12mm are used for connecting
different units. See photo. The black jointing structure made of polyocetar are used for
connecting rope with mat.
(10) Layout of the AFI on the water
Layout of AFI doesnot have so many restrictions. Usually layout arrangement is
decided according to the purpose of the AFI. In the 2 cases in Lake Jonuma, we just
arrange the layout freely.
(11) Fixing of the AFI
In this case, we use the anchor for fixing the AFI. The installation of anchor see
photo. The boat carriers the anchor near the mat a certain distance away and drop the
anchor into water. The anchor can automatically grab soil and keep the AFI stable
after dropped into the water. On the newly finished AFI, totally 8 anchors are installed
with a weight of 55Kg each.,
- 24 -
Figure 2-16 Dropping of the anchor
- 25 -
3. Attached Lagoon and Artificial Lagoon Method
3.1 Features and Function
One type of lagoons, in Japanese called Naico, that originally attached to the lake
or artificially excavated within lake, is developed as an effective way for non-point
pollution influent treatment into lake in recent years in Japan. Naiko method has two
forms, one is natural lagoon form, making use of the natural existing lagoons usually
called attached lagoon, the other is artificial lagoon form located near the river mouth.
The both forms of Naiko are believed to have a function to reduce non-point pollutant
by working like a sedimentation tank in a sewage treatment.
(1) Removal of non-point pollutants;
(2) Creating of a natural habitat for vegetation, birds, and fishes.
(3) Promoting the littoral landscape.
influent
Pollutant C.
effluent
time
Figure3- 1 Influent and effluent of lagoon during storm period (13)
3.2 Application case in Lake Biwa
3.2.1 Introduction
Lake Biwa has been suffered from increasing non-point pollution from rivers with
the growth of population and agriculture in the watershed. The Naico application case
in Lake Biwa is called the attached lagoon method which make use of the attached
lagoons to purify water and increase ecological capacity. In Lake Biwa there are 22
attached lagoons now. The Moriyama river which is a bigger river in the Biwa lake and
carries about 20t N, 2t P into lake annually. In order to reduce pollutant load from the
Moriyama river into the lake, the lagoons which is naturally attached to the lake at
Miriyama River mouth is developed for water purification purpose.
- 26 -
Figure3-2 Purification system of attached lagoon in the Moriyama river (23)
3.2.2 Operation
During normal time and flood period, water flow is operated differently. (23)
(1) Normal water level time: river water directly flows into lagoon and purified by
aquatic plant, mainly of reeds and cattail, and then into lake.
(2) During storm period: at the initial stage, river water is temporarily held in a
detention pond to settle pollutants and discharge only supernatant. At the later stages,
pollutants are naturally settled in the lagoon to reduce the pollution inflow to the lake.
3.2.3 effects (23)
(1) A survey conducted in 2000 found that the Naiko serves as a good means to
control nutrient loads from inflowing rivers. Pollutant removal rate: COD 7%, TN 37%,
TP 34%.
(2) Besides, it also acts as a breeding and resting places for fishes and other
wildlife. 9 species of fish and 51 species of birds was found living in the area.
3.3 Artificial lagoon case in Lake Kasumikaura
3.3.1 Introduction
Artificial lagoon (AL) is an artificially constructed small pond at river mouth of a
lake or within a river. The idea of artificial lagoon is derived from natural lagoon in
Lake Biwa.
The AF installed at the Kasumikaura Lake was constructed in 1998 as a
- 27 -
countermeasure for non-point pollutant at the river mouth of Kawajiri River that flow
into Lake Kasumikaura. This river has a basin area of 9.02km2, which is mainly
farmlands and livestock farming and has a population of 1,300 people. All the effluent
form the farmland is discharged into the Kawajiri River which than flows into the lake.
The effluent, non-point pollutant consists of 35.8% total nitrogen and 21.9% total
phosphorus (1995). It shows a very high nutrient load, which needs to be taken care off
to reduce the existing eutrophication in the lake. (12)
The artificial lagoon has an area of 30,000m2 and surrounded by rubble mound,
which is porous and has opening at the west to allow for water exchange and ecological
networks. The AL is divided into 2 parts that is the mud pit and sedimentation area.
The mud pit, which is 2m deep, acts as a pool for sedimentation for larger particles
while the sedimentation area, which is 0.5 – 1m deep and wider area, allows finer
particles to settle.
The vegetative planting is in the form of floating island using coconut fibers with
seedlings, placed at the periphery of the lake bank which was previously concrete lined.
This is to create a more natural surrounding for habitats such as birds and fishes while
the root systems is for the nutrient uptake.
Figure 3-1
Design discharge
(m3/s)
6
Speculation of experiment facility (12)
Retention time
(h)
1.5
Water depth
(m)
1.0(mud pit 2.0)
Volume
(m3)
30000
Area
(m2)
30000
Rubble Mound
Lake Kasumigaura
Sedimentation area
Mud pit
(2m)
(0.5 - 1.0 m)
Mud pit
Vegetative planting
Lake bank
lake bank
Kawajiri River
Figure 3-2
Artificial lagoon at Lake Kasumikaura (25)
- 28 -
Length
(m)
350
Width
(m)
60-100
3.3.2 Effects
The results of the study (surveyed in 2000 and 2001) reveal that AF is effective on
removal of non-point pollutants: the removal ratio of the AL ( calculated as the ratio of
trapped sediment to inflow load during strom), is 28-40% of T-N, and 34-56% of TP of
storm water. Annual removal ratio ( calculated as the ratio of accumulated sediment in
artificial lagoon to annual inflow load from the Kawajiri River) of the AL is calculated
40% of COD, 18% of TN, and 42% of TP was accumulated in AL against inflow load.
Besides, many kinds of birds are living in AL and swan’s egg was hatched in the spring
of 2000. A lot of young fish have also observed in AL. The AL is also considered
beneficial for restoration of littoral vegetation. (12)
3.3.3 Some Key Points from AL case
(1) To select a river which is mainly of agricultural non-point source pollution.
(2) To decide the AL area based on the lake current direction, it should be
compliant with the lake main current direction so that to make the AL stable and
scientific.
(3) If it has adequate area outside of the lakeshore area, it is better to install the
AL out of the lakeshore instead of occupying the water surface area.
(4) Construction of AL is very easy, just enclose the pilot area with net, and then
construct a rubble mound along the fenced area based on the design. The stone needed
is better from nearby places. Because from lake restoration engineering point of view,
all the material needed for the engineering should taken from the nearby area, or from
the lake basin area. It is required not to damage the other ecosystem try to recover one
place. This principle is very important in the ecological restoration.
(5) The AL mainly deals with the raining water, especially the initial raining water.
To get good removal effectiveness, detention time and other hydraulic parameters
should be considered
(6) Cost of AF is not high, In Lake Kasumikaura’s case, total investment of the AL
is about 2 million Japanese Yen.
(7) Maintenance: The mud pit has to be regularly dredged (every several years) to
maintain the required depth, if not it would not be effective as the mud pit tends to be
anaerobic towards the bottom. These can cause adverse impacts such as phosphorus to
accumulate and nitrification to occur. Thus dredging design and investment should be
considered in the AF design.
In Lake Kasumikaura’s case, it has run for 3 years and still works well without
dredging
- 29 -
(8) Some negative aspects of construction of AL
a. In terms of ecological problems, the mud pit reduces the spawning area for
habitats such as fishes and prawns which need sandy river mouth. Thus a further
study on this matter is required in order to make it more ecologically sound.
b. The rubble mound breaks the continuity of the water surface.
- 30 -
4. Constructed Wetland Purification Method
4.1 Features and advantages
4.1.1 Introduction
Constructed wetland is designed and manmade systems characterized by emergent
aquatic vegetation (reed is most popular used plant), which aimed at simulating the
treatment wastewater into lake, mainly non-point pollution water. The systems have
been seem to purify water by moving organic matter (BOD) and oxidizing ammonia,
reducing nitrogen and reducing phosphorous. Besides water purification function,
wetland also can perform as habitat for bird nesting and organism resting as well as
improve the landscape around the lake. Constructed wetlands have been a hot topic in
the UK and worldwide in the past 10 years.
4.1.2 Advantage
Constructed wetlands is the most promising technologies for application in
developing countries, due to their characteristic properties like utilization of natural
processes, simple construction, simple operation and maintenance, process stability,
cost effectiveness, etc. (28)
(1) low construction cost, low operation cost;
(2) a possible treatment for small flows from single houses, remote hotels, camping
sites, and visitor centers; also a possible method of treating storm sewage flows
for small sites;
(3) they are seem as a natural process and hence as a green process;
(4) they fit in well with the countryside and provide wildlife habitat.
For these reasons, the constructed wetlands also can be installed near lakeshore
for treatment of the non-point pollution.
4.1.3 Types
According to the structure, the constructed wetland is classified into the free-water
surface system(FWS) type and the subsurface flow system(SFS) type. (3)
(1) Free Flow Surface Water Type(FSW)
In this type, the wastewater is fed in at the inlet and flows slowly through the
surface of the plant bed in a horizontal path until it reaches the outlet of zone where it
is collected together before leaving via the level control arrangement at the outlet. See
figure. In the FWS system, the plants can contribute to treatment through uptake of
nutrients and other wastewater constitutes, but most important part are the
submerged portion of leaves, stalks, and litter, which serves as the substrate for
- 31 -
attached microbial growth which occur aerobically. So the system tend to be
oxygen-limited since the reeds cannot supply the oxygen at the rate required by the
wastewater load and so FWS is similar to natural wetland system as not so efficient for
nitrogen removal.
A lot has been studied on wetland purification systems (Free water surface, FWS).
This system is interesting not only due to its purification effects but also the ability to
bring back natural habitats and to certain extend flood control. However, it is difficult
to adopt the FWS, wetland system in urban areas or places where land is insufficient
or limited like Japan, since FWS system requires larger area.
influent
effluent
Figure4-1
FSW type
(2) Subsurface flow Wetland Type (SF)
The SF type comprises a plant bed of sand or other material with aquatic plant
growing. The difference is that wastewater is dosed on the bed in a large batch evenly
and then gradually drains down through the bed and collected by a drainage network
at the base. In the SF, the soil are anaerobic because of being submerged for long
period, but due to that the plant such as reeds and cattails can transfer oxygen to the
root zone, it keep aerobic around the rhizosphere. As a result of nitrification and
denitrifiation, the SF type tend to be more efficient for nitrogen removal. But the SF
system seem not so efficient for suspended removal.
By adapting subsurface flow, the SF come out with a drastically cutting of the
space. It can get the same removal result with much smaller space compared with FWS
type. Due to this reason, it was favored by many researchers and especially adapt to
urban areas or land limited areas for pollution treatment.
- 32 -
influent
effluent
Figure4-2
SF type
4.2 Design criteria for constructed wetland
Design of the constructed wetland mainly includes sizing the system, depth
determination, inlet and outlet arrangement, and media selection, etc.
4.2.1 FWS Wetland
(1) Sizing
The specific design criteria presented below are suitable for low to organic loadings.
The organic loading should be distributed over a significant portion of the area and not
applied at a single point.
Ce/Co = A exp(-0.7*Kt*(Av)1.75*t)
(1)
(3)
Ce = Effluent BOD, mg/l;
C0 = influent BOD, mg/l;
A = fraction of BOD not removed as settleable solids near headwork of the system;
Av = Specific surface area for microbial activity, m2/m3;
Kt = temperature-dependent first-order reaction rate constant, d-1
Kt = K20(1.1)(t-20)
K20 is the rate constant at 200C.
n = function of the porosity
t = hydraulic resdience time
Q = flow rate
t=Length * Width * Depth/Q
m3/d
The preceding mentioned coefficient in the equation (1) have been estimated as
follows:
- 33 -
A = 0.52,
K20=0.0057d-1, AV = 15.7 m2/m3, n=0.75
From the equation (1), if we know the influent BOD and desired effluent, we can easily
calculate the designed capacity of the FWS system.
(2) Depth
The design water depth of the SFW system should be 60cm or less to ensure the
adequate oxygen distribution, and partial effluent recirculation might be considered in
the summer months to overcome evapotranspiration losses and maintain design flow
rate and oxygen levels.
4.2.2 SF Wetland
(1) Sizing
The area required for the SF wetland can be described as in the following equation:
As = ( Q ( lnC0- lnCe )) / (Kt * Depth *n )
(2)
(3)
Ce = Effluent BOD, mg/l;
C0 = influent BOD, mg/l;
Kt = temperature-dependent first-order reaction rate constant, d-1
Kt = K20(1.1)(t-20)
K20 is the rate constant at 200C.
n = porosity of the bed
As = Surface area of the system, m2
t = hydraulic resdience time
Q = flow rate
t=Length * Width * Depth/Q = As * Depth/Q
m3/d
Depth = Depth of submergence, m
(2) Media
According to the equation (2), the coefficient n changes with different media.
Obviously the area of the SF system needed differs a lot when choosing different
medium type. Typical media used for SF wetland including medium to coarse sand
have K20 value values of approximately 1.28d-1. The flowing Table listed some expected
porosities, hydraulic conductivity, and K20 value of tested media.
Table4-1
Media Characteristics for Subsurface Flow Systems
Media type
Grain
Size(mm)
Porosity(n)
Medium sand
Coarse sand
Gravelly sand
1
2
8
0.42
0.39
0.35
- 34 -
Hydraulic
Conductivity
(Ks), M3/m2.d
420
480
500
(3)
K20
1.84
1.35
0.86
4.3 Compact wetland and its advantages
4.3.1 Features and advantageous
A study in Japan has been made to implement the SF system but in a much
smaller area. This system is called the compact wetland system. The PWRI
conducting research of compact wetland. Compact wetland is the kind of SF system
which make use of
artificial media as the substrate of the wetland. A compact
wetland is a downsized wetland water purification system and can be used in urban
areas. It has the features as follows: (18)
(1) Reducing the size by using a pre-treatment facility
In the compact wetland, sand and BOD are partly removed in a pre-treatment
facility, which reduces the load on the wetland.
(2) Reducing the size by using seepage flow
Seepage flow, which is common outside Japan but has only been experimentally
tested in Japan, is adopted instead of the commonly used surface-flow method.
(3) Reducing the size by improving filling materials
Gravel is usually used as filling materials in the conventional seepage flow
systems. The facility area of the seepage-flow system is expressed by Equation (1).
The larger the void ratio is, the smaller the facility area needed. The void ratio of
gravel is approximately 0.4. The void ratio was increased to 0.95 by using artificial
vegetation bases. Theoretically, the facility area is halved according to the equation
(2).
4.3.2 Structure
This new system treats water effectively by combination with pre-treatment and
an artificial bed material. Figure 1, shows a summary of compact wetland system. (18)
- 35 -
Git chamber Pre-treatment
SF wetland
Into lake
system
Porous
artificial
filling
Removal of sand
Aerobic condition
Nitification
Sedimentation/adhension
anaerobic condition
Denitrification
Absorption
Sedimentation/adhension
Figure 4-3 Schematic diagram of compact wetland system
Water inlet
Water outlet
Figure4-4
Constructed wetland experiment in Sanno River
- 36 -
4.3.3 Effects
Nakamura etal. carried out the field experiments of a compact wetland since
August 1997. Three types of wetland are compared: surface-flow type, seepage-flow
with gravel type, and seepage-flow with artificial media type. The area is 48 m2 for
each type. The water depth of the surface-flow type is 0.1 m. The penetration layers
of the seepage-flow types are 0.6 m thick. The experiment was started in 1997, and
reeds are growing well in 1998.
Result reveals that, two kinds of SF wetlands purify water better than FWS,
however there is no obvious difference between two kinds of wetlands with gravel
and artificial fillings. Two SF wetlands are able to remove nitrogen efficiently with a
removal rate of 66 and 77% percentage under the condition of water temperature 15
degree Celsius and dissolved oxygen is less than 3 mg/l. (18)
4.4 Operation and maintenance
The constructed wetland is easily operated, and the maintenance of the
constructed wetland mainly includes: (28)
(1) Clogging problems
For seepage-flow type wetland, clogging is long-term operation problem that must
be considered. For solid from the influent and decaying of reeds will accumulate
gradually and may reduce the pore space. It may cause some surface flow. So it is
important to examine at a interval for effective operation and sustainability of the
system.
While in the compact wetland case, we examined sediment accumulation after the
experiment. The examination showed no sedimentation, and a compact wetland
system with artificial media should be useful for at least 10 years. (18)
(2) Routine maintenance
The solid may accumulate in the inlet distribution systems and can cause poor
flow distribution along the inlet. The inlet system should be cleaned at a frequency
from months to 6 months intervals.
4.5 Bio-park in Lake Kasumikaura
4.5.1 Introduction
Bio-park in Lake Kasumikaura is located at the Port of Tsuchiura, the front gate of
Kasumikaura. It was started in August 1995. It is kind of FSW wetland and has a
- 37 -
surface area of 3,400 m2, with length of 78m and width of 46.5m. The park is a water
purification facility aiming at (1) purify water for the Port of Tsuchiura; (2) cultivate
and harvest vegetable and flowers by citizen, enjoying touch contact with nature by
cultivating aquatic plants. (3)Creating a new signtseeing spot of Kasumikaura as a
resting area to enjoy native wild grass.
In the facility, approximately 10000t/d of
water is pumped up and pass through the root system of cultivated vegetation and
flowers. (22)
4.5.2 Layout
The layout of the bio-park is showed as follows:
78.0m
cress
46.5m
cress
dropwort
cress
cress
cress
cress
dropwort
cress
cress
mint
Forget-me-not
dropwort
cress
cress
cress
Park-bung
Area; 3400m2 W78m x L46.5m,
Water volume: 0.087m3/s
Depth:0.05-0.10m
Gradient: 1/100
Figure 4-5 Layout of the Bio-park (22)
Plant selection: At the bio-park, for effective water quality purification, aquatic
plants had been selected from the view points of (1) thin root and wide spreading for
easy catching of planktons;(2) grow fast and absorb well nitrogen and phosphorus as
nutrient; (3) grow easily in the shallow water flowing parts and are suited to the
facility’s structure; (4) the plants used are possible for decorative use or service as food.
The main species selected include: Park-Bung Convolvulaceae, cress, dropwort,
forget-me-not, Loosestrife, mint, great waterrush, etc. (22)
- 38 -
Plant harvest: To maintain the purification ability of the bio-park, it is necessary
to take out aquatic plants. Since some plants are eatable and decoratable, cultivation of
them can be performed with great pleasure. In the Bio-park case, citizens are asked
to harvest aquatic plants and take home to use. (22)
4.5.3 Effects
(1) Water purification effects
The removal ratio at the Bio-park is approximately 70% by SS and approximately
60% by Chla; The SD of treatment lake water has been improved around three times
from about 30cm to more than 100cm.
The removal ratio of nitrogen and phosphorus is around 20-40%, and depending on
the growth rate of plants, it is expected that the removal ratio will further improved.
(22)
(2) Social effects
The Bio-park offers easy access to the water and every citizen can freely visit there.
Though harvest aquatic plant, citizen not only take out plants containing nutrient, but
also increase the awareness of lake protection. (22)
- 39 -
5. Lake Littoral Restoration Method
5.1 Introduction
The littoral area in lakes acts as an eco-tone between the terrestrial and aquatic
environments, it is an important transitional zone for water purification, serves as the
most important habitat for aquatic plants, fish, birds, insects and other aquatic life,
and also provides scenic beauty of the landscape. During the last few decades, rapid
urbanization has happened and human activities surrounding lakes intensified. As a
result, most natural littoral zone in Japan has been disturbed, degraded or destroyed
by over-utilization, artificial modification and other activities: (29)
(1) Reclamation for agricultural purpose. Since World War II, a large area of costal
lakes were reclaimed to produce crops. The land of more than 10km2 has been
reclaimed
in
L.
Kasumikaura(10km2),
Hachirogata(167km2),
L.
Inbanuma(14km2),
L.
and L.
Kahokugata(15km2),
L.
Nakaumi(11km2).
(2) Embankment for flood-prevention purpose. For example, at Kasumikaura,
more than 90% of the whole lakeshore has been artificialized where the water’s
edge is contact with concrete revetment directly.
(3) Artificially manipulation of natural water level for power plant purpose or
increasing water demands, which has caused continuous erosion of the shore
platform and undesirable change of littoral environment.
Due to its unique characteristics and important role of littoral zone,
rehabilitation/restoration of lake littoral area has attracted more and more researcher’s
eyes and become a hot topic in the ecological engineering field in recent years.
Figure5-1
Structure of a natural lake shoreline
- 40 -
(30)
5.2 Restoration key points
Some keypoints that may contribute to a successful restoration of littoral zone are
discussed here.
5.2.1 Understanding of geomorphology of shoreline
To understand the geomorphology of the lake shoreline both in history and at
present is preliminary and necessary step in littoral restoration. The present terrain
can be understood well after carefully on-site treading. To know the geomorphology in
history, all kinds of basic description materials, geological maps and aerial photos in
different years with different scales are required to be collected. You should try to
comprehensively analyze all the datas and scientific researching results and
understand the original terrain of the shoreline before altered. Geomorphological
development which may be presented as transformation of land use caused by human’s
activities during different ages will help give idea for littoral base rehabilitation in the
restoration work. (15)
5.2.2 Succession of the shoreline vegetation
To collect as much as possible the vegetation surveying datas in the history so as to
have a good knowledge of vegetation change, including structure and species in the
shoreline. Vegetation succession may give a view of the natural shoreline as well as
plant structure in different ages. Understanding of vegetation succession may help
select pioneering specie of plants and set up adaptable, healthy, desired littoral plant
structure for restoration work.
5.2.3 Relation between wave strength and erosion
Research of relation between wave strength and growth of vegetation is critical
since it will influence the success of the project. Till know, there are quite a lot projects
about lake littoral zone restorations were carried out, but some cases were failed
because of lack of engineering knowledge. To create stable littoral zone for successful
restorations, the knowledge of the costal engineering is necessary because lakeshore
change is induced by wind waves.
The littoral zone of lake is tend to suffered from erosion caused by wind and water
current timely. As a result, the sand, soil, or other sediment may be moved away.
Consequently, vegetation decreases due to lose of living base. Uda2) has carried out
studied about the relation between the wave strength and erosion at littoral zone in
Lake Biwa and Lake Kasumikaura. He found that and littoral stability coefficient C
value is determined by wave height, wave length, shore slope and median diameter of
- 41 -
foreshore materials: (15)
C=H･L-1･(tanB)0.27･(d50/L)-0.67
(1)
C: stability coefficient of the littoral zone
H: Wave hight
(m)
L: Wave length (m)
TanB: angle of the slope
d50 (m)：diameter of the sediment
He also point out that the wave height and littoral stability coefficient C value
related to the existence of vegetation. In the Lake Biwa’s case, it is found on the place
where C value exceeds 4, vegetation is difficult to grow.
5.3 Restoration model
The restoration of the littoral zone should take comprehensive consideration on
ecology, hydrology, and geomorphology, etc so as to get a successful and desired result.
Here according to the main shoreline states, two kinds of restoration models are
discussed.
Tree&grass
Emergent plant
Submerged plant
Gradient 1 to 50-100
100m
Concrete bank cover
50kg
Figure5-2
Beach sand
0.3-0.5mm
Gradient 1 to 10
Erosion prevention
100mm
Typical cross section of Littoral restoration in Lake Kasumigaura (15)
(1) Aquatic plant restoration model
To restore the aquatic plant such as reed and some floating-leave plant, sand from
nearby places and good for reed growth is transported and filled in the littoral to form a
flat and continuous slope. The newly filled inclination provides base for support reed
growth. Wave dissipate work is important part for forming stabilization habitat for
aquatic plant growth. It is usually a gabion with granite stones filled in it. See Lake
- 42 -
Biwa’s case in Chapter 5.4.
(2) The cliff concrete bank improvement model
The concrete revetment has been a popular shoreline type at present in many
lakes. A common way to restore the abiotic concrete bank is to covering the concrete
with soil or sand to form a mild inclination. In case of the erect cliff, some part of the
cliff are cut off to form a continuous biotic view. Grass or plants are naturally or
artificially restored on the new substrate. Wave dissipation is composed of two rows of
piles with wood bush filled in it. See Lake Constance’s case in Chapter 5.7.
5.4 Application case in Lake Biwa
Lake Biwa has retained an abundant natural environment, with the natural
lakefront such as sandy beaches or reed marshes covering 60% of the overall shoreline.
However, in recent years, lakefront development, a decreasing supply of earth from its
tributary and erosion by the construction of lakefront structures are diminishing the
natural shoreline. To recover the diverse shoreline and its landscape, many projects
concerning preservation and restoration of the natural shoreline was carried out. Here
two littoral restoration engineering project sites in Moriyama where I visited 2 month
ago are showed.
The Moriyama area, before restored, is characterized with dike and concrete bank.
Restoration is desired to restore it into a reed field. It takes consideration on both wave
breaking and beach refilling. It contents greenery zone (3m), reed zone (20m), and
wave dissipation zone(6m). Refers to Figure5-4. (23)
(1) Construction of an artificial slop: A flat slop from 1/50 to 1/100 was formed by
filling sand suitable for reed growth. The slop provides good base for reed
vegetating.
(2) Wave breaking: Two rows of wood were rowed into substrate, with gabion of
stones laid inside. It acts as signal post, important function of wave dissipation,
as well as prevents submerged plant from invading from water column into the
newly restored field and competing with reed colony.
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Wave dissipation zone
Sand-drifting prevention
Reed mat plantation
Figure 5-3 Photos 1 year after restoration
(3) Two species of reed were planted in zone for comparison: one is the native one
in Lake Biwa, the other is a narrow leave one, imported from other drainage area, with
high economic profit. To enhance the alive rate, the imported reed was bought from the
nursery and planted with mat.
5.5 Application case in Lake Kasumikaura
The
aquatic
plant
in
Kasumikaura,
especially
the
floating-leaved
plant-Nymphoides Peltata is diminished quickly. To protect Nymphoides Peltata, 18
emergency projects are carried out in Lake Kasumikaura from 2001-2002. The
following Figure shows one of the restoration project at Ishikawa creating adaptable
growing place for the restoration of Nymphoides Peltata community in Kasumikaura.
Nymphoides Peltata is a floating-leave plant and prefer still water flow. Therefore
the restoration project is necessary to build up some wavebroken works for stopping
the detrimental effects of waves and create a adaptable environment for Nymphoides
Peltata. In the places that I visited, it is implemented as follows: (1) The wave-broken
work: double pile rows with a fixed brushwood between is built for dissipate wave
action. Besides, some densely rows of palisades are rammed for create static growing
placing for Asaza. (2) The vegetation base: Dredged sediment from the lake is filled to
from a flat slope for restoration of the reed and other aquatic plant. It is believed that
the sediment of the lake is a seed bank containing a lot of aquatic plant seeds. The
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formerly concrete bank is covered with soil from nearby areas act as the vegetation
base for grass, etc.(3) plantation: Reed and Asaza is planted on the nourishment beach,
other aquatic plants is believed to restore naturally from the seed bank. In the soil
revetment, grass seed is distributed inside.
For wave dissipation
For restoratio of Asaza
For bank improvement
Figure5-4
Littoral zone restoration Project in Lake Kasumikaura
Engineering measures will cost a lot of money in the littoral restoration of Lake
Kasumikaura. But after the engineering measures, a continuous, diverse habitat will
provide for recovery of organism.
5.6 Application case in Lake Shinji
The application case that we visited is built near Greenpark of Lake Shinji. It is
finished in 1998. The original bank of the zone was concrete revetment. The restoration
work covered the concrete bank with soil from nearby area to form a mild slope. Three
semi-arc breakwater structures are constructed to form a semi-circle for wave
dissipation. See photo in the following.
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Figure 5-5 Littoral restoration case in Lake Shinji
5.7 The littoral zone naturalization case in Lake Constance
Lake Constance is the second largest European pre-alpine lakes. It is an
international lake as condomninium area between Austria, German and Switzerland.
Due to human s activities, over 50% of shoreline has been built up in few decades.
Dr. Berthold Siessegger from Institute of Lake Research, Langenargen German
carried out lakeshore renaturization of Lake Constant. He developed the model for to
rehabilitate eroded or damaged natural shoreline as well as built-up shore as follows:
Figure5-6
Method to rehabilitate built-up (Siessegger 2001)
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From the model, at the low water level in winter time, a bank of pepple stones as
big as first, is integrated into the bottom to form a slope base. The newly formed slope
base can breaks down and protects the substrate suiting to the locality from being
eroded. The built-up wall is pulled down or the top of the wall be cut off. A new shore
area with flat slope be laid out and vegetation be planted.
Based on this rehabilitation model, 25km of the shoreline of Lake Constance have
been restored in the past 20 years.
5.8 Application Case in Lake Suwa
Lake Suwa is a typical lake in Nagano Prefecture, it is an urban lake located at
Kamisuwa City. It has an drainage area of 531.2km2, water surface area of 13.3km2
with average depth of 4.7m and total water resource of 62987000m3. It has 31 inflowing
rivers and only one outflowing river. Human activities has done great destruction to
Lake Suwa due to that it is close to urban area.
10 years ago, the local government conducted masterplan for protect and treatment
of Lake Suwa, part of the plan are already finished now. In 19th, April, we visited Lake
Suwa, the following is the photo of the 2 littoral restoration places.
Photo after restored
Concrete bank before restored
Figure5-7
Photo of littoral zone before and after restoration
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Figure5-8 Natural view 10 years after restoration
In the previous cases, concrete banks are covered with sand from nearby areas to
be restored to the mild slope. From Figure5-8, we can see that the restored littoral zone
takes on a natural look 10 years after restoration.
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6.Others
6.1 Vegetable purification case by a private organization
In Japan, Environmental problems has been recognized not only by government,
but also among publics. Many common people have participated in environmental
protection campaign and made great efforts in pollution treatment by themselves. The
vegetable purification facility installed in a river flowing into Tone River is such an
effort. It is installed by a private organization with a big part of cost from donation.
The purposes of the facility are (1) try to purify water through a floating vegetable
structure, (2) call for people’s environmental consciousness.
6.1.1 Installation
See the photos for installation. The purification facility is composed of many sets of
unit. Each unit is supported by floater with 4 floating boxes acting as buoys, each box
costing 100yuan. Different units are connected with ropes and fixed by piled bamboo
poles as anchor. For maintaining and harvesting purpose, some wooden boards are laid
to form a path for people walking on. They use plastic baskets for supporting plant
growth. A net is put in the basket and seed spread on the net, after some time, the seed
will germernate and grow. In this case, all the materials use include: bamboo pole for
fixing, wood for frame of unit, wooden board for walking path, rope for connecting and
fixing, basket for plantation.
6.1.2 Vegetable species
Vegetable are selected according to its purification ability. In this case, 3-4 species
of vegetable are selected and planted. Kongxincai, which is originally from China is
planted in summer, and some others are planted in winter.
The vegetable will be harvested and sold in the supermarket, Surrounding people
also can freely pick it for cooking. Vegetable from the purification facility tastes crispy
and has long rhizome.
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Vegetable in Winter
Figure 6-1 On-site photo of the Purification facility
6.1.3 Cost
Total cost are about 30000 Japanese Yuan. All money is funded by privates. To save
money, all the unit are made by themselves.
6.1.4 Effects
A container with river water and river sediment is laid near river for vegetable
purification experimental purpose. Different species of vegetable are put into the
container for observation of change of water quality. It is observed that sediment was
disappeared 1 week later and vegetable with long and rich roots is considered not only
able to uptake nutrition from water but also trap the sediment. And the rhizome of
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vegetable is found a good habitat for aquatic organisms.
Figure6-2 Effects of vegetable
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7. Summary
This Report has described some newly developed, successful and applicable
ecological engineering methods for lake pollution treatment and ecological restoration
in Japan, including the artificial floating island method (AFI), the Niako method, the
constructed wetland method, and the littoral restoration method. Many typical
application cases of each method are illustrated. The following is a summary of them:
(1) Ecological engineering provides a creative, cost-effective, and environmental
sound ways to control water pollution as well as improving our natural
environment at the same time. It has gained widespread interest in Japan in
lake and river restoration in recent years.
(2) The Artificial floating island makes use of the water surface to create habitat
for aquatic organism. Besides, it can purify water, improve landscape, and
preserve lakeshore by wave absorption. Artificial floating island method is a
effective way for the dam lakes with violent fluctuations in the water level. In
this report, the classification of AFI, the structure design, and the stability
design is discussed.
(3) Naiko, that originally attached to the lake or artificially excavated out within
lake, is developed as an easy and effective way for non-point pollution
treatment as well as accelerating littoral restoration. In this Report, the
attached lagoon in Moriyama River in Lake Biwa and the artificial lagoon in
Lake Kasumikaura is discussed.
(4) Constructed wetlands is the most promising technologies for application in
developing countries, due to their characteristic like simple construction,
simple operation and maintenance, and cost effectiveness. It has two type of
FSW and SFS. In this report, the design criteria of FWS and SFS is discussed.
The compacted wetland is recommended to be used at urban areas or land
limited areas due to it makes use of the high porous artificial media and thus
require small area and effective for N removal.
(5) Conservation and rehabilitation of the shorelines of Lake will contribute to the
improvement of water quality, and natural habitat of its wildlife as well as
maintaining the lake’s historic landscapes. In this report, two models of
aquatic plant restoration model and concrete bank improvement model is
discussed. And many application case about littoral restoration in Lake Biwa,
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Lake Kasumikaura, Lake Shinji, Lake Suwa are illustrated.
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