Restoration of rivers and lakes in Japan

Transcription

1 Restoration of rivers and lakes in Japan (English abstracts of River Restoration in Japan written by Yukihiro Shimatani, Head of River Environment Division of PWRI, arranged by Keigo Nakamura) Keigo NAKAMURA River Restoration Team, Water Environment Research Group Public Works Research Institute URL:

2 1 Introduction In 1990, the Ministry of Construction commenced the Naturally Diverse River Improvements (NADRIM), or River Restoration Projects in Japan. Some pilot attempts were already made before 1990, however NADRIM enhanced river restorations in Japan incorporating a wide variety of ideas. History of River Improvement Projects 1936 The Kamo River improved (Kyoto) 1941 The meeting point between the Kamo River and the Kouya River designated as the Aoi Park Dredging works commenced in the Sumida River 1958 A dispute of the Edo River Plant of the Honshu paper manufacturing, Ltd. broken out. Rivers in Tokyo and Yokohama overflowed by an attack by the KanoRiver Typhoon. This caused an urban-type flood The Tokyo Olympic game held 1966 The first River terrace utilization program planned out 1970 The term easy-access-to-water used for the first time in Japan 1972 National the National Yoda Park opened 1974 Furukawa Shinsui Park, the first aquatic recreational park completed (Tokyo) Firefly Revetment of the Ichinosaka River completed (Yamaguchi pref.) 1975 The Sakai River Sinsui Park of the Komatsu River completed Fish Nest blocks used for the first time in Kagoshima 1976 Nishikawa Ryokudo opened The Yanagawa River Canal project commenced (Fukuoka) 1979 Motomachi Revetment of the Ohta River partially completed (Hiroshima) The Ohara River River Pool completed (Yamaguchi) 1982 The Itachi River Improvement works partially completed (Yokohama) How can be River Environment reported by the River Council The Nakajima River heavily overflowed (Nagasaki) 1984 The revetment of the Nogawa River, a tributary of the Tama River partially completed (Tokyo) Waseda Community Channel completed (Gifu) 1985 The Super-levee Construction project established 1987 The Kama River 2-Layer River partially completed (Tochigi) The Hometown River Modelling project established 1990 Naturally Diverse River Improvement has commenced The Morizari River project of Nature-abundant River Restoration implemented (Hokkaido) 1997 The River Law revised. The clause Improvement and conservation of the river environment added to the objectives(flood control, water resources) of river management The Law of Environmental Impact Assessment established - 2 -

3 2 Basic Concept of River Restoration 2.1 Consider definitely flood control To make a plan for conserving and restoring a river space environment, it is most important that the relationship with the flood control plan is firmly considered especially the following points. Contents of the flood control planning The contents concerning flood control planning should be examine closely including the scale of the plan (how probability is used), control method (Whether the watercourse or the basin such as retarding pond is focused on), shape of waterway, and flood type. For example, before appropriate environment elements can be conserved, different problems must have been resolved including; any flexibility can be found in the flood control plan; and how the planner should compromise between both the plans. To achieve this, it is essential that the contents of the flood control plan be precisely grasped. Hydraulic calculation To conserve good environmental units, any impact of them on a raise in water level, flow detection, and flow velocity should be quantitatively recognized. For the purpose, even for small- and middle-scaled rivers, at least varied flow calculation (a one-dimensional calculation method, which calculates a change in water level in the lateral direction) must be done. If the planner wants to know a difference in rises of water level depending on the vegetation, he may a quasi two-dimensional varied low calculation (a one-dimensional calculation allowing two-dimensional (planer) distribution of flow velocities to be found taking a difference in resistances in the lateral direction into account. The resistance can be changed depending on the size and density of the vegetation.) should be made. For example, the Kita River compromised between both the plans considering the results from hydraulic calculations and the level of the environmental impact due to cutting out riparian trees. Several pairs of points, where trees should be cut out and where the excavation work should be done on the high-water channel base, were determined and the water levels of them were calculated to find desired water levels. If the satisfactory level could not be reached, they repeated the calculation until the results reached the desired levels by modifying the way to cut trees and the way to excavate the high-water channel base many times. 2.2 Clearly recognize the current environmental state based on historical data To make a plan for conserving and restoring a river space environment, the current state of the environment and the result from comparison with historical data should be well understood. Only a biological survey may not precisely reveal the current state of the environment. To achieve this, biological data must be compared with data on the environment where living things grow and live. When data is compared, The Environmental Information Drawing (EID) is useful. This EID illustrates the water area, land area, and information on living things on single sheet for convenience. For example, information on the water area tells us the morphology and distributions a run, pool, backwater, sand bar, and submerged plants as well as how the water streams there. For an visual image to give correct information, the direction of a flow, the states of a run, pool, and vegetation must be easy to burn into one s mind at glance. It is required to incorporate information on living things in the Environmental Information Drawing. The - 3 -

4 animals, to which special attention should be paid, are extracted from the result of the biological survey to designate it as a focus species. If any focus specie is found, that point is marked in the drawing. Important living environment should be desired in it including spawning places and group nesting places. Based on this EID, what point of environment should be preserved and what point of environment should be modified are estimated. Thus, to make a precise environmental information drawing, it is required that data from the environmental survey such as the Aquatic Census Survey is used or the same level of survey is done. For the small- and middle-scaled river, in some cases, the surveys such as a biological one are hart to be implemented because of insufficient budget. In such a case, it is recommended to walk along the river with specialists to make a map of information obtained then. Another important point is to watch the current environment over time. For the planner to set the objectives for natural environment conservation and restoration and forecast the easiness to preserve the future environment, it is very important to recognize how the current environment has been changed from the original one or how it is changing. For living things, the information on what kinds of living things survived until when and where they had egg laying places are useful. The information sources include specialists, inhabitants, local magazines, fisheries experimental stations, and newspapers. In addition, the information on changes in river morphology and in living spaces, the old geographical maps, aerial photographs, drawings, and photographs may be used. Historical data on floods, draughts, large-scaled improvement works, and alteration of forest must be examined to find the causes. 2.3 Establish deterministic objectives Among the past restoration projects, some had vague targets. Establishing clear targets is the first step when the plan for conserving and restoring a river space environment is made. To make a practical plan, further actual objectives must be focused. 2.4 Correctly understand the targets to be conserved and restored with their scales It is required that the targets to be conserved and restored are made clear to conserve and restore a river space environment. The targets may be largely classified into the physico-chemistry environment (a growing and living environment), which enables he natural environment to establish, and the living things or groups of them. The projects are divided into three groups for convenience; a large-scaled control technology at a basin level; middle scaled-technology concerning a given reach with a watercourse plan prepared; and small-scaled technology such as installation of groynes, restoration of reed beds, and restoration or creation of backwaters and wetlands. The larger the scale, the more the space and time are required for conservation and restoration. For example, a large-scaled technology includes one for the water cycle system in the basin. In smalland middle-scaled rivers, a change in water cycle has occurred due to urbanization. Decreased permeable and retention areas, increased drainage, reduced permeability into underground, and less wetlands, all of them caused decreases in normal flow rate of rivers and spring waters, and disconnection among individual water areas. Finally, various kinds of living things are affected by these impacts. To address these problems, such - 4 -

5 elemental technologies are systematically combined an integrated one to restore the water circulation rate such as the permeability and surface overflow as rainfall retention, permeability, water re-utilization, preservation and creation of green lands, and purified sewage re-utilization. At the basin level, sediment control and flow rate control are also important. At the middle level, the watercourse plan is important for river space environment conservation, which had incorporated the positional relationship between the river and its surroundings, curve points in the watercourse, the width/depth/gradient of a low-water channel. Such points should be discussed whether any cliff or tree land is adjacent to the river; a plain design is prepared for maintaining shallows and deep waters accompanied with curved points; a cross sectional design is prepared for connecting with a tributary and irrigation channel and addressing a sudden head in the cross sectional direction; riverbed is flattened; and the height of a high-water channel base and flood frequency may bring thick forests in future. They are the safety precautions at the watercourse level. At the small level, various types of efforts for conserving habitats are being made. In recent years, the river improvement works and the development of the basin have caused the reduction and fragmentation of habitats in floodplain such as a backwater, creek, and wetland. To restore these deteriorated environmental elements, groynes nature-abundant revetments, backwaters, and wetlands have been restored and fish ways have been constructed for preserving continuity in many rivers. As known from the descriptions above, it is important that the targets to be conserved and restored are correctly recognized with their scales. 2.5 Accept expected changes One of the basic concepts for the technology designed to conserve and restore a natural environment is to accept original geography to transform. This idea assumes that vegetation transit and topography transform. Such method is considered to control transition of plants that a difference in relative height to the water surface is reduced. It is, however, difficult to control it completely. The backwater developing in rivers, most of which are remaining watercourses formed at a flood, change in morphology, size, and location each time a flood occurs. It is very important to accept such type of changes. 2.6 Take full use of natural energy The Nuki River improvement widened the river width and installed large stones to give variation to the river based on the concept of Naturally Diverse River Improvements (NADRIM). At the point one year passed after completion, normally the width of a water surface, where the water flows, has returned to its original one and fine shallows and deep waters have formed by the megalithic work (Case-22: Nuki River). The Nuki River near to the sediment-producing source returns autonomously to its original width. This section is a nature recovery action called a channel narrowing mechanism. The point of this river plan was to give a freedom to the river by widening the river width. In addition, large stones were placed there, which trigger such an action to facilitate sedimentation, finally resulting in shallows and deep waters. These large stones provide excellent meandering points to create the varied environment

6 The case of the Nuki river teaches us that it is important to make much of river potential to restore a river environment. The underlying philosophy for the technology designed to conserve and restore a river space environment is that a river itself forms autonomously its morphology and human being just assists such an action. In other word, a river is the leading role while human being is a secondary role. 2.7 Understand living things having homes there It is essential to collect the information such as life histories for each species, the living environment, and the relationship among them and arrange them in order for finding the best environment for them. This will leads you to further knowledge of a river and to the teaching that rivers grow living things. 3 Case study 01 Hattoh Riv. Restoration of waterway Restoration of riffles and pools. Original scenario was reproduced using old maps and interview with the old. The methods used are useful. 02 Shojin Riv. Re-naturalization of waterway Naturally Diverse River Improvements by removing the revetment. This project was conducted because of low risk of flooding by a diversion channel. 03 Itachi Riv. Re-naturalization of waterway A part of riverbed of the cross sectional waterway was dug out. At the ends of the waterway, banking is done. This case is so famous that it is called the Itachi Riv. method. 04 Kanou Riv. Conservation of waterway Re-production of run and pool in the mountain stream. Natural energy is utilized. The works are very interesting in that wooden grillage beam is used, which provides a beautiful scenery. 05 Habu Riv. Conservation and restoration of waterway Delicate patterns were made along the water front by changing the slope gradient of river banks. This method is well planned out; the river runs along the boundary of the mountains. 06 Takahashi Riv. Nisuke Riv. Conservation and improvement of waterway In the Nisuke River case, riffles and pools were created. In the Takahashi River case, a porous revetment was constructed. Useful case study for a river, which includes fine-grain sediment. 07 Sugata Riv. Restoration of waterway Based on the knowledge of river engineering, the width of a low water channel and the wave length of a - 6 -

7 meander were determined. Introduction of the river restoration concept reduced construction cost by 30% and CO 2 exhausted from the works to 1/7 compared with a traditional work. 08 Usonoki Riv. Improvement of river bank A good example when improvement of river banks, grass cutting, and the natural environment are focused on. 09 Asahata Riv. Restoration of waterway Restoration of a river, of which original state is hard to imagine. 10 Kohra Riv. Diversification of waterway One of the early attempts of river restorations in Japan. Various ideas were incorporated. 11 Takatsu Riv. Restoration of deeps An attempt to restore pools using a Ushi (groyne), a traditional flood control method. 12 Midori Riv. The varied environment was introduced into the river banks. The work using natural and artificial materials was employed. 13 Lake Kasumigaura Restoration of flora on river banks Wave dissipation works were installed. Restoration of flora along the lakeside using mild sloped banks. 14 Shimanto Riv. Restoration of river banks In the Shimanto River, natural large stones are seen even in the lower basin. This case teaches that it is important to recognize natural shapes. 15 Kitakami Riv. A nature-abundant revetment in the lower basin of a large river. Transplantation of bog reeds was successful by moving soil with roots mixed using a construction machine. 16 Saba Riv. Creation of the varied river bank environment using Large stone groynes. The result of assessment by monitoring is interesting. 17 Yoshino Riv. The old revetment was destroyed to improve the river banks in the lower basin. A beautiful field of bog reeds was restored. All the waste materials were re-used for construction

8 18 Onga Riv. Diversification of the waterfront space using groynes and backwaters and others. Special attention was paid to construction; notes were written in the drawings. 19 Koyoshi Riv. Protection of the water colliding front and willows were conserved using large-scaled groynes. Two-dimensional hydraulic calculation was done. 20 Tama Riv. Restoration of backwater Creation of a cross-sectional thin backwater with the downstream side open. A spring and water circulation were preserved taking full use of a head between the opening and the mainstream at the backwater end. 21 Yodo Riv. Compensation of backwater Compensation of backwater, which was destroyed by flood control work. The water circulation method and its size were determined based on the result from the current backwater state. 22 Nuki Riv. Improvement of waterway This case teaches dynamic restoration power of nature. 23 Oda Riv. A good example in case that the relationship between the scales of disturbance in the river and of nature-abundant restoration is focused on. 24 Nagara Riv. Conservation of backwater An example of mitigation focusing on minimizing adverse effect of construction on the backwater. 25 Kushiro Riv. Mitigation Comprehensive countermeasure for minimizing adverse effect of recovery works on salamandrella keyserlingii, japanese crane, water quality, water circulation and noise, as well as training the workers after the Kushiro Earthquake. 26 Takinoyaya Riv. Conservation of giant salamander The ecology of giant salamander discovered during recovery works form disaster was focused on. The case in which the highest priority was assigned to the living environment for living things. 27 Ishikari Riv. Conservation of skunk cabbage Protection of habitat of skunk cabbage accompanied with bank construction Protection type river restoration and few cases

9 28 Kasu Riv. Conservation of riverside wood The case in which island shape of wood was left. The project was carried out in consolidation with the park construction project and special attention was paid to the landscape. The history of river improvement can be learned even at a sort stretch. 29 Azusa Riv. Conservation of Salix chosenia The sabo or sediment control works to conserve a willow tree, or Salix chosenia requiring disturbance and stabilize the waterway. Compromising between both targets to be protected is important. 30 Yahagi Riv. Conservation of riparian wood by thinning An attempt to restore the riparian forest, which was excessively thick due to a flood or negligence, to its original state by thinning trees out. 31 Chikuma Riv. Conservation of riparian wood An island-shaped riparian wood was left and another water channel was dug out when the waterway was excavated. 32 Ara Riv. Large-scaled biotope Creation of a large-scaled biotope aiming at restoration of the ecosystem in which a predatory bird, may live. 33 Hikichi Riv. Network of biotopes This case avoided disconnection in a biotope due to road and raccoon dogs may move up to the downstream area. An example for a biotope network. 34 Ohta Riv. Improvement of fish ways Creation of the river, in which any kind of fish may return easily back to the upper basin. Different types of fish ways were installed depending on fish type. 35 Oirase Riv. Flow regime management Flow regime management brought beautiful scenery, in which moss attached to the stones along the water front, by controlling any change in flow rate. A good example in case that the flow regime and the river environment are focused on. 4 Aquatic Research Restoration Center for the understanding of river environments 4.1 Purposes of Aqua Restoration Research Center Based on the current awareness of river and lakes as invaluable natural resources, the Ministry of - 9 -

10 Construction in Japan has been working on establishing of a river control method which emphasizes on conservation of its natural environment, however the technology which supports river improvement method harmonious with the natural environment has not developed sufficiently because the research based on this technology is interdisciplinary field part between civil engineering and ecology. The Aqua Restoration Research Center was planned to solve these problems, and was constructed in 1997.This facility is located in three divergent areas along Kiso river in Gifu Prefecture, which cuts through the mid point of Japan. The Kiso River was chosen since it has a wide variety of habitats and its environmental condition is highly applicable to other rivers in Japan. This facility consists of three main facilities, the research center, three experimental rivers, and six ponds. 4.2 Research subjects The experimental river consists of three 800m-long rivers. River A is a straight channel and has a very homogeneous habitat. The discharge, 0.1m3/s is constant. Rivers B and C have the same shape but a considerably diversified habitat. We established six zones according to the purpose of the research. In order to evaluate the fluctuation of water flow, river B has a constant flow, the same as river A. However river C has a fluctuating discharge with the maximum discharge of 2m3/s. The Bed slope is from 1/200 to 1/800. The six research zones are mentioned below. Habitat Research Zone Shallows and deep water in river which we can see is an important habitat for fish to feed and rest. We want to establish the way to conserve and restore habitat efficiently. So research in this zone seeks to find the relation between aquatic organisms and habitat, for example the types and size of habitat. River Bank Development Zone Riverbank which is a point of border between land and river is an important habitat for the inhabitation of life, where fish spawn and rest. Various newly developed materials and methods are tested here in order to develop a method of river bank improvement that is suitable for the inhabitation of life. Backwater Research Zone In backwater fish spawn, fry grow up, and where is a place for refuge on flood. Research into the relation between backwater with different shape and water circulation to inhabitation of life is carried out. Inundation Frequency Research Zone The vegetation on waterside make up rich environment and which is important component from the landscape. In this zone, we research the intimate relationship between multiplication of the vegetation on waterside and various frequencies of inundation. And the effect of various frequencies of inundation on the vegetation and the effect of human work such as mowing on vegetation succession are evaluated. Gravel Bar Plant Conservation Research Zone The plant (gravel bar plant)for the gravel place of the river is in the decrease tendency according to the decrease of the gravel bar area in recent years. The gravel bar is disarranged by the inundation and the disturbance by flood that these plants are survived, and it is necessary to continue the gravel bar. In this zone, the relationship between actual situation of the gravel bar plant and the inundation frequency would be made cleared. And it would be developed and how to conserve the gravel bar plant

11 Sedimentation Research Zone The geological age of Japanese river is rather young and thus, has a high amount of sediment run-off at the upstream. Consequently, sedimentation occurs at which the river width is large resulting in the rapid reduction of the river width. Researches are carried out to develop a technique to speedily recover the natural shape of the river when damaged. The technique utilizes the sedimentation effect of the river. 5 Lake restoration 5.1 Restoration of Lake littoral zone Formerly water pollution was main problem for lake Environment, however recently because of water pollution and lake bank construction lake littoral zone has deteriorated. In Japan restoration of Lake littoral zone has started in many lakes such as Lake Biwa, Lake Kasumigaura, etc. 5.2 Artificial Floating Island Originally, a floating island is a piece of natural vegetation floating in the water, which is caused by the floating of a peat layer. In this study, a floating island is an artificial floating body on which aquatic plants such as common reeds grow. As a result of growing interest in environmental protection, people are becoming interested in familiar waterside environments. Artificial floating islands, which not only purify water but restore aquatic ecosystems, offer much potential. 5.3 Artificial Lagoon for non- point pollutants Artificial lagoon that aims restoration of littoral zone in lake and non-point pollutants control was constructed in 1998 at the river mouth of Kawajiri River which flows into Lake Kasumigaura in Japan. This artificial lagoon has an area of ca. 30,000 m2 and a depth of 1.0 m. The function of artificial lagoon for pollutant control was surveyed in 1999 and Water quality in artificial lagoon is mid-range between river and lake under normal weather condition. Artificial lagoon cuts % of SS, % of T-N, and % of T-P of runoff of rainwater. Annual removal ration of artificial lagoon was estimated between December '98 and November '99. Removal ratio was calculated as the ratio between sedimentation weight in artificial lagoon and annual load of Kawajiri river. 191% of SS, 19% of T-N, and 83% of T-P was removed by artificial lagoon. This SS probably includes not only river load but also lake load. Useful URL to know the river environment in Japan. Public Works Research Institute River Restoration Team Aquatic Restoration R.C. Lake Biwa Research Institute