1、 附录 Ecological engineering methods for soil and water conservation in Taiwan Huei-Long Wua and Zheng-yi Fengb aSoil and Water Conservation Bureau, Council of Agriculture, Nantou City 540, Taiwan bDepartment of Soil and Water Conservation, National Chung Hsing University, Taichung 402, Taiwan Abstrac
2、t:This paper describes the development of Taiwans localized ecological engineering methods to make the mitigation works more effective. To strengthen the soil and water conservation and protection of the ecological environment, comprehensive mitigation planning is necessary with considerations that
3、include balancing the safety, ecology, and landscape, and treating the whole watershed as a unit. To demonstrate the achievement of the promotion of the ecological engineering methods in Taiwan, this paper illustrates two complete mitigation examples for a debris flow torrent and a stream. Most of t
4、he mitigation works have survived and are still stable (with some minor damages) after the two strong typhoons of 2004. We show that the developed ecological engineering methods are very suitable in mitigation and worthwhile for further promotion for Taiwans ecological environment. Keywords: Water a
5、nd soil conservation； Ecological engineering methods； Hazard mitigation； Habitat； Erosion control Article Outline 1. Introduction 2. Ecological engineering methods and habitats 2.1. The functions of ecological engineering methods 2.2. The functions of the ecological corridor 2.3. Some drawbacks of c
6、onventional engineering 3. Planning and design of stream mitigation using the ecological engineering methods 3.1. Fundamental concepts 3.2. The principles of integrated design for streams 4. Selected examples of the ecological engineering methods of Taiwan 5. Inspection of the ecological engineering
7、 methods in Taiwan 6. Integrated mitigation for debris flow Torrentan example of Hua-shan Creek in Gu-keng County, Taiwan 7. Integrated mitigation for a streaman example of Ding-zi-lan-keng Creek in Taipei County 8. Challenge for promoting ecological engineering method in Taiwan 9. Concluding Remark
8、s Acknowledgements 1. Introduction One of the important measures in soil and water conservation in Taiwan is the ecological engineering method. It can be an index of protection and restoration for ecology. In 2001, the Soil and Water Conservation Bureau (SWCB) in Taiwan began to promote the innovati
9、ve ecological engineering methods. Disaster prevention, ecological conservation and recreation have been interwoven by the adoption of ecological engineering. Ecological engineering methods are suitable for regions with medium size flooding potentials. They can be used to regulate stream course, gui
10、de dangerous current to floodplain or detention ponds for safety, and reduce some sweeping forces of rapid currents. The method should not be considered a complete flood control measure. With debris flow torrents or very rapid stream flow, conventional engineering may be inevitable to maintain the o
11、verall stability of areas vulnerable to landslides or debris flow, and to control any debris overflow. If the much stronger conventional structures such as slit dams and check dams are indicated, environment friendly considerations should be made as much as possible while building them. When the uns
12、table hazard zone is properly protected by conventional works, the risk of washout/failure of the much more flexible ecological engineering methods can also be reduced； and the functions of ecological engineering methods can develop faster and help the environment and habitats to restore gradually.
13、This is like an ecological therapy to nurse the once damaged environment. For ecological engineering, two major approaches were adopted: develop new techniques and apply newly developed ecological engineering methods. The tasks for promoting ecological engineering methods include the development of
14、reference drawings for ecological engineering methods, ecological investigations, habitat improvement, establishment of ecological indexes, development of vegetation methods in landslide areas, and holding a series of conferences for ecological engineering methods. The methods are created to suit th
15、e domestic biological and environmental conditions. The merits of ecological engineering methods lie in the emphasis of comprehensive considerations in all aspects for soil and water conservation tasks. This paper shows that ecological engineering can be properly applied to mitigation of watershed d
16、isasters, protection and restoration of ecology. In addition, recreation infrastructures, rural community, and agricultural economic can be simultaneously developed. 2. Ecological engineering methods and habitats 2.1. The functions of ecological engineering methods (1) Improving the revival ability
17、of ecosystem (for large scale hazards such as landslide and debris flow): Ecological engineering methods can be suitable for mitigation of large scale natural hazards if the works are designed to provide the ability of revivification for the natural environment, ecosystem, and the corresponding peri
18、pheral characteristics. (2) Improving the protective ability of ecosystem (for medium scale hazards such as scouring of streambank and streambed): The methods should consider porous materials that will form many voids to provide shelter and protection for both aquatic and terrestrial animals. The mi
19、tigation should consider overall characteristics of watersheds and maintain the connections to the original natural stream environment, and avoid changing the current ecosystem or a single purpose construction. (3) Improving the recoverability of ecosystem (for small-scale hazards such as surface er
20、osion): Original local materials such as local stones, local woods, and local plants should be adopted for mitigation and the methods should have the ability to improve the recoverability of ecosystem. (4) Improving the functions of streams (for the streams with mitigation done): Design of stream mi
21、tigation and rehabilitation should consider incorporating the local environment, potential purpose of recreation and compatibility of future residential construction. The functions of stream mitigations can be improved with the incorporation of the ecological engineering methods such as building rec
22、reational area, scenic streambank, and ecological buffer zone. 2.2. The functions of the ecological corridor The objective of creating an ecological corridor is to retain or rebuild the major routes for local faunas needs for survival, breeding, food, and migration. The role of the ecological corrid
23、or includes conduit, habitat, filter, barrier, source, and sink (Noss, 1991). Some examples of ecological corridors in Taiwan are discussed below. (1) Improvement of longitudinal ecological corridor In 2003, at Liu-chung Creek in Tainan County, a longitudinal ecological corridor (a fish passage) as
24、well as a sediment control check dam were constructed upstream. A census of fish species was conducted at pre-construction, during-construction, and post-construction. The pre-construction investigation shows fewer fishes existed in the upstream due to 1.3 m gap in the creek, which prevented fish fr
25、om migrating upstream. After the corridor was implemented with a fish passage, the number of fish in the upstream measurably increased. In addition, fish appeared more active. This may be because the swimming space has expanded and the chance of inbreeding has been minimized. (2) Construction of lon
26、gitudinal corridor Hou-fan-zi-keng Creek is located in Taipei County in northern Taiwan and it is abundant with various species. In July 2001, Typhoon Nari caused the collapse and erosion of the banks. The creek changed its course and caused severe sedimentation. The habitats in the creek were destr
27、oyed and the survival of many aquatic animals was threatened. In order to revitalize the ecology, non-cement based ecological engineering methods were used, including wood-log pile shoring for bank protection and arc-shape stone streambed sill for the longitudinal corridor. It is also hoped to rebui
28、ld the natural scenery of the stream. To provide a suitable habitat, the meandering of the creek was designed to create various aquatic environments such as pool, shoal, riffle, backwater, and slack. Based on the comparison of pre- and post-construction investigations, fish and shrimp have returned
29、to the creek and increased in large numbers. The obstacle-free arc-shape streambed sills and the slacks help fish migrating between upstream and downstream. (3) Improvement of lateral corridor using gentle slopes In the debris flow mitigation at Chung-ho Village in Taipei County, gentle slopes of st
30、reambank protection were designed to fit the topographical flat area. The gentle slopes serve as an interaction base for both aquatic and terrestrial animals ensuring the continuity of the lateral corridor. (4) Example of pitfalls due to lacking gentle slope The bank mitigation design for debris flo
31、w of Da-tsu-keng Creek in Taipei County was 1:1 sloping with slit dams. There was no designated gentle slope. When a deer entered the creek for food, it fell into the channel which is 3 m lower than the bank and could not climb back up by itself. Out of fear, the deer cried out and dashed down in th
32、e creek. With great effort, people rescued it. This should teach us a lesson about the importance of having a gentle slope zone and ecological corridor. 2.3. Some drawbacks of conventional engineering Natural streambanks allow water seepage. Organic matter and minerals in the ground will be carried
33、by groundwater entering a stream. Natural porous materials enable the exchange of water, which maintains water quality. Using concrete in preventing flood and erosion is considered safer than natural streambanks. However, it will break the continuity of groundwater. Also, some channelized streams we
34、re built with smooth vertical concrete revetments. Such design will cause problems such as difficulty in planting, fish migration, and amphibious reptile travel. Tall slit dams will cut off longitudinal ecological corridors. For a perennial stream, a slit dam will block fish migration. A fish passag
35、e should be considered. Check dams with drops higher than 1 m can hinder fish migration also. For flow regulation works, a concrete paved streambed will make pool, shoal, and riffle disappear； and water quality will be easily degraded. 3. Planning and design of stream mitigation using the ecological
36、 engineering methods 3.1. Fundamental concepts (1) Consider balance in safety, ecology and landscape Consider the priority and balancing of safety, ecology and landscape according to the regional characteristics. Safety shall be the first considered for the hillslopes near urban areas. In contrast,
37、ecology should be the major factor for mountain hillslopes with various ecological systems. For other areas safety, ecology and landscape should evenly considered. (2) Develop suitable mitigation according to local environment Create integrated design to be compatible with local environments such as
38、 regional ecological resources, natural hazards, environmental characteristics, landscape scenery, historic monuments, and resident opinion. (3) Perform integrated planning and design for watersheds Plan hazard mitigation and rehabilitation by taking watersheds as a whole unit including, building na
39、tural ecological district, environmental protection area, improving habitats, and recreation areas, etc. (4) Create aqueous environments Construct facilities for aqueous ecological environments such as pool, shoal, riffle, backwater, slack, flow deflectors, fish passage, and artificial wetland. Building boulder revetment and rearranging existing rocks in streambed is an excellent method to control the flow speed and to create the above aqueous environments. (5) Create the terrestrial environment
