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Reviving past ecological functions—Restoration plan for Bie River habitat

2016-10-13

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Located in Fuli Village, Hualien County, Bie River originates in the Coastal Range as one of the tributaries of the Siouguluan River at its upper stream (Fig. 1). In the past, it was filled with fresh water turtles (bie) so it was named likewise. In addition, there is another name ci-halaay within its drainage basin, which means there are Sicyopterus japonicas. In addition to reflecting the naming culture there, these names also indicate the ecological conditions there. However, most of the fish there are alien invasive species from the western plain. As to its autochthonous species, naming fresh water turtle and Sicyopterus japonicas, only a few of them left now. According to recent investigation, there is no record of Aphyocypris kikuchii (Fig. 2), a species special to eastern Taiwan. For the goals of promoting local ecological functions, the 9th River Management Office, WRA conducted an investigation on the ecology there in 2006 to 2007 to propose preliminary improvement plan. To continue the efforts of the 9th River Management Office, WRA and the restoration of rive ecology, the Water Resources Planning Institute began to launch the restoration plan at Bie River in 2012.
The environments of rivers in Taiwan are very diverse. If we construct an environment solely in accordance with the behaviors of local animals, it will not stand the erosion of a flood brought by a typhoon. In fact, the weakening of functions of original habitat is largely the result of the interference on the force of rivers (for example, hydraulic structures or earthquake). They change the characteristics of the flow of water and sand, rendering rivers to lose their capacities for self-restoration. Therefore, it is necessary to understand a river’s characteristics and interference in order to seek improvement, replacement, or alternative measures before launching any restoration plan.    
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When examining the features of rivers, we tend to start with the large scale because the large basin features are formed in a large terrain over thousands of years. They are not easily changed, becoming limitations to environmental changes from time to time. From the geological map, Bie River basic mainly includes Duluan Mountain stratum, Dagangkou stratum, and Liji stratum (Fig. 3). Among them Duluan stratum’s hard lithology constituted gorges (such as Xiao Tianxiang), on the riverbed of which rocks are gathered. The lithology of Liji stratum is soft and weak, and it can be eroded easily. Therefore, the water there is muddy. As to Dakangkou stratum, it lies between them. Due to different geological features, a step-pool appears only in Shihcuogou River in the form of riverbed to provide clean water. Therefore, it has become the habitat of Hemimyzon formosanum, a protected species in Taitung, Taiwan. From the cross-section of the river between 1993 and 2010, there had been the tendency of downward erosion. In the most serious area, it was a deep as 6 meters. In addition to the exposure of rock ledge in part of the areas, the flood frequency of the beaches decreased significantly (Fig. 4). As rock ledges are exposed, there will be a lack of suitable sand at the riverbed, causing habitats of benthic organisms to disappear and the suitable place for fishes to lay eggs will be decreased. With the decrease of animal quantity, it means the decrease of food supply for fresh water turtles. The suitable environment for them to lay eggs is river sand. If the eggs of fresh water turtles are soaked into water, they will become stillbirth. It is deduced that the most suitable environment for them to lay eggs are beaches that be reached by small floods (the eggs will not be washed away or soaked in water) but can be reached by huge floods (that bring sand). Due to the downward erosion of the river bed and the banks are too close to the deep grooves, there are not many of such environment. In addition, such river conditions do not provide any evacuation space (slack flow area). When floods come, all the fish will be washed downstream. It will increase the time for restoration significantly. If we focus on the turtles’ egg laying behavior, they can still make use of fields by banks. However, part of the embankments is exposed without any cover. It will affect turtles’ egg-laying intention. More importantly, although certain ratios of fields on both sides of the banks adopted organic farming, for easy management many of them are paved with cement (to prevent furrows from blocking by sediments or hazards of animal such as snakes, rats, and more in some areas). The use of tea seed meal also seriously harms the water creatures nearby.

In addition, the quality of the rice grown in Fuli Township is of very high quality. Therefore, the major business at the banks is paddy rice agriculture that employs most of the land there. For the convenience of irrigation, many weirs are built along Bie River. For stabilizing the riverbed protection structures and water pipes and ducts, groundsills are installed. Therefore, there are many horizontal structures of various sizes along the river (Fig. 5). Among them, there are 11 of them have the water surface difference of more than 1 meter. General speaking, weirs will affect the ecology in: 1. Monotonous habitat. 2. Decrease of river flow. 3. Blockage of ecological corridors. To analyze their impacts, SRH2D is used to simulate the patterns of changes with and without weirs. Different water flow and curves for the suitability of fishes are applied to understand the changes of the available habitat for fishes (Fig. 6). From the analysis, it is discovered that with the demolishment of weirs, there are certain impacts on fishes’ habitat but it is not significant. However, the water flow exerts significant impacts on fishes’ habitat, especially on native fish species. When the water flow increases, there is significant increase in habitats for native fish species. It indicates that the key affecting factor for fishes’ habitat is the decrease of river water flow with its water used for irrigation purposes. Regarding the issue of ecological corridor, from the vertical distribution of fish, although there are lesser migratory fish upstream, further investigation is needed to find out whether they are affected by the horizontal structures.

During the planning period, local communities gave us recognition and ample support by providing plenty of local information, for example, the regions frequented with turtle appearances, the areas where eggs are discovered, the time for sunbathing their backs, the conditions of the river changes, and more (Fig. 7). With this information, it is possible for us to compare with the analysis above. Analysis was also conducted from the people’s perspectives to find out the reason of the decrease of turtle. They also reminded us of the catching of people should also be considered. During the discussion, they expressed the expectations and visions of restoring the ecology of the river. They even proposed the ideas of returning the land to the river and compensations to the communities. In addition, with the ample information provided by local farmers’ associations, water resources associations, and the agricultural departments of the county governments, it was greatly helpful to the planning team to grasp the local conditions. As ecological knowledge was urgently needed for the restoration of ecology, many experts and scholars were invited to inspect the place for valuable suggestions so that we can grasp detailed information on the behaviors and habits of local animals.
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Summarizing the analyses above, the strategy of the restoration of Bie River is proposed as follow:
1. Construction of river environment: In order to solve the problem of insufficient evacuation space for fishes during floods, evacuation space for fishes is built at berms for bank protection at Fengnan Village. Stairs are built in the space as water area (Fig. 8) to satisfy local residents’ expectations. In addition, at the section of the river, there is also erosion problem along the shores. Stone groundsills in layers and spurs will be built to alleviate the erosion of floods and protect the safety of river protection structures. It can also increase habitat for fishes.
2. Improvement of river corridor: There are 11 horizontal structures with the length of 1 meter along Bie River. Further investigation should be conducted to find out is it necessary to improve the river corridor. However, in the primary stage, it is necessary to coordinate with the water resource associations to educate people not to use soil or stones across the cross-section of the river to introduce water to cause dry up or subsurface water flow of the river.
3. Review of the use of irrigation water: With the agenda of assuring paddy rice agriculture of local inhabitants, the current use of water for irrigation should be reviewed. It is hoped to increase the volume of water flow to increase habitats for native fish species.
4. Construction of habitats for indicating species: As the alien invasive fish species from western Taiwan have already become the privileged species. Before removing them effectively, there are difficulties in restoring Aphyocypris kikuchii. Therefore, ex situ restoration will be used. Utilizing the water fields on both sides of the banks, wetlands are increased partially or water bamboo fields or farm ponds will be used as habitat for Aphyocypris kikuchii (Fig. 9). Part of the furrows will be improved as connecting corridors or habitat spaces. In addition, fresh water turtles prefer swamp environment. It can increase habitats for turtles too. Moreover, turtles will be predators for insects harmful to fields. Working together, the habitat will become part of local agriculture and everyday life to constitute a socio-ecological landscape.
5. Promote ecological conservation: There are still some areas suitable for turtles to lay eggs in the river. It is necessary to promote environment education to local people. The bald land derived from farming and slopes are frequent environment for turtles to lay eggs. These factors should be taken into consideration together for better management. In addition, the policy of blocking streams to protect fishes should be promoted to decrease the stress of the catching of turtles and swamp eels.

The restoration of river involves with a wide scope and it is difficult to delimit the conditions of success or completion. Only by monitoring the progress after the implementation of this plan, it is possible for us for find a suitable management pattern for local environment.
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Source: Water Resources Agency cloud
Website: https://opendata.wra.gov.tw/Mobile/Newsletter_content.aspx?s=7D8FF63E328A29E4&list=6D6E2714869A076B1573C17A95E1D56A143B0091DEB6110C8D74A5F9A1E11B79D329C98EEE36FBEC33CE0571546CD54D6E6A13519EC9F48629A201F89D64D9DCE544A73399704E2E&ms=2E732F6E01B44AC7
 

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