The Case Study of "Close-to-Nature" Restoration of Urban Rivers & Enlightenment
雷泽鑫 杨冬冬 曹 磊
LEI Zexin, YANG Dongdong, CAO Lei
雷泽鑫 / 1993 年生 / 女 / 风景园林学博士在读 / 研究方向为城市景观水文与生态工程、海绵城市建设
LEI Zexin，female，was born in 1993. She is the Ph.D. in Landscape Architecture, School of Architecture in Tianjin University. Research directions: urban landscape hydrology and eco-engineering, sponge city construction.
杨冬冬 / 1985 年生 / 女 / 清华大学景观学系博士后 / 天津大学讲师 / 研究方向为城市水环境生态修复、海绵城市建设
通讯作者邮箱（Corresponding author Email）：email@example.com
YANG Dongdong, female, was born in 1985. She is the postdoctoral candidate, Department of Landscape Sciences in Tsinghua University, and the lecturer in Tianjin University. Research directions: ecological restoration of urban water environment and sponge city construction.
曹磊 / 1962 年生 / 男 / 博士 / 天津大学建筑学院教授、博导 / 研究方向为区域及城市景观的文脉延续和生态可持续研究
CAO Lei, male, was born in 1962. He is the Ph.D., Professor and doctoral Supervisor, School of Architecture in Tianjin University. Research directions: context continuation and ecological sustainability of regional and urban landscapes.
Abstract: The channelization of urban rivers may cause stress on the river ecosystem and further deteriorate the surrounding environment. Because of the failure in realizing a virtuous cycle of ecosystem in the decontamination process, generally the treatment of urban rivers does not achieve the desired results despite of huge investment, high cost incurred therefore and application of advanced technology. Hence, it is necessary to broaden the scope of our ideas and methods, and renew our tactics and technology in treatment of urban rivers. Based on the cases of ecological restoration of urban rivers in other countries, the paper interprets the “close-to-nature" concept of river treatment from the perspective of design and construction, in order to provide a new insight for the practice in China.
Key words: urban river; ecological restoration; channelized river; close-to-nature renovation of river; landscape garden
Figure 1 The River Slope is Slow and the Water Flow is Not Smooth Before Restoration 图2 修复策略说明
Figure 2 River Restoration Strategy
Figure 3 River Biodiversity after Restoration
英格兰萨默塞特郡的萨默河因河道纵坡较缓且沿线设有阻水堰，造成水流不畅、淤堵严重（图1）。针对该问题，相关人士提出近自然化的岸坡处理技术：束窄河道，提高流速，增加河道内的自然生境空间（图2）。整体操作分为四个部分：首先，将阻水堰整体拆除的同时，保留两侧的结构，其目的是在严重干旱的时候可以安装临时隔板蓄水保持水深；然后，用当地石灰岩堆置于河岸内缘，打破原有的直线式沟渠，束窄河道且增加曲折；同时，用石头堆砌代替原来的小型堰坝，以增加整个河道水深；最后，将椰壳填塞于石灰岩堆中，在河道两岸形成蜿蜒的边缘种植带。修复前的河段平均水深 0.5 m，河道平均宽度 4.5 m。治理后的萨默河主河槽宽度减少一半，水深降低 0.1 m。在治理后的一年时间里，尽管发生了几次洪水事件，但护堤完好无损，河道沿线未受影响。
Figure 4 River Restoration Strategy 图5 切割后形成的护岸平面
Figure 5 The Plan of Slope Revetment after Restoration 图6 深挖后形成的河床纵剖面
Figure 6 The Longitudinal Section of the River Bed After Restoration
3.2 施工模式：专家现场指导 + 技术工人操作 + 多方民众参与
Figure 7 Comparison of River Morphology Before and After Restoration
Figure 8 Community Participation in River Restoration
China attaches great importance to the treatment of river pollution in the urban area in recent years, and has made a lot of investment in this regard.For example, China has continuously raised its requirements for ecological construction. As an important part of the ecosystem, water environment is in the spotlight lately. In terms of policy, the "Double Urban Restoration" initiative proposed by the Ministry of Housing and Urban-Rural Development in 2017 is committed to restoring the self-regulating function of urban rivers and other ecosystems. Improving the water environment is one of the targets of the "Three Campaigns on Building a Well-off Society in an All-round Way" proposed by General Secretary Xi in 2018. The 36 key cities in China invested more than 114 billion Yuan directly in the treatment of odorous water in 2018. In 2019, Beijing invested over 3 billion Yuan in the Dingzhou water ecological restoration project, which is upstream of the river system which provides drinkable water to Xiong'an New Area, the new sub-center of Beijing.
As the life line of urban development, as well as the important part of the municipal water system, urban rivers not only assume the basic function of flood drainage in the urban area, but also play an indispensable role in construction of an urban ecology. Therefore, ecological restoration of urban rivers is of great significance to harmonious operation of the urban system, the sustainable development of the urban area, as well as meeting the need of the people's life.
1 Current Situation of Urban River Management in China
1.1 Major Issues
Thanks to the preferential policies and financial support from the government, management of urban rivers in China may achieve quick results because of better operability. For example, Shanghai invested more than 14 billion Yuan in 10 years for the third stage of Suzhou River ecological restoration project. And attempts at use of new technologies, such as ecological water transfer, new floating bed materials for revetment protection, new energy reoxygenation & aeration technology and biological water purification technology, play a role in the purification of river environment.
However, because of a host of issues, such as the huge cost incurred, the difficulty in maintenance, as well as unsustainable treatment methods, the ecological restoration of urban rivers does not meet the desired results in the long term. There are two main reasons: (1). Passive realization of water mobility. The "hydrodynamic force, water circulation and water pollution control" of rivers are realized through mechanical work. This model can realize the circulation of river water in a short time, but it consumes a lot of manpower and material resources. Hence the unsustainability. Only by restoring the physical and chemical properties of urban rivers, as well as its natural flowing properties can the rivers’ self-purification capacity be restored and long-term treatment realized. (2). There is no comprehensive and substantial recovery in the "openness" of urban rivers. Although the commonly-used external water diversion mode can replenish water in a short period of time and artificially raise the water level, the biological chain which is interwoven with the broken "river interior and surrounding environment" is not effectively repaired, which may lead to the failure of material circulation, energy flow and information exchange between the aquatic side and the terrestrial side of the river, thus resulting in the difficulty of realizing a dynamic balance in the river ecosystem.
Ecological restoration of urban rivers is a slow and long-term process. For example, Shanghai invested a lot of human and financial resources and spent a lot of time in decontaminating Suzhou River. And it is difficult for other cities to replicate the practice of Shanghai. Therefore, against the background that the water management in China is in a transition stage from specific river management to comprehensive ecological management, it is necessary for us to make new attempts from the perspective of guiding the self-restoration of river ecosystems and realize a harmonious coexistence between the human beings and urban rivers.
1.2 The Direction in Ecological Restoration of Urban Rivers
Foreign studies pay more attention to the role that the river morphology and geomorphic process play in restoring the ecosystem health and maintaining the sustainability .Channelization of urban rivers is the biggest change in a city’s natural attributes. But homogenization of urban river morphology may cause stress on the river ecosystem . From a critical standpoint, the People's Daily pointed out that "there are many 'pseudo-ecological' behaviors in some places, which seem to be correct but actually have hidden dangers. For instance, the overall hardening and channelization of the river channel may lead to separation of water and soil, as well as separation of water and biological elements, which roughly blocks the ecological function of the river channel between the water and the banks ". Channelization is an inevitable issue in the treatment of modern urban rivers .
In recent years, the concept of "low-impact development" and the strategy of "natural work" advocated by the "sponge city" initiative have brought new inspirations to the management of urban rivers in China. Provided that the city is safe from rain and flood, the river morphology can be appropriately changed to induce the river’s self-restoration capacity, which can promote the benign development of the river ecosystem. The "close-to-nature" strategy is the key to protection and ecological restoration of urban rivers at home and abroad, and it’s also an important link in the construction of a sponge city. Based on the cases of ecological restoration of urban rivers in other countries, this article interprets the concept of “close-to-nature restoration” of urban rivers from the perspective of design and construction.
2 The Design of "Close-to-Nature Restoration” Method
Homogenization of river morphology includes straightening the river’s longitudinal layout, regularizing the geometry of the cross sections and hardening the riverbed materials. It is difficult to change the direction of urban rivers. Firstly, the limited urban land does not have enough space to restore the river to its meandering shape. Secondly, as an important flood control channel, the urban river bears the burden of diverting rainwater and flood. And it is difficult to expand the buffer space because of limitation by the banks on both sides. Finally, it is difficult to get financial support from the government if the hardened revetment is demolished. And moreover, it would lead to greater waste.
Similarly, many cities in Europe and the United States retain a large number of channelized rivers with slopes hardened by cement in order to ensure that they are safe from flood. The idea of "close-to-nature” river management proposed by Germany in the 1950s calls for application of ecological principles to change the traditional engineering methods so that the management of urban rivers conforms to the botanical and life principles (Laubetal, 2009). Up to now, the "close-tonature" restoration concept is more popular in European and American countries. And there are mature technologies for ecological restoration of small rivers in these countries. By studying these cases, this article discusses the effect of the "close-to-nature" design on the ecological restoration of channelized urban rivers in China.
2.1 Case Introduction
2.1.1 River Somer Ecological Restoration
River Somer in Somersetshire, England suffered from stagnant water flow and serious siltation due to the relatively gentle longitudinal slope of the river and the water blocking weir along the river (figure 1). In order to solve this problem, the "close-to-nature" slope treatment technology was used to narrow the river channel, speed up the water flow and increase the biological habitats in the river channel (figure 2). The overall operation divided into four parts. First, the weir was completely removed except for the structures on both sides. This is to install temporary partitions to store water and keep the water depth in case of severe drought. Then, the local limestone was piled on the inner edge of the bank to break the original layout of straight water course, narrow the river channel and create more twists and turns. The original small weir dam was replaced with stones to increase the water depth. Finally, coconut shells were packed in limestone piles to form a meandering edge which may be used as a planting belt on both sides of the river. The average water depth of the river before treatment was 0.5 m, and 4.5 m after. After treatment, the main channel of River Somer was reduced by half of the original width, and the water depth by 0.1m. In the wake of several floods within one year after the treatment, the revetment remained intact, and no there was no damage to the river channel.
Although River Somer does not break away from the existing hardened linear boundary due to the local conditions, the meandering course formed in the main channel where water flows slowly increases the channel’s variability in width and depth, which provides diversity for the water flow, as well as suitable habitats for birds, mammals and invertebrates (figure 3).
2.1.2 River Valency Ecological Restoration
After channelization, the River Valency in Cornwall, southwest England, had a steep gradient and a narrow channel, which was likely to cause soil erosion along the banks and bring rain and flood risks to the downstream areas. Two measures were mainly taken to ease the gradient, reduce the rain and flood risks, and improve the river’s biological habitats (figure 4). Firstly, the river’s flood control capacity was improved by chipping away the original steep slope and appropriately widening the river channel. The rocky revetment on both sides of the river has a strong plane of stratification and obvious crack lines along the side slope. The stone revetment is cut into serrations along the line, with one side perpendicular to the crack line and the other side inclined downward (figure 5). The native water-borne plants are fixed by silt in the grooves formed in the undulating rocky revetment to slow down water flow and deposit of sand, thus forming riparian habitats. Secondly, the original longitudinal slope which is close to 1:45 is reduced to a multistep gentle slope (figure 6) by digging deeper at appropriate portions into the river bed or paving stones on the riverbed. As result of the high-intensity scouring by water flow, the gravels generated by the cracking of the stone revetment are deposited on the riverbed. This promotes the natural stabilization of the revetment, and on the other hand, the gravels deposit in the river channel form gravel shoals, thus enriching the diversity of biological habitats.
As result of the channelization, River Valency appropriately broadens the channels, eases the gradient in a low-cost way and slows down the heavy water flow, thus improving the river’s biological habitats. Besides appropriately widening the river channel by taking advantage of the natural characteristics of the local rocky riverbed, the approach also reduces water flow with plants planted on the renovated banks. Diversified biological habitats, such as rich vegetation communities are created along and in the river by using stones chipped away from the banks, as well as other local stones to change the riverbed, and by easing the steep slope.
2.1.3 Braid Burn Ecological Restoration
Braid Burn, the brick ditches in Edinburgh, UK run through the northern edge of Inch Park. When renovating the park, important biodiversity conservation in Edinburgh, the engineers redesigned the path of the river flowing through the park to improve the river’s flood storage capacity (figure 7). 80% of the traditional ditches flowing into the river were changed into naturally meandering forms. In order to reduce the ensuing construction waste and save the construction cost, the earth and stones generated from the newly excavated meandering rivers were refilled into the old river channel. Ecological materials woven from coconut shell fibers were selected as materials for revetment of the new river channel, which not only ensures soil stabilization on the revetment, but also realizes mutual infiltration, as well as exchange of materials and energy between the water and land. One year after renovation of the park, the coconut shell fabrics were gradually covered with deposited sediment in the river channel. With the plants planted on the banks, riparian plant communities gradually formed on the ecological slopes, thus forming new wetland biological habitats. New "residents", such as otters are found in the river.
Braid Burn flows through the urban green land, providing a space for effective change of the river morphology. The meandering river course results in various forms which have different widths and depths, such as rills, shoals, deep pools, bends, etc. The morphological diversity promotes the river’s natural development process and ecological process. The habitats for animals and plants are conducive to the development of biodiversity.
In terms of protection and ecological restoration of urban rivers, it is necessary to take into account the rivers’ morphological changes and the possible ecological changes . Facts have proved that inducing the self-driving capacity of channelized rivers may create a more favorable buffer space for rainwater runoff, and it can also effectively restore the urban river’s ecosystem. Given the simplified approach in treatment of urban rivers, the above-mentioned cases provide the following as an enlightenment:
2.2.1 Change the Uniformity of Morphology
Straight channels are not the natural form of urban rivers. Maintaining the meandering nature of urban rivers is the key to protecting the diversity of river morphology . This is the first step to break away from the morphological uniformity in terms of ecological restoration of channelized urban rivers. However, it does not mean that the rivers will be completely natural. In the limited space of urban rivers, properly restoring the spontaneous dynamics can effectively improve the rivers’ fluidity.
An urban green space or unproductive land nearby may be an ideal environment for ecological restoration of the urban river. The space can provide "a certain degree of freedom for the water flow and fluctuation of the river" . Based on the practice of Braid Burn, it is necessary to appropriately change the linear layout of the river channel within this range to restore it to a meandering shape, expand the waterfront space and improve the river’s bearing capacity. However, because of limited urban land, generally there is few extra space for ecological restoration of the urban river. In the case of River Somer, stones were piled on the edge of the steep banks to narrow the river and create a meandering shape. It not only effectively improves the water flow, but also creates natural biological habitats between the water and sandy banks. At the same time, it does not affect the river’s flood control capacity. If there was a flexible margin, River Valency would be appropriately widened or deepened in the main channel by dredging deeper into the rocky bottom to increase the space of water storage and create a natural water landscape.
2.2.2 Increase the Complexity of River Channel
It is conducive to deposition of sediment in the water flow by appropriately increasing the complexity of the river channel, as well as the friction between water and the revetments. A dynamic channel which is somewhat favorable for transport and deposition of sediment is more prone to the formation of a complex river channel . Increasing the complexity of river channels, improving the quality of space for water flow and creating diversified biological habitats is the second step to break away from the simplified approach in the treatment of urban rivers.
Corresponding to the cross section of the river, changing the longitudinal layout of the river means that the flow channel would become more complicated. In the three cases above, various methods were used to enrich the cross section of the rivers. For example, a “close-to-nature” cross section was created in River Somer by stacking stones and filling silt in the river channel, and growing plants on the banks; River Valency created a multistep channel which features "rapids and deep pools" and simulates the natural state by chipping away the steep slopes and piling stones in the river channel; Braid Burn created diversified biological habitats, such as shoals, curved bays, streamlets and swamps by appropriately widening portions of the river channel within the green space.
2.2.3 Improve Connectivity between Land and Water
Softening the slopes of urban rivers does not mean demolishing the hardened portion of the banks, and instead, it uses natural permeable materials for revetment protection to realize the “close-to-nature” ecological restoration. In
China, materials such as grass-planting bricks, floating plant grids and green modules are widely used for revetment protection. However, this approach has heavy artificial traces, and it cannot restore the natural biological habitats. In the three cases above, the biological habitats are created by using local or nearby stones or growing plants on the banks. Circulation of the ecosystem can also be realized by guiding the connection between land and water through the construction of biological habitats and low-interference management. In addition, utilization of natural materials not only reduces the construction cost, and it is less difficult in the practice, and at the same time, no construction waste ensues.
3 "Close-to-Nature" Construction Method for Ecological Restoration of Urban Rivers
The construction process is not a simple "manufacturing result", but a gentle "design process". A.M. Gurnell and others studied 143 urbanized river sections in Europe and concluded that less engineering interference is conducive to the realization of river ecological diversity, habitat connectivity and diversity of vegetation structures . On the one hand, long-time, slow-motion and low-impact actions can effectively reduce the secondary interference of construction to the river ecosystem. On the other hand, the design and construction can truly realize the ecological restoration of rivers in suitable locations only with the cooperation of all parties.
3.1 Construction Period: Long Time, Slow Motion and Low Impact
In order to avoid any interference to the passage of fish and reduce the adverse impacts to the fish spawning in the vicinity, the River Babingley project  in Hillington, England alternated between installing barriers in the river channel and removing the barriers in a cycle of two or three weeks, which caused the uncomplicated project to last for three months. And as result of the slow construction process, the project effectively reduces the erosion of the river bed by the water flow, thus promoting the deposition of silt. Vegetation grows in newly exposed sludge, which is conducive to consolidating the sludge and creating new biological habitats. Shortly after the project, fish and invertebrates are found in the river, which is the proof of low interference in the construction process.
This long-time and slow-motion construction effectively reduces the impact to the river and creates a process of self-adaptation and adjustment by the river. One of the advantages of this method is that the construction combines with the natural process of the river to create a relatively stable environment for the ecological restoration of the river.
3.2 Construction Mode: On-Site Guidance by Experts, Technical Worker Operation and Multi-Party Participation
Since the ecological restoration of urban rivers is faced with complicated and changeable circumstances on the construction site, the project cannot proceed completely according to the drawings. Any unexpected issue should be solved through coordination and cooperation by the personnel involved. For example, in River Valency project, the cutting of stone revetments and reshaping of riverbeds were completed by construction workers under the guidance of engineers onsite. And public participation is also important. For example, the River Somer project was jointly completed by construction workers, volunteers and community residents. Volunteers from "Friends of the River Somer" participated in removing the garbage and harmful species from the river figure 8. In 2011, the residents living around the river were awarded "the proudest place" prize presented by the local council for environmental improvement.
Ecological restoration of channelized urban rivers is faced with a series of issues because the rivers are simple in form, but have multiple functions, and there is limited space for ecological restoration. The traditional mode of management, which is characterized by high cost, huge investment and strong implementation power, does benefit the long-term management of urban rivers.
Practice cases of river ecological restoration abroad are interpreted from two aspects of "design-construction" of river ecological restoration. It can be concluded that the ecological restoration of urban rivers can be completed in a moderate construction mode in a limited channelization space through human guidance. Design process: properly change the uniformity of the river channel shape, increase the complexity of the channel, and improve the water-land connectivity. Finally, the river will naturally do work after a certain period of time, thus realizing the "Near-Naturalization" of the urban river.
 陈兴茹. 城市河流生态修复浅议[J]. 中国水利水电科学研究院学报,2006(03):226-231.
CHEN Xingru. Brief discussion on urban river course ecorestoration[J]. Journal of China Institue of Water Resources and Hydropower Research, 2006(03):226-231.
 R.C. Grabowski, N. Surian, A.M. Gurnell. Characterizing geomorphological change to support sustainable river restoration and management.Wiley Interdisciplinary Reviews: Water, 1 (5) (2014), pp. 483-512.
 董哲仁. 水利工程对生态系统的胁迫[J]. 水利水电技术,2003(07):1-5.
DONG Zheren. Ecological stress caused by water conservancy projects [J]. Water conservancy and hydropower technology, 2003(07):1-5.
 孔方斌. 绿色发展的地，莫种“伪生态”苗[N]. 人民日报,2015.12.17.
KONG Fangbin. Green development of the land, not seedlings something Pseudo-ecology[N]. People's Daily, 2015.12.17.
 吴丹子. 城市河道近自然化研究[D]. 北京林业大学,2015.
WU Danzi. Study on near-naturalization of urban river channel [D]. Beijing forestry university, 2015.
 ANONYMO U S, A. Manual of River Restoration Techniques[R], Northamptonshire: The River Restoration Centre. 2013.
 A. Elosegi, J. Díez, M. Mutz. Effects of hydromorphological integrity on biodiversity and functioning of river ecosystems Hydrobiologia [J], 657 (1) (2010), pp. 199-215
 董哲仁. 保护和恢复河流形态多样性[J]. 中国水利,2003(11):53-56+5.
DONG Zhelen. Protection and restoration of river morphological diversity [J]. China water resources, 2003(11):53-56+5.
 于佳琳, 张晋石. 荷兰“还河流以空间”计划的空间策略分析[A]. 中国风景园林学会. 中国风景园林学会2018 年会论文集[C]. 中国风景园林学会: 中国风景园林学会,2018:9.
YU Jialin, ZHANG jinshi. Analysis of spatial strategy in the“ room for the river” in the netherlands[A]. Chinese society of landscape architecture. Proceedings of the 2018 annual meeting of the Chinese society of landscape architecture [C]. Chinese society of landscape architecture: Chinese society of landscape architecture,2018:9.
 S.J. Clarke, L. Bruce-Burgess, G. Wharton. Linking form and function: Towards an eco-hydromorphic approach to sustainable river restoration [C]. Aquatic Conservation: Marine & Freshwater Ecosystems, 13 (5) (2003), pp. 439-450.
 A.M. Gurnell, A. Lee, C. Souch. Urban rivers: Hydrology, geomorphology, ecology and opportunities for change Geography Compass [J], 1 (5) (2007), pp. 1118-1137.