Ecological Landscape Design of Urban Rivers with emphasis on Run - Off Water Control ( Case study: Ziyarat Gorgan river )

Introduction

Urbanization has made fundamental changes on the earth, air, energy resources and urban population that have had huge ecological consequences for urban habitats, including urban rivers. Rivers are the vital and supportive network of urban environment. And urban rivers can be shelters with special ecological value which is reduced in urban landscape. Excessive exploitation of natural resources than the environment capacity generates waste products that have gradually disrupted life in urban areas.
Corridors are the components of the landscape structure in the structure of landscape ecology and rivers are considered as one of the most important natural corridors in landscape structure. According to Forman and Godron theories the rivers corridors are classified to three parts such as, the channel river bank, floodplain and hill slop.
Ecologists believe that, ecosystem services provided through green infrastructure, can provide healthy environment and physical and mental health for residents, a healthy environment can improve social and economic benefits and has an important role in various cities of the world, for instance, a landscape which had been neglected in River Mother in (Qian'an City, Hebei Province, China) was rehabilitated and designed based on landscape ecology approaches and users are considered at all stages of the process, and ecological solutions were presented for rehabilitation and improvement of water quality including, municipal wastewater management system to separate urban waste water and surface water, the strategy of flexible and green river, conversation of river natural ecosystem, using native vegetation and reducing maintenance costs and eventually, creating greenway with sidewalks and cycling line.

Matherials & Methods

The area under study in this research is Gorgan city in the western part of Golestan province. The city is located in the range of latitude and longitude (36.83 ° North 54.48 ° East) on the northern slopes of Alborz mountain. This region is structurally composed of three zones including, plain, piedmont and mountainous region that the city is built in the piedmont region, the most striking landscape structural elements in Gorgan are Alborz Mountains and rainforest located in the southern region of the city.
To perform this study first using the library study the data are collected, analyzed and addressed to formulate the principles and framework. The source of the articles and information was the scientific source of ELSEVERE and SPRINGER database. After review of the literature and analysis and evaluation of the area the method that was used in this thesis is formed by combining several methods based on ecological landscape design.
This research is has been studied in three scales, the large (studying the river from Ziarat to Gharehsou basin), medium (inside the city) and micro (the area developing in the southeast of the area between Ghaleh Hassan and Seyed Masood Bridge) scales. In this study. Accordingly among the ideas of theorists Mac Harg and Ying theories are selected and their methods are applied for the analysis of the river structure in basin and urban scale. Finally the strategy was developed in the context of ecological landscape design in urban rivers and design solutions were provided for micro-scale (urban area). The stages of this study are summarized as follows:
1. Analyzing Ziarat River at large scale based on Mac Harg model
2. Mapping the topography and geographical location of Ziarat River basin and deriving the layers by GIS software
3. Identifying landscape structural elements in Gorgan city according to Ying model (middle scale and the whole city)
4. Land use mapping and extracting desired layer (ecological, hydrological and topographical, urban construction, human activity)
5. Synthesis mapping of overlaying layers in large-scale (river morphology and flooding)
6. Synthesis mapping of overlaying layers in urban scale (possibilities and limitations)
7. Strategies and actions in the ecological design landscape in Gorgan
8. Ideas and solutions (ecological rehabilitation of the river landscape with sustainable urban drainage systems and floodplains management in the urban environment)
First by overlapping the layers the knowledge about Ziarat River was obtained at large-scale. Ziarat River is located is among steep rivers that can be divided into four areas in terms of organization and preservation project. In this map four important zones (catchment (1), Naharkhoran (2), urban (3) and agriculture (4)) were identified and characterized based on overlaying layers in large-scale and middle-scale (urban) and field check of checking the status in a table of strategies and actions in the context of ecological landscape design of an urban river in river management, flood control and needs of users in these four areas. Finally the ecological landscape design of urban river are used from the two approaches of sustainable urban drainage systems (SUDS) and River Buffer Parks(RBPs) in micro scale as a method to improve the ecological structures of urban rivers, control flood and surface runoff in Gorgan.

Discussion of Results & Conclusions

The world's increased population followed by urbanization and irregular urban development has led to imbalanced presence of nature in cities which has led to serious environmental problems including the disruption of the ecological structure of rivers and increased surface runoff and flood in the city. This has attracted the attention of planners and designers to find solutions and approaches to improve situation. Among these design approaches the urban landscape ecological infrastructures such as urban rivers is among the approaches considered by ecologists, planners and urban designers Studies conducted in this study suggest that based on the purposes of river management and flood control of Ziarat River in Gorgan, it is necessary to analyze them based on two scales of Ziarat River catchment (mountains in which the river originates and heads Gharehsou River) and urban scale (Seyed Masood Bridge to the beginning of the agricultural downstream lands) in which Mac Harg (large scale) and Ying (urban scale) methods are used.
The results show that based on Mac Harg and Ying methods at large and middle scales the following cases should be considered:
Establishing integrity in ecological infrastructure (green) through the integration of the riverside vegetation and upstream forests, creating integrity in hydrologic infrastructure (water) through the integration of the urban and river drainage channels and finally overlaying two green and hydrologic infrastructures to control surface runoff and flood in urban area and river.
As a result the initial strategies and initiatives were developed in four areas based on which strategies for planning and environmental design were presented at the micro scale. According to the strategy and actions within the urban framework two essential solutions are considered for urban river ecological design and flood control including: management of floodplains using SUDS and RBPs and applying collection and transportation of water, water retention and distribution of water by recycling it.
According to micro-scale studies developing area in the southeast of the region between Ghaleh Hassan and Seyed Masood Bridge) it was found that the river is too narrow in Ghaleh Hassan and is not capable of retaining the flow of 5 years, therefore, to reduce the damage caused by floods when it rains and there is severe flood, a diversion track is built where the Ziarat and Alangdaerh rivers meet.
The RBP is planned at the beginning of Ziarat river to the urban area after Seyed Masood Bridge because of the open space and ideal conditions for the implementation and then to control the runoff from rainfall due to the slope of the area, four sites are designed to create the retention ponds and storm water treatment to prevent surface runoff flowing into the city. Also the bioswale is considered to maintain and increase water permeability and lead it to the detour and the city in areas where the slope decreases and water accumulation is likely. Such strategy and framework can help to control surface runoff, rehabilitate river and restore these corridors to their natural structure.