Integrated Water Environment Treatment

Mountainous Sponge City and Three Gorges Reservoir Region

Xiaoling Lei, Bo Lu

• Publisher: CRC Press
• Year: 2021
• Print ISBN:
  9780367674106
  9780367629434
• Edition: 1
• eBook ISBN:
  9781000300246
• Topic: Technology & Engineering
• Subtopic: Business General
• Index: Technology & Engineering

With the rapid development of Chinese urbanization in the 21st century, "urban diseases" become more serious, mainly manifested in water environmental pollution, urban flooding, water shortage, and deterioration of water ecology. It is necessary to establish a modern rainwater management system, scientifically solve the problem of excess urban rainwater and to improve water environment quality. Improvement of water environment quality is conducive to the ecological function of a sponge city. Sponge city construction has contributed to control non-point source pollution. Sponge systems cause the stagnation and purification of rainwater runoff, which is an important guarantee for water environment quality. This monograph summarizes theories and practices of the integrated water environment treatment in Chongqing, a typical representative mountainous city in the Three Gorges Reservoir Region. Based on the mountainous terrain and unique water environment characteristics in the Three Gorges Reservoir Region, the monograph analyzes measures and difficulties in the basin water environment integrated treatment. Moreover, the monograph makes suggestions for risk management amid drainage systems during the COVID-19 epidemic.

Chapter 1

Introduction

1.1 Overview of integrated water environment treatment

With the rapid development of industrialization and urbanization, the water pollution control and water environment treatment not only gradually become major issues of global concern but also are major constraints to the healthy, rapid and sustainable economic and social development of China. The imperfect environmental infrastructure, incompletely effective treatment of urban domestic pollutants, improvement-needed industrial pollution treatment and gaps in agricultural pollution control lead to the poor water quality, water eutrophication, and even black and odorous water or water quality function decline of some water bodies. The current water environment is not optimistic. We are still struggling to cope with the water resource scarcity problem and ecological destruction phenomenon that affect the human life and harm the human health. The water environment treatment mainly starts from the following five aspects:

1. Promote agricultural modernization and reduce agricultural pollution. Accelerate the agricultural development mode and actively develop agricultural circular economy to develop the green agriculture.
2. Improve the urban infrastructure and reduce the domestic pollution. With the increasing consumption of urban domestic water and discharge of domestic sewage due to the increased urban population density, the urban drainage pipes, pipe networks and domestic sewage plants shall be constructed and optimized synchronously to continuously improve the water environment.
3. Realize wastewater recycling and reduce industrial pollution. The industrial wastewater discharge keeps increasing with the development of economy. The government shall tighten its grip on the industrial wastewater to strictly prohibit the excessive sewage discharge or the discharge of sewage not meeting the treatment standard, so as to realize the transformation of wastewater resource and increase the utilization rate of water resource.
4. Improve the environmental monitoring technology level and enhance the pollution accident response capacity. Improve the technical equipment at basic-level environmental monitoring stations to enhance the pollution accident response capacity as well as the prediction and early warning abilities, monitor the dynamic changes of pollution sources and increase the monitoring frequency to reduce the sampling error, so as to timely reflect the pollution discharge situation and enhance the environmental management capability.
5. Promote the construction of sponge city. The purpose of sponge city construction is to deal with the relation between urban construction and protection of water resources and ecological environment, which reflects an upgraded understanding of the urban concept and the urban water demand. The large-scale and rapid urbanization process changes the underlying conditions and even the landforms and source water system, thereby changing the natural hydrological characteristics, such as the original evaporation, infiltration, slope runoff generation and convergence. Subsequently, the sharply reduced urban detention storage capacity will lead to a series of problems, such as the loss of stormwater resources, increase of runoff pollution and frequent waterlogging. The construction of sponge city is adopted with corresponding technical measures for the “infiltration, retention, storage, purification, utilization and discharge”, focusing on improving the urban water ecological environment and building a benign water circulation system to make the city greener, more ecological and livable. The stormwater runoff control is an important content in the construction of sponge city, usually realized by building storage ponds by means of natural water, multi-functional water storage and artificial regulation. Through stormwater retention, storage and purification, the sponge city ecological engineering can increase the water flow and environmental capacity, help the non-point source pollution control and prevent black and odorous water occurrence, which is an important guarantee for the long-term clear water.

1.2 Necessity of integrated water environment treatment

1.2.1 Current situation of water environment

After the water impoundment in the Three Gorges Reservoir Region, the pollution range further expands due to the slower flow velocity in the Reservoir Region and tributaries. Due to combined effects of the flow velocity, temperature and pollutant discharge, the eutrophication of some tributaries in the Three Gorges Reservoir Region is getting severer.

Domestic sewage is one of the major water pollution sources of the Three Gorges Reservoir Region. Although urban domestic sewage treatment facilities in the Reservoir Region have been gradually built, part of the sewage is still discharged into water bodies due to the imperfect secondary and tertiary sewage collection networks and incomplete separation of rain from sewage.

One of the major causes of water environment pollution in the Three Gorges Reservoir Region is the non-standard vessel sewage treatment and discharge to the Yangtze River.

Inadequate water self-purification capacity is one of the main causes of water environment pollution in the Three Gorges Reservoir Region. Considering the weak water environment self-purification capacity and very high total discharge of pollutants in the Three Gorges Reservoir Region, it is difficult for the accumulated pollutants to be degraded merely by river runoff.

In general, since the construction of the Three Gorges Project, China has always attached great importance to the environmental and ecological protection and construction in the Reservoir Region. Authorities concerned and all departments of the Reservoir Region have increased input and strengthened the management and control, making remarkable results in the water pollution control in the Reservoir Region. The water environment in the Three Gorges Reservoir Region is being improved gradually.

1.2.2 Hazards of water environment pollution

Water environment pollution reduces the water quality of water resources in China and affects the sustainable economic development, and also directly relates to the drinking water safety, endangering the public health and life safety.

Polluted water can directly or indirectly affect the human health. Pathogenic bacteria in dirty water can invade the human body and cause diseases, such as schistosomiasis and leptospirosis, while physical and chemical pollution may cause irreversible impacts on human genetic material.

As for agriculture and fishery, the irrigation of farmland directly with sewage containing toxic and harmful substances will pollute the farmland soil, destroy the original good soil structure, reduce the crop quality and yield and eventually lead to crop failure. Especially in arid and semi-arid areas, the sewage irrigation may increase the crop yield in the short term, but toxic substances will accumulate in vegetables and grains, threatening the human life. Besides, water pollution may lead to a sharp decline in the quantities or even extinction of fish and aquatic life in the water. Meanwhile, water pollution will also reduce the output of freshwater fishery and mariculture.

As for industrial production, water pollution may increase the industrial water consumption, resulting in increased costs. As for edible industrial water, the process inspections become more rigorous, causing a series of consequences, such as reduction of industrial production capacity and decline in output, thus affecting the normal growth of enterprises.

As for the water eutrophication, the discharge of nitrogen, phosphorus, potassium and elements leads to a sharp increase in organic content in water, providing favorable conditions for the survival of algae. The sharply increased algae cover the original clean water surface and prevent oxygen in the air from dissolving in water. Consequently, the oxygen content of water drops sharply, resulting in the death of aquatic life. Due to relatively high chemical oxygen demand (COD) of main pollutants and content of nitrogen, phosphorus and other nutrients in sewage, the eutrophication may also occur in the surface water of lakes and seas in varying degrees.

1.2.3 Development prospect of integrated treatment

With the accelerated urbanization and increasing urban population of China, the sewage discharge and water environment pollution have also increased sharply. The integrated treatment of sewage in the water environment is urgently needed, which shall keep pace with the times to improve the environment and reduce the waste of water resources. Besides, the scientific solution to integrated sewage treatment is also an important part for realizing social sustainable development, lucid waters and lush mountains.

The traditional water environment treatment usually adopts the unitary mode of “end treatment” of the river treatment. The “end treatment” is a short-term solution that “only addresses the symptoms not the causes”. The scale of investment in an end treatment project is small, generally less than nine figures, not enough for the overall purpose. The environmental goals have been overfulfilled in the early stage, but the overall water environment in each basin and urban river has not been obviously improved. After issuance of the “Ten Measures for Water Pollution Control” and other planning, the idea has been shifted from the traditional way of “end treatment” to the whole-process water pollution control mode of “pollutant discharge reduction at the source, pollutant blocking in the process and end treatment”, and the “systematic mode” featured with basin environmental units consisting of pipe networks, sewage treatment plants and rivers has also been established gradually for the environmental governance projects.

1.3 Typical mountainous city in Three Gorges Reservoir Region

1.3.1 Three Gorges Reservoir Region

1.3.1.1 Concept of Three Gorges Reservoir Region

Due to the construction of the Three Gorges Hydropower Station in Yichang, Hubei Province at the end of the Yangtze River Three Gorges, some cities and towns would be submerged due to the rising water level in areas upstream of the reservoir, so the mass migration was needed. Under such background, the Three Gorges Reservoir Region was formed, including 20 districts and counties needing mass migration due to the rising water level caused by the Three Gorges Project construction. With geographical coordinates of 106°20′–110°30′ E and 29°–31°50′ N, the Three Gorges Reservoir Region covers Yichang County, Xingshan County and Zigui County under the jurisdiction of Hubei Province; Badong County under the jurisdiction of Enshi Prefecture; Wushan County, Wuxi County, Fengjie County, Yunyang County, Kaixian County, Wanzhou District, Zhongxian County, Fuling District, Fengdu County, Wulong County, Shizhu County, Changshou County, Yubei District, Baxian County, Jiangjin City and Chongqing main urban area (including Yuzhong District, Nan’an District, Shapingba District, Dadukou District, Jiulongpo District and Jiangbei District) under the jurisdiction of Chongqing, including the Yichang–Chongqing watershed area along the Yangtze River, with the submerged land area of about 632 km².

1.3.1.2 Geographic and geomorphic conditions of Three Gorges Reservoir Region

Located at the junction of the middle and lower plains of the Yangtze River, the Three Gorges Reservoir Region covers the low mountain and valley areas of Sichuan and Hubei, East Sichuan paralleled ridge and valley area as well as low mountain and hilly area, with Daba Mountains on the north and Yunnan–Guizhou Plateau on the south. The terrain of China is divided into three levels and the second one mainly includes plateaus and basins. The Three Gorges Reservoir Region is located in the slope area on the second level and forms a great terrain elevation difference with the adjacent Hanjiang Plain on the third level, resulting in the river downcutting, which makes the Reservoir Region form the geomorphic pattern of fractured mountains and rugged terrain full of ravines. Most areas of the Reservoir Region are characterized by high mountains and deep valleys, with the hills and mountains accounting for 95.7% of the total area, among which the mountains account for 74% of the total area, while the flat area accounts only for 4.3% of the total Reservoir Region area.

The Three Gorges Reservoir Region mainly experienced the Jinning movement prior to the Sinian Period, the Yanshan movement at the end of the Jurassic Period and the Himalayan movement at the end of the Tertiary Period. The three tectonic movements formed strong folds and faults in the strata of the Reservoir Region, then the Reservoir Region entered the neotectonic period, characterized by the overall topography uplift. Due to the sea–land changes and water downcutting caused by strong geological movements, unique ravine landforms formed in the Reservoir Region and a relatively independent geographic unit was also formed. The overall terrain gradually slopes downward from the basin edge to the center. The elevation in Fengjie is about 1,000 m and the elevations of towering mountain ridges are usually about 700–800 m, gradually down to gentle hills in Changshou with elevations about 300–500 m. A flat broad valley is formed when the Yangtze River winds in a synclinal valley, and a small gorge is always formed in a cross-cutting and anticlinal section. The high mountains and steep bank slopes on both banks of the Yangtze River as well as the narrow valleys and rapid flow form the famous Three Gorges of Yangtze River.

1.3.1.3 Characteristics of water environment in Three Gorges Reservoir Region

The Three Gorges Reservoir Region in the middle and upper reaches of the Yangtze River is located in a transitional zone between the south temperate zone and the subtropical zone, and has a subtropical monsoon climate, with the annual average precipitation of 1,100–1,200 mm and rainfall evenly distributed. Due to the expanded water area and increased water evaporation after impoundment of the Three Gorges Reservoir, the day-and-night temperature difference in the Reservoir Region is reduced, changing the climatic environment in the Reservoir Region. The natural river channel in the Reservoir Region has become a reservoir, causing significant changes in hydrological characteristics of the main stream and many tributaries of the Yangtze River. The water environment in the Reservoir Region has gradually evolved from the river ecosystem of lotic environment to the lake ecosystem of lentic environment, and the migration and transformation ways and retention time of nitrogen, phosphorus and other nutrients have been changed significantly. As a result, the water eutrophication of tributaries is gradually aggravated, and there are frequent outbreaks of algal blooms in backwater areas of some tributaries. Meanwhile, with the rapid economic development in areas upstream of the Reservoir Region, the pollution load entering the Reservoir Region is constantly increasing and the deterioration trend of water environment in the Three Gorges Reservoir Region is still not relieved.

1. Point source pollution problems.
   The point source pollution mainly includes the pollution of industrial wastewater and urban domestic sewage, which are usually discharged into water bodies through fixed sewage outfalls. As for Chongqing main urban area, the point source pollution mainly has the following characteristics:
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Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Foreword
• Preface
• Abstract
• Acknowledgments
• Authors
• 1 Introduction
• 2 Situation before integrated water environment treatment in Chongqing basin
• 3 Integrated treatment strategy
• 4 Typical measures for integrated treatment
• 5 Practice of source treatment
• 6 Practice of integrated water environment treatment
• 7 Epidemic prevention and control measures for urban drainage systems in mountainous regions
• 8 Results and prospects
• Bibliography
• Index