*2.2.6 Social impact*

The loss of reservoir function, and no other projects to make up for it, may cause serious social problems. For example, if water supply or agricultural irrigation is the main reason for the removal of reservoirs and if the water supply and irrigation needs of residents cannot be effectively solved, serious social problems will arise. In addition, the scour of reservoir area silt may cause the similar problem enters downstream river course along current, silt up downstream channel or channel take water entrance, affect safety of local traffic carriage and production and domestic

use seriously. All these impacts need to be analyzed during the demonstration and planning and design of reservoir removal, and appropriate measures should be taken, such as building alternative projects, dredging river channels, rebuilding or building new water intakes, etc., so as to reduce the adverse impact on society [10].

The right to use the land in the reservoir area and the change of the value of the original lakeside land also belong to the social impact that may be caused by the removal of the reservoir, but compared with the above problems, the social impact of this problem is relatively small.

#### *2.2.7 Economic impact*

In China, the primary consideration of reservoir removal is public safety, followed by economic problems. Economic impact analysis is helpful for reservoir stakeholders and their management agencies to compare and choose dam removal schemes and posttreatment measures and optimize schemes [11]. While not every reservoir to be scrapped will undergo a formal cost-benefit analysis, basic economic assessments are needed.

Generally, the economic impact of reservoir removal is divided into two categories: cost and benefit. Cost is regarded as negative impact and benefit as positive impact. The saving of reservoir operation and maintenance cost is often regarded as the positive impact of removal, while the loss of reservoir social and economic benefits is considered as the negative impact of removal. In principle, economic value assessment can be carried out for all kinds of impacts mentioned above, which can be finally reflected through economic impact. However, it is difficult to accurately define the impact category for a small part of the influences, and quantitative and quantitative assessments are difficult for existing influences. Therefore, at current stage, it is difficult to accurately analyze the economic impact of reservoir removal.

## **3. Decision-making method for reservoir removal**

Although many cases have proved that reservoir removal can play a positive role in ecological environment restoration, due to the limitations of people's cognition of the impact of dam demolition and the complexity and unpredictability of the impact of reservoir removal, we cannot blindly be optimistic about the ecological consequences of dam demolition.

Scientific decision analysis and systematic evaluation of the impact of dam removal should be carried out before dam removal. With the help of science and technology and case data, the feasibility of scrapped schemes will be studied by conducting analysis or comprehensive evaluation on the ecological environment, social economy, dam demolition consequences, and other aspects. General, mature, and simple methods, such as mathematical model, physical model, analogue analysis, and professional judgment, should be used when making decisions.

Due to the unpredictability of social, economic, and ecological environment, it is difficult to comprehensively evaluate the impact of reservoir removal on ecological environment. In addition, multi-criteria system decision-making focuses on reflecting external interference as a whole, and it is difficult to reflect the mechanism of influencing factors on decision-making objectives, and the interaction between influencing factors is not conducive to managers to improve the decisionmaking scheme [12]. In contrast, in-depth study of the sensitivity of a single criterion to a specific pressure response can not only strengthen the comparative study of various schemes but also improve the sensitivity [13]. Therefore, the reservoir removal decision based on a single criterion is highly operable and sensitive.

**131**

*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

port with water flow.

nance costs.

cally reasonable or not.

expressed as follows:

voir can be expressed as follows:

storage function of the reservoir.

**3.1 Economic decision-making methods**

The selection of removal criteria shall reflect the characteristics of reservoir dam. If the reservoir disease risk is serious and the function atrophy, the economic theory can be used to analyze whether it is reasonable to reinforce the reservoir economically. If attention is paid to the impact of changes in the scrapped reservoir flood situation on the flood safety of downstream towns, it is necessary to conduct targeted flood risk analysis of downstream regions and evaluate the impact of river inflow on downstream towns after the scrapped reservoir. Similarly, if serious reservoir siltation is concerned about the sediment transport process after dam removal, a model can be established to simulate the development process of river sediment transport after dam removal and evaluate the impact of sediment trans-

At present, reservoir removal is composed mainly of the small reservoir in China. The social and economic benefits of reservoir, operation and maintenance, risk removal, and reinforcement costs can be measured when making decisions. From the perspective of dam economics, the rationality of risk removal and reinforcement plans and dam removal and reinforcement plans can be evaluated. In addition, some small reservoirs may still play a certain role in the urban flood control system. Although the removal of the reservoir can eliminate the risk of dam break, it will increase the risk of flood downstream if it leaves the regulation and

This method is suitable for reservoirs which lost main function and high mainte-

Peng Hui proposed to establish the evaluation model of dam removal with the help of economic theory and according to the annual economic loss and benefit of the dam [14]. The economic loss and benefit were measured by this model, and the decision was not made from the perspective of reservoir disease risk. Based on its research, this paper proposes the economic decision-making method of reservoir removal. By analyzing the payback period of investment in reservoir restoration project, this method evaluates whether the reservoir restoration project is economi-

The annual cost of reservoir includes daily operation and management costs (Vo), maintenance costs of dam and facilities (Vm), etc. The annual costs of reser-

*C* = *V*<sup>o</sup> + *V*<sup>m</sup> (1)

The annual benefits of the reservoir include the economic benefits from the functions of water supply, irrigation, power generation and shipping (Ve), the social benefits from flood regulation and storage (Vs), the recreational benefits from the reservoir landscape (Vr), etc. The annual income of the reservoir can be

Generally speaking, in the early stage of reservoir operation, only a small amount of cost is needed to meet the needs of operation, maintenance and daily management, during this period, the economic benefits of the reservoir are obvious, and greater social and economic benefits can be obtained. However, with the increase of dam age and the aging of materials and facilities, the cost of operation and maintenance increases. In contrast, long-term operation of the reservoir leads to problems such as deposition, which reduce the social and economic benefits of the reservoir. In a word, the relationship between reservoir cost input and benefit

output varies from time to time with reservoir state and operation age.

#### *Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

*Natural Hazards - Risk, Exposure, Response, and Resilience*

of this problem is relatively small.

*2.2.7 Economic impact*

assessments are needed.

use seriously. All these impacts need to be analyzed during the demonstration and planning and design of reservoir removal, and appropriate measures should be taken, such as building alternative projects, dredging river channels, rebuilding or building new water intakes, etc., so as to reduce the adverse impact on society [10]. The right to use the land in the reservoir area and the change of the value of the original lakeside land also belong to the social impact that may be caused by the removal of the reservoir, but compared with the above problems, the social impact

In China, the primary consideration of reservoir removal is public safety, followed by economic problems. Economic impact analysis is helpful for reservoir stakeholders and their management agencies to compare and choose dam removal schemes and posttreatment measures and optimize schemes [11]. While not every reservoir to be scrapped will undergo a formal cost-benefit analysis, basic economic

Generally, the economic impact of reservoir removal is divided into two categories: cost and benefit. Cost is regarded as negative impact and benefit as positive impact. The saving of reservoir operation and maintenance cost is often regarded as the positive impact of removal, while the loss of reservoir social and economic benefits is considered as the negative impact of removal. In principle, economic value assessment can be carried out for all kinds of impacts mentioned above, which can be finally reflected through economic impact. However, it is difficult to accurately define the impact category for a small part of the influences, and quantitative and quantitative assessments are difficult for existing influences. Therefore, at current stage, it is difficult to accurately analyze the economic impact of reservoir removal.

Although many cases have proved that reservoir removal can play a positive role in ecological environment restoration, due to the limitations of people's cognition of the impact of dam demolition and the complexity and unpredictability of the impact of reservoir removal, we cannot blindly be optimistic about the ecological

Scientific decision analysis and systematic evaluation of the impact of dam removal should be carried out before dam removal. With the help of science and technology and case data, the feasibility of scrapped schemes will be studied by conducting analysis or comprehensive evaluation on the ecological environment, social economy, dam demolition consequences, and other aspects. General, mature, and simple methods, such as mathematical model, physical model, analogue analy-

Due to the unpredictability of social, economic, and ecological environment, it is difficult to comprehensively evaluate the impact of reservoir removal on ecological environment. In addition, multi-criteria system decision-making focuses on reflecting external interference as a whole, and it is difficult to reflect the mechanism of influencing factors on decision-making objectives, and the interaction between influencing factors is not conducive to managers to improve the decisionmaking scheme [12]. In contrast, in-depth study of the sensitivity of a single criterion to a specific pressure response can not only strengthen the comparative study of various schemes but also improve the sensitivity [13]. Therefore, the reservoir removal decision based on a single criterion is highly operable and sensitive.

sis, and professional judgment, should be used when making decisions.

**3. Decision-making method for reservoir removal**

consequences of dam demolition.

**130**

The selection of removal criteria shall reflect the characteristics of reservoir dam. If the reservoir disease risk is serious and the function atrophy, the economic theory can be used to analyze whether it is reasonable to reinforce the reservoir economically. If attention is paid to the impact of changes in the scrapped reservoir flood situation on the flood safety of downstream towns, it is necessary to conduct targeted flood risk analysis of downstream regions and evaluate the impact of river inflow on downstream towns after the scrapped reservoir. Similarly, if serious reservoir siltation is concerned about the sediment transport process after dam removal, a model can be established to simulate the development process of river sediment transport after dam removal and evaluate the impact of sediment transport with water flow.

At present, reservoir removal is composed mainly of the small reservoir in China. The social and economic benefits of reservoir, operation and maintenance, risk removal, and reinforcement costs can be measured when making decisions. From the perspective of dam economics, the rationality of risk removal and reinforcement plans and dam removal and reinforcement plans can be evaluated. In addition, some small reservoirs may still play a certain role in the urban flood control system. Although the removal of the reservoir can eliminate the risk of dam break, it will increase the risk of flood downstream if it leaves the regulation and storage function of the reservoir.

### **3.1 Economic decision-making methods**

This method is suitable for reservoirs which lost main function and high maintenance costs.

Generally speaking, in the early stage of reservoir operation, only a small amount of cost is needed to meet the needs of operation, maintenance and daily management, during this period, the economic benefits of the reservoir are obvious, and greater social and economic benefits can be obtained. However, with the increase of dam age and the aging of materials and facilities, the cost of operation and maintenance increases. In contrast, long-term operation of the reservoir leads to problems such as deposition, which reduce the social and economic benefits of the reservoir. In a word, the relationship between reservoir cost input and benefit output varies from time to time with reservoir state and operation age.

Peng Hui proposed to establish the evaluation model of dam removal with the help of economic theory and according to the annual economic loss and benefit of the dam [14]. The economic loss and benefit were measured by this model, and the decision was not made from the perspective of reservoir disease risk. Based on its research, this paper proposes the economic decision-making method of reservoir removal. By analyzing the payback period of investment in reservoir restoration project, this method evaluates whether the reservoir restoration project is economically reasonable or not.

The annual cost of reservoir includes daily operation and management costs (Vo), maintenance costs of dam and facilities (Vm), etc. The annual costs of reservoir can be expressed as follows:

$$\mathbf{C} = \mathbf{V\_o} + \mathbf{V\_m} \tag{1}$$

The annual benefits of the reservoir include the economic benefits from the functions of water supply, irrigation, power generation and shipping (Ve), the social benefits from flood regulation and storage (Vs), the recreational benefits from the reservoir landscape (Vr), etc. The annual income of the reservoir can be expressed as follows:

$$B = V\_{\mathbf{c}} + V\_{\mathbf{s}} + V\_{\mathbf{r}} \tag{2}$$

According to the annual cost (Eq. (1)) and income (Eq. (2)), the annual cost-benefit map of the reservoir is drawn, and the change process of the cost and benefit of the reservoir is obtained. Generally speaking, the input cost of the reservoir increases gradually with the operation time, while the benefit of the reservoir is on the contrary, decreasing year by year with time. Regression analysis is carried out on multi-year data to fit the time functions c(t) and b(t) of annual cost and benefit, as shown in **Figure 1**.

With the increase of operation time, the annual input cost increases. When the reservoir is considered to make decision of retirement, the annual input cost shall be the historical maximum, denoted as the t1 in that year and the input cost as C1. Assuming that the benefits and costs only change over time, the time function of the benefit and cost can be estimated according to the actual cost and benefit function, remember c′(t) and b′(t). When the cost of the c′(t) reservoir in the t t2 year reaches C1 again, it will be deemed that the reservoir state returns to the initial decision state, and the interval from t1 to the t2 is the service life of the reservoir restoration measures. Within the interval of [t1, t2], the multi-year net income A (i.e., the shaded area in **Figure 2**) and the multi-year average net income R can be calculated as follows.

$$\mathbf{A} = \int\_{t\_1}^{t\_2} \left[ b'(t) - c'(t) \right] dt \tag{3}$$

$$\mathbf{R} = \frac{\mathbf{A}}{(\mathbf{t}\_2 - \mathbf{t}\_1)} \tag{4}$$

At t1 time point, one-off investment cost for consolidation F was input, which needs to be compensated by net income A obtained over many years during the period of time Δt = t2−t1. According to the payback period method of investment, the payback period of reinforcement investment F is set as T.

$$\mathbf{F} \begin{pmatrix} \mathbf{1} + i \end{pmatrix}^{\mathsf{T}} = \mathbf{R} \begin{pmatrix} \mathbf{1} + i \end{pmatrix}^{\mathsf{T} - \mathsf{I}} + \mathbf{R} \begin{pmatrix} \mathbf{1} + i \end{pmatrix}^{\mathsf{T} - \mathsf{I}} + \cdots \ {}\_{i}\mathsf{R} (\mathsf{I} + i) + \mathsf{R} \tag{5}$$

$$\mathbf{T} = \frac{\lg \mathbf{R} - \lg(\mathbf{R} - i\mathbf{F})}{\lg(\mathbf{1} + i)} \tag{6}$$

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*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

economically feasible

**Figure 2.**

**3.2 Consequence decision method**

ing the decision-making scheme.

economy, society, and environment.

In the equations above, *i* stands for social discount rate.

*Time t2 calculation diagram of occurrence of new disease risks of the dam after reinforcement.*

model, the calculation of flood loss, and the program assessment.

scheme based on the current flood control of reservoir.

affected by the flood and the inundation range.

The extended service life of the reinforcement project is less than the recovery life of the project cost, which indicates the project is economic irrationality and disposal can be considered; in the same way, if T≤ΔT, indicates the project is

Flood impact is an important evaluation content of reservoir removal decision under the urban background, and simulating the impact of reservoir removal on flood situation is conducive to proposing targeted reduction measures and improv-

The assessment framework for the consequences of reservoir removal covers six steps, namely, the formulation of a plan, the establishment of an assessment index system, the determination of flood loss indicators, the establishment of a flood risk

At least two schemes are selected for evaluation, and the evaluation results are compared with each other. Two schemes of reservoir current flood control and reservoir removal are usually used to evaluate the flood changes of reservoir removal

The evaluation index system criterion layer constructed in this paper consists of

Flood economic losses are divided into direct economic losses and indirect economic losses. Direct economic loss refers to the total loss of physical damage caused by flood, usually including loss of farmland production, damage to housing and facilities, and financial losses [15]. Indirect economic losses are considered to be other losses caused or implicated by direct economic losses, specifically, the stoppage and production reduction losses caused by flood disaster, the economic losses caused by the increase of intermediate investment backlog, and the loss of investment premium [16]. The inundation of downstream cities caused by the flood will affect human normal activities to varying degrees, which is the embodiment of the social impact of the flood. The degree of the impact can be measured by the number of people

The impact of flood on urban environment is divided into landscape damage and soil erosion. On the one hand, the water will carry the bare soil in the erosion

**Figure 1.** *Time function diagram of annual cost and annual income of a reservoir.*

*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

*Natural Hazards - Risk, Exposure, Response, and Resilience*

A = ∫

R = \_\_\_\_\_\_ <sup>A</sup>

the payback period of reinforcement investment F is set as T.

<sup>T</sup> <sup>=</sup> lgR <sup>−</sup> lg(R <sup>−</sup> *<sup>i</sup>*F)

*Time function diagram of annual cost and annual income of a reservoir.*

*B* = *V*<sup>e</sup> + *V*<sup>s</sup> + *V*<sup>r</sup> (2)

According to the annual cost (Eq. (1)) and income (Eq. (2)), the annual cost-benefit map of the reservoir is drawn, and the change process of the cost and benefit of the reservoir is obtained. Generally speaking, the input cost of the reservoir increases gradually with the operation time, while the benefit of the reservoir is on the contrary, decreasing year by year with time. Regression analysis is carried out on multi-year data to fit the time functions c(t) and b(t) of annual cost and benefit, as shown in **Figure 1**. With the increase of operation time, the annual input cost increases. When the reservoir is considered to make decision of retirement, the annual input cost shall be the historical maximum, denoted as the t1 in that year and the input cost as C1. Assuming that the benefits and costs only change over time, the time function of the benefit and cost can be estimated according to the actual cost and benefit function, remember c′(t) and b′(t). When the cost of the c′(t) reservoir in the t t2 year reaches C1 again, it will be deemed that the reservoir state returns to the initial decision state, and the interval from t1 to the t2 is the service life of the reservoir restoration measures. Within the interval of [t1, t2], the multi-year net income A (i.e., the shaded area in **Figure 2**) and the multi-year average net income R can be calculated as follows.

> t1 t2 [*b*′

(*t*) − *c*′

At t1 time point, one-off investment cost for consolidation F was input, which needs to be compensated by net income A obtained over many years during the period of time Δt = t2−t1. According to the payback period method of investment,

F(1 + *i*)<sup>T</sup> = R(1 + *i*)T−1 + R(1 + *i*)T−2 + ⋯ +R(1 + *i*) + R (5)

\_\_\_\_\_\_\_\_\_\_\_\_

(*t*)]d*t* (3)

(t2 <sup>−</sup> t1) (4)

lg(1 <sup>+</sup> *<sup>i</sup>*) (6)

**132**

**Figure 1.**

**Figure 2.** *Time t2 calculation diagram of occurrence of new disease risks of the dam after reinforcement.*

In the equations above, *i* stands for social discount rate.

The extended service life of the reinforcement project is less than the recovery life of the project cost, which indicates the project is economic irrationality and disposal can be considered; in the same way, if T≤ΔT, indicates the project is economically feasible

#### **3.2 Consequence decision method**

Flood impact is an important evaluation content of reservoir removal decision under the urban background, and simulating the impact of reservoir removal on flood situation is conducive to proposing targeted reduction measures and improving the decision-making scheme.

The assessment framework for the consequences of reservoir removal covers six steps, namely, the formulation of a plan, the establishment of an assessment index system, the determination of flood loss indicators, the establishment of a flood risk model, the calculation of flood loss, and the program assessment.

At least two schemes are selected for evaluation, and the evaluation results are compared with each other. Two schemes of reservoir current flood control and reservoir removal are usually used to evaluate the flood changes of reservoir removal scheme based on the current flood control of reservoir.

The evaluation index system criterion layer constructed in this paper consists of economy, society, and environment.

Flood economic losses are divided into direct economic losses and indirect economic losses. Direct economic loss refers to the total loss of physical damage caused by flood, usually including loss of farmland production, damage to housing and facilities, and financial losses [15]. Indirect economic losses are considered to be other losses caused or implicated by direct economic losses, specifically, the stoppage and production reduction losses caused by flood disaster, the economic losses caused by the increase of intermediate investment backlog, and the loss of investment premium [16].

The inundation of downstream cities caused by the flood will affect human normal activities to varying degrees, which is the embodiment of the social impact of the flood. The degree of the impact can be measured by the number of people affected by the flood and the inundation range.

The impact of flood on urban environment is divided into landscape damage and soil erosion. On the one hand, the water will carry the bare soil in the erosion area, causing a large amount of soil loss; on the other hand, the vegetation of flood areas is damaged by floods, causing losses to the urban landscape.

Take Heiwa reservoir as an example. Heiwa reservoir, located in the southwest of Chuzhou city, Anhui province, was spontaneously built and operated by villagers. It was completed and started operation in 1977 with a capacity of 560,000 m3 . The maximum height of the dam is 12.2 m. With the advancement of urbanization, the farmland in the lower reaches turned into urban area. The spillway goes straight through the new campus of Chuzhou College, which is less than 2 miles away. Buildings and population are numerous and dense, as shown in **Figure 3**. The reservoir has been identified as dangerously weak, due to poor construction quality and capacity of management, which makes downstream region a high-risk zone. Besides that, the reservoir's main function has changes from agricultural irrigation as designed to urban flood control.

In general, Heiwa reservoir, which has lost design function, needs continuously huge investment in improving dam state to prevent dam break. It is a typical case for dam removal discussion.

The lower reaches of the reservoir pass through the main urban area of Chuzhou city from the southwest to the northeast (see **Table 1** for details). Along the way, residential areas, schools, medical care, administrative institutions, and commercial shops are distributed. As shown in **Figure 4**, in case of dam break danger, huge economic loss and significant social impact will be caused.

To improve the city's flood control system, the Chuzhou water conservancy department has established an urban flood control plan by intercepting the flood in the western mountainous area of Chuzhou and protecting the central urban area and the industrial zone between the Qingliu River west and the Beijing-Shanghai railway. The key point of this plan is to discharge the reservoir water from the southwest hilly region into the Qingliu River via the newly built flood interception ditch, around the west side of the main urban area to the south side (see **Figure 4**). The western flood interception ditch intersects the reservoir channel at point B. If the flood interception ditch is completed, the flood discharge pressure of river section will be relieved. The designed maximum discharge at point B of the flood interception ditch is 50 m3 /s. There is a flood gap on the left bank of point B, and the flood exceeding the designed flow rate will be discharged into the Qingliu River by the spillway at a maximum flow rate of 8 m3 /s through the urban river channel.

**135**

as below.

*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

**No. River section River section information** 1 The reservoir—A The reservoir spillway

6 E—Qingliu River Joining Qingliu River

*Downstream channel information of reservoir.*

2 A—B South campus of Chuzhou University 3 B—C Residential landscape section 4 C—D Underground drainage ditch section

channel section

5 D—E Joining the drainage flow of Yujiawa reservoir and flowing into the open

*3.2.1 Evaluation scheme*

**Figure 4.**

**Table 1.**

In this section, three evaluation schemes are proposed for Heiwa reservoir under the condition that it encounters a flood once every 50 years: (1) flood regulation scheme for the reservoir. Under the current situation of Heiwa reservoir, the peak

/s; (2) the

/s, and

discharge from the reservoir to the discharge from the reservoir is 34.1 m3

*Regional distribution and river channel diagram of the lower reaches of the reservoir.*

into Qingliu River. The flow data of each scheme are shown in **Table 2**.

scheme of reservoir removal, and the peak inflow of the reservoir, is 54.9 m3

point D of the river meets the incoming water from Yujiawa reservoir; and (3) the reservoir was scrapped, and the city's flood control system was improved. The flood interception ditch shared the discharge of some of the water from Heiwa reservoir and Yujiawa reservoir, and the excess discharge still flowed from the river section

Based on the flood consequence criteria, a two-dimensional hydrodynamic mathematical model was established to simulate the flood evolution process, result

Without the effective urban flood control planning, the city's flood discharge capacity of the urban channel system is insufficient, and the city was seriously affected by the flood return period of 50 years. As shown in Figure **Figure 5**. Especially, due to confluence of Heiwa reservoir flood drainage and Yujiawa reservoir flow at the open channel of Huifeng Road, both sides of the road were flooded; the average water depth was about 0.25 m, maximum depth of 1.72 m; and Chuzhou Development Zone was affected seriously, with submerged depth of the water at about 0.7 m. The low-lying depression area on the east side of Beijing-Shanghai

**Figure 3.** *Satellite map of Heiwa reservoir location.*

*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*


#### **Table 1.**

*Natural Hazards - Risk, Exposure, Response, and Resilience*

as designed to urban flood control.

for dam removal discussion.

area, causing a large amount of soil loss; on the other hand, the vegetation of flood

Take Heiwa reservoir as an example. Heiwa reservoir, located in the southwest of Chuzhou city, Anhui province, was spontaneously built and operated by villagers. It was completed and started operation in 1977 with a capacity of 560,000 m3

In general, Heiwa reservoir, which has lost design function, needs continuously huge investment in improving dam state to prevent dam break. It is a typical case

The lower reaches of the reservoir pass through the main urban area of Chuzhou city from the southwest to the northeast (see **Table 1** for details). Along the way, residential areas, schools, medical care, administrative institutions, and commercial shops are distributed. As shown in **Figure 4**, in case of dam break danger, huge

To improve the city's flood control system, the Chuzhou water conservancy department has established an urban flood control plan by intercepting the flood in the western mountainous area of Chuzhou and protecting the central urban area and the industrial zone between the Qingliu River west and the Beijing-Shanghai railway. The key point of this plan is to discharge the reservoir water from the southwest hilly region into the Qingliu River via the newly built flood interception ditch, around the west side of the main urban area to the south side (see **Figure 4**). The western flood interception ditch intersects the reservoir channel at point B. If the flood interception ditch is completed, the flood discharge pressure of river section will be relieved. The designed maximum discharge at point

of point B, and the flood exceeding the designed flow rate will be discharged

into the Qingliu River by the spillway at a maximum flow rate of 8 m3

/s. There is a flood gap on the left bank

/s through

The maximum height of the dam is 12.2 m. With the advancement of urbanization, the farmland in the lower reaches turned into urban area. The spillway goes straight through the new campus of Chuzhou College, which is less than 2 miles away. Buildings and population are numerous and dense, as shown in **Figure 3**. The reservoir has been identified as dangerously weak, due to poor construction quality and capacity of management, which makes downstream region a high-risk zone. Besides that, the reservoir's main function has changes from agricultural irrigation

.

areas is damaged by floods, causing losses to the urban landscape.

economic loss and significant social impact will be caused.

B of the flood interception ditch is 50 m3

the urban river channel.

**134**

**Figure 3.**

*Satellite map of Heiwa reservoir location.*

*Downstream channel information of reservoir.*

**Figure 4.** *Regional distribution and river channel diagram of the lower reaches of the reservoir.*

#### *3.2.1 Evaluation scheme*

In this section, three evaluation schemes are proposed for Heiwa reservoir under the condition that it encounters a flood once every 50 years: (1) flood regulation scheme for the reservoir. Under the current situation of Heiwa reservoir, the peak discharge from the reservoir to the discharge from the reservoir is 34.1 m3 /s; (2) the scheme of reservoir removal, and the peak inflow of the reservoir, is 54.9 m3 /s, and point D of the river meets the incoming water from Yujiawa reservoir; and (3) the reservoir was scrapped, and the city's flood control system was improved. The flood interception ditch shared the discharge of some of the water from Heiwa reservoir and Yujiawa reservoir, and the excess discharge still flowed from the river section into Qingliu River. The flow data of each scheme are shown in **Table 2**.

Based on the flood consequence criteria, a two-dimensional hydrodynamic mathematical model was established to simulate the flood evolution process, result as below.

Without the effective urban flood control planning, the city's flood discharge capacity of the urban channel system is insufficient, and the city was seriously affected by the flood return period of 50 years. As shown in Figure **Figure 5**. Especially, due to confluence of Heiwa reservoir flood drainage and Yujiawa reservoir flow at the open channel of Huifeng Road, both sides of the road were flooded; the average water depth was about 0.25 m, maximum depth of 1.72 m; and Chuzhou Development Zone was affected seriously, with submerged depth of the water at about 0.7 m. The low-lying depression area on the east side of Beijing-Shanghai


**Table 2.**

*Flow point data of flood simulation scheme.*

railway was the most seriously flooded with a maximum depth of 3.77 m. This area is located outside the main urban area of Chuzhou and has a low population density.

Under the scheme of reservoir removal, the discharge rate of the lower discharge increases from 34.1 to 54.9 m3 /s, and the flood discharge pressure of the drainage ditch system increases; the average submerged depth is about 0.84 m, and the maximum submerged depth is 4.02 m. The submerged range increases from 1.63 to 1.83 km2 ; the newly added flooded area is mainly located in the housing area downstream of the dam site, as shown in **Figure 6**.

Under the new flood control system, the flooded area and water depth of the reservoir scrapping scheme are significantly less than that of the reservoir flood control before the implementation of the plan, as shown in **Figure 7** for details. After the implementation of flood control planning, the Xipie flood interception ditch can accommodate the flow rate of 21.2 m3 /s, and the flow rate of the flood flowing into the urban river course is 33.7 m3 /s, slightly lower than the regulated flood volume of the reservoir 34.1 m3 /s. Although the flow rate is similar, the submerged area of the former is only 35% of that of the latter. The inundation area of the downstream risk area is 0.58 km2 , mainly concentrated in underground drainage ditch CD river section. The maximum depth was reduced from 4.02 to 2.66 m; the water depth of the Beijing-Shanghai railway decreased from 1.72 to 0.30 m.

The simulation results show that, after the removal of Heiwa reservoir, the reservoir completely loses the capacity of regulating and storing. Although the discharge volume under the channel will increase by 56%, the inundation range and average inundation depth will increase by only 11 and 12%, which is relatively small compared with the flood control scheme of the reservoir. This is because the downstream

**Figure 5.** *Flood depth of the lower reaches of the reservoir flood control scheme in case of a flood once every 50 years.*

**137**

by 69%.

**Figure 7.**

*50 years.*

**Figure 6.**

*3.2.2. Flood impact assessment*

*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

discharge volume of the reservoir far exceeds the flood discharge capacity of the downstream urban channel system. In other words, the flood control effect of the reservoir is not significant, and even if the reservoir is removed, it will not significantly increase the inundation range and water depth. In comparison, although the reservoir has been scrapped and lost its flood control capacity, the flooded area of the lower reaches of the reservoir has been significantly reduced after combining with the urban flood control planning. Compared with the reservoir scrapped plan before the implementation of the planning, the flooded area of the latter has been reduced

*Flood depth in the lower reaches of the joint flood control planning scheme for flood once encountered every* 

*Flood depth downstream of reservoir abandonment scheme in case of a flood once every 50 years.*

According to the characteristics of the calculation region and the loss data of agricultural and commercial assets in typical flood disasters in history, the loss rate was determined, and the corresponding relationship between the loss rate and

According to the flood analysis and results of three schemes, combined with the regional feature distribution, to measure socio-economic indicators including

water depth was finally determined, as shown in **Table 3**.

*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

*Natural Hazards - Risk, Exposure, Response, and Resilience*

downstream of the dam site, as shown in **Figure 6**.

ditch can accommodate the flow rate of 21.2 m3

flowing into the urban river course is 33.7 m3

flood volume of the reservoir 34.1 m3

the downstream risk area is 0.58 km2

increases from 34.1 to 54.9 m3

*Flow point data of flood simulation scheme.*

to 1.83 km2

**Table 2.**

**Scheme number**

**136**

**Figure 5.**

*Flood depth of the lower reaches of the reservoir flood control scheme in case of a flood once every 50 years.*

railway was the most seriously flooded with a maximum depth of 3.77 m. This area is located outside the main urban area of Chuzhou and has a low population density. Under the scheme of reservoir removal, the discharge rate of the lower discharge

1 Reservoir flood routing 34.1 34.1 71.6 2 Reservoir removal 54.9 54.9 92.4 3 Reservoir removal + flood control planning 54.9 33.7 33.7

; the newly added flooded area is mainly located in the housing area

**Scheme description Flow rate (m3**

**Point A**

Under the new flood control system, the flooded area and water depth of the reservoir scrapping scheme are significantly less than that of the reservoir flood control before the implementation of the plan, as shown in **Figure 7** for details. After the implementation of flood control planning, the Xipie flood interception

merged area of the former is only 35% of that of the latter. The inundation area of

age ditch CD river section. The maximum depth was reduced from 4.02 to 2.66 m; the water depth of the Beijing-Shanghai railway decreased from 1.72 to 0.30 m. The simulation results show that, after the removal of Heiwa reservoir, the reservoir completely loses the capacity of regulating and storing. Although the discharge volume under the channel will increase by 56%, the inundation range and average inundation depth will increase by only 11 and 12%, which is relatively small compared with the flood control scheme of the reservoir. This is because the downstream

ditch system increases; the average submerged depth is about 0.84 m, and the maximum submerged depth is 4.02 m. The submerged range increases from 1.63

/s, and the flood discharge pressure of the drainage

/s, and the flow rate of the flood

**/s)**

**River section DE**

**River section BD**

/s, slightly lower than the regulated

/s. Although the flow rate is similar, the sub-

, mainly concentrated in underground drain-

#### **Figure 7.**

*Flood depth in the lower reaches of the joint flood control planning scheme for flood once encountered every 50 years.*

discharge volume of the reservoir far exceeds the flood discharge capacity of the downstream urban channel system. In other words, the flood control effect of the reservoir is not significant, and even if the reservoir is removed, it will not significantly increase the inundation range and water depth. In comparison, although the reservoir has been scrapped and lost its flood control capacity, the flooded area of the lower reaches of the reservoir has been significantly reduced after combining with the urban flood control planning. Compared with the reservoir scrapped plan before the implementation of the planning, the flooded area of the latter has been reduced by 69%.

#### *3.2.2. Flood impact assessment*

According to the characteristics of the calculation region and the loss data of agricultural and commercial assets in typical flood disasters in history, the loss rate was determined, and the corresponding relationship between the loss rate and water depth was finally determined, as shown in **Table 3**.

According to the flood analysis and results of three schemes, combined with the regional feature distribution, to measure socio-economic indicators including the flood area population, submerged area, submerged residential area, affected length of road and railway, affected population and GDP of each scheme. Results are shown in **Table 4**.

See **Table 5–7** for the flood loss values under different water depth levels of each simulation scheme.

The result of loss assessment shows that the building loss is between RMB 3.04 million and 26.48 million, the landscape loss is from RMB 933,300 to 8.39 million, the road loss is from RMB 14,000 to 86,100, the railway loss is from RMB 0 to 1.36 million, and the total loss is from RMB 3.99 million to 3.63 million. Among the three schemes, the total loss of scrapped reservoir is the largest, among which the loss of buildings is the largest, followed by the loss of landscape.


#### **Table 3.**

*Ground object loss rate: water depth relationship (unit, %).*


#### **Table 4.**

*Calculation of the statistical table of flooded surface features in the region.*


**139**

**4. Conclusion**

**Table 7.**

**Table 6.**

Due to the aging, poor construction quality, and maintenance, water damage and other adverse factors make it a prominent risk for the Chinese reservoir management institution. In the face of the long-term challenges of the disease-risk reservoirs, it is an effective way to solve the problems of the disease-risk reservoirs by disposing of the ones with serious disease risk, shrinking function, and technically unfeasible and economically unreasonable danger reservoirs while taking

**Depth grade (m) Building loss Landscape loss Railway loss Road loss Total** 0.05–0.5 0.00 175.99 136.80 4.41 317.20 0.5–1.0 296.00 213.32 0.00 4.20 513.52 1.0–2.0 720.00 324.25 0.00 0.00 1044.25 2.0–3.0 1440.00 53.33 0.00 0.00 1493.33 ≥3.0 192.00 72.53 0.00 0.00 264.53 Total 2648.00 839.41 136.80 8.61 3632.82

**Depth grade (m) Building loss Landscape loss Railway loss Road loss Total** 0.05–0.5 0.00 56.00 0.00 1.40 57.40 0.5–1.0 80.00 37.33 0.00 0.00 117.33 1.0–2.0 80.00 0.00 0.00 0.00 80.00 2.0–3.0 144.00 0.00 0.00 0.00 144.00 ≥3.0 0.00 0.00 0.00 0.00 0.00 Total 304.00 93.33 0.00 1.40 398.73

Based on economic rationality theory and flood consequence assessment, two decision-making methods of dam retirement are put forward. The flood consequence method is applied on the case of Heiwa reservoir; key evaluation indexes are compiled from the aspects of ecology, economy, and society; and the evaluation system based on single index is constructed. Comparing the plans of current dam situation, dam removal, and dam removal combined with urban flood control measure, the flood risk influence is evaluated. The evaluation results show that the reservoir scrapping will not have significant effects on the flooding situation in downstream cities. Besides, the urban flood control regulation measures could

My deepest gratitude first goes to Dr. Sheng Jinbao and Dr. Wang Zhaosheng, my supervisors, for their constant encouragement and guidance. My thanks would go

engineering measures to remove and reinforce them.

*Flood losses of all levels of water depth in Scheme 3 unit: RMB 10,000.*

*Flood loss table of water depth at all levels in Scheme 2 unit: RMB 10,000.*

greatly mitigate the urban flood risk.

**Acknowledgements**

*Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*

#### **Table 5.**

*Scheme 1: flood loss table of water depth at all levels unit: RMB 10,000.*

#### *Dam Retirement and Decision-Making DOI: http://dx.doi.org/10.5772/intechopen.84392*


#### **Table 6.**

*Natural Hazards - Risk, Exposure, Response, and Resilience*

buildings is the largest, followed by the loss of landscape.

**Submerged area of buildings (km2 )**

*Ground object loss rate: water depth relationship (unit, %).*

*Calculation of the statistical table of flooded surface features in the region.*

*Scheme 1: flood loss table of water depth at all levels unit: RMB 10,000.*

**Affected road length (km)**

1 1.63 0.97 3.15 0.70 0.58 6337 2798

2 1.83 1.12 3.52 0.76 0.66 7100 3184

3 0.58 0.24 0.97 0 0.21 2250 997

**Depth grade (m) Building loss Landscape loss Railway loss Road loss Total** 0.05–0.5 0.00 154.66 126.00 4.41 285.07 0.5–1.0 208.00 186.66 0.00 4.20 398.86 1.0–2.0 520.00 30.40 0.00 0.00 550.40 2.0–3.0 144.00 53.33 0.00 0.00 197.33 ≥3.0 192.00 72.53 0.00 0.00 264.53 Total 1064.00 497.57 126.00 8.61 1696.18

**Affected railway length (km)**

**Affected landscape area (km2 )** **Total GDP affected (RMB 10,000)**

**Total population affected (person)**

are shown in **Table 4**.

simulation scheme.

the flood area population, submerged area, submerged residential area, affected length of road and railway, affected population and GDP of each scheme. Results

See **Table 5–7** for the flood loss values under different water depth levels of each

The result of loss assessment shows that the building loss is between RMB 3.04 million and 26.48 million, the landscape loss is from RMB 933,300 to 8.39 million, the road loss is from RMB 14,000 to 86,100, the railway loss is from RMB 0 to 1.36 million, and the total loss is from RMB 3.99 million to 3.63 million. Among the three schemes, the total loss of scrapped reservoir is the largest, among which the loss of

**Depth (m) Building Vegetation Railway Roads** 0.05–0.5 0 5 1 2 0.5–1.0 1 10 2 3 1.0–2.0 5 19 6 10 2.0–3.0 18 50 22 28 > = 3.0 24 68 32 39

**138**

**Table 5.**

**Scheme number**

**Table 3.**

**Table 4.**

**Submerged area (km2 )**

*Flood loss table of water depth at all levels in Scheme 2 unit: RMB 10,000.*


**Table 7.**

*Flood losses of all levels of water depth in Scheme 3 unit: RMB 10,000.*
