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Frequency-Flooded Area Relationship

1. Economic benefits of small hydroelectric power stations:


The benefits of small hydropower are also of two types: direct benefits and indirect benefits.

a. Direct benefits:


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The direct benefit B is calculated from the useful electricity quantity (minus losses) E h multiplied by the current electricity price V.

B = E h . V (VND/year) B: direct benefit (VND/year)

Frequency-Flooded Area Relationship

E h : useful electricity (KWh/year) V: electricity price (VND/KWh).

Useful electricity is calculated as follows: E h = [ E(1 - ® - m ) ] (KWh/year) In which:

E: amount of electricity generated in 1 year (KWh/year)


d : power loss coefficient on the line (%E)

m : power loss coefficient in the factory (%E)

: utility coefficient (= 0.800.85)

The amount of electricity generated in a year is calculated by the following formula: E = A . Q . H . t

In there:


Q: hydroelectric station flow (m 3 /s) H: water column for electricity generation (m)

t: generation time (number of hours) in a year. For hydroelectric stations, usually t = 5000 hours/year.

A = 9.81 (usually A = 6 7)

: efficiency of the machine

=machine xturbine xtransmission

b. Indirect benefits:


Indirect benefits of hydropower are beneficial effects on local industrial development, livestock farming, cultural activities, and education and propaganda. Indirect benefits cannot be quantified.

2. Small hydropower evaluation criteria:


The following criteria are often used to evaluate small hydropower.


a. Number of hours of electricity generation per year:


After many years of use, the average number of hours of electricity generation per year will be calculated. This indicator reflects the use and damage status of the hydroelectric station.

t years =

En (ye)

N

lm


In there:


En: average annual electricity generation (KWh/year) N lm : installed capacity of hydroelectric station (KW)

Does the generation time of a hydroelectric station depend on the location of the station?

in the system and the reservoir's regulatory capacity.


For example: With a hydroelectric station at a reservoir, which mainly serves irrigation and electricity generation is only a combination:

- Unregulated reservoir then t = 5000 hours

- Regulating reservoir day t = 4500 hours

- Regulating reservoir year t = 3500 hours.

Or if the hydroelectric station is connected to the general grid:


- If not regulated t = 4500 – 5500 hours


- Day regulation t = 3500 – 4500 hours.


- Annual regulation t = 3000 – 4000 hours. (In 1 year there are: 365 x 24 = 8760 hours)

b. Unit investment cost:



K KW =

K total

N


(VND/KW)

ln


K KW : unit investment cost (VND/KW)

Total construction investment cost (VND )

N lm : installed capacity of hydroelectric station (KW)

Total investment cost includes construction, factory machinery and equipment and power lines.

c. Electricity cost:


The cost of electricity includes basic depreciation, major repairs and operating costs.

C KW =

d c d s C 0

E


(VND/KWh)


C KW : electricity cost (VND/KWh) d c : basic depreciation cost (VND/year) d c : major repair cost (VND/year)

C 0 : operating cost (VND/year)

d. Profit


The profit of hydropower is the difference between the selling price of electricity and the production cost and taxes.

L = GB – (G + T)

L: profit (VND/year)


G sx : production cost (VND/year) T: tax (VND/year)

GB : selling price .

e. Payback period:


T =​

K

B C


K: total investment capital of the project (VND) B: value earned in the year (VND/year)

C: annual operating cost (VND/year)


The payback period of the project must be less than the payback period allowed by construction regulations.

IV. Benefits of flood prevention works


1. Characteristics of flood prevention works:


In terms of economic benefits, flood prevention works compared to other types of works have differences, mainly through the following aspects:

1. Flood protection works do not directly produce material products, but their main function is to reduce the damage caused by floods. Therefore, the effectiveness of flood protection works is considered in this aspect.

2. The effectiveness of flood prevention works varies greatly from year to year. Generally speaking, big floods do not occur every year, but only once every few years. At this time, flood prevention works can only be effective, so the effectiveness of flood prevention works is "hidden".

3. The truth is both sides:

- Direct loss: Damage to material assets due to floods - Can be quantified in money.

- Indirect losses: Such as human loss, illness, and suffering of people. These losses cannot be measured in money.

4. In addition, flood damage has immediate effects in the same year, but there are also effects that last for several years. Calculating the extent of damage is also quite complicated.

5. The extent of damage caused by floods also depends on the development of the economy. For example, if the same city was flooded 10 years ago compared to this year, the extent of damage this year must be greater.

6. Flood control projects, in addition to positive effects, also have negative effects. For example, building large reservoirs to regulate floods will flood many fields and villages.

7. Flood prevention works have mainly social benefits, so the project management unit generally has no income from exploiting the works.

2. Collect and analyze documents


To calculate the effectiveness of flood protection works, the following documents need to be collected:


a. Area of ​​damage reduced by that flood.


From flood investigation documents, select a historical flood to study the damage caused by that flood, including: Flood scope; flood process; flood depth; flood situation in residential areas and cultivated land. Use hydrological and topographic documents in the area to find the following relationships:

- Relationship between flooded area and flood elevation.

- Relationship between flooded area and flooded time.

- Relationship between flood elevation and flooded cultivated area.

The above figures are for the case where no flood protection works have been built. In the planning and design of flood protection works, it is necessary to provide various methods.

projects with different frequencies. Compare the projects to choose the one.

best flood protection project


With the flood prevention plan, the damaged area is A, and for the historical flood, the damaged area is A max . So the damaged area of ​​that plan compared to the historical flood is: A = A max – A.

b. Average area of ​​damage reduction over many years:


The average area of ​​damage reduction over many years is the difference between the damaged area before and after the construction of flood protection works. To obtain this document, the following methods are often used:

Investigation method: Conduct an investigation during floods for the following data: Flooded area, level of flooding. Comparing the flooded area after construction with the data before construction, we will get the average damage reduction area over many years.

Typical year method: Based on documents on flooded area of ​​typical years with frequency P < P TK to find the average damaged area between design years before and after the construction of flood protection works. The average flooded area of ​​many years before (or after) the construction of flood protection works is calculated according to the following formula:


n

A =

P P TK


( P i 1 P i )(

A i A i 1 ) 2


A: average flooded area.


Pi , Pi +1 : flood frequency at 2 close times.

A i , A i + 1 : flooded area corresponding to frequency P i , P i + 1 .

Based on the documents and calculations according to the above formula, we will draw the frequency curve of flooded area before and after construction from P = 0 to P

= P TK .

A

A i+1

A i

A 0

A (Km 2 )


0 P i+1 P i

P TK P%


Figure 3.1 Frequency relationship with flooded area


So according to the figure above, the flooded area A at a frequency P

It is the difference between lines (1) and (2).


c. Loss value per unit area:


In the flooded area, many types of damage occurred, such as agricultural land,

Forestry land, aquaculture, residential areas, industrial parks, and roads. For convenient calculation, all types of losses are converted into money. For each type, there is a different loss value per unit area of ​​Km 2. ​​The total loss value is calculated as follows:


n

S = F i . S i (VND)

1


S: total value of damage in the flooded area. F i : area of ​​land type i flooded (Km 2 )

S i : unit loss of land type i (VND/Km 2 )

Total unit loss per 1 Km 2 is calculated as follows:

S 0 =

S (VND/Km 2 )

F


S 0 : total unit loss (VND/Km 2 )

S: total unit loss of flooded area (VND) F: total flooded area (Km 2 ) F = F i .

d. Growth coefficient of flood losses and flood protection benefits:


Flood losses and flood prevention benefits increase with the development of the national economy, but each industry has different growth rates. In general, the growth rate of production in the fields of cultivation, animal husbandry, forestry and industry and commerce is consistent with the rate of damage caused by those industries. As for losses in residential areas, concentrated industrial zones and public service agencies, their growth rate is not synchronous with the growth rate of those industries. The total loss growth coefficient can be calculated according to the formula:


n

F 0= if i i 1


f 0 : total loss growth coefficient. f i : loss growth coefficient of industry i

i : proportion of flooded area of ​​industry i over total area

flooded


3. Calculating flood prevention benefits


a. Flood prevention benefits corresponding to different flood frequency:


The value of the loss reduced after the flood protection project is completed is the flood protection benefit. After the project is built, there will be floods with different frequencies, which will have different flood protection benefit values.

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