Section 2 Environment in Reservoir

Article 83. (Article 83) Sedimentation in reservoir

This article is prepared to know a change in reservoir capacity, quantity of sediment in a reservoir and riverbed level, and to take measures in case a rise in a riverbed level causes damage to the area surrounding a reservoir.

1. Area of survey

The survey area must be entire area of a reservoir impounded by the dam and backwater area. 2. Time of survey

Measurement of sedimentation must be conducted just after the flood season unless otherwise specified.

3. Contents of activities

The following items must be conducted.

Calculation of sediment volume in a reservoir according to longitudinal or transverse survey

Calculation of flood water level based on survey of sedimentation in a reservoir

Investigation of the area affected by rise in flood water level due to progress in sedimentation

Monitoring on situation of exploitation of sediment deposit in a reservoir

Investigation and assessment on influence of progress of sedimentation on a reservoir operation rule

Taking measures against problems such as decrease in effective reservoir capacity, inundation of a backwater area of a reservoir, etc.

4.Report

A report must contain the following items.

Situation of sedimentation in a reservoir

Investigation and assessment on influence of progress of sedimentation in a reservoir

Map of the area inundated by flood

Plan of a reservoir

Longitudinal section of a reservoir

Major cross sections of a reservoir

Article 84. (Article 84) Restriction on use of chemical herbicide

Article 84 was prepared to let the Owner comply with the environmental regulations when he is obliged to use chemical herbicides.

In case it is necessary to weed outundesirable plants from a riverside or around the reservoir, the Owner must use herbicides which comply with environmental regulations so that chemical spraying may not pollute soil or reservoir water.

In case reservoir water is the source of water supply, the Owner must consult with an administrative bureau of a city water and pay close attention to selecting herbicides.

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Article 85. (Article 85) Monitoring of reservoir water quality

Article 85 was prepared to let the Owner comply with the environmental regulations by checking reservoir water quality periodically.

The Owner must check water quality of the reservoir following items and intervals which are prescribed in the environmental regulations.

Section 3 Hydro-Meteorological Activities

Article 86. (Article 86) Use of hydro-meteorological data for safe operation

Article 86 was prepared based on the requirements in Decree No.72/2007/ND-CP. Relevant articles of decrees and circulars are as follows:

Decree No.72/2007/ND-CP:

Article 12. Measurement, monitoring of dam and meteorologicalhydrological parameters

1.For large dams:

a)After taking over the works of management, the dam Owner shall organize measurement, monitoring or contracting with professional agencies to carry out measurement, gathering meteorological-hydrological data of the catchments of reservoir, progress of seepage through dam body, dam bed, dam abutment, dam displacement, dam cracks, slides in dam foot, foundation and surrounding areas, the sedimentation in the reservoir.

b)The measurement documents shall be adjusted, analyzed, evaluated, compared with the design and forecast data; finding the sudden phenomenon in order to make decision on remedial measures in time; implementation of documentation preservation in accordance to the regulation.

2.For small dams: the measurement of water levels and other measurements as specified by

the design consulting company.

The dam Owner must prepare a standard method of hydrometeorologicalsurveying following the example of those of the hydro-meteorological agencies and instruct employees incharge of hydrometeorological surveying who are working at hydropower plants under the control of the dam Owner of the standard method.

An example of a measurement method of river discharge is as follows.

1.Select a suitable place for a gauging station where a rive flow route is stable, and excessive erosion or sedimentation may not occur;

2.Survey the river cross section, and measure river depth and average velocity periodically;

3.Prepare a rating curve indicating the relation between the river water level and river discharge;

4.Install a staff on a river bank so that a person in charge of river discharge measurement can observe the river water level;

5.Observe the river water level at a staff gauge at a fixed time of a day and record river discharge from the rating curve; and

6.Survey the river section periodically and after the flood season or whenever after large flood occurs in order to review and update the rating curve.

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The dam Owner must collect hydrometeorologicaldata from his own gauging stations and fromthe hydro-meteorological agencies, and analyze them so that hydropower plants under the control of the dam Owner can control hydropower generation more efficiently, and discharge of flood water from dams safely and effectively to minimize damage to the downstream area.

Article 87. (Article 87) Grasp of daily runoff data

Article 87 was prepared to let the Owner manage quantity of water flowing out of a reservoir and record it.

In order to complete the record of reservoir operation and power plant operation, it is necessary to sum-up the records of all of the inflow and outflow items not only through power generation (though turbine) but also through civil works including low level outlet, flushing gate etc. and other facilities including ship lock and fishways. In thisregard, it is required for the owners to equip measuring device of water flow or water level gauges for calculation of runoff through spot of inflow and outflow.

An example of recording method of inflow and outflow of a hydropower plant is as follows.

1.Gathering meteorological and hydrological information from related organizations;

2.Listing up all spots of inflow and outflow at a hydropower plant;

Inflow rate is acquired from following methods;

from change in reservoir water level using a rating curve of reservoir water level and storage capacity;

from gauging station at upstream of the reservoir installed by the Dam owner, meteorological and hydrological authorities, or any other companies and organizations which observe river discharge;

Outflow rate is acquired from following methods;

from output of generators and difference of elevation between intake and outlet using an efficiency curve;

from measuring device of flow rate installed at headrace, penstock, spillway, low level outlet, flushing facilities, ship lock, fishway, or any other devices through which reservoir water is discharged to downstream;

3.Recording daily inflow and outflow thorough each spot;

4.Summing up total inflow and outflow.

Article 88. (Article 88) Survey of operating conditions and criteria

This article stipulates that the Owner must survey meteorological and hydrological data at the point of a hydropower plant and measure environmental conditions of a reservoir.

1.Locations to measure the water level must be fixed at upstream and downstream of weir intake and canal and the water level must be measured with the proper method and at proper interval.

2.Water discharge through civil works such as spillway, bottom outlet, fish way ship lock or other facilities, and hydraulic turbines must be measured with the pooper method and at proper interval.

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3.Locations to measure water turbidity and sedimentation must be fixed at proper points of a reservoir, and water turbidity and sedimentation must be measured with the pooper method and at proper interval.

4.Locations to measure water quality for power generation use and discharge from civil works must be fixed at proper points of a hydropower plant, and water quality for power generation use and discharge from civil works must be measured with the pooper method and at proper interval.

5.Locations to measure temperature of water and air must be fixed at proper points of a hydropower plant, and temperature of water and air must be measured with the pooper method and at proper interval.

Article 89. (Article 89) Reliability and accuracy of gauging stations

1. Purpose

This article aims at maintenance of accuracy in measurement of runoff by instructing details of measurement methods.

2. Installation of gauging stations

A gauging station must be installed in a place satisfying the following conditions.

River flow is not too rapid or too slow;

Watercourse does not move so much;

River water does not have reverse flow toward upstream or stagnate;

River water level does not fluctuate by tributaries or distributaries; and

Existing structures do not affect river flow conditions.

3.Facilities of gauging stations

The following facilities must be installed at gauging stations.

(1) Measuring device of river water level

A measuring device of a river water level must be installed at the place satisfying following conditions.

A place where river flow or flood does not move or wash away the device; and

A place where is convenient for measurement.

(2) Self-recording device of river water level

A self-recording device of a river water level must be installed as follows.

The most suitable device which fits the site conditions must be selected;

The device must be able to record the maximum and minimum river water level accurately; and

A staff gauge must be installed near the device to compare records of the device with reading of the staff for checking.

(3) Staff gauge

A staff gauge must be installed as follows.

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A staff gauge must be fixed firmly so that it may not be affected by flowing water or driftage;

A staff gauge must be marked off in centimeters;

In case plural staff gauges are installed in stages due to topography of a river section, each staff gauge must be installed in one alignment; and

The zero point must be installed at the elevation lower than the minimum river water level.

4.Measurement of river flow velocity

River flow velocity must be measured as follows.

River flow velocity must be measured XX times per month;

Frequency in measurement of river flow velocity can be reduced in case a river section has not changed in the past YY years; and

River flow velocity must be measured by a current meter at AA m intervals in a transverse direction of a river and at BB, CC and DD % of the depth at each section.

The criteria of XX, YY, AA, BB, CC and DD must be decided at each gauging station. 5. Calculation of river runoff

River runoff must be calculated as follows.

River runoff must be calculated by averaging river flow velocity measured at each point;

A rating curve of river water level and river runoff must be calculated by a least squares method or other appropriate method; and

A rating curve must be revised whenever topography of a river section changes due to flood or other causes.

6.measurement of river runoff

River runoff must be measured as follows.

A river water level must be measured YY times at the fixed time per day by reading a staff gauge;

In case of flood, a river water level must be measured at FF hours intervals and a peak water level must be measured;

A river water level must be converted into river runoff by a rating curve; and

In case a self recording device is installed at a gauging station, measurement of a river water level of a flood can be omitted.

Article 90. (Article 90) Notification for violation of regulation on water use

A hydropower plant may accidentally discharge turbid water stored in a reservvioirlateor regulations on water usage in an emergency situation. In such case, the Owner must informthe hydrometeorological agencies and the environmental management agencies immediately of it.

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