6.1 Hydrology and Meteorology

6.1.1 Characteristics of hydrology

In 2003, the statistical results from Huanglingmiao Hydrometric Station showed that the average flux in the whole year was 13,000m³/s. The maximum flux was 48,300 m³/s on September 4. The minimum flux was 2,820 m³/s on February 8.The annual average runoff was 4.094 × 1011m³. The runoff modulus was 1.30 × 10-2 m³/s·km². The runoff depth was 408.3mm. The average sand transmission rate was 2.81 t/s. The average sand content was 0.216 kg/m³. The section's average maximum sand content was 0.875 kg/m³ on September 6. The section's average minimum sand content was 0.003 kg/m³ on December 28.

Table 6-1 Monthly Statistics of Flux in Huanglingmiao Hydrometric Station in 2003

Unit: m³/s

Month	Jan.	Feb.	Mar.	Apr.	May.	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.
Average	4300	3430	3930	5600	9520	14900	32600	22400	30900	14100	7450	5850
Max.	4910	4080	4400	8740	16400	34600	45000	28300	48300	23900	10400	7660
Min.	3840	2820	3410	3690	5610	3500	19100	18000	18000	7220	5390	4230

Table 6-2 Monthly Statistics of Sand Content in Huanglingmiao Hydrometric Station in 2003

Unit: kg/m³

Month	Jan.	Feb.	Mar.	Apr.	May.	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.
Average	0.016	0.014	0.009	0.077	0.118	0.164	0.436	0.112	0.382	0.055	0.01	0.005
Max.	0.021	0.019	0.026	0.139	0.274	0.741	0.769	0.183	0.875	0.135	0.014	0.007
Min.	0.012	0.011	0.007	0.026	0.026	0.02	0.1	0.063	0.116	0.007	0.007	0.003

6.1.2 Characteristics of climate

In 2003, characteristics of climate in the Three Gorges reservoir dam area were much precipitation in spring and less in rainy season. Annual average temperature was a little lower than normal, but the extremely highest temperature created historical record. Thunderstorms and strong tempest disasters were frequent.

● Precipitation

Precipitation in the construction area was 1,212.8mm, 4.3% more than the average in the past years and distributed unevenly in different months. In February, April and November, the precipitation was 50% more than normal. Precipitation in May, August and December was also obviously more than normal. But in June and July, though belonging to rainy season, and January, September and October, the precipitation was quite less than normal. The number of rainy days in the whole year (precipitation ≥0.1mm) was 163, 1 day more than the average for years. The daily maximum precipitation was 78.5mm on August 3.

● Temperature

The average monthly temperature in the construction area was 16.6℃, 0.6℃ lower than the average for years. The average temperature in January and September was a little higher than normal, but the average temperature in other months was a little lower than normal. The temperature in mid July was obviously lower than normal years. The number of days with temperature higher than 37℃ was two days less than the average number for years. The days with highest temperature mainly occurred from late July to early August. From July 28 to August 2, the highest temperature exceeded 37℃. The highest temperature from August 6 to August 8 was 36℃. From May to September, the number of thunderstorms days was 21,obviously less than normal years, particularly in July.

● Wind speed

The average wind speed in the construction area was 1.5 m/s, the same as the average for years. The wind direction in the year was normally NNW with an occurrence frequency of 22%. Three times of strong wind appeared respectively on March 26 (8 scale), June 3 (10 scale) and August 24 (9 scale).

Table 6-3 Statistics of Meteorological Elements in the Three Gorges Dam Area in 2003

Month		Jan.	Feb.	Mar.	Apr.	May.	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.	Year
Temperature	Temperature (℃)	6.5	7.6	10.8	16.5	20.6	24.8	26.4	26.8	23.4	17.3	11.9	6.9	16.6
	Difference from historic average (℃)	0.9	-0.4	-0.6	-1.2	-1.5	-0.3	-1.1	-0.3	0.1	-0.4	-0.7	-1.2	-0.6
Precipitation	Precipitation (mm)	9.6	53.3	57.2	140.5	190.9	135.8	171.1	264.4	60.7	36.6	65.4	27.3	1212.8
	Difference from historic average (%)	-60.8	79.5	4.6	87.6	39.1	-13.3	-23.5	42	-40.8	-66.8	51.4	40	4.3
Wind speed	Average (m/s)	1.5	1.7	1.8	1.8	1.3	1.4	1.3	1.4	1.3	1.6	1.6	1.8	1.5
	Max.  (m/s)	7.1	6.6	13.4	8.6	8.8	10.9	6.5	9.3	5.8	6.1	6.6	7.2	10.9
	Min. (m/s)	11.5	11	18.9	15.1	13.6	25.7	11.1	18	11.3	10.5	11.3	12.3	25.7

6.2 Air Quality

Assessment on environmental air quality in construction area (working/residential area and construction site) was conducted according to the Environmental Air Quality Standard (GB3095-1996).

In 2003, the annual average concentration of SO₂ in the construction area was 0.019 mg/m³, and that of NO₂ was 0.022 mg/m³, all reached the standard for Grade I. Except on the only 2 days SO₂ was on Grade III in the construction area, and the daily average concentration of SO₂ reached or was better than the standard for Grade II. The daily average concentration of NO₂ reached the standard for Grade I as a whole.

The annual average concentration of TSP was 0.219 mg/m³ in the construction area, reaching the standard for Grade III. The daily average concentration of TSP in working and residential areas all reached or was better than the standard for Grade III. The proportions of daily average TSP concentration in the construction area reaching the standards for Grade I, Grade II and Grade III and exceeding Grade III were 9.3%, 60.5%, 24.8% and 5.4% respectively.

Compared with 2002, the environmental air quality in the construction area was improved as a whole in 2003. The annual average concentration of SO₂ was a little higher and the annual average concentration of NO₂ and TSP dropped a little. The main pollutant in the environmental air in the construction area was still TSP.

6.3 Water Quality

According to the Water Quality Standard for Surface Water Environment (GB3838-2002), 13 indicators of pH, dissolved oxygen, ammonia nitrogen, COD, permanganate index, BOD₅, volatile phenol, cyanide, arsenic, hexad chromium, copper, lead and cadmium, were selected for assessment on the water quality in the construction area. Anion detergent was added for the assessment on the water quality of the near bank water area.

In 2003, the overall water quality in the main stream of the Yangtze River and along the bank in the construction area was pretty good, reaching or being better than the standard for Grade III. Compared with the first half of 2002, the total hardness and total alkalinity parameters in the water body of the mainstream of the Yangtze River were relatively stable with conductivity a little higher and oxidation reduction potential (ORP) dropping a little. Permanganate index, total phosphorus and heavy metal etc. also decreased in certain degrees.

Table 6-4  Water Quality in Sections of Mainstream of the River in Construction Area in 2003

Name of sections	1st Quarter	2nd Quarter	3rd Quarter	4thQuarter	Whole Year
Taipingxi	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅱ
Dongyuemiao	Ⅰ	Ⅰ	Ⅲ	Ⅰ	Ⅱ
Letianxi	Ⅰ	Ⅰ	Ⅲ	Ⅰ	Ⅱ

Table 6-5  Water Quality Along the Bank of The River in Construction Area in 2003

Monitoring points		1st Quarter	2nd Quarter	3rd Quarter	4thQuarter	Whole Year
Left Bank	Navigation route	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅱ
(30m away from	in upstream
the bank)	Navigation route	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅱ
	in downstream
Right Bank	Laomaoping	Ⅰ	Ⅰ
(30m away from the bank)	Town
	River mouth	Ⅱ	Ⅱ
	of Maopingxi
	Fuba			Ⅱ	Ⅱ

Note: After July, monitoring points at Laomaoping Town and river mouth of Maopingxi on the right bank were deleted and Fuba monitoring point was added.

6.4 Noise

The average values of environmental noise in working and residential area were 60.6dB(A) and 53.8dB(A) respectively at daytime and night, all reaching the Environmental Noise Standard in Urban Area (GB 3096-93) for Grade III. The equivalent sound levels of noise at daytime and night in the construction area all met the requirement of the threshold of 90 dB(A) set by the national Design Norms for Noise Control in Industrial Enterprises (GBJ87-85) for production workshops and operation site. Noise at the sensitive points outside the boundary attained the threshold set by the Noise Threshold for Boundary of Construction Site (GB12523-90).

Compared with 2002, the average values of environmental noise in working and residential area at daytime and night increased by 4.9dB(A) and 3.4dB(A) respectively. The average values  of environmental noise in the construction site at daytime and night increased by 2.4dB(A) and 0.6dB(A) respectively. The annual average value of traffic noise in the construction site dropped by 2.0dB(A) to 73.9dB(A).