6.1 Hydrological and Meteorological Conditions

6.1.1 Hydrological characteristics

In 2005, actual statistics from Huanglingmiao Hydrological Station downstream the Three Gorges Pivotal Project indicated that the annual average flow was 14,600 m³/s with the maximum of 47,900 m³/s on July 10 and the minimum of 3,680 m³/s on February 18. The annual average sediment discharge rate was 3.27 t/s, and the average sand concentration was 0.224 kg/m³. The maximum average sand concentration in the monitored section was 1.43 kg/m³ occurring on August 21, and the minimum was 0.001 kg/m³ on Feb.9 and December 25. Compared with the previous year, the annual average flow, annual average sediment discharge rate and average sand concentration increased to some extents.

Table 6-1  Monthly statistics of water flow of Huanglingmiao Hydrological Station in 2005

Unit: m³/s

Month	Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sept.	Oct.	Nov.	Dec.
Average	4990	4390	5460	7120	13100	17600	28800	36500	22800	17800	9400	5650
Maximum	6230	7790	8130	10000	20000	24900	47900	47500	47200	33100	14600	7480
Minimum	4140	3680	4120	4940	7140	12800	16400	24600	14000	13200	6170	4070

Table 6-2  Monthly statistics of sand concentration of Huanglingmiao
Hydrological Station in 2005

Month	Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sept.	Oct.	Nov.	Dec.
Average	0.002	0.002	0.003	0.004	0.011	0.034	0.392	0.54	0.237	0.075	0.015	0.003
Maximum	0.003	0.004	0.003	0.005	0.023	0.06	0.965	1.43	0.487	0.243	0.024	0.007
Minimum	0.002	0.001	0.002	0.003	0.003	0.014	0.035	0.178	0.049	0.013	0.006	0.001

6.1.2 Meteorological characteristics

In 2005, the climate in the Three Gorges Reservoir Area was characterized by mild weather with less rainfall and higher-than-normal temperature. The temperature of most months of the year turned out to be normal. The precipitation was less than historical average.

● Precipitation

The annual precipitation in the construction area totaled 984.6mm, 14.7% less than the historical average. The annual precipitation was quite uneven in the twelve months mainly dominating from May to September. The maximum daily rainfall reached 137.0 mm on July 10. The longest consecutive rainy days across the year reached 11 days occurring in August and the longest non-precipitation consecutive period lasted for 28 days occurring in December. A total of 34 days experienced thunderstorms in the whole year.

● Temperature

The annual average temperature in the construction area was 17.0℃, 0.2℃ lower than the historical average. The highest temperature reached 40.8℃ on July 4, and the lowest temperature was -2.4℃ on January 1.

● Wind speed

The annual average wind speed was 1.4 m/s with the extreme speed hitting 16.8 m/s on August 13. The wind direction changed frequently over the year with the dominant wind direction of NNW, accounting for 20% of the total.

Table 6-3  Statistics of important meteorological elements in the Three Gorges Dam Area in 2005

Month		Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sept.	Oct.	Nov.	Dec.	Whole year
Temperature	Temperature (℃)	4.8	4.4	11.2	19.8	21.6	26.8	28.5	25.2	23.6	17.5	14	7	17
	Difference to the historical average (℃)	-1	-3.6	-0.5	2	-0.2	1.6	1	-1.5	0.3	-0.2	1.3	-0.8	-0.2
Precipitation	Precipitation (mm)	12.1	36.1	31.4	45.6	124.5	63.3	229.8	266.2	94.2	63.7	12.3	5.4	984.6
	Difference to the historical average (%)	-10.6	1.1	-20.6	-39.3	-23.2	-86.6	25	64.8	-4.6	-28.2	-33.1	-14.5	-169.8
Wind speed	Average (m/s)	1.7	1.6	1.6	1.5	1.1	1.3	1.3	1.1	1.1	1.3	1.4	1.5	1.4
	Maximum (m/s)	7.7	6.6	9.3	8.7	6.1	10.3	7.9	10.5	9.4	5.1	6.1	6.7	10.5
	Extreme (m/s)	11.1	10.3	14.3	15.3	9.7	16.2	14.3	16.8	15.4	9.9	9.7	11.6	16.8

6.2 Air Quality

The assessment of the ambient air quality of the construction area (including office buildings, residential areas and construction sites) was conducted in accordance with Ambient Air Quality Standard (GB3095-1996).

In 2005, the annual average concentration of SO₂ in the construction area was 0.043 mg/m3, meeting Grade II national air quality standard.

The annual average level of NO₂ was 0.029 mg/m³, meeting Grade I national air quality standard. The daily average concentration of SO₂ of each day of 2005 met or was better than Grade II national air quality standard with only one exception. In addition, all the daily average concentrations of NO₂ met Grade I air quality standard in the year.

The annual average concentration of total suspended particles (TSP) in the construction area was 0.195 mg/m³, meeting Grade II national air quality standard. Among them, all the daily average concentrations of TSP in office and residential areas met or were better than Grade III air quality standard. In the construction area, the percentage of days whose daily average of TSP meeting Grade I air quality standard was 18.2%, that meeting Grade II air quality standard was 54.7%, that meeting Grade III air quality standards was 20.4% and that failing to meet Grade III standard was 6.6% of the total respectively.

The overall ambient air quality in the construction area during 2005 had some improvement compared with that of the previous year. The annual average concentration of NO₂ remained unchanged; the annual average of SO₂ increased a bit, and the annual average level of TSP went down by 39.6%. TSP remained to be the dominant pollutant in ambient air of the construction area.

6.3 Water Quality

According to the Environmental Quality Standard for Surface Water (GB3838－2002), 13 items such as pH value, dissolved oxygen, ammonia nitrogen, COD, permanganate index, BOD₅, volatile phenol, cyanide, arsenic, hexavalent chromium, copper, lead and cadmium were included to assess the water quality in the construction area. Anionic surfactants were added to the list for the assessment of the water quality of waters near or along the bank.

The water quality of all sections in mainstream of the Yangtze River and waters near the bank was good in 2005, all meeting or being superior to Grade II national surface water quality standard. Compared with in 2004, the concentration of suspended particles of the water of the sections of the mainstream of the Yangtze River under construction project had a further drop while other monitoring indicators were relatively stable. The water quality of Letianxi Section shifted to Grade II from Grade I in the second quarter, but remained the same in other seasons.

Table 6-4  Water quality of the mainstream sections of the Yangtze River
in the construction area in 2005

Section name	The 1st quarter	The 2nd quarter	The 3rd quarter	The 4th quarter	Whole year
Taipingxi	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅱ
Letianxi	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅱ

Table 6-5  Water quality of alongshore water areas of the Yangtze River in the construction area in 2005

Sampling point		The 1st quarter	The 2nd quarter	The 3rd quarter	The 4th quarter	The whole year
Left bank (30m away from the bank)	Upstream navigation channel	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅰ
	Downstream navigation channel	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅱ
Right bank (30m away from the bank)	Auxiliary dam	Ⅰ	Ⅱ	Ⅱ	Ⅱ	Ⅱ

6.4 Noise

The average daytime and night noise of the office and residential areas of the construction area in 2005 was 57.8 dB and 51.3 dB respectively. The average daytime noise met Grade II standard of the Standard for Urban Regional Environmental Noise (GB3096－93), while the night noise met Grade III national noise standard. The daytime and night sound equivalent levels of the construction area were in conformity with the requirements for the noise limits of production workshop and operational sites stipulated by the Design Standards for the Control of Noise of Industrial Enterprises (GBJ87－85). The noise level at sensitive points outside the boundary was in conformity with the requirements of Noise Limit for the Boundary of Construction Sites (GB 12523－90).

Environmental noise of each area of the construction sites enjoyed some improvement compared with that of the previous year. The average daytime and night noise levels of the office and residential areas dropped by 1.0 dB and 0.9 dB respectively. The average daytime and night noise levels of the construction sites decreased by 3.0 dB and 3.3 dB respectively. The average traffic noise of all the construction sites reduced by 2.2 dB compared with that of the previous year.