Study regional natural environment and social economy
2.2.1 Natural environment
2.2.1.1 Geographical location
Guilin is a world-famous scenic tourist city and a famous historical and cultural city. The urban area of Guilin is located in Guangxi In the northeastern part of the Zhuang Autonomous Region, in the middle of Guilin City (Figure 2.2), in the Lijiang River Valley Basin of the Hunan-Guangxi Corridor, it is distributed in a north-south strip on both sides of the upper reaches of the Lijiang River. It is located between 110°12′58″～110°21′29″ east longitude and 25°00′～25°21′43″ north latitude. It borders Lingchuan County to the east and north, and Lingui to the west and southwest. It is adjacent to the county and Yangshuo County in the southeast. The urban area is 40km long from north to south, 10.0 to 22.5km wide from east to west, and has a total area of 565km2.
2.2.1.2 Topography
Guilin City. The terrain of the district is roughly in the shape of a river valley basin centered on Zhemu Town. This basin extends to the south between Santang and Liangfeng, and forms a large gap to the west. The surrounding terrain is higher, with stone mountains and earth mountains distributed, mostly hilly slopes. The basin has become the gathering point of various rivers. The Taohua River comes from the northwest, and the Liangfeng River comes from the southwest. The terrain is relatively flat and the water network is dense, which provides benefits for farmland irrigation. It is the main base of agricultural production in the urban area. Yaoshan in the northeast is a huge mountain with steep slopes, with the highest peak at an altitude of 909.3m. It and Yanshan in the south and west are all earth-rock mountains. The hills in the Longquan area near Huangcun in the south of Changling are mainly composed of the Lianhuashan Formation and Sipai Formation shale of the Lower Devonian. The two sides of the Lijiang River in the north and the towns in the south are mostly hilly slopes, most of which belong to the Fourth Formation. The soil layer is deep brown and red. Most of the soil in the northwest and southeast is undulating limestone, which is a typical karst landform.
Figure 2.2 Administrative division map of Guilin City
Figure 2.3 Three-dimensional map of Guilin's urban landforms
The urban area develops two series of karst landforms and flowing water landforms. The landform types are complex and diverse in form, including low mountains, hills, basins, and flatlands. Mainly flat land, accounting for 60.9% of the total urban area. 96% of the urban area belongs to karst landforms, and the two major landforms are Fenglin plain and Fengcong depression (Figure 2.3). The base of Fenglin plain is carbon. Salt rock, covered by laterite and debris accumulation, constitutes the main agricultural area. The altitude of the plain is 145-180m, and there are towering, independent, varying density, different sizes and varying heights. The relative height of the peaks is mostly within 100m, with steep peak slopes and slope angles greater than 50°, with various shapes, caves, abundant groundwater, shallow burials, and karst lakes and rivers. It consists of cone-shaped peaks and karst depressions and valleys. The peaks are clustered together with steep slopes, with a slope of more than 45°. The depressions are dotted with local valleys, presenting a peak-cluster-depression-valley landscape. In addition, karst caves are densely developed and numerous. , there are 389 caves of a certain size exposed on the surface, such as Qixing Rock, Reed Flute Rock, Guan Rock, Chuanshan Rock, etc.
2.2.1.3 Climate Characteristics
Guilin. The urban area is located at low latitudes, with a warm and humid climate. It belongs to the subtropical monsoon climate zone. The climate is mild throughout the year, with long summers and short winters, and four distinct seasons. It rains continuously in spring with more rainy days; it is hot and humid in summer with concentrated heavy rains; the rainfall decreases significantly in autumn, and the climate is dry. , autumn droughts are frequent; in winter, due to the invasion of cold waves, short-term cold weather such as frost occasionally occurs. The multi-year average temperature in Guilin urban area ranges from 18.8 to 19.2°C. The measured extreme maximum temperature is 39.4°C and the extreme minimum temperature is -4.9°C. July is the hottest month with an average monthly temperature of 28.3°C. January is the coldest month with an average monthly temperature of 7.9°C. The annual average relative humidity of the air is 76%. It is rich in heat and sufficient sunlight. The average sunshine hours for many years are 1625-1667 hours, and the sunshine percentage is 37.1%-38.1%. Due to the subtropical monsoon climate and the influence of the Yuechengling Mountains, the urban area has abundant rainfall, with an average annual precipitation of 1646~1917mm. Due to terrain factors, rainfall is unevenly distributed between the north and the south, with slightly more rainfall in the north and slightly less rainfall in the south. Due to the influence of the monsoon, the distribution of precipitation in each season is extremely uneven. Generally, the rainfall from March to August accounts for about 75.73% of the annual rainfall, of which May and June have the most rainfall, accounting for about 35.35% of the annual rainfall. The multi-year average evaporation is 1380~1560mm, with the maximum evaporation in July, with a monthly average of 190.3mm. The average annual frost-free period is 304 to 309 days. The wind direction throughout the year is mainly from northeast to north, with an average wind speed of 2.6m/s.
2.2.1.4 River system
There are many rivers, lakes and ponds in Guilin urban area and the water system is developed. The rivers passing through the urban area include the Li River, Taohua River, Liangfeng River, and Nanxi River; the rivers in the urban area include Lingjian River, Xiaodong River, Chaoyang River, Ningyuan River, Nanwan River, Wayaochong, etc., with a total length of 142km. , the river network density is 0.25km/km2. These rivers all belong to the Pearl River Basin and Xijiang River System. The total area of lakes and ponds in the urban area reaches 13.65km2. The larger lakes and ponds include Rong Lake, Shan Lake, Gui Lake, West Lake, Mulong Lake, Bajiao Pond, etc.
(1) Lijiang River
Lijiang River is the common name for the middle and upper reaches of Guijiang River. The river section is 214km long. It originates from the northeast of Maoer Mountain in Huajiang Township, Xing'an County and runs through A major river in the urban area enters the urban area of Guilin from Qinjia, Lingchuan County in the north, passes through the urban area in the south, joins the Taohua River, flows southeast to Douji Mountain, passes through Daxu Town, and winds south again, on the lawn of Yanshan District. It flows out of the urban area into Yangshuo at Guanyan in Hui Township, and the section flowing through the urban area is 49.3km long.
The rainwater collection area above the section of the Lijiang Guilin Hydrological Station (located in Wayaodutou Village) is 2860km2. The multi-year average rainfall in the basin is 1935mm. The multi-year average runoff is 41.30×108m3. The highest flood level in history occurred in 1885. On June 14, the water level was 148.58m and the flow rate was 7810m3/s. The measured lowest water level was 140.18m (December 20, 1989), and the minimum flow rate was 3.80m3/s (February 7, 1951). The multi-year average flow is 129.03m3/s, and the multi-year average monthly flow in the dry season is 22.7m3/s.
The riverbed of the Lijiang River in Guilin City is composed of pebbles, gravel and sand. Along the riverbed, there are alternating beaches and pools. The beaches are long and the pools are deep. The water depth in low water is 1~3m. In the shallows, the depth is 0.6~0.9m. The deepest pool is 12m, the average gradient of the riverbed longitudinal section from Baishitan to Zhelimu Town is 0.32‰. The width of low-water rivers is generally 150 to 190m. Due to the small low-water flow, the riverbed in some river sections is seriously exposed, and some only have about 20m left. The river channel covers an area of about 14km2, with an average width of 280m, a narrowest point of 165m, and a maximum width of 460m. The average height and width from the low water surface to the river bank is 5m, the lowest point is 4m, and the highest point is about 7m. In addition, there are many rivers and islands in the urban area, including 9 larger islands. The safe flood discharge flow of the urban section of the Lijiang River is 2580m3/s. When the water level at the hydrological station reaches 146.5m, the urban area is severely flooded.
(2) Taohua River
Taohua River, also known as Yangjiang, originates from the southeast side of the Central Ridge at the junction of Wutong Town, Lingui County and Qingshitan Township, Lingchuan County. The main stream flows eastward from north to south through Wutong Town and Miaoling Township in Lingui County. It turns north at Wuxianba in the urban area and passes through Dingjiang Township in Lingchuan County. It passes through Shuinan Village and enters Jiashan Township in the urban area from north to south. Near the Jiashan Township Government, it turns east and passes through the city. At the downstream of Nanmen Bridge, it flows into the Li River from Xiangshan and Luobozhouwei respectively. The main stream is 65km long and is a first-level tributary of the Lijiang River. The section flowing through the urban area is 19.1km long.
The rainwater collection area of Taohua River is 298km2, the average annual rainfall in the basin is 1900~2000mm, the average annual runoff is 3.66×108m3, the maximum flow rate in the survey is 840m3/s (1885), and the minimum flow rate in the measurement is 0.637m3/s. (1972). The average flow rate for many years is 11.6m3/s.
The average gradient of the longitudinal section of the Taohua River from Wuxianba to Zhishanqiao is 0.44‰, the low water water surface ratio is 0.43‰, and the flood water surface ratio is 0.30‰. The width of dry rivers is generally 40 to 0.9m. The section below Hongqiao Dam to Luobozhou is called the Ningyuan River, which is the main outlet channel for floods in the Taohua River during the flood season. During the dry season, the Ningyuan River basically stops flowing, and the river water flows into the Li River from the Elephant Trunk Mountain. The Taohua River trough is generally 50 to 60m wide, and the Feiluan Bridge is as wide as 71m. The section below Hongqiao Dam is wider, with a groove width of 60 to 70m. The river bank along the river is very low. The distance from the dry water surface to the river bank is generally 2 to 3 meters. The highest cross-section of Shengli Bridge is only 4 meters. The river course has a large curvature. The length of the river from Wuxianba to Feiluan Bridge is nearly 10km, and the straight section is only 2.1km. The water along the river is divided by weirs and dams, making the dry water surface into a ladder shape. The flood-carrying capacity of the existing river is very low. The safe discharge flow of the river section above Nanmen Bridge is only 260-300m3/s. The two banks will be inundated before the flood occurs once in five years.
(3) Liangfeng River
Liangfeng River, also known as Qifeng River, originates from the vanilla rock at the junction of Yangshuo, Yongfu and Lingui counties, and passes through Lingui from south to north. It flows into the urban area from Shizikou and Nanbian Mountain in the county, flows through Liangfeng in Yanshan District, then turns to the northeast, passes through Qifeng Town, and flows into the Li River at Huziyan in Zhemu Town. The main stream is 69km long and is a first-level tributary of the Lijiang River. The section flowing through the urban area is 31.5km long.
The rain collection area of Liangfeng River is 528km2, the average annual rainfall in the basin is 1700mm, the average annual runoff is 5.17×108m3, the maximum flow is 836m3/s, and the minimum flow is 0.484m3/s. The average flow rate for many years is 164m3/s.
The average slope of the Liangfeng River from Huangjin Dam to the river mouth is 0.49‰, and the low water surface ratio is 0.39‰. The river width above Liangfeng is 20~30m, the water depth in dry season is 0.6~1.2m, and the river bank height is 3~4m; below Liangfeng to the mouth of the river, the river width is 30~50m, the low water depth is 1.0~1.4m, and the river bank height is 5~8m.
(4) Nanxi River
Nanxi River originates from the foothills of Gou Mountain in Miaoling Township, Lingui. The main stream flows from north to south, reaches Hantang, turns east and enters Guilin City. Along the way It flows through Tangjia and Guanqiao villages in Jiashan Township on the outskirts of the city, enters the city at the Black Mountain Botanical Garden, and flows around Nanxi Mountain and joins the Li River on the north side of Douji Mountain. The main stream is 13km long and the urban section is 10.6km2 long. It is a first-class tributary of the Li River. .
The rain collection area of Nanxi River is 24km2, the average annual rainfall in the basin is 1860mm, the average annual runoff is 0.29×108m3, the average annual flow rate is 0.92m3/s, and the average flow rate in the driest month is 0.2m3/s.
Nanxi River is winding like a catwalk, and its width varies greatly. The widest is about 50m and the narrowest is less than 10m. The average slope of the river bed is 1.1‰.
(5) Xiaodongjiang
The Xiaodongjiang is a branch of the Li River, and the entire river course is within the territory of Chuanshan Township. Starting from the Erjiangkou on the east bank of the Li River at the foot of Diecai Mountain in the north, it flows from north to south. Lingjian Creek joins from the left bank at the downstream of Xinqiao. It merges with Lingjian Creek and continues southward, flowing back to the Li River at Chuanshan Park and passing through Qixing The district's Qixing and Chuanshan Village Committees, Guishan Hotel, and Qixing and Chuanshan Parks have a total length of 5.7km, a river width of 40-70m, and a bank height of 3-4m. Along both sides of the river, there are famous scenic spots such as Qixing Park, Longyin Rock, Tashan, and Chuanshan Park.
The Lijiang River basin above the Erjiangkou covers an area of 2,550km2, with a multi-year average flow of 114m3/s. The five months from October to February of the following year belong to the dry season of the Lijiang River, with an average flow of about 30m3/s.
(6) Lakes and ponds
The total area of existing lakes and ponds in the urban area reaches 13.65km2, mainly distributed in Jiashan Township in the west of the city, Huangyingyan in the east, and Yanshan in the south of the city. Town, Zhemu Town and urban center. The main lakes and ponds with larger areas include: Rong Lake, Shan Lake, Gui Lake (including Xiqing Lake, Baoxian Lake, Lize Lake), West Lake, Mulong Lake and Bajiao Pond, etc. The basic information of the main ponds and lakes is shown in Table 2.1.
Table 2.1 Basic situation of major lakes and ponds in Guilin urban area
2.2.2 Social and economic development forecast
Socioeconomic development goals are an important basis for water resource demand forecasting . Its impact on the growth of water resources demand is mainly reflected in: population growth and urbanization process; industrial structure adjustment and total industrial output value; agricultural development and irrigation area growth. For these development indicators, comprehensively consider water resources conditions and regional development goals, predict their possible upper and lower bounds respectively, and then combine the predicted values of each sub-indicator based on the internal connections in various aspects to form different development scenarios. Finally, Based on these development scenarios, predictions of domestic, industrial, agricultural, and ecological water demands are made. The analysis of socioeconomic development indicators mainly includes the following aspects:
1) Population is a strong restricting factor for socioeconomic development, which mainly includes three indicators: population, urban population and rural population. When predicting the total population, the "direct estimation method" is used, that is, based on the population in the base period, direct estimation is carried out according to a certain increase rate. The formula is
Pn=Po(1+K)n
In the formula: Pn is the population in the forecast period; Po is the population in the base period; K is the annual growth rate during the forecast period. ; n is the number of years between forecast periods.
The main factors affecting population growth are changes in the birth rate, death rate and migration of the population. The analysis and prediction parameter K for the population adopts the annual population growth rate. Considering the urbanization development trend of Guilin and referring to the "Guilin Urban Master Plan (2001-2010)" to strictly control the excessive growth of the total population, the urban population will reach 700,000 by 2010, and the parameters from 2001 to 2010 will be The annual growth rate of urban population is about 3.67%, and the annual growth rate from 2011 to 2020 is about 0.70%. The annual growth rate of rural population from 2001 to 2010 was about 0.53%, and from 2011 to 2020, it was about 0.35%. The total urban population in 2000 was 643,000, including 488,100 in urban areas and 154,900 in rural areas. After calculation, it is predicted that the total population in 2005 will be 743,500, including 584,500 urban and 159,000 rural; the total population in 2010 will be 863,300, including 700,000 urban and 163,300 rural; and the total population in 2020 will be 919,700. Among them, 75.06 are in urban areas and 169,100 are in rural areas.
2) According to the “Tenth Five-Year Plan” for Guilin’s national economic and social development, the total industrial output value of Guilin’s urban area was 12.16 billion yuan in 2000. During the “Tenth Five-Year Plan” period, the average annual industrial growth rate was 12.2%. The annual total industrial output value reached 21.62 billion yuan; during the "Eleventh Five-Year Plan" period, the average annual industrial growth rate was 9.2%, and the total industrial output value in 2010 was 33.57 billion yuan; the long-term goal is for the average annual industrial growth rate of 5.2% in 2020, and the total industrial output value in 2020 is 557.3 billion.
3) Although the area of cultivated land in Guilin urban area has not changed much since 1990, it has been slightly decreasing. The potential for the expansion of effective irrigation area is not great. The annual decline rate of cultivated land is predicted to be 0.4%. The annual increase rate of effective irrigation area is about 0.2%. The actual irrigation rates in 2005, 2010, and 2020 were 70%, 75%, and 80% respectively. Among them, the paddy field irrigation area accounted for about 85% of the actual irrigation area.
In 2000, the cultivated land area was 7879hm2, of which the effective irrigated area was 6747hm2, the actual irrigated area was 4609hm2, and the irrigation rate was 68%, including 3918hm2 of paddy fields and 691hm2 of irrigated land. By 2005, the cultivated land area was 7723hm2, of which the effective irrigated area was 7723hm2. 6814hm2, the actual irrigated area is 4770hm2, including 4054hm2 of paddy fields and 716hm2 of irrigated land; in 2010 it was 7571hm2, of which the effective irrigated area was 6883hm2, and the actual irrigated area was 5162hm2, including 4388hm2 of paddy fields and 774hm2 of irrigated land; in 2020 it was 7274hm2, of which the effective irrigated area was 7022hm2, the actual irrigation area is 5618hm2, including 4775hm2 of paddy fields and 843hm2 of irrigated land.
The development of animal husbandry. In 2000, the number of large livestock was 16,900, and the number of small livestock was 121,500. According to the development trend of the livestock industry, the number of livestock is predicted to grow at a rate of about 5% in the next 20 years. By 2005, the number of livestock will be 175,300, in 2010, the number of livestock will be 223,800, and in 2020 it will be 364,600.
4) The total output value of the tertiary industry in 2000 was 4.94 billion yuan, accounting for 49.5% of the city's total tertiary industry output value. After 2005, due to the advancement of urbanization and the increase in urban population, the growth momentum of the tertiary industry will be stronger, and the proportion will increase. The urban area will account for 60% of the city's total output value of the tertiary industry for division. During the "Tenth Five-Year Plan" period, the average annual growth rate of the tertiary industry was 11.8%. In 2005, the total output value of the city's tertiary industry was 18.90 billion yuan, and that of the urban area was 11.34 billion yuan. During the "11th Five-Year Plan" period, the long-term goal of the tertiary industry in 2020 is The average growth rate was 9.4%. In 2010, the total output value of the city's tertiary industry was 29.62 billion yuan, while that in the urban area was 17.77 billion yuan. In 2020, the total output value of the city's tertiary industry was 72.73 billion yuan, while that in the urban area was 43.64 billion yuan.