Study the regional natural environment and social economy.

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 the northeast of Guangxi Zhuang Autonomous Region, in the middle of Guilin (Figure 2.2), in the valley basin of Lijiang River in Xianggui Corridor, and distributed on both sides of the upper reaches of Lijiang River in the north-south direction. It is located between east longitude11012' 58 "~1021'29" and north latitude 25 00' ~ 25 21'43 ". The urban area is 40km long from north to south and 10.0 ~ 22.5km wide from east to west, with a total area of 565km2.

2.2. 1.2 Terrain

The topography of Guilin city is roughly a valley basin centered on Zhemu Town. This basin extends from Tang San to Liangfeng in the south, forming a big gap in the west. The surrounding terrain is high, with rocky mountains and earth mountains, mostly hilly slopes. This basin has become a concentration of rivers. Taohuajiang comes from the northwest, Liangfengjiang comes from the southwest, and * * * joins the Lijiang River. The relatively flat terrain and dense water network in the basin provide favorable conditions for farmland irrigation and are the main bases for urban agricultural production. Yaoshan Mountain in the northeast is majestic and steep, with the highest peak at 909.3 meters above sea level. It and Yanshan Mountain in the south and west are both earth-rock mountains. The hills around Yaoshan, Yanshan Daling, Dapu and Longquan near Huangcun in the south of Changling are mainly composed of Lower Devonian Lianhuashan Formation and Sipai Formation shales. The banks of the Lijiang River in the north and the towns in the south are mostly hilly slopes, mostly Quaternary red soil, and the developed soil layer is dark brown red. The northwest and southeast are mostly limestone with undulating peaks and forests, which is a typical karst landform.

Figure 2.2 Administrative Division Map of Guilin City

Figure 2.3 stereoscopic view of Guilin landform

There are two series of karst landforms and flowing water landforms in urban areas, with complex landform types and diverse forms. Low mountains, hills, basins and flat land are all distributed, mainly flat land, accounting for 60.9% of the total urban area. 96% of the urban area belongs to karst landform, mainly including peak forest plain and peak cluster depression (Figure 2.3). The basement of LAM Raymond Plain is carbonate rock, which is covered with laterite and clastic sediments, forming the main agricultural areas. The elevation of the plain is 145 ~ 180 m, and there are independent peaks with different densities, sizes and heights. The relative heights of mountain peaks are mostly within 100m, and the peaks are steep, with a slope angle greater than 50, with various shapes, developed caves, rich groundwater, shallow burial and karst lakes. The peak-cluster depression consists of many interconnected conical peaks, karst depressions and valleys. The peak is steep, with a slope of over 45 degrees. The depressions are dotted with local valleys, showing the landscape of peaks and valleys. In addition, caves are densely developed and numerous. According to statistics, there are 389 caves with a certain scale exposed to the earth's surface, such as Qixingyan, reed flute cave, Yan Guan and Chuanshanyan.

2.2. 1.3 climate characteristics

Guilin is located in low latitude, with warm and humid climate, belonging to subtropical monsoon climate zone. The climate is mild throughout the year, with long summer and short winter, four distinct seasons, rainy spring and more rainy days; Summer is hot and humid, and heavy rain is concentrated; Autumn rainfall is obviously reduced, the climate is dry, and autumn drought is frequent; In winter, due to the cold wave, there are occasional short-term cold weather such as frost. The annual average temperature in Guilin is 18.8 ~ 19.2℃, the measured extreme maximum temperature is 39.4℃, the extreme minimum temperature is -4.9℃, the hottest in July, the monthly average temperature is 28.3℃, the coldest in 1 month, and the monthly average temperature is 7.9℃. The annual average relative humidity of air is 76%. Rich in heat and abundant sunshine, the average sunshine hours for many years are 1625 ~ 1667 h, and the sunshine percentage is 37. 1% ~ 38. 1%. Due to the influence of subtropical monsoon climate and Yuechengling mountain range, there is abundant rainfall in the urban area, and the annual average precipitation is1646 ~1917mm. Due to topographical factors, the rainfall distribution between north and south is uneven, with more rainfall in the north and less rainfall in the south. Due to the influence of 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 whole year, and the rainfall from May to June is the most, accounting for about 35.35% of the annual rainfall. The annual average evaporation is 1380 ~ 1560mm, with the largest evaporation in July, the monthly average evaporation is 190.3mm, and the average frost-free period for many years is 304 ~ 309 d. The wind direction throughout the year is mainly northeast wind with an average wind speed of 2.6 m/s.

2.2. 1.4 water system

There are many rivers, lakes and ponds in Guilin, and the water system is developed. Rivers passing through the city include Lijiang River, taohuajiang, Liangfeng River and nanxi river. Rivers in the urban area include Lingjian Stream, Jiang Xiaodong, chaoyang river, Ningyuan River, Nanwan River and Wayaochong, with a total length of 142km and a river network density of 0.25km/km2. These rivers belong to the Pearl River Basin and Xijiang River System. The total area of urban lakes and ponds is 13.65km2, and the lakes and ponds with larger areas include Ronghu, Shanshan, Gui Hu, West Lake, Longmu Lake and Bajiaotang.

(1) Lijiang River

Lijiang River is the customary name of the middle and upper reaches of Gui Jiang, with a total length of 2 14km. Originated in the north of Maoershan, Huajiang Township, Xing 'an, it is a major river running through the urban area. From Qinjia, lingchuan county, it enters Guilin City in the north, passes through the city in the south, flows into taohuajiang, flows to Douji Mountain in the southeast, winds south after passing through Dawei Town, and flows out of the city to Yangshuo, Yan Guan, a lawn Hui township in Yanshan District, flowing through the city for 49.3 kilometers.

Guilin Hydrological Station of Lijiang River (located in Wayao Dutou Village) has a rainfall collection area of 2860km2, with annual average rainfall of 1.935mm and annual average runoff of 4 1.30× 108 m3. The highest flood level in history occurred in June of 14, with a water level of 654338. The measured lowest water level140.18m (1989 65438+February 20th), and the minimum discharge is 3.80m3/s (19565438+February 7th, 0). Annual average flow 129.03m3/s, and monthly average flow in dry season is 22.7m3/s. ..

The riverbed of Lijiang River in Guilin is composed of pebbles, gravel and sand, and the riverbed is alternated with the beach along the river. The beach is long and deep, with low water depth 1 ~ 3m, shallow water depth of 0.6~0.9m and maximum water depth 12m. The average ratio of the riverbed profile from Baishitan to Zhemuzhen is 0.32‰. In dry season, the river width is generally150 ~190 m. Due to the low flow, some river beds are seriously exposed, some of which are only about 20 m ... The river area is about 14km2, with an average width of 280m, the narrowest 165m and the widest 460m, and the dry surface. In addition, there are many tributaries and islands in the urban area, including 9 islands. The urban section of Lijiang River has a safe flood discharge of 2580m3/s, and the urban area is seriously flooded when the water level of hydrological station reaches146.5m..

(2) taohuajiang

Taohuajiang, also known as Yangjiang, originated in the southeast of the central ridge at the junction of Wu Tong Town in Lingui County and Qingshitan Township in lingchuan county. The main stream flows from north to south to east through Wu Tong Town and Miaoling Township in Lingui County, flows north through Dingjiang Township in lingchuan county at Wuxianba in the urban area, enters Jiashan Township in the urban area from north to south through Shuinan Village, flows east through the urban area near Jiashan Township Government, and flows into Lijiang River downstream of Nanmenqiao from Xiangshan and Luobozhou respectively. The main stream is 65km long and is a first-class tributary of Lijiang River. The section flowing through the urban area is 19. 1km.

The rainwater harvesting area in taohuajiang is 298km2, with the average annual rainfall of1900 ~ 2000mm and the average annual runoff of 3.66x108m3. The investigated maximum discharge is 840m3/s( 1885), and the measured minimum discharge is 0.637m3/s( 1972). The annual average flow is11.6m3/s.

The average ratio of riverbed profile of Wuxianba-Luoshan Bridge in taohuajiang decreased to 0.44‰, the ratio of dry water to surface was 0.43‰, and the ratio of flood water to surface was 0.30‰. The width of the dry river is generally 40 ~ 0.9m The section from Hongqiao Dam to Luobozhou is called Ningyuan River, which is the main outflow channel of flood in taohuajiang during flood season. In the dry season, Ningyuan River is basically cut off, and the river flows into Lijiang River from Elephant Trunk Mountain. The width of taohuajiang trough is generally 50 ~ 60m, and the maximum width of Feiluan Bridge is 71m.. The section below Hongqiao Dam is wide, and the groove width is 60 ~ 70m. The riverbank along the river is very low, and the dry surface to the riverbank is generally 2 ~ 3m. The section of Shengli Bridge is only 4m at the highest, and the river is very curved. The total length of the river from Wuxianba to Feiluanqiao is nearly 10km, and the straight line is only 2. 1km. The flowing water along the river is divided by weirs and dams, so that the low water level is stepped. The flood discharge capacity of the existing river course is very low, and the safe discharge flow of the river course above Nanmenqiao is only 260 ~ 300m3/s, and the river bank will be flooded once every five years.

(3) Liangfenghe

Liangfeng River, also known as Qifeng River, originates from the vanilla rock at the junction of Yangshuo, Yongfu and Lingui counties, flows into the urban area from south to north through Shizikou and Nanbianshan in Lingui County, flows through the cool breeze in Yanshan District, then turns northeast, passes through Qifeng Town and flows into Lijiang River at Huziyan in Zhemu Town. The main stream is 69km long and is a first-class tributary of Lijiang River. The section flowing through the urban area is 3 1.5km long.

The rainwater collection area of Liangfeng River is 528km2, with annual average rainfall of 1700mm, annual average runoff of 5. 17× 108m3, maximum flow of 836m3/s, minimum flow of 0.484m3/s .. and annual average flow of164m3/.

The average ratio of Liangfeng River from Jinba to the riverbed of estuary is reduced to 0.49‰, and the ratio of dry water to surface is 0.39‰. The river width above the cool breeze is 20 ~ 30m, the water depth in dry season is 0.6 ~ 1.2m, and the bank height is 3 ~ 4m. From cool breeze to estuary, the river width is 30 ~ 50m, the water depth is low 1.0 ~ 1.4m, and the river bank is 5 ~ 8m high.

(4) nanxi river

Nanxi river originated at the foot of Goushan Mountain in Miaoling Township, Lingui, and its main stream turned from north to south to Han and Tang Dynasties and entered the urban area of Guilin. It flows through Tangjia Village and Guanqiao Village in Jiashan Township on the outskirts of the city, enters the urban area at Heishan Botanical Garden, bypasses Nanxi Mountain and joins the Lijiang River on the north side of Jidu Mountain. The main stream is 13km long and the urban section is 10.6km2 long. It is a first-class tributary of the Lijiang River.

The rainfall collection area in nanxi river is 24km2, with the average annual rainfall 1860mm, the average annual runoff of 0.29× 108m3, the average annual flow of 0.92m3/s and the average monthly flow of 0.2m3/s in the driest month.

Nanxi river twists and turns like a narrow path, and its width varies greatly, with the widest being about 50m and the narrowest being less than 10m. The average riverbed gradient is 1. 1‰.

(5) Jiang Xiaodong River

Jiang Xiaodong is a tributary of Lijiang River, and the whole river is in Chuanshan Township. It starts from Erjiangkou on the east bank of Lijiang River under Diecai Mountain in the north and flows from north to south. At the lower reaches of Xinqiao, Lingjian Stream flows out from the left bank, flows into Lingjian Stream, continues southward, flows back to Lijiang River in Chuanshan Park, and passes Qixing, Chuanshan Village Committee, Guishan Hotel, Qixing and Chuanshan Park in Qixing District, with a total length of 5.7km, a river width of 40-70m and a bank height of 3-4m. There are famous scenic spots such as Qixing Park, Longyinyan, Tashan and Chuanshan Park on both sides of the strait.

The Lijiang River basin above Erjiangkou covers an area of 2550km2, with annual average flow of 1 14m 3/s, and 10 is the dry season of Lijiang River from February to the following year, with an average flow of about 30m3/s. ..

(6) Hutang

The total area of existing lakes and ponds in the urban area is 13.65km2, which are mainly distributed in Jiashan Township in the west, Huangyingyan area in the east, Yanshan Town, Zhemu Town and the urban center in the south. Large lakes and ponds mainly include: Ronghu, Shanshan Lake, Gui Hu (including Xiqing Lake, Baoxian Lake and Lize Lake), West Lake, Longmu Lake and Bajiaotang. See Table 2. 1 for the basic information of major lakes and ponds.

Table 2. 1 Basic situation of main lakes and ponds in Guilin

2.2.2 Prediction of social and economic development

The goal of social and economic development is an important basis for forecasting the demand for water resources. Its influence on the growth of water resources demand is mainly reflected in: population growth and urbanization process; Adjustment of industrial structure and total industrial output value; Agricultural development and irrigation area growth. According to these development indicators, considering water resources conditions and regional development goals, the possible upper and lower limits are predicted respectively, and then according to the internal relations of various aspects, the predicted values of each sub-index are combined to form different development scenarios. Finally, based on these development scenarios, the water demand of life, industry, agriculture and ecology is predicted. The analysis of social and economic development indicators mainly includes the following aspects:

1) Population is a constraint factor of social and economic development, which mainly includes population, urban population and rural population. The "direct calculation algorithm" is used to predict the total population, that is, based on the population in the base period, it is directly calculated according to a certain increasing rate. Its formula is

Pn=Po( 1+K)n

Where: Pn is the population in the forecast period; Po is the base population; 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 the changes of birth rate, death rate and migration, and the annual population growth rate is used as the population analysis and prediction parameter K. Considering the development trend of urbanization in Guilin and referring to the overall urban planning of Guilin (200 1 ~ 20 10), the excessive growth of the total population will be strictly controlled, and the urban population will reach 700,000 by 20 10, and the annual urban population will be 20010. The annual growth rate of rural population is about 0.53% from 200 1 to 201,and it will be about 0.35% from 201to 2020. In 2000, the total population of urban areas was 643,000, including 488,654,38+0,000 in urban areas and 65,438+0,549,000 in rural areas. After calculation, it is predicted that the total population in 2005 will be 743,500, including 584,500 in cities and 654,380+059,000 in rural areas. In 20 10, the total population was 863,300, including 700,000 in cities and 0/63,300 in rural areas. In 2020, the total population will be 9 1.97 million, including 75.06 in urban areas and 0/.69110,000 in rural areas.

2) According to the Tenth Five-Year Plan for National Economic and Social Development of Guilin, the gross industrial output value of Guilin in 2000 was 65,438+0,265,438+0.6 billion yuan. During the Tenth Five-Year Plan period, the industry grew at an average annual rate of 65,438 0.2%, and the total industrial output value reached 26,543.8 0.62 billion yuan in 2005. During the Eleventh Five-Year Plan period, the industry grew at an average annual rate of 9.2%, and the total industrial output value in 20 10 was 33.57 billion yuan. The long-term goal is an average annual industrial growth of 5.2% in 2020, with a total industrial output value of 55.73 billion yuan in 2020.

3) Although the cultivated land area in Guilin has not changed much since 1990, it tends to decrease slightly, and there is little potential to expand the effective irrigation area. It is predicted that the annual decline rate of cultivated land area is about 0.4%, and the annual increase rate of effective irrigation area is about 0.2%. The actual irrigation rates in 2005, 20 10 and 2020 are 70% and 70% respectively.

In 2000, the cultivated land area was 7879hm2, of which the effective irrigation area was 6747hm2, the actual irrigation area was 4609hm2, and the irrigation rate was 68%, including paddy field 39 1.8 hm2 and irrigated land 69 1 hm2. By 2005, the cultivated land area was 7723hm2, of which the effective irrigation area was 68 1.4 hm2, and the actual irrigation area was 4770hm2, including 4054hm2 for paddy field and 7 1.6 hm2 for irrigated land. 20 10 year is 757 1hm2, in which the effective irrigation area is 6883hm2 and the actual irrigation area is 5 162hm2, in which paddy fields are 4388hm2 and 774hm2 on irrigated land. In 2020, it will be 7274hm2, including 7022hm2 of effective irrigation area and 56 18hm2 of actual irrigation area, including 4775hm2 of paddy field and 843hm2 of irrigated land.

The development of animal husbandry. In 2000, there were 0/6900 large livestock and 0/21500 small livestock. According to the development trend of animal husbandry, it is estimated that the number of livestock will increase by about 5% in the next 20 years. By 2005, the livestock population will be175.3 million, 223.8 million in 20 10, and 364.6 million in 2020.

4) In 2000, the total output value of the tertiary industry was 4.94 billion yuan, accounting for 49.5% of the total output value of the tertiary industry in the city. After 2005, due to the promotion of urbanization, the urban population will increase, and the growth momentum of the tertiary industry will be even stronger, and its proportion will increase. The urban area will be divided into 60% of the total output value of the tertiary industry in the city. During the Tenth Five-Year Plan period, the tertiary industry grew at an average annual rate of 1 1.8%. In 2005, the total output value of the tertiary industry in the city was189 billion yuan, and that in the urban area was 1 134 billion yuan. During the 11th Five-Year Plan period, the long-term goal is that the tertiary industry will grow at an average annual rate of 9.4% in 2020. In 20 10, the total output value of the tertiary industry in the city was 29.62 billion yuan, and that in the urban area was177.7 billion yuan. In 2020, the total output value of the tertiary industry in the city will be 72.73 billion yuan, and the urban area will be 43.64 billion yuan.