Geographical environment of Luannan county

Luannan County is located at the southern foot of Yanshan Mountains, the lower reaches of Luanhe River, the northern shore of Bohai Bay and the eastern edge of North China Plain. There are no mountains in the territory, the terrain is flat, the north is high and the south is low, and the landform types are simple, all of which belong to plain landform. The following are described according to the land landform and intertidal landform respectively.

Terrestrial landform

Although the land in Luannan County belongs to plain landform, the formation process is still different. Land landforms can be divided into the following categories:

The first is the flood plain.

It is mainly distributed in Luannan County and the north of Luanxian County, the northwest of Luannan County and the suburbs of Tangshan City. It is the marginal part of the alluvial fan in the north. The terrain is relatively high, generally 25 ~ 30m above sea level, and the highest can reach 38. 1 m.. The ground slope is 0.5 ~ 1.5 ‰. It is mainly Luanhe alluvial deposit, consisting of silty sand, fine sand and medium sand.

Second, the alluvial plain

Most of the land in Luannan County is alluvial plain, which was divided into alluvial plain in the west of the largest transgression boundary in the late glacial period 5000 years ago. Part of it is the river belt formed by Luanhe River in historical period. The altitude is 5 ~ 25m, and the ground slope is generally 0.5 ~ 2 ‰. There are many rivers in Luannan County, but they basically belong to Luanhe River system. Historically, the Luanhe River has changed its course many times. According to records, before 12 century, Luanhe River was exported from Qian 'an to Zhuang Lei, and went south to the sea through Baigezhuang. This period is long, with thick accumulation and obvious fan shaft shape. From14th century to19th century, Luanhe River entered the sea from southeast to south of Luanxian County and from Liuzan. There are no rules during this period, and things go back and forth, swinging a lot. It has successively entered the sea through Liuzan, Wangtan, Dongzhuang and Lianhuachi, and according to the Records of Luanxian County, the Luanhe River is fast-flowing and the shifting of quicksand on both sides is uncertain. Every summer and autumn, when it rains, the river in Luannan County overflows and carries sediment into the sea from east to west, resulting in the alluvial plain in the territory being mainly sandy, with no obvious regularity.

Three, slow hillock, sand dunes, natural dikes

Due to the flood caused by river diversion, flood alluvial and accumulation caused by wind transport, some gentle hills, sand dunes and natural dikes have formed in Luannan County, which are higher than the ground and gradually get rid of the influence of groundwater, thus forming a new landform type. Generally 2 ~ 5 meters above the ground.

Fourth, the marine plain.

The marine plain in Luannan county is the product of regression in the late Holocene, which is distributed between the high tide line and the alluvial plain, and the bandwidth of Nanbao and Sigezhuang reaches more than ten kilometers. The altitude is 0 ~ 3m, and the ground slope is about 0. 1‰, which is extremely flat. If there is no seawall, the rising water at high tide can still flood some areas, which is composed of clayey sand and sandy clay.

Verb (abbreviation for verb) earthquake landform

The main performance is seismic sand cone, which was ejected along the pore of the cover due to liquefaction during the Tangshan earthquake, with a diameter of 1 ~ 5 meters, mostly distributed in the alluvial plain of Luannan County.

Intertidal landform

The intertidal zone in the coastal zone of Luannan County is very broad, and there are geomorphological types dominated by rivers and seawater, and there are also geomorphological types dominated by rivers and oceans.

There are beaches in Caofeidian area. The average slope of the beach is 5 degrees. Sediments are composed of grayish yellow medium-fine sand and medium-coarse sand, often containing coarse sand and small gravel.

Luannan county is located in the eastern monsoon region and belongs to the continental climate of warm temperate coastal semi-humid areas. It is characterized by four distinct seasons, abundant sunshine, less rainfall, uneven distribution, cold winter and warm spring, hot summer and cool autumn, and large temperature difference.

First, at the beginning of the season in beginning of spring, cold and warm air currents frequently cross, the temperature changes greatly, and the weather is occasionally cold in early spring. The climate characteristics of this season are: the temperature rises rapidly, it is dry, windy, the evaporation is large, and the precipitation increases month by month. The seasonal average temperature is 1 1. 1℃, and the precipitation is 77.3mm, accounting for 1 1.8% of the annual precipitation. The maximum precipitation in spring over the years is125.0mm (1971year) and the minimum is 35.5mm (1986). The extreme minimum temperature in April is-3.2℃ (1976 April 1 1), and the extreme maximum temperature in May is 35.5℃ (1980 May 27th), with a range of about 38℃. Because the temperature rises rapidly, the number of windy days increases, the climate is dry, and the soil moisture loss is serious, the climate characteristics of "nine droughts in ten years" in this county are quite remarkable. Even in years with more precipitation, there will be different degrees of spring drought due to uneven distribution of rainfall. This season is the windiest season of the year. According to statistics from 1967 to 1986, the number of windy days accounts for 55.2% of the total number of windy days in the whole year, and the number of hail days accounts for 30.8% of the total number of hail days in the whole year.

Second, summer is the period from the awn of the lunar calendar to the summer solar terms. High temperature and large and concentrated precipitation have a great relationship with the growth of crops. The average annual precipitation is 487.6 mm, accounting for 74.7% of the whole year. The maximum seasonal precipitation is 783.0mm (1977), and the minimum seasonal precipitation is132.2mm (1968). The average number of rainy days in the whole season for many years is 35 days, and there is precipitation once every three days. Over the years, the daily maximum precipitation was 236.9 mm (1July 3, 975), the longest continuous precipitation days was 7 days (1July 23 -29, 978), and the accumulated precipitation was 263.9 mm. From mid-July to early August, precipitation was concentrated and there were many rainstorms, accounting for 66.7% of the annual rainstorm. Low-lying areas are prone to floods. From mid-July to mid-August, it is a "three-volt" period, often controlled by subtropical high, and the weather is sultry. With the enhancement of convection, thunderstorms often occur in some areas, accompanied by hail weather. The seasonal average temperature is 24.0℃, and the extreme maximum temperature is 38.6℃ (1June 5, 968).

Third, around the autumn equinox, under the influence of cold air, cold and warm air flows cross again. The climate is characterized by a large temperature difference between day and night, a slow wave-like decline in temperature and a gradual decrease in rain, which can be described as "the sky is high and the clouds are light, and the autumn is crisp". The average seasonal precipitation is 72. 1 mm, accounting for 1 1% of the total annual precipitation. Foggy days account for 70% of foggy days, with sunshine hours of 690.5 hours, accounting for 25% of sunshine hours. The average temperature is 65438 02.0℃.

Four, after the light snow in winter, that is, entering the winter, the cold air in the north frequently goes south, the temperature drops suddenly, and the northwest and northerly winds prevail, with an average wind speed of 3.0 m/s, and the climate is dry and cold, with occasional cold waves. The seasonal average temperature is -4.6℃, the extreme minimum temperature is-21.7℃ (1973 65438+1October 26th), and the average minimum temperature is between -6 ~- 13℃. Precipitation 15.7mm, maximum snow depth of 23 cm (1973 65438+1October 25th). Luannan county has good water resources conditions, with an average annual precipitation of 808 million cubic meters and self-produced runoff of 65.438+0.27 billion cubic meters, but its storage capacity is poor, and only 7.5 million cubic meters can be utilized in 2065.438+02. The average annual recharge of groundwater is 1.2 1 100 million cubic meters, which can be developed and utilized.

Surface water-river course

There are major rivers such as Luanhe River, Little qinglong river River, Shuanglong River, Beihe River, Xiaoqing River, Hesui River, Yuejiahe River and Manqiu River, and major channels such as Baigezhuang Water Delivery Channel, Luanle Main Canal, First Spillway and Second Spillway, with a total length of 202.4 kilometers. The total water area of surface runoff is 1.27 square kilometers, and the average runoff depth for many years is 100.2 mm, resulting in runoff of 1.27 billion cubic meters, which flows into Yuejiahe, Shuanglong River, Xiaoqinglong river, Beihe River, Manqiu River, Hesui River, Baigezhuang main canal, Luanle main canal and Xiaoqing River respectively.

Nearshore waters

According to the requirements of "Regulations on Comprehensive Investigation of Beach Resources in Marine Zones" and the needs of developing sea areas in Hebei Province, the scope of shallow water investigation in Hebei Province is determined as 0 ~ 20m isobath. 1986, Hebei Provincial Bureau of Surveying and Mapping used the topographic map of Hebei Province1:200,000 coastal zone and TAMAYAPLanix5000 digital area meter of Japan to measure the shallow sea area of Luannan County of 784 square kilometers, namely1176,000 mu. Among them, the water depth from 0 to 5 meters is 304 square kilometers, accounting for 456,000 mu; 5 ~10m water depth area168.8km2, accounting for 253,200 mu; 10 ~ 20m water depth 3 1 1.2km2, 466,800 mu.

underground water

I. Groundwater zoning

Luannan County is located in the horizontal plain and coastal plain on the front slope of Yanshan Mountains, both of which belong to the thick Quaternary loose strata. From north to south, the particles are coarse to fine, from sandy pebbles and gravels to silty sand, and pebbles and gravels gradually disappear. The water content changes from thick to thin, from single layer to multi-layer, the water quantity changes from large to small, the water quality changes from good to bad (the deep confined water in the south is still good), and the groundwater flows from north to south to east. According to the underground hydrogeological conditions, the county can be divided into three areas: one is the slope plain area located in the middle of the Luanhe River alluvial fan; The second area is the completely shallow groundwater area in the eastern depression plain; The three regions are coastal plain salt water areas.

Second, the amount of groundwater available.

The available groundwater in Luannan County is mainly fresh water area, with a total area of 9 15.7 square kilometers. Available groundwater mainly comes from the recharge of atmospheric precipitation. The average annual precipitation infiltration recharge in the county is 1. 1.83 billion cubic meters. The average lateral recharge in salt water area for many years is 3 million cubic meters. In addition, due to the side supply of Luanhe River, Luanle main canal and Luanbai main canal, the county seat is still a resource-rich county. The lateral recharge of groundwater in the county is 70 million cubic meters. In the year of average rainfall, the available groundwater in the county is 654.38+88.3 million cubic meters. In rainy years with 50% frequency, 654.38+82.3 million cubic meters of groundwater can be used; In rainy years with 75% frequency, the available groundwater is 654.38+56.5 million cubic meters.