| The upstream watershed stratum of Qinjiang river is the Triassic Daye-Jia lingjiang group(T1j-T1d), Dyas Changxing group(P2c), Dyas Xixia-Maokou group(P1q-Pim), and Cambrian-Ordovician(€～O). The stratum lithology is carbonatite mainly. There’re many karst depressions, funnels, hoje, trough valleys, underground avens, karst caves and underground rivers on the earth’s surface. Moreover, there’re abundant precipitation and hard rain in this area, especially from April to October. So the river level rises and falls sharply. Qingjiang River is definitely a mountain river. Therefore, studying on the typical Karst watershed hydrological processes has important science significance. Enshi city is located in the hinterland of Enshi Basin, Qingjiang River meanders through the city. However, the river course in the city is flat and the protective equipment is weak, and there is no control water storage project in the upstream. It makes the flood control situation of this city harder. The flood control system of Enshi city need to promote immediately. This research provides scientific evidence about rational development and utilization of water resources in the river basin, so does the planning and construction of city flood control system.This paper took the river basin controlled by Enshi city section as a subject investigated, the influence factors, characteristics and change rule of Qingjiang River runoff above Enshi section were studied deeply, and then hydrological processes was forecasted scientifically by choosing rational hydrological model and prediction method. At present, the study on karst watershed boundary condition is weak. There are many karst depressions, funnels and underground avens, it’s hard to confirm the karst watershed boundary condition.The watershed boundary condition of Qingjiang River was studied by tracer test deeply in this paper. There were four tracer test in the west, south and north of the river basin. The west boundary of Qingjiang River Basin is the east karst valley, Qiyueshan anticline core part. The south boundary is the watershed area in the south of Huaping. The north boundary is the watershed area in the north of Hamakou. The karst underground river system of Baiguoba east boundary isn’t controlled by Baiguoba anticline, draining in Dalongtan reservoir In the upper reaches of Qingjiang River, but mingles the lower reaches of the Qingjiang River in Enshi section, out of Basin range controlled by Qingjiang River in Enshi section. So as to determine the measure of area about the river basin above Enshi section is 2928km".According to the daily data from 1960 to 2012 of Enshi hydrologic station and 1978 to 2012 of Lichuan hydrologic station, the change characteristic and rule of Qingjiang River upstream runoff were analysed by the trend analysis method and hydrological statistics analysis method.The following conclusions are obtained.(1) The annual average runoff amount of Qingjiang River upstream descended as a whole from 1960 to 2012, obviously in 0.05 level, and the change trend isn’t the same completely in different period, with stepped change characteristic. The annual average runoff amount of Qingjiang River upstream from 1960 to 2012 changed slowly, about 88.2m3/s, and descended from 1985 to 2012, 83.7m2/s in 198 to 65.2 m3/s in 2012.(2) The annual average runoff amount of Qingjiang River upstream from 1960 to 2012 rose in drought period, especially in December, January and February, when runoff amount increased. The average runoff amount descended in normal water period, especially in March, September and October.(3) The runoff coefficient, modulus and peak flow of Qingjiang upstream river basin descends obviously in 0.05 significant level. The runoff coefficient descended from 0.64 in 1960 to 0.55 in 2012,0.0288 m3(km2·s) in1960 to 0.0223 m3/(km2·s) in 2012 about runoff modulus and 2030m3/s in 1960 to 861m3/s in 2012 about peak flow amount.(4) There were three stages about karst river basin change base flow amount of Qingjiang River upstream. The base flow amount descended from 31.9 m3/s in 1960 to 23.6m3/s in 1976; increased from 23.6m3/s in 1976 to 35.7m3/s in 2000; descended from 2001 to 2012.(5) There were two stages about karst river basin change base flow index number of Qingjiang River upstream, descended from 0.38 in 1960 to 0.33 in 1976, the average number is 0.32, and increased from 0.33 in 1976 to 0.44 in 2012.In this study, according to the daily data from 1960 to 2012 of 11 rainfall stations in the upstream Qingjiang River and other rainfall data, the runoff amount influenced by rainfall for a long term was analysed, and so did the hydrological process in Enshi section before and after water conservancy and hydropower project construction. Studying on land utilization in the upstream Qingjiang River, especially the vegetation change, the runoff amount influenced by the forest was discovered.(1) Rainfall is the main factor to the change of runoff amount in upstream Qingjiang River, annual rainfall decides annual runoff. The rainfall of abundant water period, normal water period, drought period in Enshi section is severally 0.8414,0.7034 and 0.5422, meaning the influence degree is:bundant water period> normal water period> drought period. The main reason is the rainfall is more abundant in abundant and normal water period, and the runoff amount is bigger. Water conservancy and Hydropower Engineering or other factors is weaker by contrast. In drought period, especially in December and January, the runoff amount recharges by groundwater mainly. Moreover, a large number of runoff amounts retains in the upstream reservoir, so the runoff amount is decided by the drain amount from the reservoir.(2) By studying on 50mm/d, 100mm/d and 160mm/d rainfall, the shape of the runoff duration curve is similar in types of rainfall condition, increasing sharply and descending slowly, but obviously different with the different rainfalls. The runoff duration curve with 160mm/d rainfall increases and descends more quickly, looked like thinner and taller. The other two curve increase and descend more slowly, looked like fatter and shorter.(3) The rainfall duration curve with 160mm/d spent 7 hours from the increase term to the peak term,50mm/d’s and 100mm/d’s were 11-12 hours. At the same time, the runoff duration curves were all about 80 hours. The shape of the runoff duration curve is decided by the two mark time.(4) By analysing the rainfalls and runoff amount before and after building Cheba reservoir, I found out the average annual runoff reduced by 13m3/s after building the reservoir. Water conservancy and hydropower engineering could reduce the runoff amount because of the increasing evaporation capacity.(5) Before and after building Chebahe and Dalongtan reservoir, by studying on selecting respectively two similar rainfalls duration curves with 80mm/d, the result displayed the lag of time about flood peak increased obviously after building reservoir in the same rainfall, and the flood peak reduced. By counting four rainfalls duration curves, four runoff amount influenced by rain was respectively 1.54×108m3(before building Chebahe reservoir),1.24×108m3 after building Chebahe reservoir),1.12×108m3 (before building Dalongtan reservoir) and 1.00×108m3 (after building Dalongtan reservoir). It means the runoff amount reduces contrarily in the same rainfall condition, the main reason is a little runoff is retained by reservoir.(6) Research shows that the forest coverage rate of upstream Qingjiang Basin is an important reason to influence the change of base flow the forest coverage rate shows a significant positive correlation with base flow and base flow index. The vegetation and litter on the ground have stagnant water action, rainfall infiltration and base flow increasing.On the basis of analyzing the runoff characteristic and influence factors in karst river basin of upstream Qingjiang River, the semi distributed hydrological forecasting model (TOPMODEL) of upstream Qingjiang River basin was built by the method of watershed hydrological model. According to the hydrologic characteristic parameters obtained by hydrogeological investigation and analyzing rainfalls-runoff duration, using short sequences and high resolution, the typical rainfall-hydrological process model identification was carried out, and checked by long sequences annual rainfall. The flood peak duration once 200 years in Enshi section was predicted.The following conclusions were found out.(1) In this paper, using 50mm/d,80 mm/d,100 mm/d and 160 mm/d rainfalls to identify model, the result is TOPMODEL model has a good effect in runoff prediction simulation. The ime and value of flood peak simulation is close to the measured value, but the speed of the reduction is more slowly than the measured value.(2) Checked the model by rainfall-runoff duration curve in 2002, The results showed the rainfall-runoff simulation value(70m3/s) was similar to the measured value(83.5m3/s), the tolerance rate was 16%.(3) Predicting Flood rain-runoff duration in 0.5% frequency showed that the flood peak runoff amount once 200 years in Enshi section was 7300m3/s and the lag time of flood peak was 16 hours. |
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