EFFECTS OF URBAN LAKES ON QUANTITY AND QUALITY OF BASEFLOW
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ABSTRACT: Man‐made lakes have significant impacts on the hydrologic conditions in the watershed in which they are built. This paper examines the nature of the impact upon baseflow by comparing baseflow conditions at the outlet of the lakes with those elsewhere in the watershed. Situated in the upper reaches of a small watershed, the lakes studied have only a minor effect upon the magnitude of baseflow discharge, increasing it slightly from October to January, and decreasing it from May to September. Baseflow quality is substantially affected. Natural dissolved ions, as represented by magnesium, are generally decreased in concentration and total load by the lakes. Road salt related inons are substantially increased in both concentration and total load in the baseflow. Surface runoff stored in the lakes is extremely enriched in salt in the winter, and the storage capacity of the lakes is sufficient to maintain winter salt concentrations in the baseflow near the lakes until summer. The storage effect also tends to damp out seasonal fluctuations in baseflow chloride content which are extreme in suburban watersheds. The difference in quality between the lake and non‐lake baseflows and the linear distance needed for complete mixing are used as measures of the magnitude and distal extent of the lake effect on baseflow quality.Keywords:
Base flow
Variations in surface storage capacity over a watershed produce partial areas of saturation overland flow, which vary from storm to storm. A method is described by which the proportions of a watershed that contributes overland flow in different storms and at different times during the same storm can be determined by analysis of rainfall and runoff records. The method is demonstrated on two catchments in Queensland, Australia, with different hydrological characteristics. One watershed is 16.8 ha in area with only two to three events per year of overland flow (no baseflow) averaging 35 mm per annum runoff; the other is 7 km in area with substantial baseflow and an average of 920 mm per annum runoff. The calculated amounts and proportions of surface storage capacity are incorporated into water balance models of watershed runoff to show the accuracy of runoff estimation.
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The analysis of baseflow contribution is very significant in Korea because most rivers have high variability of streamflow due to the monsoon climate. Recently, the importance of such analysis is being more evident especially in terms of river management because of the changing pattern of rainfall and runoff resulted from climate change. Various baseflow separation methods have been developed to separate baseflow from streamflow. However, it is very difficult to identify which method is the most accurate way due to the lack of measured baseflow data. Moreover, it is inappropriate to analyze the annual baseflow contribution for Korean rivers because rainfall patterns varies significantly with the seasons. Thus, this study compared the baseflow contributions at various time-scales (annual, seasonal and monthly) for the 4 major river basins through BFI (baseflow index) and suggested baseflow contribution of each basin by the BFI ranges searched from different baseflow separation methods (e.g., BFLOW, HYSEP, PART, WHAT). Based on the comparison of baseflow contributions at the three time scales, this study showed that the baseflow contributions from the monthly and seasonal analysis are more reasonable than that from the annual analysis. Furthermore, this study proposes that defining BFI with its range is more proper than a specific value for a watershed, considering the difference of BFIs between various baseflow separation methods.
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Precipitation is very important to the formation of runoff, and studying of runoff variation and its response to precipitation has practical significance to sustainable utilization of water resources. The study used Mann-Kendall test, anomaly accumulation method, and precipitation elasticity of runoff method to analyze the changes in the relation of precipitation and runoff and the contribution of precipitation to runoff change in the Hekou-Longmen region (from 1957 to 2010), Huangfuchuan watershed (from 1954 to 2010), and Yanhe watershed (from 1952 to 2010) in the middle reaches of the Yellow River. The results showed that runoff appeared a significant decreasing trend( P = 0.01 )
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A method is presented by which the proportions of a watershed that contribute surface runoff in different storms and at different times during the same storm can be determined by analysis of rainfall and runoff records. The method is a modification of a method described in an earlier paper, which eliminates the need for subjective selection of particular runoff events for analysis. The method is illustrated using data from a 16.8‐ha watershed in Queensland, Australia, and the estimates of runoff from the different source areas are compared with actual records of runoff from the whole watershed. Runoff occurred from the entire watershed area on only three occasions in the 15‐yr study period, about 10% of runoff events. In about two‐thirds of runoff events, runoff came only from the 15% of the watershed that has the smallest surface storage capacity.
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Runoff regeneration processes are one of the key processes in the water cycles. Runoff can be separated into direct runoff and baseflow according to the response rate to precipitation.The baseflow is generally defined as the part of river runoff come from groundwater storage and other delayed water, while the direct runoff is defined as the part of river runoff direct response to precipitation. Based on this theory, the impact of climate factors on runoff is analyzed by investigating the conversion rate of precipitation to total runoff, baseflow and direct runoff. In the sources regions of the Yellow river, runoff coefficient was in positive relation with precipitation and in negative relation with air temperature; runoff increased with the precipitation. In the 1990s the sharp decrease of precipitation and increase of temperature contributed to the decrease of runoff. Impacts of climate on runoff were different in different subbasin in the source regions of the Yellow river. In subbasins above Jimai hydrologic station with mean annual temperature below -3.0 ℃, temperature was the key factors affecting runoff. With the increase of temperature runoff will decrease. In subbasin between Jimai hydrologic station and Maqu, runoff and baseflow both increased with the increase of precipitation, and decreased with the increase of temperature. In subbasin between Maqu and Tangnaihai hydrologic stations, precipitation was the vital climate factor affecting runoff(including baseflow and direct flow and total runoff), only direct flow are slightly influenced by temperature.
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Catchment storage capacity is an important factor in the determination of catchment sensitivity to climate variability. Quantification of catchment sensitivity is in turn important in the regional assessment of the effects of possible climate change. In the present paper, an empirical regional model is proposed that quantifies catchment sensitivity as the ratio of present maximum reservoir storage to catchment storage capacity. Catchment storage capacity is defined theoretically using readily available catchment variables. Present maximum reservoir storage in a catchment, as determined from recession analysis, is expressed as a fraction of catchment storage capacity; the fraction defines catchment sensitivity and depends on storage capacity and annual net precipitation. Average annual conditions for present maximum reservoir storage and average annual net precipitation are used to test the developed model. Although the study used data from only 15 catchments in the Upper Loire region in France, the model proved statistically valid. Storage capacity calculated with the model compares favourably with the baseflow index and a storage index defined in previous research. Values of storage capacity are probable with respect to reported water resources in the area. With the model catchment sensitivity can easily be assessed. Flood or drought prone catchments can be identified as well as a catchment's sensitivity to a catchment-type transition (baseflow versus direct flow dominated catchments). © 1998 John Wiley & Sons, Ltd.
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In this paper,measured data of precipitation,evaporation,temperature and runoff from meteorological and hydrometric stations in the studied basins were used for researching the changing trend and features of the runoff from the mountain areas of some main rivers in the region.The result shows that there is a decreasing trend of mean annual runoff in Shiyang river drainage basin,in easten and middle reaches,there is a decreasing trend,but in weasten reaches is tend to increase.The average distribution of the runoff due to the conditions of supply,the runoff of season in turn for the summer,autumn and spring and winter.There is a decreasing trend in the observations on runoff in four seasons,most significant decreases occur in summer,the least in winter;It is also found that the vibration periods of 6~7 a,9~10 a long period and 2~3 a short period are displayed very clear in Shiyang river drainage basin.The probability of mean water is the biggest in different age in Shiyang river drainage basin.On the attribution,we calculated the correlation coefficients of climate factors with runoff,positive correlation between runoff and regional precipitation is significant,and negative correlation between runoff and regional evaporation is also significant,indicating that the variations of regional precipitation and evaporation have predominant effect on the runoff variations,and maximum temperature is important factor.And the regional mean and minimum temperature also have different influences on the runoff variations.Synthetic effect of regional climatic elements is the prime cause for runoff variations in the source region of the Shiyang river drainage basin.
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Baseflow plays an important role in water security,food security,water resource assessment and investigation,and water allocation.Baseflow is mainly the recharges from groundwater.The characteristics of recharge and discharge of groundwater are very important to efficient groundwater management and sustainable development,and are vital to the control of pollution.Runoff of the source regions of the Yellow River accounts for more than 35% of the total ruhoff of the Yellow River basin.Baseflow is a very important water supply source in the low flow season and also an important supply cource in the headwaters,hence,it's essential to estimate baseflow in this area.There are numerous baseflow separation methods such as analytic methods and graphic methods,but they have their own shortcomings and can't be applied extensively.In this study,two physically based and two parameters based baseflow separation methods-Kalinin method and digital filiter method-were selected.First the Kalinin baseflow separation method was improved based on the climate condition of the study area and a new procedure was developed and then the sensitivity analysis was conducted for the two methods.The results show that the baseflow separated by digital filter baseflow separation method is very sensitive to the parameter's variation,and the filter parameter β is the control factors of the baseflow.With the increase of β the separated baseflow decreases and vice versa.The sensitivity(analysis) curves are very alike as to the runoff of different years.The baseflow separated by the modified Kalinin method is strongly affected by the runoff hydrograph,generally,the baseflow increases with the increase of recession coefficient and is not sensitive to the variation of parameters.
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