NUTRIENT LOAD ESTIMATION METHODS FOR RIVERS

Pollutant load estimation is essential for watershed management and water pollution control. For most watersheds, only sparse water quality measurements (e.g. monthly data) are available. The influence of input data on the accuracy of non-point source pollution load estimation is studied using the water quality and stream flow data from a small watershed in Hong Kong. Comparison and analysis of the results using 8 different methods show that the accuracy of stream-flow runoff is the single most important factor for the calculation of pollutant load. Based on the results, the stream flow correction coefficient is advanced to provide a more reliable load estimation. The improved method of pollutant load estimation can be easily applied in practice since the stream-flow runoff can be measured by hydrological station or estimated with various hydrological methods.     

AMÉNAGEMENT GÉOHYDROLOGIQUE DES TERRITOIRES ET PLANS DE COORDINATION RÉGIONAUX CONCERNANT PARTICULIÈREMENT L'ITALIE

Summary

A test is presented to reveal automatically doubtful water levels and to detect sudden or gradual modifications of the stream flow.

Each hydrometric station in a catchment area, homogeneous as to climatic conditions, is compared with a reference station. For this purpose we consider the ratios of the daily “reduced” water levels of the station under examination to the corresponding levels of the reference station. The “reduction” of the daily water stages is achieved by a fictitious shifting of the scale so that the mean yearly water level is placed at a predetermined level (the same everywhere) and by a dilatation (or a shrinking) of this scale so that the range Δ (the difference between the largest and the smallest monthly water levels) is equal to the range Δ₀ of the reference station. The daily ratios of the reduced water levels are consequently approximately 1 either with high or low water. When a daily ratio deviates too much (more than 10 % for instance) from the mean monthly ratio, the corresponding water level is considered as doubtful and must be verified. If the running mean monthly ratios do not remain approximately uniform but change suddenly or slowly, it is because the stream flow is disturbed and the reason for this disturbance must be investigated.

The test, used in a converse way, can also be satisfactorily used for filling in gaps in the observational data.

Some examples enable the value of the method to be assessed.     

Cross-spectral analysis of rainfall and runoff for Raritan and Mullica river basins in New Jersey

Cross-correlation and cross-spectral analysis were employed in the analysis of rainfall and runoff in two river basins: the Raritan and Mullica River basins in New Jersey. Cross-covariance and coherence were studied in the correlograms for the following correlation cases: (a) rainfall-runoff for each one basin separately; (b) rainfall-rainfall analysis for two main meteorological stations in each one of the basins; (c) runoff-runoff for two main gaging stations in each one of the basins. From the estimates of the coherence at various frequencies the cross-spectral analysis shows a highly nonlinear relationship between rainfall and runoff in Raritan and Mullica River basins. A poor coherence observed at the annual cycles for each basin makes it difficult to predict the annual oscillations of runoff from those of rain-fall by a linear regression model. The high coherence between rainfall (or runoff) at the first station and rainfall (or runoff) at the second station within the same basin at almost all frequencies establishes an accurate prediction on a linear basis.     

Runoff reduction by forest growth in Hiji River basin,Japan / Diminution de l'écoulement causée par la croissance forestière dans le bassin versant du Fleuve Hiji,Japon

Abstract

Forest growth unfavourably reduces low flows and annual runoff in a basin in Japan. Annual precipitation and runoff of the watershed are summarized from observed daily rainfall and discharge, and annual evapotranspiration is estimated from the annual water balance. The water balance analysis shows obvious trends: reduced annual runoff and increased evapotranspiration over a 36-year period when forest growth increased the leaf area index. Between two periods, 1960–1969 and 1983–1992, mean annual runoff decreased 11%, from 1258 to 1118 mm, due to a 37% increase in evapotranspiration (precipitation minus runoff) from 464 to 637 mm. This increase in evapotranspiration cannot be attributed to changed evaporative demand, based on climatic variability over the 36-year period of record. Flow duration curves show reduced flows in response to forest growth. In particular, they suggest stronger absolute changes for higher flows but stronger proportional changes for medium and lower flows. A distributed model is applied to simulate the influences of five scenarios based on a 30% change in leaf area index and 5% change in soil storage capacity. From the simulation results, canopy growth appears to contribute much more to flow reduction than changes in soil storage capacity.     

INTÉERÉET D'ÉETUDES HYDROLOGIQUES APPROFONDIES SUR DES BASSINS EXPÉERIMENTAUX OCCUPANT PLUSIEURS MILLIERS DE KM2

Abstract

A relationship of hydrologic variables with stream salinity was determined statistically for two ephemeral streams located in western Oklahoma. The hydrologic variables employed in this study are measures of streamflow, precipitation, anteccedent conditions, and agricultural land use.

The best single estimate of stream salinity was achieved by use of those variables classed as direct measures of precipitation, with the greatest variability in stream salinity (51%) being predicted by maximum daily P, the maximum amount of precipitation received at any rain gage zone in the watershed during one month. Maximum daily P predicts nearly double the variability in stream salinity predicted by flow. Antecedent conditions did not correlate well with stream salinity, except for the variable describing the antecedent stream salinity. Similarly, the areal location of precipitation within the watershed and agricultural land use did not correlate significantly with stream salinity, except for a variable designating the distance between the stream gaging station and the rain gage zone receiving the most precipitation for the month.

The best overall estimate of salinity was given by a multiple regression equation chosen on the basis of a factor analysis. This equation accounted for 65 percent of the variability in salinity and emphasized the contribution of variables classed as direct measures of precipitation. In comparing the two streams, the watershed having the most intensive rain gage network produced the best prediction equation.     

REPRODUCTION OF THE RUNOFF-RECORD OF THE RIO MOTATAN BY RAIN DATA,ESTABLISHING THE TRUE MONTHLY RUNOFF-FACTOR

Abstract

In 1950 only 10 years of streamflow observations and runoff data existed on the Rio Motatan in Western Venezuela (4,200 km² of watershed, Anden territory) with 24 raingauge stations in or near the watershed having a simultaneous record but only 3 recording stations with 30 years of observation. The “curve of dry spell”—January to April—was first determined on semilog hydrographs (logs of daily discharge vs. time) and by splitting the total flow into surface and groundwater components an abacus was established, relating the average monthly rain with the “true runoff”. (True runoff) = (observed runoff)—(part due to former month of rain) + (share in following months). For checking purposes the observed runoff record was reproduced, using data based on rain, reaching a high degree of accuracy. Then the same abacus was applied to the 20 years of isolated rain data and the corresponding runoff values were obtained. Recently seven more years of runoff data were successfully checked against the graphs.     

Base flow‐driven shifts in tropical stream temperature regimes across a mean annual rainfall gradient

Climate change is expected to affect air temperature and watershed hydrology, but the degree to which these concurrent changes affect stream temperature is not well documented in the tropics. How stream temperature varies over time under changing hydrologic conditions is difficult to isolate from seasonal changes in air temperature. Groundwater and bank storage contributions to stream flow (i.e., base flow [BF]) buffer water temperatures against seasonal and daily fluctuations in solar radiation and air temperature, whereas rainfall‐driven runoff produces flooding events that also influence stream temperature. We used a space‐for‐time substitution to examine how shifts in BF and runoff alter thermal regimes in streams by analyzing hydrological and temperature data collected from similar elevations (400–510 m above sea level) across a 3,500‐mm mean annual rainfall gradient on Hawai'i Island. Sub‐daily water temperature and stream flow gathered for 3 years were analyzed for daily, monthly, and seasonal trends and compared with air temperature measured at multiple elevations. Results indicate that decreases in median BF increased mean, maximum, and minimum water temperatures as well as daily temperature range. Monthly and daily trends in stream temperature among watersheds were more pronounced than air temperature, driven by differences in groundwater inputs and runoff. Stream temperature was strongly negatively correlated to BF during the dry season but not during the wet season due to frequent wet season runoff events contributing to total flow. In addition to projected increases in global air temperature, climate driven shifts in rainfall and runoff are likely to affect stream flow and groundwater recharge, with concurrent influences on BF resulting in shifts in water temperature that are likely to affect aquatic ecosystems.     

Simulating the impacts of land-use and climate change on water resource availability for a large south Indian catchment

Abstract

A monthly rainfall-runoff model was calibrated for a large tropical catchment in southern India. Various land-use and climatic change scenarios were tested to assess their effects on mean annual runoff and assured water yield at the Bhavanisagar Reservoir in Tamil Nadu, India. The largest increase in runoff (19%) came from converting forest and savanna (the indigenous control scenario) to agriculture. Mean annual runoff decreased by 35% after conversion to commercial forest and 6% after partial conversion to tea plantations. The predicted climate scenarios of reduced dry season rainfall decreased the annual runoff by 5% while enhanced annual rainfall caused a 17% increase in runoff. Even if land-use and climate changes had relatively large effects on runoff, the changes in reservoir yield which can be assured every year, were often less severe. This was probably due to the buffering effect of the reservoir and variation in the mean annual runoff.     

Long‐term growth of a valley‐bottom gully,western Iowa

Growth of a permanent, valley‐bottom gully from 1964 to 2000 was determined annually from survey and sediment‐discharge data and compared with runoff and base?ow discharges. Data were analysed to test the hypothesis that rates of gully growth decay exponentially with time in response to shrinking catchment area caused by gully enlargement. Also, monthly values of growth rates and runoff, averaged over the 36‐year record, were analysed with mass‐wasting data to determine the extent to which colluvium availability affected growth rates seasonally. From 1964 to 2000, the gully volume increased by 9200 m³, accounting for 34 per cent of sediment yield from the watershed. There were tight power‐law relationships between annual growth rates and annual runoff, with runoff exponents of 1·57 and 1·30 for headward and volumetric growth, respectively. Increases in gully length, area, and volume were ?tted successfully assuming an exponential decay in growth rate with time. Rather than being due to a decrease in catchment area, however, the decline in growth rate was caused by a 77 per cent decrease in the ratio of runoff to base?ow, which also widened the gully and reduced the mean slope of its banks. Order‐of‐magnitude seasonal changes in erosion ef?ciency, de?ned as the fraction of stream power used to evacuate sediment from the gully, were roughly correlated with colluvium availability, as indicated by seasonal changes in the number of bank mass‐wasting events. No more than 2·2 per cent of stream power was used to evacuate sediment during any month. This study demonstrates the danger of attributing declining rates of gully growth to a shrinking catchment area if corroborative runoff and base?ow data are not available. Moreover, it illustrates that stream power alone provides only a rough and physically indirect measure of erosion potential. Copyright © 2004 John Wiley & Sons, Ltd.     

Variations in runoff,sediment load,and their relationship for a major sediment source area of the Jialing River basin,southern China

Investigation of the variations in runoff, sediment load, and their dynamic relation is conducive to understanding hydrological regime changes and supporting channel regulation and fluvial management. This study is undertaken in the Xihanshui catchment, which is known for its high sediment-laden in the Jialing River of the Yangtze River basin, southern China, to evaluate the change characteristics of runoff, sediment load, and their relationship at multi-temporal scales from 1966 to 2016. The results showed that runoff changed significantly for more months, whereas the significant changes in monthly sediment load occurred from April to September. The contributions of runoff in summer and autumn and sediment load in summer to their annual value changes were greater. Annual runoff and sediment load in the Xihanshui catchment both exhibited significant decreasing trends (p < 0.05) with a significant mutation in 1993 (p < 0.05). The average annual runoff in the change period (1994–2016) decreased by 49.58% and annual sediment load displayed a substantial decline with a reduction of 77.77% in comparison with the reference period (1966–1993) due to climate change and intensive human activity. The power functions were satisfactory to describe annual and extreme monthly runoff–sediment relationships, whereas the monthly runoff–sediment relationship and extreme monthly sediment-runoff relationship were changeable. Spatially, annual runoff–sediment relationship alteration could be partly attributed to sediment load changes in the upstream area and runoff variations in the downstream region. Three quantitative methods revealed that the main driver for significant reductions of annual runoff and sediment load is the human activity dominated by soil and water conservation measures, while climate change only contributed 22.73%–38.99% (mean 32.07%) to the total runoff reduction and 3.39%–35.56% (mean 17.32%) to the total decrease in sediment load.     

Estimation of Columbia River virgin flow: 1879 to 1928

The Columbia River is a major source of and conduit for Pacific Northwest economic activity, and is one of the more heavily modified rivers in North America. Understanding human and climate‐induced changes in its hydrologic properties is, therefore, vital. Long streamflow records are essential to determining how runoff has changed over time, and Columbia River daily streamflow record at The Dalles began in 1878. To understand and separate anthropogenic and climate effects, however, it is also necessary to have a basin‐scale estimate of virgin or naturalized flow. The United States Geological Survey has calculated a monthly averaged adjusted river flow at The Dalles for 1879–1999 that accounts for the effects of flow regulation. The Bonneville Power Administration has estimated the monthly averaged virgin flow at The Dalles, i.e. the flow in the absence of both flow regulation and irrigation depletion for 1929–89. We have estimated the monthly virgin flow of the Columbia River at The Dalles from records of irrigated area for the missing early years, i.e. for the period 1879–1928. In addition, to allow hindcasting of a virgin flow sediment transport for the system, a daily virgin flow index with realistic higher moments and spectral properties has been calculated. Examination of the virgin flow record shows that climate change since the late 19th century has decreased annual average flow volume by > 7%; irrigation depletion has reduced the flow by another ∼7%. Copyright © 2005 John Wiley & Sons, Ltd.     

Estimation of monthly runoff from small catchments in India

Abstract

Data from 31 non-snowfed catchments in India having catchment areas less than 1515 km² have been analysed to develop a simple method for the estimation of monthly runoff for the monsoon months of June to October. One of the parameters of this method was found to vary with the catchment area, the percentage of forest cover in the catchment and the monthly average temperature. The value of another parameter of the proposed method was found to be constant during any one month in a hydrologically homogeneous region. The method proposed herein is useful for estimating the monthly runoff during the monsoon period from catchments having scarce data.     

GCM-related uncertainty in river flow projections at the threshold for “dangerous” climate change: the Kalu Ganga river,Sri Lanka

The Kalu Ganga catchment is one of the largest in Sri Lanka, and is home to 5% of the national population. A first assessment is provided here of the sensitivity of Kalu Ganga runoff to a 2°C increase in global mean temperature – the supposed threshold for “dangerous” climate change. Runoff is simulated using the HBV-Light hydrological model and scenario data from seven general circulation models (GCMs). Precipitation is the strongest cause of change in runoff. Substantial inter-GCM differences in scenario precipitation lead to uncertainty in the direction of change in mean annual runoff from the baseline (range ?25% to +19%). Scenario monthly runoff ranges from ?41% to +124% of the baseline values at its most extreme (March); June is the only month with a consistent direction of change (range ?17% to ?65%) – thus indicating that climate change may lead to a substantially different hydrological regime in the Kalu Ganga catchment.     

A variable-length block bootstrap method for multi-site synthetic streamflow generation

Abstract

The complexity of stochastic streamflow generators limits their practical use, highlighting the need for effective but simpler approaches. An attempt to meet this objective is presented using variable-length bootstrapping (VLB) of annual flows, and a weighted method of fragments for disaggregation and perturbing the bootstrapped annual flows. The perturbations enable generation of annual flows different from those present in the historical record, thereby overcoming one of the main limitations of the classical bootstrap method. The VLB replicates adequately nine historical annual statistics of a five-site problem, and reproduces the annual serial and cross-correlations better than STOMSA—a state-of-the-art parametric generator. The VLB achieves reasonable validation using the sum of minimum flows and the reservoir storage size test. Because of the modification of the monthly flow distribution caused by the weighted averaging of fragments, the VLB cannot be safely used for within-year analysis, but is a potentially robust annual streamflow generator.

Citation Ndiritu, J. (2011) A variable length block bootstrap for multi-site synthetic streamflow generation. Hydrol. Sci. J. 56(3), 362–379.     

Copula-based identification of the non-stationarity of the relation between runoff and sediment load

It is important to identify the non-stationarity in the relation between runoff and sediment load under the backdrop of the changing environment. This relation helps to further understand the mechanisms of runoff and sediment yield. A copula-based method was used to detect possible change points in the relation between runoff and sediment load in the Wei River Basin (WRB), China, where soil erosion is a very severe issue. The modified Mann-Kendall trend test method was applied to obtain the trends of runoff and sediment load spanning 1960–2010 at monthly and annual timescales. Finally, the causes of the identified non-stationarity of the relation between runoff and sediment load were roughly analyzed from the perspective of climate change and human activities. Results indicated that:(1) the runoff and sediment load in the Jinghe and Wei rivers were generally characterized by noticeably decreasing trends at both monthly and annual timescales;(2) both the Jinghe and Wei rivers had a common change point (2002), implying that the stationarity of the relation between runoff and sediment load in the Jinghe and Wei River was invalid; (3) human activities including increasing water consumption and growing application of soil conservation practices are dominant factors resulting in non-stationarity in the rela-tion between runoff and sediment load in the WRB. This study provides a new idea for identifying the non-stationarity of multivariate relation in the hydro-meteorological field under the background of the changing environment.     

A spreadsheet-based technique (Lotus 1-2-3) for separating tropical forest storm hydrographs using Hewlett and Hibbert's slope

The inclined line separation technique of Hewlett and Hibbert has been widely adopted to separate delayed flow from the total stream storm runoff. Presented here is the application of the technique to highly responsive storm hydrographs using a personal computer method based on a Lotus 1-2-3 spreadsheet. Using discharge measurements (in m³ s⁻¹), catchment area (in km²) and time (in Julian days), the separation slope is adjusted on the monitor screen until the precise time at which the end of quickflow as storm runoff gives way to delayed flow may be established. The application of the inclined line method is compared with other separation techniques applied to the same dataset. The annual stream quickflow runoff for the study catchment was calculated by the four different separating lines — (i) best-fit curve, (ii) N-day after peak, (iii) inclined line and (iv) horizontal line — was 250, 312, 368, and 588 mm, amounting to 33, 31, 51 and 78 per cent respectively of the annual total stream runoff. Separation of flow by computer spreadsheet methods may be consistently applied throughout a dataset and therefore have a comparative advantage over more arbitrary techniques. © 1997 John Wiley & Sons, Ltd.     

三峡水库运行前后长江中下游干流及两湖的径流过程变化

为探索三峡水库运行前后长江中下游干流及两湖径流过程的变化及其驱动因素,利用宜昌、监利、大通、七里山、湖口共5个水文站的流量资料,分析了各站径流过程的变化特征及其成因。结论:(1)各站年径流量均减少,但除七里山站之外,其它各站减少比例均小于10%且变化不显著;(2)干流各站月径流量最大减幅发生在10月,而七里山站、湖口站分别发生在7月、4月;(3)干流各站月径流量最大增幅发生在3月,而七里山站、湖口站分别发生在1月、6月;(4)宜昌站,1—4月径流量增加是三峡水库入库径流增加和水库调度的共同作用结果,6—8月径流量减少的主因是三峡水库入库径流量减少,5、9、10月径流量变化的主因是三峡水库调度;(5)监利站,径流量的变化与宜昌站表现出高度的一致性,但冬季各月径流量的增幅均大于宜昌站;(6)大通站,4—6月径流量变化方向与湖口站一致,其它月份变化方向均与宜昌站一致。(7)七里山站,7月径流量减少的主因是洞庭湖流域来水减少,9、10月径流量减少的主要原因是荆江分流减少,但洞庭湖流域来水减少也是重要原因。(8)湖口站,4、5月径流量减少的主因是流域降水减少,9、10月径流量减少的主要原因是鄱阳...     

Characteristics of annual runoff variation in major rivers of China

The statistical properties of annual runoff in major rivers of China are studied based on the theory of stochastic process and technology of time series analysis. These properties include the characteristics of intra‐annual and inter‐annual variations of runoff, trends, abrupt changes and periodicities. The new findings from the intensive calculations and appropriate analysis of data in longer period are as follows: (i) compared with the nonuniformity of intra‐annual runoff before 1980, the nonuniformity of intra‐annual runoff in China generally decreased after 1980, except for Huaihe River and Songhua River; (ii) compared with the annual runoff before 1980, the annual runoff in China generally decreased after 1980 except for WangJiaba station in Huaihe River and Ha‐Erbin station in Songhua River; the frequency of continuous low flow and continuous high flow in Haihe River and the downstream of Yellow River is higher than those in other rivers in China; (iii) annual runoff shows a downward trend in major rivers of China especially in Haihe River, Liao River and the midstream and downstream of Yellow River; (iv) there exist certain abrupt changes of annual runoff in major rivers of China; the abrupt change‐points are different among different river basins; and (v) almost periodicities of annual runoff sequences in major rivers of China are generally 20 years below, that is, 3~7 and 12~20 years. The reasons for these changes are mainly caused by climate change and human activities. Copyright © 2011 John Wiley & Sons, Ltd.     

Separation of base flow from streamflow using groundwater levels—illustrated for the Pang catchment (UK)

A new filter to separate base flow from streamflow has developed that uses observed groundwater levels. To relate the base flow to the observed groundwater levels, a non‐linear relation was used. This relation is suitable for unconfined aquifers with deep groundwater levels that do not respond to individual rainfall event. Because the filter was calibrated using total streamflow, an estimate of the direct runoff was also needed. The direct runoff was estimated from precipitation and potential evapotranspiration using a water balance model. The parameters for the base flow and direct runoff were estimated simultaneously using a Monte Carlo approach. Instead of one best solution, a range of satisfactory solutions was accepted. The filter was applied to data from two nested gauging stations in the Pang catchment (UK). Streamflow at the upstream station (Frilsham) is strongly dominated by base flow from the main aquifer, whereas at the downstream station (Pangbourne) a significant component of direct runoff also occurs. The filter appeared to provide satisfactory estimates at both stations. For Pangbourne, the rise of the base flow was strongly delayed compared with the rise of the streamflow. However, base flow exceeded streamflow on several occasions, especially during summer and autumn, which might be explained by evapotranspiration from riparian vegetation. To evaluate the results, the base flow was also estimated using three existing base‐flow separation filters: an arithmetic filter (BFI), a digital filter (Boughton) and another filter based on groundwater levels (Kliner and Knĕz̆ek). Both the BFI and Boughton filters showed a much smaller difference in base flow between the two stations. The Kliner and Knĕz̆ek filter gave consistently lower estimates of the base flow. Differences and lack of clarity in the definition of base flow complicated the comparison between the filters. An advantage of the method introduced in this paper is the clear interpretation of the separated components. A disadvantage is the high data requirement. Copyright © 2004 John Wiley & Sons, Ltd.