珠江流域氮、磷营养盐入河量估算及预测

针对日益严重的流域营养盐污染问题,以珠江流域为例,采用系统动力学模型与多主体农户和农村环境管理模型耦合构建反映农户生产决策实际污染过程的流域氮、磷营养盐排放仿真系统,模拟2000—2030年不同污染源的营养盐产生、排放和进入河流的污染过程,分析其污染特征、影响因素和演变趋势.结果表明:在基准情境下,珠江流域总氮(TN)入河量从2000年的5.79×10~5t增加到2030年9.45×10~5t,在2027年达到峰值(9.53×10~5t);总磷(TP)入河量逐年递增,年均增长率为2.0%,从2000年的7.9×10~4t增加到2030年1.4×10~5t.在TN入河量中,种植业贡献最多,其次是城镇污水、养殖业和农村污水,2000—2030年期间年均贡献率相应为43.5%、32.5%、19.2%和4.9%.在TP入河量中,2000—2030年种植业、养殖业、城镇污水和农村污水的年均贡献比例分别为35.6%、28.8%、21.5%和14.1%;2000—2010年,养殖业为第一污染源,其次是种植业、城镇污水和农村污水;2011年种植业的贡献比例(31.6%)开始超过养殖业(30.8%)成为首要污染.研究显示,流域营养盐排放仿真系统可为营养盐控制提供技术支持和理论依据.     

Assessment of transmission losses and groundwater recharge from runoff events in a wadi under shortage of data on lateral inflow,Negev, Israel

A hydrological–lithostratigraphical model was developed for assessment of transmission losses and groundwater recharge from runoff events in arid water courses where hydrological and meteorological records are incomplete. Water balance equations were established for reaches between hydrometric stations. Because rainfall and tributary flow data are scarce, lateral inflow, which is an essential component of the water balance equation, could not be estimated directly. The solution was obtained by developing a method which includes a hydrological–lithostratigraphical analogy. This is based on the following assumptions: (a) runoff resulting from a given rainfall event is related to the watershed surface lithology; (b) for a given event, the spatial distribution of runoff reflects the distribution of rainfall: and (c) transmission losses are uniquely related to the total inflow to the reach. The latter relationship, called the loss function, and the water balance equation comprise a model which simultaneously assesses lateral inflow and transmission losses for runoff events recorded at the terminal stations. The model was applied to three reaches of the arid Nahal Tsin in Israel. In this case study, the transmission losses were of the same order of magnitude as the flow at the major hydrometric stations. The losses were subdivided into channel moistening, which subsequently evaporates, and deep percolation, which recharges groundwater. For large runoff events, evaporation was substantially smaller than the losses. The mean annual recharge of groundwater from runoff events in the Tsin watershed was 4·1×10⁶ m³, while the mean annual flow volume at the major stations ranged from 0·6 to 1·5×10⁶ m³. Once in 100 years, the annual recharge may be seven times higher than the mean annual value, but the recharge during most years is very small. Copyright © 1999 John Wiley & Sons, Ltd.     

Hazards resulting from hydrological extremes in the upstream catchment of the Prut River

Taking into account the fact that during the last decades domestic readers were poorly familiar with the hydrology of this region, it was considered appropriate to study the extreme situations within the Prut basin. By means of very simple mathematical calculation we have highlighted the role of reservoirs in change of relationships between extreme rainfall and floods/droughts, estimate the confidence degree of these estimations, etc. The Prut watershed is characterized by a temperate-continental climate with excessive influences in the middle and lower parts. Probabilistic analysis of the annual maximum flow indicates high values in the summer. The high flows recorded in 2005, 2008, and 2010 were caused by the most serious floods for the last 35 years. The maximum flow values had an exceeding probability of 2–10%, which explained the frequency of the phenomenon. Only the historical value (4240 m³ s^–1) at Radauti-Prut exceeded the flow rate with 1% probability. The results obtained for the hydrometric station located downstream underlined the role of Stanca–Costesti Accumulation Lake in flood protection. Simple linear regression identified the strength of the relationship between the predictor variable (total monthly rainfall) and the criterion variable (average monthly flow). The indicator used in this study to highlight the size effect, R ² (the regression coefficient), is based on the degree of association between variables and describes the percentage of variability explained by each variable in relation to the other. The results indicated a large effect size at the Radauti–Prut station that decreased gradually downstream, as a result of the flow regularization function played by the reservoir. The minimum flow study revealed 7 consecutive years with drought, from 1982–1988. In the current period, the extremely severe drought began in the late autumn of 2011 and was maintained at the end of the winter, summer, and autumn of 2012.     

Evaluation of hydrologic impact of an irrigation curtailment program using Landsat satellite data

Upper Klamath Lake (UKL) is the source of the Klamath River that flows through southern Oregon and northern California. The UKL Basin provides water for 81,000+ ha (200,000+ acres) of irrigation on the U.S. Bureau of Reclamation Klamath Project located downstream of the UKL Basin. Irrigated agriculture also occurs along the tributaries to UKL. During 2013–2016, water rights calls resulted in various levels of curtailment of irrigation diversions from the tributaries to UKL. However, information on the extent of curtailment, how much irrigation water was saved, and its impact on the UKL is unknown. In this study, we combined Landsat-based actual evapotranspiration (ETa) data obtained from the Operational Simplified Surface Energy Balance model with gridded precipitation and U.S. Geological Survey station discharge data to evaluate the hydrologic impact of the curtailment program. Analysis was performed for 2004, 2006, 2008–2010 (base years), and 2013–2016 (target years) over irrigated areas above UKL. Our results indicate that the savings from the curtailment program over the June to September time period were highest during 2013 and declined in each of the following years. The total on-field water savings was approximately 60 hm³ in 2013 and 2014, 44 hm³ in 2015, and 32 hm³ in 2016 (1 hm3 = 10,000 m³ or 810.7 ac-ft). The instream water flow changes or extra water available were 92, 68, 45, and 26 hm³, respectively, for 2013, 2014, 2015, and 2016. Highest water savings came from pasture and wetlands. Alfalfa showed the most decline in water use among grain crops. The resulting extra water available from the curtailment contributed to a maximum of 19% of the lake inflows and 50% of the lake volume. The Landsat-based ETa and other remote sensing datasets used in this study can be used to monitor crop water use at the irrigation district scale and to quantify water savings as a result of land-water management changes.     

A geostatistical approach for assessing population exposure to NO2 in a complex urban area (Beirut,Lebanon)

Few studies in the Middle East region estimated the spatial distribution of air pollutants for exposure studies. This paper presents a geostatistical approach to assess background NO₂ spatial distribution and the associated exposed population in a Mediterranean city with a complex topography, Beirut. Such modeling gave an accurate mapping of the 2010 yearly background average value of NO₂: it varies between 35 and 67 μg m^?3 with a mean of 53 μg m^?3. The mean SD of the estimated error was about 3 μg m^?3. The results showed that the spatial distribution of NO₂ follows a nested structuring, with a major structure related to topoclimatic characteristics (interaction topography/atmospheric flow at large scale) and a minor one linked to micro-environment and micro-climatic characteristics (interactions urban morphology/atmospheric flows at fine scale). The probability for the city’s inhabitants to be exposed to NO₂ levels exceeding 40 μg m^?3 threshold limit set by the World Health Organization (WHO) showed that Beirut city has a real sanitary risk to the NO₂ pollution. 93 % of the population (around 358,459 people) is 100 % sure to be exposed to a yearly average exceeding 40 μg m^?3. This knowledge will be certainly useful for developing a tool for decision support in order to implement policies of reducing air pollution in Beirut, which is, given the results, very urgent.     

Spatio-temporal patterns of the interaction between groundwater and surface water in plains

The study of the dynamics of anthropic disturbances that have an effect on the hydrological systems in plains requires integral simulation tools for their diagnosis. The objective of this article is, first, to analyse and reproduce the spatio-temporal interactions between groundwater (GW) and surface water, net recharge, GW level, surface run-off, and evapotranspiration in the upper creek basin of Del Azul, which is located in the centre of the province of Buenos Aires, Argentina, and second, to obtain insights to apply the methodology to other similar situations. For this purpose, a model coupling the semidistributed hydrological model (Soil and Water Assessment Tool [SWAT]) and the hydrogeological model (MODFLOW) has been used. A simulation was carried out for a period of 13 years (2003–2015) on a daily scale. The application of the SWAT–MODFLOW coupling gave good results based on the adjustment between the calculated flows and levels, reaching a Nash–Sutcliffe of 0.6 and R²0.6 at the Seminario hydrometric station located at the watershed outlet point. According to the annual average balance, out of the total rainfall, evapotranspiration accounts for 85%, recharge accounts for 10.2%, and surface run-off accounts for 4.8%. Annual and monthly trends of the stream–aquifer interaction were determined, obtaining on average an annual GW discharge of 34 mm and an annual average recharge of the stream to the aquifer of 1.4 mm. Monthly GW discharges are higher in winter–spring (July to December with an average of 3.3 mm) and lower in summer–autumn (January to June with an average of 2.8 mm). The monthly average recharge of the stream towards the aquifer varies from 0.02 to 0.36 mm and is higher in March, May, and August, when water excess is produced in the basin. Through the analysis of coupled modelling, it is possible to analyse and reproduce the spatio-temporal transitions of flow existing between the stream, the hyporheic zone, and the aquifer.     

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.     

Operation of two major reservoirs of Iran under IPCC scenarios during the XXI century

We assess the effects of prospective climate change until 2100 on water management of two major reservoirs of Iran, namely, Dez (3.34 × 10⁹ m³) and Alavian (6 × 10⁷ m³). We tune the Poly‐Hydro model suited for simulation of hydrological cycle in high altitude snow‐fed catchments. We assess optimal operation rules (ORs) for the reservoirs using three algorithms under dynamic and static operation and linear and non‐linear decision rules during control run (1990–2010 for Dez and 2000–2010 for Alavian). We use projected climate scenarios (plus statistical downscaling) from three general circulation models, EC‐Earth, CCSM4, and ECHAM6, and three emission scenarios, or representative concentration pathways (RCPs), RCP2.6, RCP4.5, and RCP8.5, for a grand total of nine scenarios, to mimic evolution of the hydrological cycle under future climate until 2100. We subsequently test the ORs under the future hydrological scenarios (at half century and end of century) and the need for reoptimization. Poly‐Hydro model when benchmarked against historical data well mimics the hydrological budget of both catchments, including the main processes of evapotranspiration and streamflows. Teaching–learning‐based optimization delivers the best performance in both reservoirs according to objective scores and is used for future operation. Our projections in Dez catchment depict decreased precipitation along the XXI century, with ?1% on average (of the nine scenarios) at half century and ?6% at the end of century, with changes in streamflows on average ?7% yearly and ?13% yearly, respectively. In Alavian, precipitation would decrease by ?10% on average at half century and ?13% at the end of century, with streamflows ?14% yearly and ?18% yearly, respectively. Under the projected future hydrology, reservoirs' operation would provide lower performance (i.e., larger lack of water) than now, especially for Alavian dam. Our results provide evidence of potentially decreasing water availability and less effective water management in water stressed areas like Northern Iran here during this century.     

Urmia lake water level fluctuation hydro informatics modeling using support vector machine and conjunction of wavelet and neural network

In this research, the simulation of Urmia Lake water level fluctuation by means of two models was applied. For this, Support Vector Machines (SVM), and Neural Wavelet Network (NWN) models that conjugated both the wavelet function and ANN, developed for simulating the Urmia Lake water level fluctuation. The yearly data of rainfall, temperature and discharge to the Urmia Lake and water level fluctuation were used. Urmia Lake is the biggest and the hyper saline lake in Iran. The outcome of the SVM based models are compared with the NWN. The results of SVM model performs better than NWN and offered a practical solution to the problem of water level fluctuation predictions. Analysis results showed that the optimal situation occurred with use of precipitation, temperature and discharge for all station and water level fluctuations at the lag time of one year (RMSEs) of 0.23, 0.41 m obtained by SVM, NWN, respectively, and SSEs of 0.43, 1.33 and R ² of 0.97, 0 obtained by SVM, NWN, respectively. The results of SVM model show better accuracy in comparison with the NWN model.     

Combining the SWAT model with sequential uncertainty fitting algorithm for streamflow prediction and uncertainty analysis for the Lake Dianchi Basin,China

Streams play an important role in linking the land with lakes. Nutrients released from agricultural or urban sources flow via streams to lakes, causing water quality deterioration and eutrophication. Therefore, accurate simulation of streamflow is helpful for water quality improvement in lake basins. Lake Dianchi has been listed in the ‘Three Important Lakes Restoration Act’ in China, and the degradation of its water quality has been of great concern since the 1980s. To assist environmental decision making, it is important to assess and predict hydrological processes at the basin scale. This study evaluated the performance of the soil and water assessment tool (SWAT) and the feasibility of using this model as a decision support tool for predicting streamflow in the Lake Dianchi Basin. The model was calibrated and validated using monthly observed streamflow values at three flow stations within the Lake Dianchi Basin through application of the sequential uncertainty fitting algorithm (SUFI‐2). The results of the autocalibration method for calibrating and the prediction uncertainty from different sources were also examined. Together, the p‐factor (the percentage of measured data bracketed by 95% prediction of uncertainty, or 95PPU) and the r‐factor (the average thickness of the 95PPU band divided by the standard deviation of the measured data) indicated the strength of the calibration and uncertainty analysis. The results showed that the SUFI‐2 algorithm performed better than the autocalibration method. Comparison of the SUFI‐2 algorithm and autocalibration results showed that some snowmelt factors were sensitive to model output upstream at the Panlongjiang flow station. The 95PPU captured more than 70% of the observed streamflow at the three flow stations. The corresponding p‐factors and r‐factors suggested that some flow stations had relatively large uncertainty, especially in the prediction of some peak flows. Although uncertainty existed, statistical criteria including R² and Nash–Sutcliffe efficiency were reasonably determined. The model produced a useful result and can be used for further applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Simulating streamflow in the Upper Halda Basin of southeastern Bangladesh using SWAT model

ABSTRACT

Most catchments in tropical regions are ungauged and data deficient, complicating the simulation of water quantity and quality. Yet, developing and testing hydrological models in data-poor regions is vital to support water management. Here, we used the Soil and Water Assessment Tool (SWAT) to predict stream runoff in Halda Basin in Bangladesh. While the calibrated model’s performance was satisfactory (R² = 0.80, NSE = 0.71), the model was unable to track the extreme low flow peaks due to the temporal and spatial variability of rainfall which may not be fully captured by using data from one rainfall gauging station. Groundwater delay time, baseflow alpha factor and curve number were the most sensitive parameters influencing model performance. This study improves understanding of the key processes of a catchment in a data-poor, monsoon driven, small river basin and could serve as a baseline for scenario modelling for future water management and policy framework.     

长江流域水库"过滤器效应"对入海溶解硅通量的影响

根据1960-2000年间长江大通水文站记录的水、沙以及硅、氮、磷等数据,结合1954-2006年间长江流域库容大于10⁸ m³的162座水库的库容、上游径流量、总磷等数据,利用Vollenweider模型分析了水库"过滤器效应"对入海溶解硅(DSi)通量的影响.结果表明:1)1990s相比1960s,长江入海DSi通量下降了约1.85×10⁶ t/a,减少了大约25.3%;入海DSi通量的下降与流域径流波动、入海悬沙通量下降以及溶解无机氮通量的增加紧密相关.2)流域水库明显改变径流的自然过程,增加径流的滞留时间,流域90%以上的水库对上游径流的滞留时间超过0.05年,水库产生显著的DSi"生物过滤器"效应.模型计算显示流域大型水库对DSi的累计滞留量可达0.85×10⁶ t/a,占年均入海DSi通量(1990-2000年)5.4×10⁶ t的15.7%,是入海DSi通量减少量(1.85×10⁶ t/a)的45.9%.3)根据保守估计,流域162座大型水库内泥沙累计淤积量达6.75×10⁸ t/a,不仅使悬沙入海通量显著下降,而且造成大量颗粒吸附的外源和内源DSi颗粒沉淀,这对入海DSi通量减少也起到重要贡献.但目前对水库"泥沙过滤器"的滞留机理并不清楚,需要展开进一步的研究.     

On the value of isotope-enabled hydrological model calibration

ABSTRACT

Calibration of hydrological models is challenging in high-latitude regions where hydrometric data are minimal. Process-based models are needed to predict future changes in water supply, yet often with high amounts of uncertainty, in part, from poor calibrations. We demonstrate the utility of stable isotopes (¹⁸O, ²H) as data employed for improving the amount and type of information available for model calibration using the isoWATFLOOD^TM model. We show that additional information added to calibration does not hurt model performance and can improve simulation of water volume. Isotope-enabled calibration improves long-term validation over traditional flow-only calibrated models and offers additional feedback on internal flowpaths and hydrological storages that can be useful for informing internal water distribution and model parameterization. The inclusion of isotope data in model calibration reduces the number of realistic parameter combinations, resulting in more constrained model parameter ranges and improved long-term simulation of large-scale water balance.     

东江流域典型子流域土地利用/覆被变化对地表径流影响

应用SWAT模型对东江上中下游典型流域的地表径流进行模拟,采用1977 - 1981年和1996-2000年胜前、顺天和九州三个出口控制站逐月实测径流资料进行模型校准和验证,确定模型的敏感性参数,采用相关系数R2和Nash-Suttclife模型效率系数ENS,对SWAT模型模拟结果进行评价,结果显示模拟精度较高,R2...     

The assessment of surface water resources for the semi‐arid Yongding River Basin from 1956 to 2000 and the impact of land use change

The assessment of surface water resources (SWRs) in the semi‐arid Yongding River Basin is vital as the basin has been in a continuous state of serious water shortage over the last 20 years. In this study, the first version of the geomorphology‐based hydrological model (GBHM) has been applied to the basin over a long period of time (1956–2000) as part of an SWR assessment. This was done by simulating the natural hydrological processes in the basin. The model was first evaluated at 18 stream gauges during the period from 1990 to 1992 to evaluate both the daily streamflows and the annual SWRs using the land use data for 1990. The model was further validated in 2000 with the annual SWRs at seven major stream gauges. Second, the verified model was used in a 45‐year simulation to estimate the annual SWRs for the basin from 1956 to 2000 using the 1990 land use data. An empirical correlation between the annual precipitation and the annual SWRs was developed for the basin. Spatial distribution of the long‐term mean runoff coefficients for all 177 sub‐basins was also achieved. Third, an additional 10‐year (1991–2000) simulation was performed with the 2000 land use data to investigate the impact of land use changes from 1990 to 2000 on the long‐term annual SWRs. The results suggest that the 10‐year land use changes have led to a decrease of 8·3 × 10⁷ m³ (7·9% of total) for the 10‐year mean annual SWRs in the simulation. To our knowledge, this work is the first attempt to assess the long‐term SWRs and the impact of land use change in the semi‐arid Yongding River Basin using a semi‐distributed hillslope hydrological model. Copyright © 2010 John Wiley & Sons, Ltd.     

A combined methodology for estimating the potential natural aquifer recharge in an arid environment

ABSTRACT

An innovative methodology that combines an indirect physiography-based method for determining the runoff coefficient at a sub-basin scale and a water balance model applied on a daily time scale was developed to calculate the natural groundwater recharge in three watersheds within the Oum Zessar arid area, Tunisia. The effective infiltration was calculated as part of the water surplus by considering the average available water content (AWC) of soil and an average runoff coefficient for each sub-basin. The model indicates that the sub-basins covered mainly by the “artificial” soils of tabias and jessour, characterized by average AWC values greater than 150 mm, did not contribute to natural groundwater recharge over the 10-year period (2003–2012) considered. The estimated volume for the Triassic aquifer amounted to about 4.5 hm³ year^?1, which is consistent with previous studies. For the Jurassic and Cretaceous aquifers, the estimated volumes amounted to about 200 dm³ year^?1.     

Shaping and maintaining a medium-sized main channel in the Lower Yellow River

This paper studies relations between bankfull discharge,lateral cross section variation and the incoming flow and sediment condition in the Lower Yellow River using measured data from 1950 to 2003.Since 1950 the bankfull discharge has obviously decreased and the ratio of channel width to flow depth has increased.The critical annual average incoming sediment coefficient（defined as the ratio of sediment concentration to discharge） and discharge at the Huayuankou station are approximately 0.012 and 1,850 m³s^-1,respectively,for no accumulative deposition occurring in the reach from Huayuankou to Lijin.On this basis,a mathematical model is used to study the scale of the main channel in the Lower Yellow River and its corresponding bankfull discharge under possible incoming flow and sediment conditions in the near future.The main factors influencing the scale of the main channel are analyzed,and measures to shape and maintain a medium-sized channel are discussed.The results show the effect of various water and sediment combinations released from the Xiaolangdi Reservoir on the shaping of the main channel and suggest that under recent incoming flow and sediment conditions,it is possible to shape and maintain a medium-sized channel with a bankfull discharge of approximate 4,000 m³ s^-1.     

Announcements

Abstract

This paper investigates for a 25-year period the sediment distribution in a semi-arid Brazilian basin (2 × 10⁴ km²) with a network containing more than 4000 surface reservoirs. The methodology is based on rating curves and fitted parameters derived from field data. The results showed that suspended load corresponded to 70% of the total sediment yield (148 t km^-2 year^-1). The relatively low contribution of the suspended load (compared with other semi-arid regions) was attributed to the impact of the numerous upstream reservoirs, which retained 235 t km^-2 year^-1. The micro (<1 hm³), small (1–10 hm³), medium-sized (10–50 hm³), and large or strategic (>50 hm³) reservoirs responded to, respectively, 5, 17, 30 and 48% of the total sediment retention by the reservoir network. This indicates that retention in the non-strategic reservoirs has a positive impact on water availability, since siltation of the strategic reservoirs would be expected to more than double if only such reservoirs existed.

Citation Lima Neto, I. E., Wiegand, M. C. &; de Araújo, J. C. (2011) Sediment redistribution due to a dense reservoir network in a large semi-arid Brazilian basin. Hydrol. Sci. J. 56(2), 319–333.     

Rainfall–runoff modelling for estimating Latonyanda River flow contributions to Luvuvhu River downstream of Albasini Dam

Rainfall–runoff modelling was conducted to estimate the flows that Latonyanda River contribute to Luvuvhu River downstream of Albasini Dam. The confluence of Latonyanda and Luvuvhu Rivers is ungauged. The contributed flows compensate for upstream water abstractions and periodic lack of releases from Albasini Dam. The flow contributions from tributaries to Luvuvhu River are important for ecosystem sustenance, meeting downstream domestic and agricultural water demand and ecological water requirements particularly in Kruger National Park. The upper Latonyanda River Quaternary Catchment (LRQC), with streamflow gauging station number A9H027 was delineated and used for rainfall–runoff modelling. The simulation was done using Mike 11 NAM rainfall–runoff model. Calibration and verification runs of Mike 11 NAM rainfall–runoff model were carried out using data for periods of 4 and 2 years, respectively. The model was calibrated using shuffled complex evolution optimizer. The model efficiency was tested using coefficient of determination (R²), root mean square error (RMSE), overall water balance error (OWBE) and percentage bias (PBIAS). The model parameters obtained from the upper LRQC were transferred and used together with rainfall and evaporation data for 40 years period in the simulation of runoff for the LRQC. The flows that Latonyanda River contribute to Luvuvhu River were computed by subtracting irrigation abstractions and runoff drained to Tshakhuma Dam from the simulated runoff time series of the LRQC. The observed and the simulated runoff showed similar trends and measures of performances for both calibration and verification runs fell within acceptable ranges. The pairs of values obtained for R², RMSE, OWBE and PBIAS for calibration and verification were 0.86 and 0.73, 0.21 and 0.2, 2.1 and 1.3, and 4.1 and 3.4, respectively. The simulated runoff for LRQC correlated well with the areal rainfall showing that the results are reasonable. The mean and maximum daily flow contributions from the Latonyanda River are 0.91 and 49 m³/s respectively. The estimation of these ungauged flows makes it possible to plan and manage the water requirements for the downstream users.     

The distribution of bomb-produced tritium and radiocarbon at GEOSECS station 347 in the eastern North Pacific

Following Roether et al. [1] an upwelling model has been tested to explain the distribution of bomb-produced tritium at the GEOSECS I test station off Baja, California. We have extended their treatment to include the time histories for tritium and for bomb radiocarbon now available for this station. If the CO₂ gas exchange rate at this station is similar to the ocean average value of 20 moles/m² yr, then the upwelling rate must be quite small (<3 m/yr). However, a satisfactory match to the time histories of¹⁴C and of³H is achieved only if an upwelling rate of 40 m/yr is used. In this case, however, a CO₂ exchange rate of 70 moles/m² yr would be required to match the observed surface water¹⁴C/C ratios and a tritium input 4 times the expected value would be needed. The inconsistency in the bomb¹⁴C time history obtained using the accepted CO₂ exchange rate is likely the result of horizontal effects which void the validity of one dimensional modeling in this region of the ocean.