Nonpoint N Runoff from Agricultural Watersheds into the Great Lakes

Eleven agricultural watersheds were continuously monitored for discharge and intensively sampled for runoff N, 1975-77, as part of the IJC Pollution from Land Use Activities Reference Group (PLUARG), Task Group C (Canadian). The watersheds, located in southern Ontario, were sampled between 30 to more than 500 times for NH₄-N, N0₃+N0₂-N, and total Kjeldahl N (TKN).The predominant chemical form of runoff N was N0₃-N with flow weighted concentration means on sampled days ranging from 0.57 to 5.62 mg/L. In contrast, TKN means ranged from 0.64 mg/L to 2.37 mg/L while average soluble NH₄-N concentrations varied from 0.03 mg/L to 0.60 mg/L. High runoff N0₃-N concentrations occurred from watersheds with extensive areas of tile drainage, row crops (especially com), and high kg/ha fertilizer N application rates. Elevated stream TKN concentrations were associated with watersheds with more impermeable soils.Stream N0₃-N loadings ranged from 2.1 ± 0.2 to 39.0 ± 7.6 kg N0₃-N/watershed ha. Significant N fertility losses in excess of 30 kg N0₃-N ha occurred from some watersheds, while other watersheds with extensive areas of hay and pasture and unimproved land gained more N0₃-N in precipitation than was lost as runoff. TKN loads averaged 32% and 25% of total N runoff for the 11 watersheds in 1975 and 1976 respectively. Efforts to reduce Ontario watershed N runoff should concentrate first on soluble N and therefore on improved efficiency of N fertilizer use on the extensive areas of tile drained corn in the lower Great Lakes basin. The effectiveness of standard soil erosion control methods, including grassed waterways and contour planting, should be investigated for reduction of TKN runoff.     

Development of Regional Flood Frequency Relationships Using L-moments for Middle Ganga Plains Subzone 1(f) of India

In this study, screening of the data has been carried out basedon the discordancy measure (D _i) in terms of the L-moments. Homogeneity of the region has been tested using the L-moments based heterogeneity measure, H. For computing the heterogeneity measure H, 500 simulations were carried out using the four parameter Kappa distribution. Based on this test, it has been observed that the data of 8 out of 11 bridge sites constitute ahomogeneous region. Hence, the data of these 8 sites have been used in this study. Catchment areas of these 8 sites vary from 32.89 to 447.76 km² and their mean annual peak floods varyfrom 24.29 to 555.21 m³ s^-1. Comparative regional floodfrequency analysis studies have been carried out using the various L-moments based frequency distributions viz. Extreme value (EV1), General extreme value (GEV), Logistic (LOS), Generalized logistic (GLO), Normal (NOR), Generalized normal (GNO), Uniform (UNF), Pearson Type-III (PE3), Exponential (EXP),Generalized Pareto (GPA), Kappa (KAP), and five parameter Wakeby(WAK). Based on the L-moment ratio diagram and Z _i ^dist –statistic criteria, GEV distribution has been identified as the robust distribution for the study area. For estimation of floods of various return periods for gauged catchments of the study area, regional flood frequency relationship has been developed using the L-moments based GEV distribution. Also, for estimation of floods of desiredreturn periods for ungauged catchments, regional flood frequencyrelationship has been developed by coupling the regional flood frequency relationship with the regional relationship between mean annual maximum peak flood and catchment area.     

Flood Inundation Modeling Using Nakagami-<Emphasis Type="Italic">m</Emphasis> Distribution Based GIUH for a Partially Gauged Catchment

Flood inundation extent is highly dependent on intensive rainfall and topography of floodplain. This paper presents a study to develop a flood inundation model for partially gauged upper Ganga catchment. For design flood computations, 100-year return period of 1 h duration rainfall is adopted. This is obtained by intensity duration frequency (IDF) relationship based on Self Recording Rain Gauge (SRRG) data of the study area. The SCS-CN method is used for rainfall excess computations. The Nakagami-m distribution has been used to compute Geomorphological Instantaneous Unit Hydrograph (GIUH) of different sub-catchments of upper Ganga river system because of non-availability of observed hydrograph. Routing of the hydrograph has been done by the Kinematic Wave (KW) approach. KW equations have been solved through Preissmann implicit method. The most sensitive KW parameters (i.e. overland roughness and channel roughness) have been estimated for a stretch on river Bhagirathi, a tributary of river Ganga. Nakagami-m distribution based GIUHs have been fed at the upper (i.e. input to the proposed model) as well as at downstream point (i.e. output to the proposed model) of that river stretch. Consequently, KW parameters have been calibrated by comparing the computed hydrograph with output hydrograph. Validation of estimated KW parameters has been carried out in the catchment of river Alaknanda which is another significant tributary of river Ganga. Thereafter, adopted KW parameters have been applied to calculate the design flood peak at the outlet of study area i.e. downstream of Haridwar city. Computations of overtopping water above the natural levees downstream of Haridwar city have been carried out considering the levee as broad crested weir. Topographic features of the floodplain have been obtained from freely available Shuttle Radar Topography Mission (SRTM) data. Finally, extents of submerged areas in different flood hours corresponding to design rainfall have been developed by ArcGIS 9.2 software.     

Post‐flooding distribution and characteristics of large woody debris piles along the semi‐arid Sabie River,South Africa

The formation of large woody debris (LWD) piles has a profound impact on channel patterns and riparian succession in temperate rivers. The opportunity to study LWD along the Sabie River, a river in the semi‐arid region of Kruger National Park, South Africa, arose in February 2000 after a significant flood (c. 100‐year return interval) removed a large proportion of the fully mature riparian forest and other plant communities. Much of the uprooted vegetation was deposited as LWD piles (woody vegetation accumulations deposited on the ground > 0.1 m³) throughout the riparian and upland zones. In this article we describe the spatial distribution patterns of LWD as related to geomorphic channel type and flood frequency zone, and assess pile composition characteristics six months after the flood. Within the areas surveyed there were 68 LWD piles per hectare, the median size of LWD piles was 4.6 m³ but pile sizes (by volume) varied widely. Pool/rapid geomorphic channel types had the highest density of LWD piles (79 ha^?1) and the largest piles (by volume) were in the bedrock anastomosing channels (mean = 124 m³). Piles were larger in the seasonal and ephemeral flood frequency zones (mean = 54 m³ and 55 m³) than piles in the active zone (c. 2 m³). The patterns of distribution and volume of LWD will affect the subsequent development of vegetation communities as debris piles form a mosaic of patches of surviving organisms and propagules that can strongly influence the initial trajectory of succession. The amount, distribution, and subsequent decomposition of LWD are different from that reported for temperate rivers, suggesting that the role of LWD may be different on non‐floodplain rivers such as the Sabie in semi‐arid South Africa. Copyright © 2004 John Wiley & Sons, Ltd.     

Evaluation of the Adequacy of Statistical Distribution Functions for Deriving Unit Hydrograph

The unit hydrograph (UH) is one of the commonly employed techniques for the determination of flood hydrographs. Since the UH satisfies all the properties of a probability distribution function (PDF), it seems logical that PDFs can be employed for deriving the UH. In practice, the gamma distribution function has been commonly employed to derive the UH. In this paper, Beta (Beta), Exponential (EXP), Gamma (GM), Normal, Lognormal (LN), Weibull (WB), Logistic (LG), Generalized logistic (GLG) and Pearson Type 3 (PT 3) distribution functions were employed for the derivation of UH. Parameters of these distribution functions were estimated using the real coded genetic algorithm optimization technique. These distributions were tested on the 13 watersheds of different characteristics and it was observed that except for the EXP distribution function, most other distribution functions produced UHs which were in satisfactory agreement with observed UHs. However, three-parameter distributions GLG, PT 3 and two parameter LG were not capable of reproducing UHs for large watersheds having drainage areas of 3,360 and 4,300 km². For such large watersheds WB reproduced UHs satisfactorily. Combining the overall performance of the distributions over 13 watersheds, the order of ranking the suitability of distributions were as: GM > PT 3 > Beta ≥ GLG ≥ LN > WB.     

Investigation of stage-discharge model performance for streamflow estimating: A case study of the Gono River,Japan

In water resource studies, long-term measurements of river streamflow are essential. They allow us to observe trends and natural cycles and are prerequisites for hydraulic and hydrology models. This paper presents a new application of the stage-discharge rating curve model introduced by Maghrebi et al. (2016) to estimate continuous streamflow along the Gono River, Japan. The proposed method, named single stage-discharge (SSD) method, needs only one observed data to estimate the continuous streamflow. However, other similar methods require more than one observational data to fit the curve. The results of the discharge estimation by the SSD are compared with the improved fluvial acoustic tomography system (FATS), conventional rating curve (RC), and flow-area rating curve (FARC). Some statistical indicators, such as the coefficient of determination (R²), root mean square error (RMSE), percent bias (PBAIS), mean absolute error (MAE), and Kling-Gupta efficiency (KGE), are used to assess the performance of the proposed model. ADCP data are used as a benchmark for comparing four studied models. As a result of the comparison, the SSD method outperformed of FATS method. Also, the three studied RC methods were highly accurate at estimating streamflow if all observed data were used in calibration. However, if the observed data in calibration was reduced, the SSD method by R² = 0.99, RMSE = 2.83 (m³/s), PBIAS = 0.715(%), MAE = 2.30 (m³/s), and KGE = 0.972 showed the best performance compared to other methods. It can be summarized that the SSD method is the feasible method in the data-scarce region and delivers a strong potential for streamflow estimation.     

A real-time flood forecasting model based on maximum-entropy spectral analysis: II. Application

The MESA-based model, developed in the first paper, for real-time flood forecasting was verified on five watersheds from different regions of the world. The sampling time interval and forecast lead time varied from several minutes to one day. The model was found to be superior to a state-space model for all events where it was difficult to obtain prior information about model parameters. The mathematical form of the model was found to be similar to a bivariate autoregressive (AR) model, and under certain conditions, these two models became equivalent.Notation A _k parameter matrix of the bivariate AR model - B backshift operator in time series analysis - eT forecast error (vector) at timet = T - _t uncorrelated random series (white noise) - F _k forward extension matrix of the entropy model forkth lag - I identity matrix - m order of the entropy model - N number of observations - P order of the AR model - Q _p peak of the direct runoff hydrograph - R correlation matrix - t _p time to peak of the direct runoff hydrograph - ₁ coefficient of variation - ₂ ratio of absolute error to the mean - forecasted runoff - x _i observed runoff - mean of the observed runoff - X ^–1 inverse ofX matrix - X* transpose of theX matrix Abbreviations AIC Akaike information criterion - AR autoregressive (model) - AR(p) autoregressive process of thepth order - ARIMA autoregressive integrated moving average (model) - acf autocorrelation function - ccf cross-correlation function - FLT forecast lead time - MESA maximum entropy spectral analysis - MSE mean square error - STI sampling time interval     

Estimating design floods based on the critical storm duration for small watersheds

The objective of this study was to propose a new method to determine design floods using the critical storm duration concept. Five different models, including the Rational, SCS, and Clark methods, were used to estimate peak discharges, while the uniform distribution, Mononobe, Huff, and Yen and Chow methods were applied for the determination of temporal rainfall distribution. Two small watersheds, Baran (HP#6) and Banweol (WS#1), for which watershed hydrologic data were available since 1996, were selected as the study areas. A total of 41 rainfall events was chosen from the study watersheds to calculate peak runoffs and evaluate the performances of the selected hydrological models based on the statistics of RMSE, Nash efficiency criterion (NEC), and R² value. The Clark method performed the best overall among the selected models, with both NEC and R² values greater than 0.95. The Huff method resulted in the longest critical storm duration, which was much greater than the times of concentration. The increase in the recurrence interval decreased the critical storm duration while increasing the peak flow rates. The SCS model estimated the greatest design floods, 94.2 m³/s for HP#6 and 56.4 m³/s for WS#1, with a 25-year return period. The design floods for the study watersheds that were estimated by the selected hydrologic models ranged from 68.3 to 132.1% of those estimated by the Rational method. The greatest to the smallest peak flows resulted from the SCS, WFRP, Clark and Nakayasu methods in order. As an alternative to the Rational method, the WFRP method may be appropriate for rural watershed areas in Korea, where paddy fields commonly exist, whereas the SCS model may be more suitable for urban areas, where most land surfaces are covered with impervious material. It was concluded that the incorporation of a critical storm duration concept can contribute to the advance of design flood estimation method in Korea.     

Instream flows for recreation are closely correlated with mean discharge for rivers of western North America

Effective river regulation requires consideration for environmental and economic aspects and also for social aspects including recreation. Our study investigated relationships between river hydrology and recreational flows (RF) for canoes, kayaks, rafts and other non‐motorized boats, for 27 river reaches in the Red Deer and Bow river basins of southern Alberta, Canada. A subjective RF method involved regression analyses of data from River Trip Report Cards, volunteer postcard‐style surveys rating flow sufficiency. A total of 958 trip reports were submitted for the rivers between 1983 and 1997 and about 30 reports permitted confident regression analysis for a river reach. Values from these analyses were very consistent with values from the ‘depth discharge method’, a hydraulic modelling approach that used stage–discharge ratings to determine flows that would produce typical depths of 60 and 75 cm for minimal and preferred flows, respectively. Values were also consistent with expert opinions from river guidebooks and maps and aggregate values were calculated from the combined RF methods. These were very closely correlated with mean discharge (Q_m) across the rivers (r² = 0.94 for minimal and 0.96 for preferred flows). The relationship best fitted a power function (straight plot on log versus log scales) with a consistent slope but vertical offset for minimal versus preferred flows. Close relationships between guidebook estimates of RF and Q_m were also observed for rivers in the American Rocky Mountain states of Idaho (r² = 0.55 and 0.74), Montana (r² = 0.34 and 0.80) and Colorado (r² = 0.43 and 0.51), but the association was weaker for the Pacific Northwest state of Oregon (r² = 0.35 and 0.26). These analyses indicate that RF can be confidently determined through a combination of subjective and hydraulic methods and reveal that RF values represent a systematic function of discharge for a broad range of alluvial and constrained river reaches. From these analyses we provide the ‘Alberta equation’: minimal recreational flow = 3 × Q_m^0.59 (Q_m in m³/s), and preferred flows would typically be 1.5 times higher. For other river regions the exponent ‘0.59’ may be relatively constant but adjustments to the coefficient ‘3’ could be applicable. Copyright © 2005 John Wiley & Sons, Ltd.     

Utility of Ten-Day Climate Model Ensemble Simulations for Water Resources Applications in Korean Watersheds

We demonstrate the use of a quantitative measure of the effectiveness of using climate model simulations of surface precipitation and temperature for water resources applications involving extremes of watershed average precipitation and temperature, and watershed discharge. This diagnostic measure is considered in association with the use of climate information to condition ensemble seasonal predictions of watershed variables. Seven watersheds in the Korean peninsula constitute the application sites. The climate model effectiveness is expressed by a utility index E_P that measures the ability of the climate model simulations of an indicator variable (i.e., nodal precipitation or temperature) to discriminate observed distributions of the highs and lows of a watershed target variable (i.e., mean areal precipitation and temperature as well as outlet discharge). Monte Carlo simulations provide estimates of the significance of the E_p values. For apparently the first time, ten-member ensemble simulations of daily surface precipitation and temperature from the Korean Meteorological Agency climate model are used to evaluate the climate-model utility index E_P for a temporal interval of 10 days for each application watershed. The results show that, in spite of the high uncertainty of climate simulations, there are several Korean watersheds that can benefit from the use of climate model simulations of high temporal resolution for planning and management studies that involve precipitation, temperature and discharge. In particular, seasonal ensemble prediction of watershed variables stands to gain from conditioning on high-temporal resolution climate forecasts.     

Effects of residence time on summer nitrate uptake in mississippi river flow‐regulated backwaters

Nitrate uptake may be improved in regulated floodplain rivers by increasing hydrological connectivity to backwaters. We examined summer nitrate uptake in a series of morphologically similar backwaters on the Upper Mississippi River receiving flow‐regulated nitrate loads via gated culverts. Flows into individual backwaters were held constant over a summer period but varied in the summers of 2003 and 2004 to provide a range of hydraulic loads and residence times (τ). The objectives were to determine optimum loading and τ for maximum summer uptake. Higher flow adjustment led to increased loading but lower τ and contact time for uptake. For highest flows, τ was less than 1 day resulting in lower uptake rates (U_net < 300 mg m^?2 day^?1), low uptake efficiency (U% < 20%) and a long uptake length (S_net > 4000 m). For low flows, τ was greater than 5 days and U% approached 100%, but U_net was 200 mg m^?2 day^?1. S_net was < half the length of the backwaters under these conditions indicating that most of the load was assimilated in the upper reaches, leading to limited delivery to lower portions. U_net was maximal (384–629 mg m^?2 day^?1) for intermediate flows and τ ranging between 1 and 1.5 days. Longer S_net (2000–4000 m) and lower U% (20–40%) reflected limitation of uptake in upper reaches by contact time, leading to transport to lower reaches for additional uptake. Uptake by ～10 000 ha of reconnected backwaters along the Upper Mississippi River (13% of the total backwater surface area) at a U_net of ～630 mg m^?2 day^?1 would be the equivalent of ～40% of the summer nitrate load (155 mg day^?1) discharged from Lock and Dam 4. These results indicate that backwater nitrate uptake can play an important role in reducing nitrate loading to the Gulf of Mexico. Copyright © 2008 John Wiley & Sons, Ltd.     

Then and now: Revisiting nutrient export in agricultural watersheds within southern Ontario’s lower Great Lakes basin

An enhanced understanding of nonpoint source (NPS) nutrient export to the lower Great Lakes is needed to inform land use and land management decisions within southern Ontario. However, this understanding is limited by a lack of long-term, temporally-intensive monitoring. To address this knowledge gap, we revisit six agriculturally-dominated subwatersheds in southern Ontario, which were intensively studied during the mid-1970s, to assess changes in hydrology and NPS nutrient contributions. We compared 1975–1977 to 2016–2018 stream runoff, nutrient export (kg/day∙km²), and flow-weighted mean concentrations (FWMCs) of total phosphorus (TP), total dissolved phosphorus (TDP), total nitrogen (TN), nitrates (NO₃^–+NO₂^–) and Total Kjeldahl Nitrogen (TKN). Relative to the 1970s, runoff increased at three of six watersheds (by ~20–35%) while TP and TDP export increased at five watersheds (by ~50–125%). The increases in TP and TDP FWMCs were lower relative to phosphorus export changes at the three watersheds with increased runoff, suggesting that hydrology is an important driver of phosphorus export at these sites. Interestingly, export of TN and nitrates increased while TKN export decreased at most watersheds. We further note a shift in the timing of nutrient export at most sites, with ~40–70% of export now occurring during the winter and fall seasons whereas ~40–85% of past export occurred during spring and summer. These findings support an enhanced importance of non-growing season nutrient export from agricultural watersheds since the mid-1970s and stresses the need for targeted best management practices specific to the fall and winter seasons.     

Development of Geomorphology Based Regional Nash Model for Data Scares Central India Region

The development of rainfall runoff relationship for ungauged watersheds using topography, geomorphology and other regional information remains the most active area of research in the field of hydrology. In the developing countries, some thumb rules and very old equations are in practice for designing water resources structures which sometimes provide erroneous results. In the proposed study, regional relationships have been developed for computation of peak velocity and scale parameters of Nash model using geomorphological and fluvial characteristics of 41 watersheds of varying characteristics in Central India region. The regional relationships developed to determine scale parameter (k) of Nash model from a morpho-fluvial factor, has facilitated derivation of at-site regional and regional only instantaneous unit hydrograph (IUH), unit hydrograph (UH) and direct surface runoff (DSRO). The performance of proposed regional model has been evaluated using spatial correlation coefficient, integral square error, relative mean absolute error, root mean square error, relative error in peak, coefficient of residual mass and model efficiency. The response of proposed regional model have been found comparable with the observed values as the Nash-Sutcliffe efficiency of proposed model during calibration varies from 69.7 % to 95.2 % for site specific approach, 60.6 % to 97.7 % for at-site regional and 67.1 % to 98.7 % for regional only approach. Similarly, the performance of proposed model have been found satisfactorily during validation as the efficiency varies from 81.3 % to 99.9 % for site specific approach, 83.5 % to 99.9 % for at-site regional and 82.7 % to 99.9 % for regional only approach. The simple regional relationships developed in the study can be used for event based rainfall-runoff modeling and estimation of design flood in ungauged catchments of central Indian region.     

目标函数对滦河流域SWAT模型径流模拟不确定性的影响

针对水文模型参数和径流模拟结果不确定性问题,选取2Nash-Sutcliffe效率系数(NSE)、改进的决定系数(R_m²)、相对误差(PBIAS)、Kling-Gupta效率系数(KGE)4种目标函数,对构建的滦河流域潘家口水库上游SWAT模型进行参数率定及验证,分析了不同目标函数下模型参数的敏感性差异及径流模拟的不确定性。结果表明：参数敏感性会随迭代次数增加和抽样范围变化发生改变,不同目标函数下率定的参数范围和最优值显著不同;NSE和KGE作为目标函数在各站点径流模拟中更稳健,分别表现出较高的模拟精度和较低的模拟不确定性。     

Determination of optimal unit hydrographs by linear programming

A unit hydrograph (UH) obtained from past storms can be used to predict a direct runoff hydrograph (DRH) based on the effective rainfall hyetograph (ERH) of a new storm. The objective functions in commonly used linear programming (LP) formulations for obtaining an optimal UH are (1) minimizing the sum of absolute deviations (MSAD) and (2) minimizing the largest absolute deviation (MLAD). This paper proposes two alternative LP formulations for obtaining an optimal UH, namely, (1) minimizing the weighted sum of absolute deviations (MWSAD) and (2) minimizing the range of deviations (MRNG). In this paper the predicted DRHs as well as the regenerated DRHs by using the UHs obtained from different LP formulations were compared using a statistical cross-validation technique. The golden section search method was used to determine the optimal weights for the model of MWSAD. The numerical results show that the UH by MRNG is better than that by MLAD in regenerating and predicting DRHs. It is also found that the model MWSAD with a properly selected weighing function would produce a UH that is better in predicting the DRHs than the commonly used MSAD.Notations M number of effective rainfall increments - N number of direct runoff hydrograph ordinates - R number of storms - MSAD minimize sum of absolute deviation - MWSAD minimize weighted sum of absolute deviation - MLAD minimize the largest absolute deviation - MRNG minimize the range of deviation - RMSE root mean square error - P _m effective rainfall in time interval [(m–1)t,mt] - Q _n direct runoff at discrete timent - U _k unit hydrograph ordinate at discrete timekt - W _n weight assigned to error associated with estimatingQ _n - _n ⁺ error associated with over-estimation ofQ _n - _n ^– error associated with under-estimation ofQ _n - _max ⁺ maximum positive error in fitting direct runoff hydrograph - _max ^– maximum negative error in fitting direct runoff hydrograph - _max largest absolute error in fitting obtained direct runoff - E _r,1 thelth error criterion measuring the fit between the observed DRHs and the predicted (or reproduced) DRHs for therth storm - E ₁ averaged value of error criterion overR storms     

新疆膜下滴灌棉田暗管排盐的数值模拟与分析Ⅱ:模型应用

为了降低新疆地区盐碱棉田根区土壤盐分含量,尤其是排走长期使用膜下滴灌技术造成的下部根系层(40~60 cm)累积盐分,针对当地实际情况设计了2种改进排盐模式,分别是淋洗防渗排盐模式(情景1)和暗管局部冲洗排盐模式(情景2),利用经过校验的模型和参数对不同模式下暗管排水、排盐动态过程进行模拟。情景1在暗管下方铺设一定宽度(L_f,分别设定为20、50、100、250和500 cm)的防渗材料以增加汇流面积,提高排水、排盐量;情景2先通过暗管直接供水湿润周围土壤,达到设定时间(T_i,分别设定为0.25~10 d的9种情形)后停止供水,然后再通过暗管进行排水、排盐,以期利用较小的冲洗定额达到排盐的目的。对情景1进行模拟时,以0~40 cm和40~60 cm土壤含盐量分别低于3 g/kg和6 g/kg作为结束淋洗的标准进行对比分析,结果表明:当暗管处于非饱和区域、下方无防渗处理(传统暗管排盐模式)时,其排盐率仅为9.8%,单方水的排盐效率约1.86 kg/m~3;在暗管下方进行防渗处理有利于增加暗管排盐量,排盐率可达11.9%~32.1%,排盐效率可提高至2.27~3.15 kg/m~3;然而,随着Lf增加,施工难度和成本均会大幅上升,尤其是当Lf100 cm,单方水排盐效率的提高程度却较为有限,因此建议Lf在100 cm以内。而采用暗管供水进行局部冲洗(情景2)时,即使在暗管下方进行防渗处理,其单方水的排盐效率最高也不超过0.6 kg/m~3,整体表现并不理想,在新疆地区使用不太现实。     

Event-based Sediment Yield Modeling using Artificial Neural Network

In the present study, a back propagation feedforward artificial neural network (ANN) model was developed for the computation of event-based temporal variation of sediment yield from the watersheds. The training of the network was performed by using the gradient descent algorithm with automated Bayesian regularization, and different ANN structures were tried with different input patterns. The model was developed from the storm event data (i.e. rainfall intensity, runoff and sediment flow) registered over the two small watersheds and the responses were computed in terms of runoff hydrographs and sedimentographs. Selection of input variables was made by using the autocorrelation and cross-correlation analysis of the data as well as by using the concept of travel time of the watershed. Finally, the best fit ANN model with suitable combination of input variables was selected using the statistical criteria such as root mean square error (RMSE), correlation coefficient (CC) and Nash efficiency (CE), and used for the computation of runoff hydrographs and sedimentographs. Further, the relative performance of the ANN model was also evaluated by comparing the results obtained from the linear transfer function model. The error criteria viz. Nash efficiency (CE), error in peak sediment flow rate (EPS), error in time to peak (ETP) and error in total sediment yield (ESY) for the storm events were estimated for the performance evaluation of the models. Based on these criteria, ANN based model results better agreement than the linear transfer function model for the computation of runoff hydrographs and sedimentographs for both the watersheds.     

Impact of an urban centre on the nitrogen cycle processes of epilithic biofilms during a summer low‐water period *

Nitrogen transformations in epilithic biofilms of a large gravel bed river, the Garonne, France, has been studied upstream (one site) and downstream (four sites) of a large urban centre (Toulouse, 740 000 inhabitants). High biomass, up to 49 g AFDM m^?2 (ashes free dry matter) and 300 mg chlorophyll a m^?2 (Chl. a), were recorded at 6 and 12 km downstream from the main wastewater treatment plant outlet. The lowest records upstream and larger downstream (less than 16 g AFDM m^?2 or 120 mg Chl. a m^?2) could be explained by recent water fall (early summer low‐water period). Measurements of nitrogen exchange at the biofilm–overlying water interface were performed in incubation chambers under light and dark conditions. The addition of acetylene at the mid‐incubation time allowed evaluation of both nitrification (variation in NH₄⁺ flux after the ammonium monooxygenase inhibition) and denitrification (N₂O accumulation related to the inhibition of N₂O reduction). Denitrification (D_w) and nitrification rates were maximum at sites close to the city discharges in dark conditions (up to 9.1 and 5.6 mg N m^?2 h^?1, respectively). Unexpected denitrification activities in light conditions (up to 1.4 mg N m^?2 h^?1) at these sites provided evidence for enhanced nitrogen self‐purification downstream. As confirmed by most probable number (MPN) counts, high nitrification rates in biofilm close downstream were related to enhanced (more than almost 3 log) nitrifying bacteria densities (up to 7.6×10⁹ MPN m^?2). Downstream of an urban centre, nitrogen transformations in the biofilm appeared to be influenced by the occurrence of an adapted microflora which is inoculated or stimulated by anthropic pollution. Copyright © 2002 John Wiley & Sons, Ltd.     

Variability of mesohabitat characteristics in riffle‐pool reaches: Testing an integrative evaluation concept (FGC) for MEM‐application

This paper investigates the variability of mesohabitat characteristics in various riffle‐pool reaches. The tested river sections (n = 13) feature clear variation in slope (0.0004–0.0132) and low flow discharge (0.05–915 m³s^?1) in different river types (straight to meandering). Mesohabitat characteristics (water depth, flow velocity, bottom shear stress) were calibrated according to the MEM‐concept (MEM—Mesohabitat Evaluation Model). Statistical analysis clearly revealed significant differences (p < 0.001) for the same mesohabitats (e.g. riffles) in different rivers concerning the tested abiotic habitat parameters. A comparative analysis of hydromorphological parameters (width‐depth variance, Froude number) showed no correlation to mesohabitat variability based on 2D/3D numerical modelling related to a range of flows (n = 10) (low flow to annual flood). Only an increasing hydraulic radius (R_hy) was correlated to an increase in fast run and a decrease in run habitats. In a case study, a Fish Guild Concept (FGC) is presented which links mesohabitats to the rheophilic fish guild (12 fish species grouped) at the Sulm River. Mesohabitat suitability (preferred, useable and avoided) for the FGC was determined for spawning, juveniles (0+, 1+), sub‐adult and adult stages based on meso‐unit and point abundance electro‐fishing. Copyright © 2010 John Wiley & Sons, Ltd. This article was published online on March 3, 2010. An error was subsequently identified in Figure 1 . This notice is included in the online and print versions to indicate that both have been corrected [March 10, 2010].     

Aggregated runoff from small watersheds based on stochastic representation of storm events

This paper is concerned with the estimation of aggregated direct runoff from small watersheds during a time interval (0,t), homogeneous with respect to rainfall characteristics. The storm events are simulated by a Poisson process, whereas direct runoff is estimated by the SCS method or a linear regression model. The probability of the occurrence of direct runoff is incorporated in the proposed method by examining the possibility of each storm exceeding the watershed losses index. A closed form solution is derived for the expected total direct runoff in the interval (0,t). Finally, the proposed method is applied to a particular set of conditions.Notation Q direct runoff - P rainfall depth - S index of watershed storage - CN Curve Number of SCS method - t time - T _i time interval between successive storm events (i andi+1) - X _i storm depth of theith event (case a) excess storm depth of theith event (case b) - Y(t) total direct runoff in (0,t) - N(t) number of storm events in (0,t) - F(t) distribution function of the time between storm events - G(x) distribution function of the storm depth - F _n(t),F _n+1(t) n-fold and (n+1)-fold convolution ofF(t), respectively - G _n(x),G _n+1(x) n-fold and (n+1)-fold convolution ofG(x), respectively - E[X] expected mean value - p probability of exceeding the thresholde,p+q=1 - * convolution operation