Antecedent Flow Research Articles

Instream habitat use by blue duck (Hymenolaimus malacorhynchos) in a New Zealand river

1. The feeding habitat of a river specialist, blue duck (Hymenolaimus malacorhynchos (Gmelin 1789): Anatidae), was characterized in terms of water depth and velocity on eight occasions over a 13‐month period in a river in the central North Island of New Zealand using video to record activity and relocate feeding sites.2. Of the five feeding activities identified (‘pecking’, ‘grazing’, ‘head‐dipping’,up‐ending’ and ‘diving’), adult blue duck used mostly head‐dipping (> 60% of feeding events on all dates), although diving or grazing from submerged surfaces of exposed boulders comprised major proportions of feeding behaviour (up to 33%) on occasions. Variations in feeding behaviour between dates partly reflected changes in antecedent flow conditions and the annual cycle of the birds.3. Grazing and diving occurred in significantly faster water (mostly 0.3–0.45 m s–1) and at significantly different depths (mean = 0.10 and 0.55 m, respectively) than head‐dipping (0.20 m depth and 0.28 m s–1 velocity). Adult feeding depths and velocities at four sites on different dates averaged 0.20 m and 0.31 m s–1, respectively. Most feeding by 3–4‐week‐old ducklings occurred over a similar distribution of water velocities to adults but over a wider range of depths.4. Adult birds fed in significantly shallower and lower velocity water than was available on the two dates that comparisons could be made. Ducklings also fed over a slower range of water velocities but were not selective in terms of water depth.5. Energetically more expensive search methods were employed at times of high apparent energy demand to access flow microhabitats where larger bodied prey were more likely to be encountered.6. These data indicate that, like other aquatic organisms, river birds can be influenced by basic hydraulic elements of river flow, but show at the same time that adult blue duck can accommodate variable lotic environments efficiently.

Early Water Yield Effects of Conversion of Slopes of a Eucalypt Forest Catchment to Radiata Pine Plantation

Between 1975 and 1987 the water yield from three small, contiguous, forested catchments carrying similar vegetation in southeastern Australia was measured. These were located in humid, steep foothill areas subject to a major plantation program. At the project start all catchments carried mature, natural eucalypt forest. In their natural state the catchments exhibited similar annual hydrologic variation and water yields, with a pronounced low‐flow period in summer and autumn, and high flows in winter and spring. One catchment was converted from native eucalypt forest to radiata pine by clearing, burning, and planting in December 1979. A 30‐m buffer was retained along the stream. The treatment increased the water yield of the catchment by up to 3.5 ML ha−1, a 47% increase on average. The actual yield increase varied from year to year, and appeared to decline slowly with time from the conversion. Most of the increase was as increased storm flow in the early part of winter. The relation between the storm flow, causal rainfall, and antecedent flow did not appear to be changed by the treatment, suggesting that most of the storm flow response is attributable to increased catchment wetness at the end of the dry summer period.

A Migratory Anticyclone Event during Project GALE

Abstract A case study of a transitory anticyclone is conducted as part of the Genesis of Atlantic Lows Experiment (GALE) for the Intensive Observing Period (IOP) of 7–9 March 1986. The special GALE data networks were activated in anticipation of possible Appalachian cold air damming. Cold air damming did not occur and the purpose of the case study is to diagnose a nonevent so that processes associated with cold air damming can be better isolated. An important finding is that the configuration of the antecedent synoptic-scale flow is crucial in determining whether cold air damming will evolve and be sustained. In the 7–9 March 1986 case a surface anticyclone moved steadily southeastward from west of the Great Lakes to the Middle Atlantic coast and offshore as part of a progressive westerly flow regime aloft. The typical cold air damming signature consisting of 1) a slow moving surface anticyclone along the United States-Canada border with a “U” shaped pressure ridge in the sea level isobars east of the App...

Application of a digital filter for modelling river suspended sediment concentrations

The relationship between suspended sediment concentration and discharge in a river system is the result of a complex interaction of factors within the basin and of specific storm events. Nevertheless, estimation of suspended sediment concentrations during storm events is essential for prediction of loadings from storm-controlled river basins to the receiving waters. The Venoge River, a tributary of Lake Geneva, Switzerland, with a basin area of 237 km 2, has been monitored during eight storm events between October 1986 and November 1987. A digital filter is used to simulate the suspended sediment response during individual events with the principal factors being antecedent flow, maximum discharge and time during which maximum flow was attained. The measured and calculated sediment concentration curves were assessed using a x 2-test. It was concluded that the two curves were similar in shape at 95% confidence interval. However, the model is not always capable of simulating the phase lead effect of the sediment distribution curve relative to the hydrograph. This problem is most evident during high-intensity storms at periods of low base flow; and consequently, loadings calculated for individual storms of this type could be overestimated. Fortunately, the model provides good predictions during less-intense, longer-duration events and therefore loadings calculated by summing events for an annual period will tend not to be overestimated. Further work is necessary to evaluate the model for additional events, in particular spring snow melt, and to determine its applicability to other river systems.

Use of weighted integral variables to determine the relation between rainfall intensity and storm flow and peak flow generation

Hewlett's (1977) work using his storm flow separation technique has established that peak rainfall intensities have little predictive value in the determination of storm flow depth or storm peak flow from small upland streams emanating from forested catchments. A logical but disconcerting inference is that storm rainfall intensities have little influence on either the volume of storm flow or peak flow. To obtain additional information a variant of the technique was applied to excellent records from two separate, steep, upland catchments in southern Australia. The catchments were regarded as having quite distinct rainfall response characteristics by hydrologists involved in data collection. Antecedent flow, storm rainfall, and measures of maximum rainfall intensity were supplemented by weighted integrals of rainfall intensity with time to test whether they gave additional insight into the influence of rainfall intensity. As expected, regression analysis showed that knowledge of maximum intensities gave little increase in predictive ability over storm rainfall. However, the time integral of rainfall intensity to the power of 1.5 was better correlated with peak flow than any other measure on both catchments. The results suggest that rainfall intensities are more important in the generation of peak flows than indicated by regression analysis using only peak rainfall intensities. Comparison of independent measurements of the variables using separated rain gauges showed that independent measures of the weighted variables were better correlated than measures of storm maximum intensities, indicating that they are also a more precise measure.

Predicting pH, Alkalinity, and Total Acidity in Stream Water During Episodic Events

Acid precipitation was found to significantly influence the chemistry of a small headwater stream in central Pennsylvania. Stream discharge during 18 storms was sampled and analyzed for pH, bicarbonate alkalinity, and titratable acidity levels. The precipitation events varied considerably in their amounts, durations, and intensities and also produced highly variable hydrologic responses from the watershed. Stream pH and alkalinity levels were found to react inversely to stream discharge during storm flow periods, with their lowest levels occurring almost simultaneously with peak flow. In comparison, storm flow acidity was directly related to the discharge rate, with the peaks nearly coinciding. Models predicting the fluctuations in storm flow pH, alkalinity, and total acidity were developed. These models, which explained 88, 91, and 80% of the variations in stream pH, alkalinity, and acidity, respectively, used as their independent variables such hydrometeorological parameters as antecedent flow rate, time to peak, peak flow rate, quick flow volume, and storm precipitation amounts. These results suggest strongly that the hydrologic response of a watershed has potential application as an index of stream sensitivity to changes in pH, alkalinity, and acidity during acid precipitation/snowmelt events.

The effect of rainfall intensity on storm flow and peak discharge from forest land

Analysis of an excellent 30‐year record of rainfall and storm flow (545 events) from a 3‐mi2 forested watershed in the southern Appalachians was made to determine whether rainfall intensity influences storm flow volume or peak discharge per unit area. For all practical purposes, hourly and minutely rainfall intensities during storms had no effect on storm flow volumes delivered by the basin. Storm rainfall P, antecedent flow I, season (winter or summer), and duration of the rainstorm D accounted for 86.4% of the total variation in the log of storm flow. Addition of maximum 60‐, 30‐, 15‐, and 5‐min intensities raised this to 86.7% (the increase was not significant at the 0.05 level) but reduced the standard error (0.354 in logs) by less than ½%. The same four variables (P, I,S, and D) accounted for 72% of the variation in the log of peak flow. Addition of the intensity variables raised this to 76.7% (increase significant at the 0.01 level). Thus only 4.7% of the total variation in the log of peak flow was attributable to intensity. Analysis by eight storm rainfall classes reinforced the conclusion that intensity added nothing to storm rainfall as a predictor of storm flow regardless of storm magnitude. P, I, S, and D accounted for 25–65% of the total variation in the log peak flows within storm classes; addition of all intensity variables raised this to 36–85%, but the increases were nonsignificant at the 0.05 level in four of the eight classes. A strong inference is made that neither estimates nor measurements of hourly and minutely rainfall intensity are of practical value in predicting storm flow volume from this forested basin. Furthermore, intensity played a much smaller role in peak discharge generation on this basin than was expected. The hypothesis is offered that rainfall intensity variation is not a dominant variable controlling flood generation in humid region, wild land watersheds.

Stochastic simulation of monthly streamflow by a multiple regression model utilizing precipitation data

A model for simulation of monthly streamflow series is developed by a multiple regression approach, which includes both precipitation and flow, instead of the simple regression Markovian model, which is based on the antecedent flow alone. The variables in the regression function represent the previous month's flow, current precipitation, antecedent month's precipitation, and the accumulated precipitation as independent variables, while the dependent variable is the current streamflow. A procedure is suggested for generating precipitation data which can be used in the multiple regression. The frequency distribution of the flow record in each month is determined by statistical analysis. These monthly distributions are later imposed on the model in order to reproduce data with the same statistical parameters and distributions. For each month the optimal combination of variables for the regression model is selected according to least variance, largest coefficient of determination, and the results of significance tests for the regression coefficients. Three watersheds with different physiographic characteristics were selected. Streamflows were simulated for each basin and results have been compared with the historic record in terms of statistical parameters and frequency distribution. The results were also compared with those obtained by the simple regression model using only streamflow data. Results in general show good agreement with the historical data, mainly in terms of mean, standard deviation, and frequency distribution. Poorer agreement was found in the case of the less reliable parameters like skew coefficient and serial correlation. However, in most cases a definite improvement is achieved over the simple regression model.