Estimated Peak Discharge Research Articles

Peak Discharge for Small Agricultural Watersheds

Accurate peak discharge estimates are important when sizing highway culverts to prevent possible flood damages and to ensure economic design. The purpose of the undertaken study was to find the most acceptable peak-discharge-estimation method for use on small agricultural watersheds in Nebraska. An analysis of time of concentration t c methods was undertaken because of this parameter's importance in many peak-flow methods. Seven t c equations were compared to recorded t c values from four watersheds each less than 2 sq mi (5.18 km 2) in area. Field t c values were derived from a hyetograph-hydrograph analysis. Six peak-flow methods were then compared to the recorded peaks and historical records to find the best estimation method. Based on three storm seasons of data, a modified form of the Kirpich equation and the U.S. Soil Conservation Service average-velocity equation estimate the time of concentration adequately. Peak discharges were most closely predicted using statewide regression equations, the Fletcher method, and the rational method. Results for the 25-year event (culvert design event) tentatively support the use of statewide regression equations.

Indirect estimation of ungauged peak discharges in a bedrock channel with reference to design discharge selection

AbstractGeomorphological evidence and recent trash lines were used as stage indicators in a step‐backwater computer model of high discharges through an ungauged bedrock channel. The simulation indicated that the peak discharge from the 26.7 m2 catchment was close to 150m3s−1 during the passage of Hurricane Charlie in August 1986. This estimate can be compared with an estimate of 130–160 m3s−1 obtained using the Flood Studies Report (FSR) unit hydrograph methodology. Other palaeostage marks indicate that higher stages have occurred at an earlier time associated with a discharge of 200 m3s−1. However, consideration of both the geometry of a plunge pool and transport criteria for bedrock blocks in the channel indicates that floods since 1986 have not exceeded 150 m3s−1. Given that the estimated probable maximum flood (PMF) calculated from revised FSR procedure is at least 240 m3s−1, it is concluded that compelling evidence for floods equal to the PMF is lacking. Taking into consideration the uncertainty of the discharge estimation, the 1986 flood computed using field evidence has a minimum return period of 100 years using the FSR procedure. This may be compared with a return period for the same event in the neighbouring gauged River Greta of > 100 years and a rainfall return period of 190 years. In as much as discharges of similar order to FSR estimates are indicated, it is concluded (a) that regional geomorphological evidence and flood simulation within ungauged catchments may be useful as a verification for hydrological estimates of recent widespread flood magnitude and (b) that palaeohydraulic computation can be useful in determining the magnitude of the local maximum [historic] flood when determining design discharges for hydraulic structures within specific catchments.

Hydrologic hazards in the lower Drift River basin associated with the 1989–1990 eruptions of Redoubt Volcano, Alaska

The eruptions of Redoubt Volcano between December 14, 1989 and April 26, 1990 triggered flows of snow, ice, water, sediment, and debris that traveled down the Drift River as far as its mouth, about 40 km downstream. A major explosive eruption and dome collapse on January 2, 1990 produced the largest flow. The peak discharge of this flow at a location 22 km downstream from the volcano was estimated to be between 12,000 and 60,000 m 3 per second. The estimated peak discharge of this event is more than 100 times larger than the 100-year meteorologically generated flood estimated for the Drift River. Pyroclastic flows and hot meltwater scoured the surface of Drift Glacier on the north flank of the volcano and were transformed into multipulsed, multiphased debris flows. Several other significant flows were generated by eruptions during this period: the two largest of these occurred on December 15, 1989 and February 15, 1990. Subsequent channel changes threatened the Drift River Oil Terminal built on an alluvial fan near the mouth of the Drift River.

Paleofloods and a dam-failure flood on the Virgin River, Utah and Arizona

Flood deposits on the Virgin River in southern Utah and northern Arizona preserve a record of the magnitude and frequency of the largest natural floods that have occurred on the river since AD 900. In the Virgin River gorge, several of the natural paleoflood discharges were comparable with, or even greater than, the flood from a catastrophic dam failure in 1989 that produced an estimated peak discharge of 1730 m 3 s −1 in this reach of the Virgin River. To estimate the paleoflood discharges, the heights of slackwater flood deposits in the lower bedrock gorge of the Virgin River were compared with water-surface elevations calculated with the HEC-2 step-backwater hydraulic model. The timing of the paleofloods was determined by the ages of layers rich in human artifacts that are interbedded with the flood deposits. The estimates of both the 1989 flood and the paleofloods were carried out in the Virgin River gorge, about 60 km downstream of the dam break site. No natural floods of this magnitude have occurred within the relatively short period of the gaged record. This study illustrates how incorporating rare, extreme events from the long-term paleoflood record improves the database for flood frequency analysis. The 1989 flood serves as an analog to the effects of rare natural floods with similar magnitudes along the lower Virgin River.

The 1987 debris flows in Switzerland: documentation and analysis

A great number of debris flows occurred during the flood catastrophes of the summer of 1987 in the Swiss Alps. Aerial photography, field investigations and eyewitness accounts documented and analysed the events. As an example of the reconstructed major events, the large debris flow in the Varuna valley involved an estimated peak discharge between 400 and 800 m 3/s and an event magnitude of 200,000 m 3. Several single pulses were observed; the duration of each of them appeared to be not more than a few minutes. Apart from incision into weak bedrock, the maximum erosion depth seemed to depend on the channel gradient. Based on approximately 600 events, typical starting zones and rainfall conditions are discussed with regard to the triggering conditions. Existing and new empirical formulae are proposed to estimate the most important flow parameters. These values are compared to debris flow data from Canada and Japan.

Jökulhlaups in Iceland: prediction, characteristics and simulation

Jökulhlaups drain regularly from six subglacial geothermal areas in Iceland. From Grímsvötn in Vatnajökull, jökulhlaups have occurred at 4 to 6 yearly-intervals since the 1940s with peak discharges of 600 to 10000 m3s−1, durations of 2 to 3 weeks and total volumes of 0.5 to 3.0 km3. Prior to that, about one jökulhlaup occurred per decade, with an estimated discharge of 5 km of water and a peak discharge of approximately 30000 m3s−1. Clarke’s (1982) modification of Nye’s (1976) general model of discharge of jökulhlaups gives, in many respects, satisfactory simulations for jökulhlaups from Grímsvötn the best fit being obtained for Manning roughness coefficients n = 0.08 to 0.09 m−1/3s and a constant lake temperature of 0.2°C (which is the present lake temperature). The rapid ascent of the exceptional jökulhlaup of 1938, which accompanied a volcanic eruption, can only be simulated by a lake temperature of the order of 4°C.Jökulhlaups originating at geothermal areas beneath ice cauldrons located 10 to 15 km northwest of Grímsvötn have a peak discharge of 200 to 1500 m3s−1in 1 to 3 days, with total volume of 50 to 350 × 106m3, and they recede slowly in 1 to 2 weeks. The form of the hydrograph has reversed asymmetry to that of a typical Grímsvötn hydrograph. The reservoir water temperature must be well above the melting point (10 to 20°C) and the flowing water seems not to be confined to a tunnel but to spread out beneath the glacier and later gradually to collect back to conduits.Since the time of the settlement of Iceland (870 AD), at least 80 subglacial volcanic eruptions have been reported, many of them causing tremendous jökulhlaups with dramatic impact on inhabited areas and landforms. The peak discharges of the largest floods (from Katla) have been estimated at the order of 100 000 to 300 000 m3s−1, with durations of 3 to 5 days and total volume of the order of 1 km3. It is now apparent that the potentially largest and most catastrophic jökulhlaups may be caused by eruptions in the voluminous ice-filled calderas in northern Vatnajökull (of Bárdharbunga and Kverkfjöll). They may be the source of prehistoric jökulhlaups, with estimated peak discharge of 400 000 m3s−1.At present, jökulhlaups originate from some 15 marginal ice-dammed lakes in Iceland. Typical values for peak discharges are 1000 to 3000 m3s−1, with durations of 2 to 5 days and total volumes of 2000 × 106m3. Hydrographs for jökulhlaups from marginal lakes have a shape similar to those of the typical Grímsvötn jökulhlaup. Simulations describe reasonably well the ascending phase of the hydrographs assuming a constant lake temperature of about 1°C; but they fail to describe the recession. Some floods from marginal lakes, however, have reached their peaks exceptionally rapidly, in a single day. Such rapid ascent can be simulated by assuming drainage of lake water at 4 to 8°C.An empirical power-law relationship is obtained between peak discharge,Qmax, and total volumeVtof the jökulhlaups from Grímsvötn:Qmax= KVtb, whereQmaxis measured in m3s−1,Vtin 106m3, Κ = 4.15 × 10−3s−1m2and b = 1.84. In general, the jökulhlaups (excepting those caused by eruptions) occur when the lake has risen to a critical level, but before a lake level required for simple flotation of the ice dam is reached. The difference between the hydrostatic water pressure maintained by the lake and the ice overburden pressure of the ice dam is of the order 2 to 6 bar.

Jökulhlaups in Iceland: prediction, characteristics and simulation

Jökulhlaups drain regularly from six subglacial geothermal areas in Iceland. From Grímsvötn in Vatnajökull, jökulhlaups have occurred at 4 to 6 yearly-intervals since the 1940s with peak discharges of 600 to 10000 m3s−1, durations of 2 to 3 weeks and total volumes of 0.5 to 3.0 km3. Prior to that, about one jökulhlaup occurred per decade, with an estimated discharge of 5 km of water and a peak discharge of approximately 30000 m3s−1. Clarke’s (1982) modification of Nye’s (1976) general model of discharge of jökulhlaups gives, in many respects, satisfactory simulations for jökulhlaups from Grímsvötn the best fit being obtained for Manning roughness coefficients n = 0.08 to 0.09 m−1/3s and a constant lake temperature of 0.2°C (which is the present lake temperature). The rapid ascent of the exceptional jökulhlaup of 1938, which accompanied a volcanic eruption, can only be simulated by a lake temperature of the order of 4°C.Jökulhlaups originating at geothermal areas beneath ice cauldrons located 10 to 15 km northwest of Grímsvötn have a peak discharge of 200 to 1500 m3s−1 in 1 to 3 days, with total volume of 50 to 350 × 106m3, and they recede slowly in 1 to 2 weeks. The form of the hydrograph has reversed asymmetry to that of a typical Grímsvötn hydrograph. The reservoir water temperature must be well above the melting point (10 to 20°C) and the flowing water seems not to be confined to a tunnel but to spread out beneath the glacier and later gradually to collect back to conduits.Since the time of the settlement of Iceland (870 AD), at least 80 subglacial volcanic eruptions have been reported, many of them causing tremendous jökulhlaups with dramatic impact on inhabited areas and landforms. The peak discharges of the largest floods (from Katla) have been estimated at the order of 100 000 to 300 000 m3 s−1, with durations of 3 to 5 days and total volume of the order of 1 km3. It is now apparent that the potentially largest and most catastrophic jökulhlaups may be caused by eruptions in the voluminous ice-filled calderas in northern Vatnajökull (of Bárdharbunga and Kverkfjöll). They may be the source of prehistoric jökulhlaups, with estimated peak discharge of 400 000 m3 s−1.At present, jökulhlaups originate from some 15 marginal ice-dammed lakes in Iceland. Typical values for peak discharges are 1000 to 3000 m3s−1, with durations of 2 to 5 days and total volumes of 2000 × 106 m3. Hydrographs for jökulhlaups from marginal lakes have a shape similar to those of the typical Grímsvötn jökulhlaup. Simulations describe reasonably well the ascending phase of the hydrographs assuming a constant lake temperature of about 1°C; but they fail to describe the recession. Some floods from marginal lakes, however, have reached their peaks exceptionally rapidly, in a single day. Such rapid ascent can be simulated by assuming drainage of lake water at 4 to 8°C.An empirical power-law relationship is obtained between peak discharge, Qmax, and total volume Vt of the jökulhlaups from Grímsvötn: Qmax = KVtb, where Qmax is measured in m3s−1, Vt in 106m3, Κ = 4.15 × 10−3s−1 m2 and b = 1.84. In general, the jökulhlaups (excepting those caused by eruptions) occur when the lake has risen to a critical level, but before a lake level required for simple flotation of the ice dam is reached. The difference between the hydrostatic water pressure maintained by the lake and the ice overburden pressure of the ice dam is of the order 2 to 6 bar.

Precipitation Distributions and Green‐Ampt Runoff

One‐hundred‐year and 10‐year storm runoff volumes and peak discharges were computed with a Green‐Ampt infiltration model and the Soil Conservation Service's (SCS) TR‐20 hydrograph model. The results for six different standard design storm temporal distributions were compared with predictions made with the U.S. Geological Survey's (USGS) regional regression equations relating peak discharge to drainage area. Hypothetical watersheds similar to those in eastern Montana were used for the comparisons, which were made over a wide range of hydraulic‐conductivity values for drainage areas of one to 400 sq mi. Runoff volumes computed with the Green‐Ampt equation vary significantly with the rainfall distribution. The design storms, which included the independent duration (ID) frequency analysis for all durations within the event, resulted in estimates of both volume and peak discharge that were significantly greater than predicted by the USGS equations. The SCS type‐I distribution resulted in the best comparison over the range of frequencies and drainage areas examined.

Output Reliability as Guide for Selection of Rainfall‐Runoff Models

Selection of rainfall‐runoff models is dependent on the modeling objectives and the simulation accuracy required. Output reliability is proposed as a measure to help in choosing the appropriate model for a given rainfall‐runoff model use. Output reliability can be expressed by the output variable cumulative distribution function, probability density function, confidence limits, standard deviation, or probability of acceptable percent deviation from the predicted value. Approximations of these reliability measures could be established by methods such as first‐order second‐moment reliability analysis. To demonstrate the approach, an example is given of estimating peak discharge for a watershed in central Illinois using both the HEC‐1 and RORB rainfall‐runoff models.

On the Inversely Estimated Peak Discharge of 1904 Flood Event in Isikari River by Okazaki and Effects of Short. Cut on the Formation of Ilydrograph.

[in Japanese]

Geomorphological effects of catastrophic flooding on a small subtropical Estuary

AbstractThe Mgeni Estuary is situated on the east coast of South Africa. Tidal salinity changes commonly extend 2.5 km upstream from the mouth. The subtropical climatic regime causes seasonal flooding, the geomorphological effects of which are increased by a steep river gradient. A 120‐150 year flood event during September 1987, with an estimated peak discharge of 10800 cumecs, resulted in the erosion of 1.86 × 106 m3 of sediment from the estuary. The normal high tide volume of the estuary (0.35 × 106 m3) increased to 1.85 × 106 m3 after the flood. The post‐flood intertidal volume (tidal prism) of the estuary was 0.43 × 106 m3 compared to 0.19 × 106 m3 before the event.The nature and extent of erosion in the estuary was controlled by the composition of the estuary banks and bed material. Gravel and sand substrates were preferentially eroded from the estuary bed before the cohesive bank materials were undercut in sections of the estuary. Mud and fine sand were deposited on overbank areas when the flood waned and a lag of coarse sand and gravel was produced on the estuary bed. Approximately 46 per cent of the bedload sediment supplied to the estuary since 1917 was retained in the estuary until the 1987 flood. The remainder was transported through the system and into the Indian Ocean. Results show that catastrophic floods play an important role in sedimentation in small estuaries.

Estimates of Peak Discharge from the Drainage of Ice-Dammed Ape Lake, British Columbia, Canada

AbstractThe first known occurrence of outburst flooding at Ape Lake, British Columbia, was in October 1984 following the formation of a subglacial tunnel in an ice dam created by Fyles Glacier. Following tunnel closure, the lake refilled in 150 d and then a second outburst flood occurred in August 1986. During both events, 55% of the Apc Lake volume or 46 × 106m3was released in less than 24 h into the 50 km long, ungauged Noeick River, producing an average discharge of 540 m3s−1. Channel and flood-plain erosion, damage to access roads, bridges, a logging camp, and an airstrip were related to the peak or maximum instantaneous discharge. In the absence of direct measurements, and to facilitate planning for future flood events, several independent methods were employed to estimate peak discharge. A modified version of the Clague-Mathews formula and the slope-area method yield consistent estimates which approach 1600 m3s−1near the ice-dam outlet. Attenuation of the flood peak in Noeick River is as high as 25% in the upper 12 km due to channel and flood-plain storage. Results using Clarke’s (1982) physical-based model suggest lower discharges and may be related to the irregular morphology of Ape Lake. Since Fyles Glacier is in continuous retreat, drainage around the margin of the ice dam which began in the summer of 1987 is expected to continue and no further outburst floods are anticipated.

Estimates of Peak Discharge from the Drainage of Ice-Dammed Ape Lake, British Columbia, Canada

AbstractThe first known occurrence of outburst flooding at Ape Lake, British Columbia, was in October 1984 following the formation of a subglacial tunnel in an ice dam created by Fyles Glacier. Following tunnel closure, the lake refilled in 150 d and then a second outburst flood occurred in August 1986. During both events, 55% of the Apc Lake volume or 46 × 106 m3 was released in less than 24 h into the 50 km long, ungauged Noeick River, producing an average discharge of 540 m3 s−1. Channel and flood-plain erosion, damage to access roads, bridges, a logging camp, and an airstrip were related to the peak or maximum instantaneous discharge. In the absence of direct measurements, and to facilitate planning for future flood events, several independent methods were employed to estimate peak discharge. A modified version of the Clague-Mathews formula and the slope-area method yield consistent estimates which approach 1600 m3 s−1 near the ice-dam outlet. Attenuation of the flood peak in Noeick River is as high as 25% in the upper 12 km due to channel and flood-plain storage. Results using Clarke’s (1982) physical-based model suggest lower discharges and may be related to the irregular morphology of Ape Lake. Since Fyles Glacier is in continuous retreat, drainage around the margin of the ice dam which began in the summer of 1987 is expected to continue and no further outburst floods are anticipated.

A Method Of Estimating Design Flood Hydrograph Shape In An Arid Region

ABSTRACT Unithydrograph techniques developed for design hydrographs in temperates wnes do not work well for arid zones. This is mainly attributed to the cellular nature of rainfall invalidating unit hydrograph theory. A technique is required that yields hydrograph shapes that are consistent with those measured in arid zones. A methodology has been developed that provides hydrograph shapes for catchment sizes ranging from 170 to 2672 km2. The method is based on analyses of 32 flood hydrographs in south west Saudi Arabia. The method, however, must be used concurrently with estimates of peak discharge obtained from regional studies.

Mechanics of an Earth Spillway Failure

ABSTRACT Severe storms in Mississippi during May of 1983 produced flooding that resulted in one of the few flood control reservoir auxiliary spillway failures on record. Subsequent analysis of the breach using state of the art procedures reproduced the downstream observations of high water, but failed to reproduce the observed timing of the failure or conditions observed at the site during spillway operation and failure. The present effort uses the observed failure conditions, site geology, and a simplified model of failure mechanics to develop an independent estimate of the breach outflow hydrograph. Agreement with the previously estimated peak discharge is surprisingly good. The analysis, although site specific, clearly demonstrates the important role of surface and soil discontinuities in the failure process.

The potential for catastrophic dam failure at Lake Nyos maar, Cameroon

The upper 40 m of Lake Nyos is bounded on the north by a narrow dam of poorly consolidated pyroclastic rocks, emplaced during the eruptive formation of the Lake Nyos maar a few hundred years ago. This 50-m-wide natural dam is structurally weak and is being eroded at an uncertain, but geologically alarming, rate. The eventual failure of the dam could cause a major flood (estimated peak discharge, 17000 m3/s) that would have a tragic impact on downstream areas as far as Nigeria, 108 km away. This serious hazard could be eliminated by lowering the lake level, either by controlled removal of the dam or by construction of a 680-m-long drainage tunnel about 65 m below the present lake surface. Either strategy would also lessen the lethal effects of future massive CO2 gas releases, such as the one that occurred in August 1986.

AN EMPIRICAL RELATION BETWEEN VOLUME AND PEAK OF DIRECT RUNOFF1

ABSTRACT: A linear two‐parameter relation in log space between volume and peak of direct runoff was established and verified on 134 basins in the United States, Australia, Greece and Italy. The intercept of this log relation was found to be strongly correlated with such basic characteristics as drainage area, channel slope and channel length; more than 86 percent of variance was explained. The log volume‐log peak relation can be used to explain linearity or nonlinearity of drainage basins, estimate peak discharge from data‐scarce basins, identify hydrologically similar or dissimilar basins, estimate sediment yield from upland areas, and construct unit hydrographs and unit sediment graphs for ungaged basins.

Estimating Urban Time of Concentration

Hydrologic flood‐flow design methods generally require one time parameter, such as the time of concentration, as input, and the accuracy of the estimated peak discharge or flood hydrograph is sensitive to the accuracy of the estimated time parameter. Numerous equations for estimating the time of concentration have been proposed. Eleven equations for estimating tc are compared using data collected from 48 urban watersheds located in most regions of the country. All the watersheds had areas less than 4,000 acres; the average impervious was 29.1%, and the mean time of concentration was 1.49 hr. Using accuracy and bias as the criteria for comparison, the eleven equations show wide variation in accuracy and bias. Two equations are calibrated with the data; the rainfall intensity is found to be the most important input parameter. The mean time of concentration computed by the velocity method for the 48 watersheds agrees very closely with the mean time computed from rainfall and hydrograph data. However, for ind...

FLOOD FREQUENCY ANALYSIS FOR SMALL WATERSHEDS IN SOUTHERN ILLINOIS1

ABSTRACT: Twenty‐two gaging stations were selected for developing a regional flood frequency curve for small (area less than 2 square miles) watersheds in southern Illinois. Five probability functions were compared, and the extreme value type I function was selected to develop the regional flood curve. The curve was generated with the index flood method and also another empirical method that related the function parameters to the watershed area. Estimated peak discharges with various return periods were compared with the results obtained from multiple regression analysis.

Relation Between Curve Number and Runoff Coefficient

The rational method is probably the one most widely used for estimating peak discharges for inlet designs on small watersheds. The basic input requirements include the drainage area, a rainfall intensity for the design return period, and a runoff coefficient (C). The Soil Conservation Service TR-55 graphical method is another widely used technique for estimating peak discharges for small drainage areas. Input includes the drainage area, the 24 hr precipitation depth for the design return period, the runoff curve number, and the time of concentration. The objective of this study is to demonstrate that the two runoff indices are related.