Hydrologic Sciences Taking Stock and Looking Ahead (1998) / Chapter Skim
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5 Streamflow Prediction: Capabilities, Opportunities, and Challenges
5 Streamflow Prediction: Capabilities, Opportunities, and Challenges
Pages 101-134
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From page 101... ...
Water Science and Technology Board is in honor of one of the great scientistengineers of the century. This colloquium, which expands the scope of the annual lecture, is a fitting way to discuss some of the developments that resulted from the Eagleson committee's report Opportunities in the Hydrologic Sciences (NRC, 1991a)
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From page 102... ...
A comprehensive coverage of the hydroclimatology related to floods and droughts, flood forecasting and drought prediction, water supply forecasting, and flood and drought management, is given in Paulson et al.
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From page 103... ...
The most important forecasts are for anticipated seasonal flow patterns. Over-year storage is provided when the reservoir is on the order of the mean annual flow volume or larger and the annual release schedule is on the order of 50 percent or larger of the mean annual inflow volume.
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From page 104... ...
, realtime or relatively short lead-time forecasts of river flow rates and inundation levels can have different degrees of usefulness and precision. Forecasts can be made with greatest precision when the lead time is short or when an upstream stream gage measures the hydrograph that, after propagation downstream, creates the flood hazard.
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From page 105... ...
This case study emphasized the importance of human judgment in issuing a flood warning for convective storms. Two rain gages in the basin of interest and nine nearby gages were used to estimate basin average rainfall (1.44 in.)
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From page 106... ...
. Nonstandard rain gages provided approximate point estimates of total rainfall at five locations.
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From page 107... ...
o to to us 0 cn 0 ~0 cut x AL o A ~ ~ ~ ~ A ~ rain discharge Do., 6/27 5UTC 6/2710UTC 6/2715UTC 6/27 20UTC 6/28 1UTC 1am EDT 6am EDT 11am EDT 4pm EDT 9pm EDT FIGURE 1 Estimated discharge hydrograph for the Rapidan River at Ruckersville, Virginia, and 6-minute time series of basin-averaged rainfall rate for the Rapidan River upstream of Ruckersville for June 27, 1995. Source: Reprinted, with permission, from Smith et al.
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From page 108... ...
FIGURE 3 Map of storm total rainfall accumulations (in millimeters) , June 27, 00002000 UTC (Universial Time Coordinates)
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From page 109... ...
There are several questions concerning possibilities for spatial precipitation runoff modeling for situations similar to the Rapidan River basin. The basin has high relief and should be amenable to distributed spatial hillslope hydrologic modeling using models similar to that of Wigmosta et al.
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From page 110... ...
There is no apparent simple correction scheme that can be implemented to adjust the tipping bucket rainfall rate record to reflect actual rainfall reaching the ground. Figure 4 presents information for the storm of June 9, 1996, to emphasize variations in precipitation rate and accumulated depth as estimated from radar reflectivities or as measured directly.
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From page 111... ...
FIGURE 4 Time series of instantaneous rainfall rate determined from radar reflectivity and ground-based disdrometer and accumulated rainfall determined from radar reflectivity, disdrometer accumulations, and a tipping bucket rain gage, Goodwin Creek, Mississippi, June 9, 1996. Source: Reprinted, with permission, from Steiner et al.
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From page 112... ...
Figure 4b shows the accumulated rainfall depth on a linear scale. For this storm the radar-estimated rainfall and the disdrometer-measured rainfall rates and accumulated amounts are in close agreement.
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From page 113... ...
Evaporation and transpiration are represented as physical water transport rather than as energy fluxes. Any desired degree of spatial disaggregation can be used for precipitation input and representation of hillslope and channel hydrologic processes.
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From page 114... ...
. A single rain gage was used in both situations to represent precipitation input.
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From page 115... ...
The two years where wet and dry season evapotranspiration rates were almost equal correspond to low wet season rainfall with increased evaporation occurring during the wet season. The till leakage provides recharge to a deeper aquifer that provides sustained water supply to down-basin streams.
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From page 116... ...
rain gages were used to construct the rain contour map; the maximum contour shows a depth of 55 mm. While the rainfall cumulative total is relatively uniform, a single tipping bucket recording rain gage is inadequate to capture all the features of the spatial rainfall pattern that are needed to predict flow production and delivery to the channel.
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From page 117... ...
FIGURE 8 Modeled hydrographs for five combinations of one, two, three, and four recording rain gages in Watershed LH-104 (August 3, 1990~. Source: Reprinted, with permission, from Faures et al.
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From page 118... ...
In principle, if the control volume were extended above the watershed to include the complete airshed and all water and energy fluxes across both boundaries were measured, it would be effective to do approximate major catchment plan view pixel hydrologic modeling using the moisture accounting models developed 30 years ago. The need to model surface energy fluxes as well as hydrologic fluxes and water storage states, at whatever pixel size is being used, has necessitated the development of models that do both energy and moisture accounting.
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From page 119... ...
The bulk of the work to date involving hydrology at the continental river basin scale has focused on coupling hydrology with GCM and mesoscale meteorology representations of the surface water and energy fluxes and corresponding river flow. The enormously complicated issue of determining the (residual)
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From page 120... ...
120 o IL a UJ a: to z o a: .
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From page 121... ...
This figure shows clearly that there are decadal periods of substantially above- and below-average river flow volume. Figure lo shows systemwide river flow volume for the Salt-Verde River Basin in Anzona.
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From page 122... ...
The historical record gives us other information that suggests actions that are needed for extended climatic variability prediction. Figure 11 shows an apparent relationship between the grouping of superfloods in the Upper Mississippi and Missouri river basins and aspects of the Southern Oscillation Index (SOI)
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From page 123... ...
_ E o or N . _ ~ -1 0 o 123 20 : 5 o 5 Cumulative Number of Superfloods SOI 11 ~ A" REV ~l~ - ~~ · ~hi, ~ s v V ~ ~ t t M+ S · ~ · 1 ~ · I ~ 1 1 ~ · ~ 1 , ~, i VS 1 ~ ~ ~ ~ 1 ~ ~ ~ ~ 1 ~, ~ 1955 1960 1965 1970 1975 1980 1985 FIGI~E 11 Monthly anomalies of Southern Oscillation Index and number of superfloods for the Upper Mississippi and Missouri river basin.
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From page 124... ...
More recently, a National Research Council committee (NRC, 1996) has emphasized the need for a closer connection between QPFs and how they will be used in hydrologic models for hydrologic prediction, particularly short-term flood warning.
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From page 125... ...
The target is to provide 25,50, and 75 percent exceedance flow rate forecasts for days, to weeks, to multiple months ahead. The potential benefits from spatial modeling and implementation of the WARES program highlighted here are important.
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From page 126... ...
A Final Grand Challenge Figure 13 shows the time series of May to April water year cumulative inflow volume to the surface reservoirs that serve the southwestern region of western Australia, including the Perth metropolitan area, for the period from 1911 to 1994. The annual inflow volume is expressed in billions of liters (giga liters, or GL)
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From page 127... ...
The uncertainty of inflow volumes to the multiple reservoir system is a major cause of concern for the society. The population served is approximately 1.2 million.
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From page 128... ...
The rain that falls on the Perth water supply catchments infiltrates readily into the highly permeable lateritic soils. If a substantial storm follows closely a series of antecedent storms that have made the soil column relatively wet, subsurface flow is delivered to the channels.
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From page 129... ...
Larger inflow volumes are associated with larger than usual wet season rainfall. Prediction of likely increased wet season rainfall should be a target.
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From page 130... ...
summarized the findings of research needs identified by research scientists and engineers who participated in a workshop that was held in Perth in 1996 to address the critical water supply issue for the growing Perth region. The summary calls for pushing the scientific limits of coupled ocean, atmospheric, and hydrologic models particularly the limits of prediction of likely precipitation over decade-long periods.
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From page 131... ...
In all that is attempted there are many intellectual and developmental challenges. The "grand challenge" is working toward connecting ocean, atmosphere, and hydrosphere interactions into a coherent approach that will yield hydrologically useful information at the hillslope, catchment, and continental river basin scale for time scales up to the order of a decade.
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From page 132... ...
1993. Use of WSR-88D and Surface Rain Gage Network in Issuing Flash Flood Warnings and Main Stem Flood Forecasts Over Osage County, Oklahoma, June 5, 1991.
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From page 133... ...
1995. Impact of small-scale spatial rainfall variability on runoff modeling.
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From page 134... ...
1997. Use of RADAR for remote monitoring of rainfall rate and rainfall kinetic energy on a variety of scales.
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