Peak Flow Forecasts, April 1, 2011   www.cbrfc.noaa.gov


NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents


Introduction

NEW: Starting in May 2011, we now estimate, where possible, an instantaneous flow for each mean daily flow forecast. These instantaneous flows are estimated from a historical regression analysis at each point. For more information view the regression plots.

Streamflow varies dramatically over the course of the snowmelt season. To characterize the magnitude of a year with a single seasonal peak sometimes can be an oversimplification. Hydrographs (or graphs of mean daily flow versus time) for each site can be viewed by clicking on the site name. The hydrographs include an example high and low year alongside last year and this year.

River recreationists often ask what are the high and low years. Rankings of a sites peak flows can be viewed by clicking the site name below. Reservoir regulation plays a major role in determining observed peak flows. As would be expected, higher (but more short-lived) peaks are generally observed in the pre-regulatory era (before 1960).


Upper Colorado Peak Flow Forecasts

Prepared by: Alcorn, Cox, Nielson
2011 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2010
Peak
2010
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Colorado
Kremmling, Nr
Mean Daily Flow 12,700 3,900 10,150 5,870 6/15 N/A N/A N/A N/A N/A 5/15 - 6/27
Eagle
Gypsum, Blo
Mean Daily Flow 6,580 3,600 6,410 6,160 6/08 3300 3700 4500 5300 6500 6/1 - 6/21 4/1
Instantaneous Flow 3700 4100 5000 5900 7200
Colorado
Dotsero, Nr
Mean Daily Flow 20,800 9,425 17,000 13,700 6/09 10000 11000 14200 17000 21000 5/25 - 6/20 4/1
Instantaneous Flow 11000 12000 15000 18000 22000
Crystal
Redstone, Nr, Avalanche Ck
Mean Daily Flow 3,500 1,965 3,100 3,110 6/09 1700 1950 2200 2400 2800 5/29 - 6/22 4/1
Instantaneous Flow 2000 2300 2600 2800 3300
Roaring Fork
Glenwood Springs
Mean Daily Flow 11,800 6,150 16,800 8,710 6/11 5500 6400 7400 8400 10000 6/3 - 6/18 4/1
Instantaneous Flow 6200 7200 8300 9400 11000
Colorado
Cameo, Nr
Mean Daily Flow 38,000 17,500 25,350 23,600 6/09 18000 20000 23000 28000 36000 5/29 - 6/18 4/1
Instantaneous Flow 19000 21000 24000 29000 37000
Plateau Ck
Cameo, Nr
Mean Daily Flow 4,100 1,460 4,160 1,410 5/30 1100 1400 1800 2300 2600 5/9 - 6/11 4/1
Instantaneous Flow 1400 1700 2200 2800 3100
East
Almont, Nr
Mean Daily Flow 5,000 2,080 2,970 2,300 6/08 1750 2000 2300 2600 3000 5/28 - 6/17 4/1
Instantaneous Flow 1900 2200 2500 2900 3300
Nf Gunnison
Somerset, Nr
Mean Daily Flow 7,080 3,310 10,565 2,700 6/07 2700 3100 3700 4200 4600 5/11 - 6/2 4/1
Instantaneous Flow 3100 3600 4300 5000 5500
Surface Ck
Cedaredge
Mean Daily Flow 640 210 1,611 140 4/23 220 250 290 350 420 5/3 - 6/8 4/1
Instantaneous Flow 320 360 420 510 610
Gunnison
Grand Junction, Nr (see Notes Below)
Mean Daily Flow 23,200 9,660 19,556 7,400 5/19 7000 8500 10000 11000 12000 5/3 - 6/12 4/1
Instantaneous Flow 7700 9200 11000 12000 13000
Colorado
Co-ut Stateline, Nr
Mean Daily Flow 68,300 26,150 47,550 29,600 6/10 24000 27000 34000 38000 48000 5/22 - 6/16 4/1
Instantaneous Flow 25000 28000 35000 39000 49000
Dolores
Dolores
Mean Daily Flow 6,950 2,980 7,820 2,700 5/30 1500 1800 2100 2400 2800 5/9 - 6/4 4/1
Instantaneous Flow 1700 2100 2400 2800 3300
San Miguel
Placerville, Nr
Mean Daily Flow 2,740 1,310 3,040 1,500 6/07 790 870 1000 1100 1300 5/26 - 6/23 4/1
Instantaneous Flow 930 1000 1200 1300 1500
Colorado
Cisco, Nr
Mean Daily Flow 69,500 28,800 57,800 30,300 6/10 24000 28000 36000 40000 53000 5/20 - 6/15 4/1
Instantaneous Flow 25000 29000 37000 41000 54000
Green
Daniel, Nr, Warren Bridge, At
Mean Daily Flow 5,620 2,975 N/A 2,190 6/10 2000 2200 2600 3100 3500 5/30 - 6/30 4/1
Instantaneous Flow 2000 2300 2700 3200 3600
New Fork
Big Piney, Nr
Mean Daily Flow 9,110 5,285 9,800 5,470 6/13 3200 3700 4500 5000 6000 5/31 - 6/24 4/1
Instantaneous Flow 3300 3800 4600 5100 6200
Green
Labarge, Nr
Mean Daily Flow 18,800 9,270 14,000 8,350 6/13 N/A N/A N/A N/A N/A 5/30 - 6/24 -
Big Sandy
Farson, Nr
Mean Daily Flow 1,690 820 N/A 929 6/12 N/A N/A N/A N/A N/A 5/28 - 6/23 -
Green
Green Rvr Wy, Nr
Mean Daily Flow 15,400 7,110 12,500 2,820 7/05 N/A N/A N/A N/A N/A 5/23 - 7/11 -
Hams Fork
Frontier, Nr, Pole Ck, Blo
Mean Daily Flow 2,000 825 1,800 635 6/11 780 950 1150 1300 1500 5/10 - 6/9 4/1
Instantaneous Flow 840 1000 1200 1400 1600
Blacks Fork
Little America, Nr
Mean Daily Flow 6,970 2,440 4,400 4,070 6/15 2600 2800 3400 4200 5000 5/2 - 6/27 4/1
Instantaneous Flow 2800 3000 3600 4500 5300
Elk
Nr Milner
Mean Daily Flow 6,100 4,160 5,800 6,100 6/09 4200 4500 5000 6000 6500 5/19 - 6/12 4/1
Instantaneous Flow 4600 4900 5400 6400 6900
Yampa
Steamboat Springs
Mean Daily Flow 5,870 3,240 5,500 3,690 6/08 3400 3800 4500 5000 5550 5/19 - 6/12 4/1
Instantaneous Flow 3700 4200 4900 5400 5900
Maybell, Nr
Mean Daily Flow 24,400 10,475 21,000 11,500 6/10 12000 14000 16000 17500 20000 5/13 - 6/10 4/1
Instantaneous Flow 12000 15000 17000 18000 21000
Little Snake
Lily, Nr
Mean Daily Flow 13,400 4,745 14,000 5,540 6/16 4500 5500 6500 8500 10000 5/5 - 6/12 4/1
Instantaneous Flow 5100 6200 7400 9600 11000
Yampa
Deerlodge Park
Mean Daily Flow 32,300 13,955 17,000 17,000 6/11 17000 19000 22000 25000 28000 5/11 - 6/6 4/1
Instantaneous Flow 18000 20000 23000 26000 29000
Green
Jensen, Nr (see Note1 Below)
Mean Daily Flow 38,500 17,600 25,000 19,400 6/11 22000 24000 27000 30000 33000 5/14 - 6/11 4/1
Instantaneous Flow 23000 25000 28000 31000 34000
Rock Ck
Upr Stillwater Res
Mean Daily Flow 2,080 1,350 N/A 2,040 6/08 1450 1750 2050 2400 2700 5/25 - 6/20 4/1
Uinta
Neola, Nr
Mean Daily Flow 3,000 1,640 5,600 2,230 6/06 1300 1450 1700 2000 2300 5/25 - 6/15 4/1
Instantaneous Flow 1900 2100 2500 2900 3400
White Rocks
Whiterocks, Nr
Mean Daily Flow 2,300 1,230 2,800 1,120 6/08 650 750 880 1050 1200 5/10 -6/10 4/1
Instantaneous Flow 860 1000 1200 1500 1700
Duchesne
Tabiona, Nr
Mean Daily Flow 2,320 765 4,100 1,070 6/9 1200 1400 1700 1900 2200 5/15 - 6/15 4/1
Instantaneous Flow 1400 1600 1900 2100 2500
Randlett, Nr
Mean Daily Flow 11,500 2,755 7,400 2,920 6/08 4700 5500 7000 8500 10500 4/27 - 7/5 4/1
Instantaneous Flow 5100 5800 7300 8800 11000
White
Meeker, Nr
Mean Daily Flow 6,320 3,200 11,000 3,310 6/09 2900 3100 3500 4100 5000 5/21 - 6/14 4/1
Instantaneous Flow 3100 3300 3800 4400 5400
Green
Green River, Ut (see Note1 Below)
Mean Daily Flow 47,200 22,560 47,000 24,200 6/11 31000 34000 39000 44000 51000 5/18 - 6/16 4/1
Instantaneous Flow 32000 35000 40000 45000 52000
Cataract Canyon (estimated)
Mean Daily Flow 116,700 51,350 N/A 53,400 6/11 55000 62000 75000 84000 104000 5/20 - 6/16 4/1
San Rafael
Green River, Nr
Mean Daily Flow 3,600 910 N/A 307 6/16 1300 1700 2000 2300 2700 5/17 - 7/16 4/1
Muddy Ck
Emery, Nr
Mean Daily Flow 515 205 N/A 160 6/10 230 260 310 390 480 5/19 - 6/18 4/1
Dirty Devil
Hanksville, Nr, Poison Spgs **
Mean Daily Flow 1,690 445 N/A 798 6/14 N/A N/A N/A N/A N/A 3/12 - 5/31 -
Escalante
Escalante, Nr ***
Mean Daily Flow 307 72 N/A 96 7/27 40 50 70 100 130 3/24 - 6/2 4/1
San Juan
Pagosa Springs
Mean Daily Flow 4,640 2,485 6,750 2,450 5/30 1650 1800 2050 2350 2700 5/15 - 6/12 4/1
Instantaneous Flow 1900 2100 2400 2700 3100
Animas
Durango
Mean Daily Flow 10,700 4,675 9,554 4,500 5/30 2900 3300 3800 4400 5000 5/28 - 6/14 4/1
Instantaneous Flow 3200 3600 4200 4800 5500
Farmington (see Note 2 Below)
Mean Daily Flow 11,000 4,900 8,810 4,000 5/31 2800 3300 3900 4600 5500 5/31 - 6/15 4/1
San Juan
Bluff, Nr (see Note 1 Below)
Mean Daily Flow 15,600 7,340 33,838 4,300 6/01 7000 7500 8000 8500 9000 5/21 - 7/4 4/1
Instantaneous Flow 8100 8600 9100 9600 10000

Red=Forecast Above Flood Flow, Yellow=Forecast Above Historic Peak.
N/A = Not Available (Not a flood forecast point or no forecast procedure exists.)
* = Flood flow is for current year only and is an instantaneous value.
- = Exceedance value has already occurred during the current runoff season.
Note1 - Peak flow forecasts on the Green River below Flaming Gorge Reservoir are based on USBR planned regulation.
Note2 - Peak flow forecasts on the San Juan below Navajo Reservoir are based on USBR planned regulation.
Note3 - Peak flow forecasts on the Gunnison below Crystal Reservoir are based on USBR planned regulation.
Note4 - Peak flow forecasts account for CUWCD planned operations.
** = Runoff period March - June.
*** = Runoff period March - June does not include contribution from Boulder Creek.


Great Salt Lake Peak Flow Forecasts

Prepared by: Bernard
2011 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2010
Peak
2010
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Bear
Utah-wyoming Stateline, Nr
Mean Daily Flow 2,980 1,610 3,675 2310 6/8 1800 1950 2230 2650 3100 5/22 - 6/14 4/5
Instantaneous Flow 2200 2400 2800 3300 3900
Logan
Logan, Nr, State Dam, Abv
Mean Daily Flow 2,450 985 1,355 852 6/8 1440 1570 1730 1850 2010 5/18 - 6/10 4/5
Instantaneous Flow 1500 1700 1800 1900 2100
Blacksmith Fork
Hyrum, Nr, Up&l Dam
Mean Daily Flow 1,650 490 935 150 4/23 830 870 940 1040 1170 4/24 - 5/20 4/5
Instantaneous Flow 960 1000 1100 1200 1400
Weber
Oakley, Nr
Mean Daily Flow 4,170 1,625 1,950 2600 6/8 2020 2210 2550 2950 3350 5/24 - 6/16 4/5
Instantaneous Flow 2400 2600 3000 3500 4000
Chalk Ck
Coalville
Mean Daily Flow 1,790 600 1,200 535 6/14 860 940 1120 1380 1680 5/5 - 5/31 4/5
Instantaneous Flow 990 1100 1300 1600 2000
Provo
Woodland, Nr (regulated)
Mean Daily Flow 6,040 1,685 3,150 2820 6/8 1750 1980 2210 2460 2920 5/11 - 6/6 4/5
Instantaneous Flow 2000 2300 2600 2800 3400
Little Cottonwood Ck
Salt Lake City, Nr
Mean Daily Flow 762 470 800 800e 6/8 460 520 580 610 670 5/23 - 6/20 4/5
Big Cottonwood Ck
Salt Lake City, Nr
Mean Daily Flow 980 430 800 700e 6/8 380 420 480 530 590 5/18 - 6/9 4/5
Mill Ck
Salt Lake City, Nr
Mean Daily Flow 153 65 155 60 6/9 60 65 75 85 90 5/18 - 6/10 4/5
Emigration Ck
Salt Lake City, Nr
Mean Daily Flow 164 55 130 25 5/24 65 75 90 110 140 4/11 - 5/19 4/5
City Ck
Salt Lake City, Nr
Mean Daily Flow 322 90 210 70 6/7 120 130 145 170 220 5/12 - 6/1 4/5
Sevier
Hatch
Mean Daily Flow 1,990 594 1,185 670 6/07 850 910 1020 1130 1230 5/4 - 6/15 4/5
Instantaneous Flow 910 980 1100 1200 1300

Red=Forecast Above Flood Flow, Yellow=Forecast Above Historic Peak.
N/A = Not Available (Not a flood forecast point or no forecast procedure exists.)
* = Flood flow is for current year only and is an instantaneous value.
- = Exceedance value has already occurred during the current runoff season.


Lower Colorado Peak Flow Forecasts

Prepared by: G. Smith
2011 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2010
Peak
2010
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Virgin
Virgin
Mean Daily Flow 10,600 780 5,083 1,310 4/22 990 1030 1100 1330 1760 3/13 - 5/4 4/5
North Fork Virgin
Springdale, Nr
Mean Daily Flow 2,820 570 5,514 709 4/22 790 900 1020 1160 4/10 - 5/15 4/5
Santa Clara
Pine Valley, Nr
Mean Daily Flow 393 65 N/A 89 6/08 100 120 150 210 390 4/25 - 5/25 4/5

Red=Forecast Above Flood Flow, Yellow=Forecast Above Historic Peak.
N/A = Not Available (Not a flood forecast point or no forecast procedure exists.)
* = Flood flow is for current year only and is an instantaneous value.
- = Exceedance value has already occurred during the current runoff season.


River Running Permits/Information



Definitions

Peak Flow
The peak flow forecast represents the maximum mean daily flow (the highest average flow for an entire day during the runoff season) at a point during the April through July period, unless otherwise noted. It does not represent the instantaneous peak (the maximum flow at a single moment). In the case of smooth snowmelt regimes (hydrographs), it may be acceptable to approximate one with the other. In Arizona, the normal snowmelt period is from February to May. Occasionally, heavy rainfall events can produce higher peak flows than the snowmelt peak flows. For verification and calibration purposes, the maximum mean daily flow during the February through May period was used regardless of the runoff source. The Average Peak and Normal Time of Peak (defined as the average date of peak plus/minus one standard deviation which should include approximately 70% of the peaks) for a given gage are all derived from 1971 through 2000 data whereas the Historic Peak is derived from the period of record, including the most recent years, after reservoir regulation began.

Forecast Probabilities
Peak flow forecasts are presented in terms of probabilities or, more specifically, exceedance probabilities. The forecast labeled "most probable" is actually the 50% exceedance level meaning there are equal chances of being below the value or above the value (i.e., 50 chances out of 100 of being exceeded). The other exceedance probabilities associate the likelihood of exceeding other levels. In general, a close bunching of the exceedance forecasts indicates low variability and that the user can have a high degree of confidence in the forecast information. Conversely, a large spread in the exceedance forecasts indicates high variability.

Modeling Techniques
The peak flow forecasts that follow have been derived using a combination of (1) physically-based conceptual models and (2) statistical regression models. The conceptual model is the National Weather Service River Forecasting System in the Ensemble Streamflow Prediction (ESP) mode. Since the conceptual model requires reservoir operation plans for up to five months into the future, ESP application is limited to basins where regulation is minimal (mostly in the headwater areas). The farther downstream a forecast point is, the more likely it is that a statistical regression was used between natural snowmelt runoff volume and the observed maximum mean daily flow to generate the forecast. Such an approach performs better when the correlation between regulated and unregulated flow is strong and is constant from year to year.


Additional Information

Flow extremes, Not Supply
Peak flow forecasts are fundamentally different than water supply volume forecasts. Although the watershed snowpack is a principal component in both analyses, peak flows are not a supply question at all. Rather, peak flows characterize runoff extremes by predicting maximum mean daily flow at a single point during the spring snowmelt season. This extreme is related to the water supply volume, but the relationship is not direct or constant from year to year. As such, peak flow forecasts contain much more uncertainty than water supply volume forecasts.

Regulated vs. Natural Flows
An even more fundamental limitation is that peak forecasts describe regulated (actual or observed) in-stream flow well into the future, something difficult to do considering the quantity and changing nature of diversions in the Colorado River and Great Basin watersheds. (Note: supply forecasts deal with hypothetical "natural" flow - that which would have resulted in the absence of regulation). The Colorado Basin River Forecast Center routinely forecasts regulated streamflow, but only for several days into the future. Further into the future the ability to forecast reservoir regulation becomes more limited.

Different Uses and Users
Peak flow forecasts are used for different purposes than water supply volume forecasts. Users of these forecasts would include river recreationists, flood control agencies, emergency service directors, wildlife managers and anyone interested in the combined effect of watershed yield and human regulation on the actual (observed) in-stream maximum mean daily flows at a site.

Flood Flows
The National Weather Service defines flood flow as the flow at which damage to structures begins to occur. Over-bank flow may occur but still be below the defined flood flow. Flood flows contained in this document change from year to year due to such channel processes as deposition and scouring. Therefore, the flood flows that follow should only be applied to the current runoff season. It should also be noted that they are instantaneous flows and not maximum mean daily flows.