Peak Flow Forecasts, May 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 N/A N/A
Eagle
Gypsum, Blo
Mean Daily Flow 6,580 3,600 6,410 6,160 6/08 4500 5000 5700 6700 7800 6/1 - 6/21 5/5
Instantaneous Flow 5000 5500 6300 7400 8600
Colorado
Dotsero, Nr
Mean Daily Flow 20,800 9,425 17,000 13,700 6/09 13500 15000 17500 20000 24000 5/25 - 6/20 5/5
Instantaneous Flow 14000 16000 18000 21000 25000
Crystal
Redstone, Nr, Avalanche Ck
Mean Daily Flow 3,500 1,965 3,020 3,110 6/09 2200 2400 2600 2900 3200 5/29 - 6/22 5/5
Instantaneous Flow 2600 2800 3000 3400 3800
Roaring Fork
Glenwood Springs
Mean Daily Flow 11,800 6,150 16,800 8,710 6/11 7500 8000 9500 10500 11500 6/3 - 6/18 5/5
Instantaneous Flow 8400 8900 11000 12000 13000
Colorado
Cameo, Nr
Mean Daily Flow 38,000 17,500 25,350 23,600 6/09 24000 26000 31000 36000 41000 5/29 - 6/18 5/5
Instantaneous Flow 25000 27000 32000 37000 42000
Plateau Ck
Cameo, Nr
Mean Daily Flow 4,100 1,460 4,160 1,410 5/30 1500 1700 2000 2400 3200 5/9 - 6/11 5/5
Instantaneous Flow 1800 2100 2400 2900 3800
East
Almont, Nr
Mean Daily Flow 5,000 2,080 2,970 2,300 6/08 2500 2700 3100 3500 3900 5/28 - 6/17 5/5
Instantaneous Flow 2800 3000 3400 3900 4300
Nf Gunnison
Somerset, Nr
Mean Daily Flow 7,080 3,310 10,565 2,700 6/07 3400 3600 3900 4400 5000 5/11 - 6/2 5/5
Instantaneous Flow 4000 4200 4600 5200 6000
Surface Ck
Cedaredge
Mean Daily Flow 640 210 1,621 140 4/23 270 280 320 370 430 5/3 - 6/8 5/5
Instantaneous Flow 390 410 470 540 630
Gunnison
Grand Junction, Nr (see Notes Below)
Mean Daily Flow 23,200 9,660 19,556 7,400 5/19 7500 8500 10500 11000 12000 5/3 - 6/12 5/5
Instantaneous Flow 8200 9200 11000 12000 13000
Colorado
Co-ut Stateline, Nr
Mean Daily Flow 68,300 26,150 47,550 29,600 6/10 33000 37000 43000 50000 58000 5/22 - 6/16 5/5
Instantaneous Flow 34000 38000 44000 51000 59000
Dolores
Dolores
Mean Daily Flow 6,950 2,980 7,820 2,700 5/30 1900 2100 2300 2500 2900 5/9 - 6/4 5/5
Instantaneous Flow 2200 2400 2700 2900 3400
San Miguel
Placerville, Nr
Mean Daily Flow 2,740 1,310 3,040 1,500 6/07 890 970 1050 1150 1250 5/26 - 6/23 5/5
Instantaneous Flow 1000 1100 1200 1300 1500
Colorado
Cisco, Nr
Mean Daily Flow 69,500 28,800 59,500 30,300 6/10 34000 38000 46000 53000 60000 5/20 - 6/15 5/5
Instantaneous Flow 35000 39000 47000 54000 62000
Green
Daniel, Nr, Warren Bridge, At
Mean Daily Flow 5,620 2,975 N/A 2,190 6/10 3200 3400 3800 3900 4200 5/30 - 6/30 5/5
Instantaneous Flow 3300 3500 3900 4000 4300
New Fork
Big Piney, Nr
Mean Daily Flow 9,110 5,285 9,800 5,470 6/13 4700 5000 6000 7000 7700 5/31 - 6/24 5/5
Instantaneous Flow 4800 5100 6200 7200 7900
Green
Labarge, Nr
Mean Daily Flow 18,800 9,270 14,000 8,350 6/13 11000 12000 14000 15500 16500 5/30 - 6/24 5/5
Instantaneous Flow 11000 12000 14000 16000 17000
Green Rvr Wy, Nr
Mean Daily Flow 15,400 7,110 12,500 2,820 7/05 10000 10500 11500 12500 14500 5/23 - 7/11 5/5
Instantaneous Flow 10000 11000 12000 13000 15000
Hams Fork
Frontier, Nr, Pole Ck, Blo
Mean Daily Flow 2,000 825 1,800 635 6/11 1150 1300 1550 1750 2000 5/10 - 6/9 5/5
Instantaneous Flow 1200 1400 1700 1900 2200
Blacks Fork
Little America, Nr
Mean Daily Flow 6,970 2,440 4,400 4,070 6/15 4300 4900 6500 7000 8000 5/2 - 6/27 5/5
Instantaneous Flow 4600 5200 6900 7400 8500
Elk
Nr Milner
Mean Daily Flow 6,100 4,160 5,800 6,100 6/09 5800 6000 7000 8000 9000 5/19 - 6/12 5/5
Instantaneous Flow 6200 6400 7400 8500 9500
Yampa
Steamboat Springs
Mean Daily Flow 5,870 3,240 5,500 3,690 6/08 4700 5500 6000 7000 8000 5/19 - 6/12 5/5
Instantaneous Flow 5100 5900 6400 7400 8500
Maybell, Nr
Mean Daily Flow 24,400 10,475 21,000 11,500 6/10 17000 19000 21000 24000 26000 5/13 - 6/10 5/5
Instantaneous Flow 18000 20000 22000 25000 27000
Little Snake
Lily, Nr
Mean Daily Flow 13,400 4,745 14,000 5,540 6/16 6000 8000 10000 125000 14500 5/5 - 6/12 5/5
Instantaneous Flow 6800 9100 11000 143000 17000
Yampa
Deerlodge Park
Mean Daily Flow 32,300 13,955 17,000 17,000 6/11 24000 26000 29000 34000 39000 5/11 - 6/6 5/5
Instantaneous Flow 25000 27000 30000 35000 40000
Green
Jensen, Nr (see Note1 Below)
Mean Daily Flow 38,500 17,600 25,000 19,400 6/11 26000 28000 31000 36000 41000 5/14 - 6/11 5/5
Instantaneous Flow 27000 29000 32000 37000 42000
Rock Ck
Upr Stillwater Res
Mean Daily Flow 2,080 1,350 N/A 2,040 6/08 2600 3000 3400 3800 4200 5/25 - 6/20 5/5
Currant Ck
Currant Ck Res
Mean Daily Flow 600 700 750 800 900 5/5
Strawberry
Strawberry Res
Mean Daily Flow 1600 1770 2050 2400 2800 5/5
Starvation Res, Duchesne, Nr (see Note4 Below)
Mean Daily Flow 1370 1470 1600 1700 1850 5/5
West Fork Duchesne
Vat Diverison, Blo (see Note4 Below)
Mean Daily Flow 500 600 780 980 1130 5/5
Uinta
Neola, Nr
Mean Daily Flow 3,000 1,640 5,600 2,230 6/06 1650 1800 2100 2650 2900 5/25 - 6/15 5/5
Instantaneous Flow 2400 2600 3100 3900 4300
White Rocks
Whiterocks, Nr
Mean Daily Flow 2,300 1,230 2,800 1,120 6/08 1050 1150 1300 1450 1700 5/10 -6/10 5/5
Instantaneous Flow 1500 1600 1800 2100 2400
Duchesne
Tabiona, Nr (see Note4 Below)
Mean Daily Flow 2,320 765 4,100 1,070 6/9 2250 2450 2700 3050 3400 5/15 - 6/15 5/5
Instantaneous Flow 2500 2700 3000 3400 3800
Duchesne, Nr, Knight Div, Abv (see Note4 Below)
Mean Daily Flow 4200 4800 5500 6000 6300 5/5
Randlett, Nr
Mean Daily Flow 11,500 2,755 7,400 2,920 6/08 7000 8800 10300 11200 12000 4/27 - 7/5 5/5
Instantaneous Flow 7300 9100 11000 11000 12000
White
Meeker, Nr
Mean Daily Flow 6,320 3,200 11,000 3,310 6/09 3700 4000 4500 5200 6000 5/21 - 6/14 5/5
Instantaneous Flow 4000 4300 4800 5600 6400
Watson, Nr
Mean Daily Flow 3800 4100 4600 5300 6000 5/5
Green
Green River, Ut (see Note1 Below)
Mean Daily Flow 47,200 22,560 47,000 24,200 6/11 38000 42000 46000 54000 61000 5/18 - 6/16 5/5
Instantaneous Flow 39000 43000 47000 55000 62000
Cataract Canyon (estimated)
Mean Daily Flow 116,700 51,350 N/A 53,400 6/11 72000 80000 92000 107000 121000 5/20 - 6/16 5/5
San Rafael
Green River, Nr
Mean Daily Flow 3,600 910 N/A 307 6/16 1860 2100 2400 2800 3200 5/17 - 7/16 5/5
Muddy Ck
Emery, Nr
Mean Daily Flow 515 205 N/A 160 6/10 410 450 500 570 650 5/19 - 6/18 5/5
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 5/5
Escalante
Escalante, Nr ***
Mean Daily Flow 307 72 N/A 96 7/27 50 70 90 110 150 3/24 - 6/2 5/5
San Juan
Pagosa Springs
Mean Daily Flow 4,640 2,485 6,750 2,450 5/30 1600 1850 2000 2150 2300 5/15 - 6/12 5/5
Instantaneous Flow 1800 2100 2300 2500 2600
Animas
Durango
Mean Daily Flow 10,700 4,675 9,560 4,500 5/30 3500 3700 4100 4600 5000 5/28 - 6/14 5/5
Instantaneous Flow 3900 4100 4500 5100 5500
Farmington (see Note 2 Below)
Mean Daily Flow 11,000 4,900 8,810 4,000 5/31 3500 3800 4300 4700 5300 5/31 - 6/15 5/5
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 5/5
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 2390 6/8 2500 2800 3400 3750 4350 5/22 - 6/14 5/5
Instantaneous Flow 3100 3500 4200 4700 5500
Logan
Logan, Nr, State Dam, Abv
Mean Daily Flow 2,450 985 1,355 852 6/8 1800 1950 2000 2150 2500 5/18 - 6/10 5/5
Instantaneous Flow 1900 2000 2100 2200 2600
Blacksmith Fork
Hyrum, Nr, Up&l Dam
Mean Daily Flow 1,650 490 830 150 4/22 1050 1100 1200 1300 1400 4/24 - 5/20 5/5
Instantaneous Flow 1200 1300 1400 1500 1600
Weber
Oakley, Nr
Mean Daily Flow 4,170 1,625 1,950 2600 6/8 2400 2700 3200 3700 4100 5/24 - 6/16 5/5
Instantaneous Flow 2800 3200 3800 4400 4900
Chalk Ck
Coalville
Mean Daily Flow 1,790 600 1,300 535 6/14 1550 1700 1900 2150 2500 5/5 - 5/31 5/5
Instantaneous Flow 1800 2000 2200 2500 2900
Provo
Woodland, Nr (duchesne Tun. Regulated)
Mean Daily Flow 6,040 1,685 3,150 2820 6/8 2300 2450 2750 3100 3600 5/11 - 6/6 5/5
Instantaneous Flow 2700 2800 3200 3600 4100
Little Cottonwood Ck
Salt Lake City, Nr
Mean Daily Flow 800 470 800 800e 6/8 590 620 800 820 850 5/23 - 6/20 5/5
Big Cottonwood Ck
Salt Lake City, Nr
Mean Daily Flow 980 430 800 700e 6/8 560 580 720 800 840 5/18 - 6/9 5/5
Mill Ck
Salt Lake City, Nr
Mean Daily Flow 153 65 155 60 6/9 90 100 100 110 120 5/18 - 6/10 5/5
Emigration Ck
Salt Lake City, Nr
Mean Daily Flow 164 55 130 25 5/24 - 120 135 160 180 4/11 - 5/19 5/5 110 4/19
Red Butte Ck
Fort Douglas At Salt Lake City
Mean Daily Flow 105 22 85 12 5/25 53 56 63 80 116 4/11 - 5/19 5/5
City Ck
Salt Lake City, Nr
Mean Daily Flow 322 90 210 70 6/7 150 170 210 245 290 5/12 - 6/1 5/5
Spanish Fork
Castilla, Nr (regulated)
Mean Daily Flow 5,000 1,455 2,050 640 7/2 1950 1960 2000 2050 2200 5/12 - 6/1 5/5
Sevier
Hatch
Mean Daily Flow 1,990 594 1,185 670 6/07 850 900 1000 1100 1200 5/4 - 6/15 5/5
Instantaneous Flow 910 970 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 1500 1650 1900 3/13 - 5/4 5/5 1,640 4/21
North Fork Virgin
Springdale, Nr
Mean Daily Flow 2,820 570 5,514 709 4/22 1220 1300 1430 1680 4/10 - 5/15 5/5 1,210 4/21
Santa Clara
Pine Valley, Nr
Mean Daily Flow 393 65 N/A 89 6/08 75 85 95 110 130 4/25 - 5/25 5/5 62 4/21

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.