Peak Flow Forecasts, June 1, 2012   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, Smith, Nielson
2012 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2011
Peak
2011
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Blue
Blue River
Mean Daily Flow 580 185 835 410 7/20 5/28 - 7/5 6/6 23 5/12
Dillon, Nr
Mean Daily Flow 1,160 505 1,770 955 7/20 5/27 - 6/25 6/6 90 5/25
Snake
Montezuma, Nr
Mean Daily Flow 870 435 2,080 790 7/02 5/31 - 6/18 6/6 85 6/2
Tenmile Ck
Frisco, Nr
Mean Daily Flow 1,480 760 1,640 1,060 6/18 5/27 - 6/17 6/6 200 5/23
Fraser
Winter Park
Mean Daily Flow 440 180 360 295 7/03 6/1 - 6/29 6/6 17 5/24
Granby
Mean Daily Flow 2,080 940 2,700 1,520 7/01 5/4 - 6/21 6/6 157 4/27
Colorado
Kremmling, Nr
Mean Daily Flow 12,700 3,850 10,180 9,480 6/27 N/A N/A N/A N/A N/A 5/18 - 7/4 6/6 625 4/28
Eagle
Gypsum, Blo
Mean Daily Flow 6,580 3,600 6,410 5,450 6/08 5/27 - 6/16 6/6 1240 5/23
Colorado
Dotsero, Nr
Mean Daily Flow 20,800 8,700 17,000 17,500 6/08 5/22 - 6/13 6/6 1880 4/28
Crystal
Redstone, Nr, Avalanche Ck
Mean Daily Flow 3,500 1,930 3,440 3,030 6/25 5/25 - 6/18 6/6 800 6/2
Roaring Fork
Glenwood Springs
Mean Daily Flow 11,800 5,920 16,800 8,200 7/02 5/29 - 6/23 6/6 1870 6/2
Colorado
Cameo, Nr
Mean Daily Flow 38,000 17,000 26,000 29,200 6/09 5/24 - 6/12 6/6 4160 5/24
Plateau Ck
Cameo, Nr
Mean Daily Flow 4,100 1,470 4,160 2,550 6/08 5/5 - 6/8 6/6 275 4/27
East
Almont, Nr
Mean Daily Flow 5,000 2,000 2,980 2,580 6/08 5/21 - 6/11 6/6 597 5/23
Nf Gunnison
Somerset, Nr
Mean Daily Flow 7,080 3,120 11,400 4,020 6/08 5/8 - 5/31 6/6 795 4/27
Surface Ck
Cedaredge
Mean Daily Flow 640 210 1,600 200 6/10 5/1 - 6/1 6/6 91 4/01
Gunnison
Grand Junction, Nr (see Notes Below)
Mean Daily Flow 35,200 8,890 19,510 14,800 6/09 5/1 - 6/3 6/6 2,480 4/02
Colorado
Co-ut Stateline, Nr
Mean Daily Flow 68,300 25,500 46,200 46,800 6/10 5/19 - 6/11 6/6 5250 4/3
Dolores
Dolores
Mean Daily Flow 6,950 2,940 7,820 3,050 5/31 5/6 - 5/30 6/6 1,360 4/27
San Miguel
Placerville, Nr
Mean Daily Flow 2,740 1,260 3,040 1,430 6/08 560 5/21 - 6/16 6/6 532 5/23
Colorado
Cisco, Nr
Mean Daily Flow 69,500 27,500 59,500 48,500 6/10 5/16 - 6/12 6/6 5840 4/3
Green
Daniel, Nr, Warren Bridge, At
Mean Daily Flow 5,620 2,695 6,100 3,960 7/2 Peak Soon, See Daily Forecast 5/27 - 6/28 6/6 2,210 6/05
New Fork
Big Piney, Nr
Mean Daily Flow 9,110 4,730 8,850 7,750 7/03 Peak Soon, See Daily Forecast 5/26 - 6/23 6/6 2,960 6/05
Green
Labarge, Nr
Mean Daily Flow 18,800 8,000 11,500 13,000 7/4 Peak Soon, See Daily Forecast 5/26 - 6/21 6/6 4,400 6/05
Green Rvr Wy, Nr
Mean Daily Flow 15,400 5,790 11,050 9,620 7/19 1500 2500 3000 3500 4500 5/5 - 7/8 6/6 1,060 4/01
Instantaneous Flow 1600 2600 3100 3600 4600
Hams Fork
Frontier, Nr, Pole Ck, Blo
Mean Daily Flow 2,000 710 1,740 1,190 6/17 5/9 - 6/6 6/6 389 4/27
Blacks Fork
Little America, Nr
Mean Daily Flow 6,970 2,090 4,720 4,630 6/01 5/1 - 6/30 6/6 314 4/29
Elk
Nr Milner
Mean Daily Flow 7,000 3,865 5,750 7,000 6/08 5/17 - 6/3 6/6 1,860 4/28
Yampa
Steamboat Springs
Mean Daily Flow 5,870 3,070 5,930 4,970 6/08 5/19 - 6/10 6/6 1,460 4/27
Maybell, Nr
Mean Daily Flow 24,400 10,300 21,200 19,600 6/09 5/12 - 6/5 6/6 4,220 4/28
Little Snake
Lily, Nr
Mean Daily Flow 13,400 4,320 N/A 9,580 6/10 5/3 - 6/4 6/6 1,390 4/29
Yampa
Deerlodge Park
Mean Daily Flow 32,300 13,470 N/A 26,700 6/10 5/11 - 6/4 6/6 5,380 4/29
Green
Jensen, Nr (see Note1 Below)
Mean Daily Flow 38,500 16,990 23,900 31,300 6/12 5/11 - 6/7 6/6 10,200 5/24
Rock Ck
Upr Stillwater Res
Mean Daily Flow 2,090 1,225 N/A 2,033 6/25 5/17 - 6/13 6/6 530 5/11
Currant Ck
Currant Ck Res
Mean Daily Flow 654 302 N/A 511 6/09 5/3-5/23 6/6 127 4/24
Strawberry
Strawberry Res
Mean Daily Flow 2,770 900 N/A 1,222 6/09 4/25-6/7 6/6 207 4/24
Starvation Res, Duchesne, Nr (see Note4 Below)
Mean Daily Flow 2,010 560 N/A 1,350 5/29 4/28-6/14 6/6 268 4/14
West Fork Duchesne
Vat Diverison, Blo (see Note4 Below)
Mean Daily Flow 661 185 N/A 661 6/16 5/10-6/3 6/6 46 4/23
Uinta
Neola, Nr
Mean Daily Flow 3,000 1,245 5,620 2,400 7/01 5/15 - 6/11 6/6 320 5/05
White Rocks
Whiterocks, Nr
Mean Daily Flow 2,300 820 N/A 1,510 7/01 5/8 -6/14 6/6 240 5/05
Big Brush Ck
Vernal, Nr, Red Fleet
Mean Daily Flow 414 235 N/A 245 6/22 5/4-6/1 6/6 116 4/27
Duchesne
Tabiona, Nr (see Note4 Below)
Mean Daily Flow 2,810 925 3,100 2,810 6/17 5/14 - 6/12 6/6 193 4/27
Duchesne, Nr, Knight Div, Abv (see Note4 Below)
Mean Daily Flow 4,670 1,490 N/A 4,410 7/1 5/17-6/20 6/6 216 4/28
Randlett, Nr
Mean Daily Flow 11,500 3,070 N/A 9,230 7/02 4/29 - 6/28 6/6 359 4/02
White
Meeker, Nr
Mean Daily Flow 6,320 3,040 8,030 5,480 6/08 5/17 - 6/9 6/6 1,070 4/27
Watson, Nr
Mean Daily Flow 8,160 2,815 N/A 4,980 6/20 5/16-6/8 6/6 991 4/29
Green
Green River, Ut (see Note1 Below)
Mean Daily Flow 47,200 21,700 36,400 43,700 6/15 5/16 - 6/11 6/6 10,900 5/27
Cataract Canyon (estimated)
Mean Daily Flow 117,000 48,000 N/A 86,300 6/12 5/17 - 6/12 6/6 15000 5/28
San Rafael
Green River, Nr
Mean Daily Flow 3,600 810 N/A 2,330 6/28 5/6 - 7/9 6/6 36 4/01
Muddy Ck
Emery, Nr
Mean Daily Flow 515 182 N/A 331 6/18 5/18 - 6/10 6/6 54 5/05
Dirty Devil
Hanksville, Nr, Poison Spgs **
Mean Daily Flow 1,690 445 N/A 380 6/20 N/A N/A N/A N/A N/A 3/18 - 6/6 6/6 140 4/01
Escalante
Escalante, Nr ***
Mean Daily Flow 307 73 N/A 102 5/30 3/13 - 5/21 6/6 20 4/01
San Juan
Pagosa Springs
Mean Daily Flow 4,640 2,460 2,240 6/08 5/9 - 6/5 6/6 1,160 4/27
Animas
Durango
Mean Daily Flow 10,700 4,575 9,555 5,120 6/06 5/20 - 6/8 6/6 2,140 5/06
Farmington (see Note 5 Below)
Mean Daily Flow 11,000 4,710 8,810 4,860 6/08 5/20 - 6/9 6/6 1,700 5/06
San Juan
Bluff, Nr (see Note 2 Below)
Mean Daily Flow 15,200 7,340 33,838 4,300 6/01 5/15 - 6/28 6/6 5,650 5/26

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.
** = Runoff period March - June.
- = 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.
Note5 - Peak flow forecasts on the Animas at Farmington are affected by the Durango Pumping Plant.
*** = Runoff period March - June does not include contribution from Boulder Creek.


Great Salt Lake Peak Flow Forecasts

Prepared by: Bernard, Bender
2012 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2011
Peak
2011
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Bear
Utah-wyoming Stateline, Nr
Mean Daily Flow 3,030 1,600 3,670 3030 7/1 - - - - - 5/15 - 6/14 6/6 647 5/11
Logan
Logan, Nr, State Dam, Abv
Mean Daily Flow 1,870 950 1,355 1630 6/26 - - - - 455 5/16 - 6/9 6/6 429 4/27
Blacksmith Fork
Hyrum, Nr, Up&l Dam
Mean Daily Flow 1,530 445 935 1180 5/16 - - - - - 4/16-5/17 6/6 152 4/27
Weber
Oakley, Nr
Mean Daily Flow 4,170 1,645 2,510 3040 7/1 - - - - - 5/20-6/16 6/6 659 5/16
Chalk Ck
Coalville
Mean Daily Flow 1,420 560 1,335 1070 5/17 - - - - - 5/10-6/3 6/6 202 4/27
Provo
Woodland, Nr (regulated)
Mean Daily Flow 2,820 1,795 3,150 2480 6/25 - - - - - 5/12-6/7 6/6 958 5/11
Little Cottonwood Ck
Salt Lake City, Nr
Mean Daily Flow 760 455 800 653 7/3 - - - - 240 5/20-6/18 6/6 208 5/16
Big Cottonwood Ck
Salt Lake City, Nr
Mean Daily Flow 925 430 800 698 6/24 - - - - - 5/18 - 6/7 6/6 160 5/16
Mill Ck
Salt Lake City, Nr
Mean Daily Flow 153 57 155 110 6/25 - - - - - 5/13 - 6/12 6/6 16 5/19
Emigration Ck
Salt Lake City, Nr
Mean Daily Flow 164 46 130 80 5/30 - - - - - 4/14 - 5/19 6/6 5 5/1
City Ck
Salt Lake City, Nr
Mean Daily Flow 262 80 210 167 6/16 - - - - - 5/13 - 6/1 6/6 27 5/9
Sevier
Hatch
Mean Daily Flow 1,740 490 1,186 1,090 6/18 5/4-5/30 6/1 251 5/4

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.
** = Runoff period March - June.
- = Exceedance value has already occurred during the current runoff season.


Lower Colorado Peak Flow Forecasts

Prepared by: Bender
2012 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2011
Peak
2011
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Virgin
Virgin
Mean Daily Flow 6,350 800 4,950 1,860 5/10 3/19 - 5/8 258 4/15
North Fork Virgin
Springdale, Nr
Mean Daily Flow 3,000 530 6,091 1,470 5/10 4/2 - 5/14 183 4/24
Santa Clara
Pine Valley, Nr
Mean Daily Flow 212 60 N/A 94 5/29 4/16 - 5/26 30 4/24

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.
** = Runoff period March - June.
- = 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.