Difference between revisions of "Bishop Study"

Fishing

• Ideal flows for fishing are in a range around 10,000 cfs
• Constant flows are better than fluctuating flows except at very low average daily flows [2]

White-water boating

• Private boaters prefer approximately 29,000 cfs
• Commercial passengers prefer approximately 33,000 cfs
• The presence of significant river fluctuations reduces the value of the experience, except at average daily flows below 10,000 cfs, where fluctuating flows are preferred to low constant flows [3]

The study assessed the recreational impacts of two characteristics of dam releases:

• average daily flow; and
• whether flows were constant or fluctuating on a daily basis.

Average daily flows were characterized in terms of the mean release rate at the dam in cfs. Flows were classified as "constant daily flows" if the difference between the minimum and maximum release at the dam during a 24-hour day was less than 10,000 cfs. If this difference was greater than or equal to 10,000 cfs, then the flow on that day was classified as a "fluctuating daily flow," Based on survey research, described below, the 10,000 cfs threshold was determined to be the point at which fluctuations begin to be perceptible to recreationists.

Data relating to recreation came from three main sources:

• surveys of and informal contacts with guides and private trip leaders;
• attribute surveys of anglers and white-water boaters; and
• contingent valuation surveys of the two user groups.

Some on-site interviews of anglers were conducted but all other surveying, including other angler surveys, were conducted by mail. Details regarding sampling strategies, survey design and execution, data analysis, and results are reported in Bishop, et al. (1987), and only a brief overview will be possible here.

Commercial white-water guides and private trip leaders were surveyed by mail to better understand their perceptions of how different constant and fluctuating flows affect commercial and private trips and the actions they take to mitigate the adverse effects of flows. The guides described the effects of flows in terms of the need to scout rapids, the need to ask passengers to walk around rapids, the risk of accidents in rapids, time spent on the river each day, changes in the trip itinerary, selection of campsites and mooring locations, minimum and maximum safe flow levels, and the optimal flow levels for trips. Professional fishing guides were contacted informally to gain their insights about the effects of flows on quality.[4]

Table 3. Flow Conditions Evaluated by Each Group.

Glen Canyon Anglers

• Actual Trip
• Flow constant at 3,000 cfs
• 3,000 cfs with fluctuations daily
• Constant 10,000 cfs
• 10,000 cfs with fluctuations daily
• Constant 25,000 cfs
• 25,000 cfs with daily fluctuations
• Steady 40,000 cfs
• Double chance for a trophy size fish
• Double chance of not catching fish

Grand Canyon White-Water Boaters

• Actual Trip
• Flow constant at 5,000 cfs
• 5,000 cfs with fluctuations daily
• Constant 13,000 cfs
• Constant 22,000 cfs
• 22,000 cfs with fluctuations
• Constant 40,000 cfs Reduction in beaches[5]

Thus, we concluded that dam operations do have a significant effect on fishing. The consumer surplus per trip was $60 ($24 per day} at 3,000 cfs. The value rises steadily with higher flow levels, reaching a peak of $126 ($50 per day} at 10,000 cfs constant flows. Thereafter, the value of the experience drops steadily at higher flows, declining to $64 per trip ($26 per day) for constant flows at 40,000 cfs and even lower at 45,000 cfs. Ideal flows for fishing are in a range around 10,000 cfs, and constant flows are better than fluctuating flows except at very low average daily flows. Fluctuating flows reduce the surplus values per trip by as much as 30 percent.

Lower water is desirable because it concentrates the fish and is believed to produce better fishing. However, at very low water, below 3,000 cfs, it becomes difficult or impossible to cross Three Mile Bar, a rock and gravel bar three miles upstream from Lees Ferry, with motor boats, thus restricting fishing to a much smaller area. Grounding boats and striking motors on rocks is also more frequent at low flows. Thus, very low flows are undesirable. On the other hand, high water disperses the fish, which may reduce fishing success. It also creates stronger currents, increasing problems for boat handling. Tradeoffs among these countervailing impacts result in 10,000 cfs receiving the greatest surplus value, with fishing value declining both above and, more rapidly, below this flow level.

Large fluctuations require anglers to operate part of the day at low or high flows, with the attendant disadvantages of both. Changing water levels add additional difficulties. Falling water may make it difficult to get downstream over rocks and gravel bars that had more water over them on the trip upriver. Rising water may increase the likelihood of swamping a ooat while anchored or while the bow is pulled up on shore. A few anglers did favor fluctuating flows because they believed that rising water may stimulate feeding by fish. Nevertheless, the majority of anglers felt that the disadvantages of fluctuations outweigh the advantages, except at very low flows.[6]

Thus, we conclude that dam operations do have a substantial effect on the value of the experience and that the effect is similar for private boaters and commercial passengers. The lowest consumer surplus values are produced at very low average daily flows. For example, at 5,000 cfs, private boaters received an average of $176 and commercial boaters $233 in consumer surplus per trip. This amounts to about $10 per day for private boaters and $30 per day for commercial boaters. The value of the trip rises steadily as flow levels increase. Private boaters received maximum consumer surplus, on average, at approximately 29,000 cfs, which results in roughly $700 per trip ($41 per day). Commercial passengers prefer approximately 33,000 cfs, which results in roughly $900 in consumer surplus per trip ($115 per day). Surplus values for commercial passengers were not affected by the type of boat they used. At flows above these preferred levels, the value of the experience falls off, but more rapidly for private boaters than commercial passengers.

These changes in recreation value appear to reflect the effects of average flow levels on important trip attributes. Time at attraction sites, such as Indian ruins and side canyons with pleasing scenery, and for layovers, depends on the speed of the current. The size and number of rapids are affected by dam releases. Boaters, particularly those on commercial trips, enjoy fairly large rapids that depend on substantial flows. At relatively low flows and flood flows, passengers, particularly those on commercial oar­ powered trips, may have to walk around rapids. This is generally considered undesirable by passengers. Flood flows may raise concerns about safety in the minds of some boaters. Some risk at rapids makes the trip more exciting, but higher flood flows (say, 40,000 cfs and above) may be perceived as too hazardous for many. The lack of crowding is also important to many boaters.

High and flood flows can contribute to crowding at campsites and attraction sites by inundating beaches. Both the guide survey and the attribute survey results agreed closely with the contingent valuation conclusions, increasing our confidence that these results are valid.

As can be seen for both private and commercial boaters, the presence of significant river fluctuations reduces the value of the experience, except at average daily flows below 10,000 cfs, where fluctuating flows are preferred to low constant flows. At higher flows, values may be lower by 25 percent or more for trips with fluctuating flows compared to constant flows at the same average daily flow. One of the primary attributes of white-water boating is experiencing the natural environment of the Grand Canyon. Attribute survey results indicate that perceptible fluctuations in water level make the canyon seem less natural to many participants. Allowing for changes in water level makes camping and mooring of boats for the night more difficult as well.

Moored boats must be checked during the night to avoid being stranded on beaches in the morning. Fluctuations also increase the likelihood of arriving at rapids at disadvantageous times, when waiting for water-level changes or walking around a rapid may be necessary. Careful scouting of rapids may be required. Running rapids during the low flows associated with fluctuations increases the risk that boats will get hung up on rocks. Being stuck on a rock may mean only a minor inconvenience, but can mean disaster for the trip if the boat is seriously damaged or injuries are sustained in trying to free it.

At average daily flows below 10,000 cfs, higher dollar values for fluctuating flows than for constant flows also seem consistent with the survey data. At such low average flows, there is a desire to have flow rates in excess of 10,000 cfs for at least part of each day. For example, many rapids become more passable at higher flows and the ride becomes more exciting for most passengers.[7]

What advice could we give dam managers, if they asked us what they could do to enhance downstream recreation, other objectives aside?

• We would assure them that there is clear evidence that how they operate the dam does have significant effects on recreational quality, effects that translate into millions of dollars.
• To enhance recreation, they should try to avoid extremes. Extremely low flows (flows significantly below 10,000 cfs), extremely high flow (flows in excess of power plant capacity), and extreme daily fluctuations (differences in daily releases of 10,000 cfs or more) are all detrimental.
• To the extent possible while observing the limits outlined in (2), water should be reallocated to the summer months and, water permitting, to the late spring and early fall. In all except the highest discharge years, benefits of $1 million to $2 million would be forthcoming, compared to current operations, if these criteria were observed.[8]

• Recreation Page
• The Lees Ferry Rainbow Trout Fishery Page
• The Long-term Experimental and Management Plan (LTEMP) Page

• The Stewart Report: Preferences of Recreation User Groups of the Colorado River in Grand Canyon. 2000
• Shelby et al. 1992. Effects of Streamflows on River Trips on the Colorado River in Grand Canyon, Arizona. Rivers. Volume 3, Number 3. Pages 191-201
• Bishop, R.C., C.A. Brown, M.P. Welsh, 1987, Grand Canyon Recreation and Glen Canyon Dam Operations: An Economic Evaluation. pg 407-436
  
• Bishop, R.C., K.J. Boyle, M.P. Welsh, R.M. Baumgartner, P.R. Rathbun, 1987, Glen Canyon Dam Releases and Down Stream Recreation: An Analysis of User Preferences and Economic Values. Report to GCES. 398 pgs.

Bishop et al. 1987

"The study assessed the recreational impacts of two characteristics of dam releases: (a) average daily flow; and (b) whether flows were constant or fluctuating on a daily basis. Average daily flows were characterized in terms of the mean release rate at the dam in cfs. Flows were classified as "constant daily flows" if the difference between the minimum and maximum release at the dam during a 24-hour day was less than 10,000 cfs. If this difference was greater than or equal to 10,000 cfs, then the flow on that day was classified as a "fluctuating daily flow." Based on survey research, described below, the 10,000 cfs threshold was determined to be the point at which fluctuations begin to be perceptible to recreationists." (page 412 of Bishop et al. 1987)

Stewart et al. 2000

Stewart et al.’s (2000) follow-up of the Bishop et al. (1987) study found that angler’s did not identify river level fluctuations, at least under the MLFF operating regime, as an issue.

2016 LTEMP

"An 8,000-cfs maximum daily fluctuation limit was established in the 1996 ROD (Reclamation 2006) to address safety, recreation, and sediment concerns (Reclamation 1995). The analysis conducted for the LTEMP EIS has not identified new evidence to suggest that these concerns are no longer relevant or that this fluctuation limit is no longer appropriate. The determination of 8,000 cfs as a maximum daily fluctuation level that is suitable for recreation was based on Bishop et al. (1995) [*]. Bishop et al. surveyed both the river guides and the general public regarding preferences, and the river guides reported a preference for a maximum of 8,000 cfs daily change for a “tolerable recreation experience” under relatively high average daily flows. The current river guide community has continued to state the preference for retaining the 8,000-cfs maximum daily fluctuation that is currently in place." (LTEMP EIS pg 2-46, Sec 2.2.4.1 Base Operations under Alternative D)

[*] Bishop et al. (1995) appears to be a typo. There is no Bishop et al. (1995) in the LTEMP Reference section, only Bishop et al. (1987).