Simulating the effects of Glen Canyon Dam releases on Grand Canyon river trips

The Shechter-Lucas wilderness use simulation model (WUSM) has been modified to quantify the effects of fluctuating Glen Canyon Dam releases on Grand Canyon river trips. The model now simulates changes in flow as predicted by the Streamflow Synthesis and Reservoir Regulation computer model for the Colorado River. This revised WUSM provides data on several flow-related effects, including delays at rapids, encounters with other parties, and the time available for visiting attraction sites. Nine flow alternatives are evaluated and compared. Analysis of these outputs provides useful information to the Bureau of Reclamation on how the operation of Glen Canyon Dam effects river trips through Grand Canyon National Park.     

External threats: the dilemma of resource management on the Colorado River in Grand Canyon National park,USA

The United States Congress established Grand Canyon National Park in 1919 to preserve for posterity the outstanding natural attributes of the canyon cut by the Colorado River. In some cases National Park Service attempts to maintain Grand Canyon's natural environment have been thwarted by activities outside the park. One of the most obvious external threats is Glen Canyon Dam, only 26 km upstream from the park boundary. Constructed in 1963, this gigantic dam has greatly altered the physicochemical and biological characteristics of 446 km of the Colorado River in Grand Canyon National Park. The river's aquatic ecosystem has been greatly modified through the loss of indigenous species and the addition of numerous exotics. We consider this anexotic ecosystem. The riparian ecosystem has been less modified, with addition of a few exotics and no loss of natives—this we consider anaturalized ecosystem.The great dilemma now faced by park managers is that, after 20 years of managing resources along a river controlled by Glen Canyon Dam, the Bureau of Reclamation has proposed major changes in operational procedures for the dam. Scientists and managers from the National Park Service, Bureau of Reclamation, and cooperating federal and state resource management agencies are using a systems analysis approach to examine the impacts of various Colorado River flow regimes on aquatic, riparian, and recreational parameters in the park. This approach will help in the development of management alternatives designed to permit the most efficient use of that river's natural resources without their destruction.     

COMPARISON OF THE MAGNITUDE OF EROSION ALONG TWO LARGE REGULATED RIVERS1

ABSTRACT: Historical inventories of sand bar number and area are sufficient to detect large-scale differences in geomorphic adjustment among regulated rivers that flow through canyons with abundant debris fans. In these canyons, bedrock and large boulders create constrictions and expansions, and alluvial bars occur in associated eddies at predictable sites. Although these bars may fluctuate considerably in size, the locations of these bars rarely change, and their characteristics can be compared through time and among rivers. The area of sand bars exposed at low discharge in Hells Canyon has decreased 50 percent since dam closure, and most of the erosion occurred in the first nine years after dam closure. The number and size of sand bars in Grand Canyon downstream from Glen Canyon Dam have decreased much less; the number of sand bars decreased by 40 percent in some 8.3-km reaches, but by less than 20 percent elsewhere. These differences are in part related to the fact that flood regulation is much greater in Grand Canyon than in Hells Canyon, and that downstream tributaries resupply sediment to Grand Canyon but not to most of Hells Canyon.     

Climate extremes and adaptive management on the Colorado River: lessons from the 1997-1998 ENSO event.

The Colorado River system exhibits the characteristics of a heavily over-allocated or 'closing water system'. In such systems, development of mechanisms to allow resource users to acknowledge interdependence and to engage in negotiations and agreements becomes necessary. Recently, after a decade of deliberations and environmental assessments, the Glen Canyon Dam Adaptive Management Program (GCDAMP) was established to monitor and analyze the effects of dam operations on the Grand Canyon ecosystem and recommend adjustments intended to preserve and enhance downstream physical, cultural and environmental values. The Glen Canyon Dam effectively separates the Colorado into its lower and upper basins. Dam operations and adaptive management decisions are strongly influenced by variations in regional climate. This paper focuses on the management of extreme climatic events within the Glen and Grand Canyon Region of the Colorado River. It illustrates how past events (both societal and physical) condition management flexibility and receptivity to new information. The types of climatic information and their appropriate entry points in the annual cycle of information gathering and decision-making (the 'hydro-climatic decision calendar') for dam operations and the adaptive management program are identified. The study then describes how the recently implemented program, lessons from past events, and new climate information on the Colorado River Basin, facilitated responses during the major El Ni?o-Southern Oscillation (ENSO) event of 1997-1998. Recommendations are made for engaging researchers and practitioners in the effective use of climatic information in similar settings where the decision stakes are complex and the system uncertainty is large.     

Environmental management of the Colorado River within the Grand Canyon

Irreversible environmental changes are occurring along the Colorado River in the Grand Canyon as a result of regulation of the river flow by the Glen Canyon Dam. The questions of primary importance in managing this great natural resource are 1) in what manner and how rapidly are the physical and ecological adjustments taking place, and 2) is the increased use of the river for recreational boating contributing to the degradation? Human use along the Colorado River is limited, for the most part, to the relic, pre-dam fluvial deposits colloquially called “beaches.” With the new river regime these deposits are positioned well above the present high-water stage, 27,000 cubic feet/second (cfs), or 765 cubic meters/second (cms), so they are not replenished periodically as they were prior to construction of the dam in 1963. The dominant natural processes now are aeolian sand transport and mass wasting. The float-trip passengers use the river beaches for hiking, camping, and. lunch stops. At the most desirable sites thirty to forty people camp on the beaches each night over a four to five month season. Human impact includes incorporation of campsite litter, burial of chemically treated waste, and the direct stress associated with people walking on the vegetation and unstable sedimentary deposits. Results of our investigations indicate that the rate of degradation at the most heavily used sites exceeds the capacity of aeolian processes to reestablish natural landscapes. Therefore, careful management of float trjps is needed if these environments are to be maintained in a natural state rather than a “sand-box” state.     

Recreational impacts on Colorado River beaches in Glen Canyon,Arizona

Recreational impact was measured on eight beaches in Glen Canyon National Recreation Area and 15 beaches in Grand Canyon National Park using permanently located transects and plots. Recreational impact indices included densities of human trash and charcoal and a measure of sand discoloration due to charcoal. Significant increases in the indices occurred on several Glen Canyon beaches over a seven-month period. Sand discoloration became significantly higher over all Glen Canyon beaches during the same time period. All indices were significantly higher in Glen Canyon than on similar Grand Canyon beaches. These differences are probably due to differences in: (a) level of impacts tolerated by the respective management regimes and, (b) in the number of user days among the two National Park Service administrative units. Management alternatives are presented for reversing the present trends of recreational impact on Glen Canyon beaches.     

The wilderness use simulation model applied to Colorado River boating in Grand Canyon National Park,USA

A modification of the Shechter-Lucas Wilderness Use Simulation Model (WUSM) for peak season boating on the Colorado River through Grand Canyon National Park, USA, is evaluated as a tool for making management decisions. A new microcomputer program to select trip itineraries for inclusion in the WUSM that was developed as part of this study is presented. This program simplifies user input and expands the WUSM's usefulness as a tool for management decisions by randomizing itinerary schedules based on probabilities developed from actual use of sites by canyon visitors. Model usefulness is demonstrated by simulating various management changes and comparing use levels of attraction sites and campgrounds as well as numbers of encounters between parties. The WUSM is being used as part of an ongoing study, to reflect the impact of fluctuating flow regimes through the turbines at Glen Canyon Dam on river trips.     

Footstep-induced sediment displacement in the Grand Canyon

The Glen Canyon Dam has severely altered the riparian zone of the Colorado River in the Grand Canyon. One result of the controlled river discharge is more efficient prediction of water stages at the major rapids, leading to higher visitor use. Increased visitation results in heavy foot traffic, trampling along the river banks, erosion of the campsite soils, and the destruction of vegetation. Erosion occurs when the surfaces are roughened, exposing them to wind transport and runoff. In addition, each footstep physically displaces sand downhill.The results of a field experiment designed to measure the amount of sand displaced by footsteps show that each year trampling alone displaces 230 m³ of sand downslope and into the river. With the controlled river flow, no natural processes exist to replace the lost sediment.     

Boater preferences for beach characteristics downstream from Glen Canyon Dam, Arizona

Release flow decisions are increasingly being influenced by an array of social values, including those related to river-based recreation. A substantial portion of past recreation research on downstream impacts of dams has focused on variability of instream flows. This study complements past research by assessing user preferences for beach characteristics affected by long-term impacts of flow regimes. Based upon a study of three recreational user groups (private trip leaders, commercial passengers, and river guides) of the Colorado River in Grand Canyon, preferences for beach size, presence of shade on beach, and presence of vegetation on beach are examined. Results indicate that large size beaches with shade from trees are setting characteristics with highly reliable and strong user preferences. The multinomial regression models developed for each user group indicate that 80% of all respondents would choose beach campsites 800 m(2); results were the same regardless of respondents' past boating experience, boat type (i.e. oar or motorized), or group size. In addition, size of beach was consistently reported to be a trip feature of moderate importance to respondents' river trip. Implications of this research are related to future prospects for controlled floods (i.e. spike flows) released from Glen Canyon Dam.     

Hydropower,adaptive management,and Biodiversity

Adaptive management is a policy framework within which an iterative process of decision making is followed based on the observed responses to and effectiveness of previous decisions. The use of adaptive management allows science-based research and monitoring of natural resource and ecological community responses, in conjunction with societal values and goals, to guide decisions concerning man's activities. The adaptive management process has been proposed for application to hydropower operations at Glen Canyon Dam on the Colorado River, a situation that requires complex balancing of natural resources requirements and competing human uses. This example is representative of the general increase in public interest in the operation of hydropower facilities and possible effects on downstream natural resources and of the growing conflicts between uses and users of river-based resources. This paper describes the adaptive management process, using the Glen Canyon Dam example, and discusses ways to make the process work effectively in managing downstream natural resources and biodiversity.     

NUMERICAL MODEL OF A TRACER TEST ON THE SANTA CLARA RWER,VENTURA COUNTY,CALIFORNIA1

ABSTRACT: To better understand the flow processes, solute-trans. port processes, and ground-water/surface-water interactions on the Santa Clara River in Ventura County, California, a 24-hour fluorescent-dye tracer study was performed under steady-state flow conditions on a 45-km reach of the river. The study reach includes perennial (uppermost and lowermost) subreaches and ephemeral subreaches of the lower Piru Creek and the middle Santa Clara River. The tracer-test data were used to calibrate a one-dimensional flow model (DAFLOW) and a solute-transport model (BLTM). The dye-arrival times at each sample location were simulated by calibrating the velocity parameters in DAFLOW. The simulations of dye transport indicated that (1) ground-water recharge explains the loss of mass in the ephemeral middle subreaches, and (2) ground-water recharge does not explain the loss of mass in the perennial uppermost and lowermost subreaches. The observed tracer curves in the perennial subreaches were indicative of sorptive dye losses, transient storage, and (or) photodecay - these phenomena were simulated using a linear decay term. However, analysis of the linear decay terms indicated that photodecay was not a dominant source of dye loss.     

LABORATORY AND NUMERICAL INVESTIGATION OF LONGITUDINAL DISPERSION IN OPEN CHANNELS1

ABSTRACT: The non-Fickian nature of the longitudinal dispersion in natural channels during low flow has been investigated using both laboratory experiments and the numerical solution of the proposed mathematical model which is based on a set of mass balance equations describing the dispersion and mass exchange mechanisms. Laboratory experiments, which involved collection of channel geometry, hydraulic, and dye dispersion test data, were conducted to obtain sets of experimental data on a model of four pool and riffle sequences in a 161-ft long tilting flume in the Hydrosystems Laboratory at the University of Illinois at Urbana-Champaign. The experimental results indicate that flow over the model pool-riffle sequences is highly nonuniform. Concentration-time curves are significantly skewed with long tails. The mixing and dispersion in the laboratory channel was simulated using a numerical solution of the mathematical model in which the finite difference method developed by Stone and Brian (1963) was used as a solution technique. The comparison between measured and predicted concentration-time curves shows that there is a good level of agreement in the general shape, peak concentration, and time to peak. The proposed model shows significant improvement over the conventional Fickian model in predicting dispersion processes in natural channels under low flow conditions.     

EFFECTS OF TIME STEP SIZE IN IMPLICIT DYNAMIC ROUTING1

ABSTRACT The effects of the size of the Δt time step used in the integration of the implicit difference equations of unsteady open-channel flow are determined for numerous typical hydrographs with durations in the order of days or even weeks. Truncation errors related to the size of the Δt time step cause a numerical distortion (dispersion and attenuation) of the computed transient. The magnitude of the distortion is related directly to the size of the time step, the length of channel reach, and the channel resistance and inversely to the time of rise of the hydrograph. The type of finite difference expression which replaces spatial derivatives and non-derivative terms in the partial differential equations of unsteady flow has an important influence on the magnitude of the numerical distortion, as well as the numerical stability of the implicit difference equations. Time step sizes in the range of 3 to 6 hrs generally tend to minimize the combination of required computation time and numerical distortion of transients having a time of rise of the order of several days.     

FLOW ROUTING MODELS FOR STREAM SYSTEM STUDIES1

ABSTRACT. Studies to determine frequency characteristics of regulated streams at points within a stream system require the use of flow routing models. This study compares several different flow routing methods using data from six river reaches. Results indicate that approximate flow routing methods yield good flow estimates when compared with observed flows. The unit response method, recently introduced, performed as well as other approximate methods for all reaches studied and gave better results for reaches subject to power releases.     

Determination of optimum minimum flow from a dam by using energy analysis

The proposed restoration of an abandoned hydroelectric dam on the Quinebaug River, Connecticut, is studied using energy analysis. The analysis considers the effects of alternative minimum flow releases, ranging from 0 to 34 cubic meters per second (cms), on the total energy flow of the affected system. The principal system components affected by differing minimum flows are hydroelectric power generation, aquatic habitat, and gross aquatic ecosystem productivity.The minimum flow alternative resulting in the highest annual energy flow in the affected system is considered optimal. From this purely analytical point of view, the optimum minimum flow is 0 cms, due to the short length and low productivity of the regulated reach, and the lack of floodplain interactions.Simulations of longer and more productive river reaches were conducted. For very short, unproductive reaches, in the absence of a floodplain, the contribution of aquatic community productivity to total system energy flow is negligible compared to hydroelectric generation. Optimum minimum flows are higher for longer and more productive reaches. For such cases the operation of hydroelectric dams could reduce total system energy flow because the energy supplied by hydroelectric generation may be offset by losses in aquatic productivity due to diminished riverine habitat.     

Regional economic impacts of Grand Canyon river runners

Economic impact analysis (EIA) of outdoor recreation can provide critical social information concerning the utilization of natural resources. Outdoor recreation and other non-consumptive uses of resources are viewed as environmentally friendly alternatives to extractive-type industries. While outdoor recreation can be an appropriate use of resources, it generates both beneficial and adverse socioeconomic impacts on rural communities. The authors used EIA to assess the regional economic impacts of rafting in Grand Canyon National Park. The Grand Canyon region of northern Arizona represents a rural US economy that is highly dependent upon tourism and recreational expenditures. The purpose of this research is twofold. The first is to ascertain the previously unknown regional economic impacts of Grand Canyon river runners. The second purpose is to examine attributes of these economic impacts in terms of regional multipliers, leakage, and types of employment created. Most of the literature on economic impacts of outdoor recreation has focused strictly on the positive economic impacts, failing to illuminate the coinciding adverse and constraining economic impacts. Examining the attributes of economic impacts can highlight deficiencies and constraints that limit the economic benefits of recreation and tourism. Regional expenditure information was obtained by surveying non-commercial boaters and commercial outfitters. The authors used IMPLAN input-output modeling to assess direct, indirect, and induced effects of Grand Canyon river runners. Multipliers were calculated for output, employment, and income. Over 22,000 people rafted on the Colorado River through Grand Canyon National Park in 2001, resulting in an estimated $21,100,000 of regional expenditures to the greater Grand Canyon economy. However, over 50% of all rafting-related expenditures were not captured by the regional economy and many of the jobs created by the rafting industry are lower-wage and seasonal. Policy recommendations are given for increasing the regional retention of rafting expenditures and for understanding both the beneficial and adverse impacts that accompany outdoor recreation in rural areas.     

Recreational impacts on backcountry campsites in Grand Canyon National Park,Arizona, USA

Backcountry campsites were studied in three desert vegetation types (pinyon-juniper, catclaw, and desert scrub) in Grand Canyon National Park, Arizona. Relationships between amount of use and amount of impact were examined within each vegetation type. The area disturbed was small, but impacts were generally severe. Important impacts were increased soil compaction and associated decreases in infiltration rates and soil moisture content; these were substantially more pronounced on high than low use sites. The only impact parameter that differed significantly between vegetation types was core area. The types of impact identified are similar to those found in the coniferous forests studied elsewhere, as is the logarithmic relationship between amount of use and amount of impact. However, Grand Canyon sites can support more visitor use before reaching near-maximum levels of impact for important impact parameters.     

Streamflow,Sediment Transport,and Geomorphic Change during the 2011 Flood on the Missouri River Near Bismarck–Mandan,ND

Geomorphic change from extreme events in large managed rivers has implications for river management. A steady‐state, quasi‐three‐dimensional hydrodynamic model was applied to a 29‐km reach of the Missouri River using 2011 flood data. Model results for an extreme flow (500‐year recurrence interval [RI]) and an elevated managed flow (75‐year RI) were used to assess sediment mobility through examination of the spatial distribution of boundary or bed shear stress (τ_b) and longitudinal patterns of average τ_b, velocity, and kurtosis of τ_b. Kurtosis of τ_b was used as an indicator of planform channel complexity and can be applied to other river systems. From differences in longitudinal patterns of sediment mobility for the two flows we can infer: (1) under extreme flow, the channel behaves as a single‐thread channel controlled primarily by flow, which enhances the meander pattern; (2) under elevated managed flows, the channel behaves as multithread channel controlled by the interaction of flow with bed and channel topography, resulting in a more complex channel; and (3) for both flows, the model reach lacks a consistent pattern of deposition or erosion, which indicates migration of areas of erosion and deposition within the reach. Despite caveats and limitations, the analysis provides useful information about geomorphic change under extreme flow and potential implications for river management. Although a 500‐year RI is rare, extreme hydrologic events such as this are predicted to increase in frequency.     

A RATING-CURVE METHOD FOR HYDRODYNAMIC SIMULATIONS IN CONTAMINANT TRANSPORT MODELING1

ABSTRACT: Accurate prediction of hydrodynamics is of great importance to modeling contaminant transport and water quality in a river. Flow conditions are needed in estimating potential exposure contamination levels and the recovery time for a no-action alternative in contaminated sediments remediation. Considering highly meandering characteristics of the Buffalo River, New York, a three-dimensional hydrodynamic model was selected to route upstream flows through the 8-km river section with limited existing information based on the model's fully predictive capability and process-oriented feature. The model was employed to simulate changes in water depth and flow velocity with space and time in response to variation in flow rate and/or water surface elevation at boundaries for given bottom morphometry and initial conditions. Flow conditions of the river reach where historical flow data are not available were computed. A rating-curve approach was developed to meet continuous and event contaminant modeling needs. Rating curves (depth-discharge and velocity-discharge relationships) were constructed at selected stations from the 3-D hydrodynamic simulations of individual flow events. The curves were obtained as steady solutions to an unsteady problem. The rating-curve approach serves to link flow information provided by the hydrodynamic model to a contaminant transport model. With the approach, the linking problem resulting from incompatible model dimensions and grid sizes can be solved. The curves will be used to simulate sediment movement and to predict contaminant fate and transport in the river.     

Water quality modeling to determine minimum instream flow for fish survival in tidal rivers

The Hsintien Stream is one of the major branches of the Danshuei River system, which runs through the metropolitan capital city of Taipei, Taiwan and receives a large amount of wastewater. The dissolved oxygen concentration is generally low in the tidal portion of the Hsintien Stream. Hypoxia/anoxia occurs often, particularly during the low-flow period when the Feitsui Reservoir, Chingtan Dam and Chihtan Dam impound the freshwater for municipal water supply. Fish kills happen from time to time. This paper describes the application of a numerical hydrodynamic and water quality model to the Danshuei River system, with special attention to the tidal portion of the Hsintien Stream. The model is recalibrated with the prototype conditions of the year 2000. The hydrodynamic portion of the model is recalibrated with measured surface elevation and velocity at various stations in the river system. The water quality portion of the model is recalibrated with respect to the field data provided by Taiwan EPA. The input data of point and nonpoint sources are also estimated. The model simulates the concentrations of various forms of nutrients, CBOD and dissolved oxygen. A series of sensitivity runs was conducted to investigate the effects of point source loadings and river flow on the DO level in the river. It is demonstrated that the augmentation of river flow has as much effect on raising DO level as the reduction of point source loadings. The completion of the Taipei sewer project is expected to reduce the point source loadings by at least 75%. Under these reduced loadings, if the daily instream flow is maintained above the monthly Q75 flow throughout the year, the minimum DO concentration in the river would not fall below 1mg/L, which is the suffocation level for most fish species in the Hsintien Stream. (Q75 is the flow which is equaled or exceeded 75% of the days in the month.) The Feitsui Reservoir, Chingtan Dam and Chihtan Dam may impound water during the high flow periods and release freshwater to maintain the flow at the Q75 value in the Hsintien Stream during the drought periods.