Historical changes in hydroclimatic characteristics in four Lower Colorado River sub-basins are examined using the Mann-Kendall test for trends and Kendall's tau-b test for statistical association to better understand the processes taking place in these arid watersheds. During the historical record of 1906-2007, in general, temperatures have increased and streamflows have decreased while there has been no change in precipitation. Streamflow was found to have statistical association with annual maximum temperatures, El Nino/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Using this knowledge, two-year and five-year streamflow predictions are made using climate data to force a statistical model. We find no predictive skill at the two-year range but significant (alpha =.05) predictive skill in two of the basins at the five-year range. The dominant climate predictor for the Paria River Basin is ENSO and for the Little Colorado River Basin it is temperature.

From Imperial Dam downstream, in addition to Mexico, the Colorado River supplies water to Arizona and California for predominantly agricultural use. In Arizona, the Colorado River is the major source of water supply to the various irrigation districts in the Yuma area. Due to legal constraints, the amount of Colorado River water available to the State of Arizona is limited. On the other hand, it was discovered that the amount of water applied to the soil in irrigation exceeds that amount needed for crop-growing. Two areas where the amount of water considerably exceeds the requirements, the mesa section of the Wellton-Mohawk Irrigation and Drainage District and the Yuma Mesa Irrigation and Drainage District, were studied in detail. The excess water applied on the mesa of the Wellton-Mohawk Irrigation and Drainage District flows into the Wellton-Mohawk Valley whence it is pumped into a conveyance channel and then discharged into the main channel of the Colorado River. This drain water has a very high salt content and therefore it adversely affects the quality of the river water. Since the drain water is discharged into the Colorado River above the point of diversion to Mexico and it is considered to be part of the Mexican water allotment, the quality of the Colorado River water has become a source of friction between the United States and the Republic of Mexico. The excess irrigation water from the Yuma Mesa Irrigation and Drainage District flows into the adjacent valleys as well as into uncultivated areas. In the adjacent valleys it is raising the water table and thus causing drainage problems. When it flows underground into the uncultivated lands, in large measure it constitutes a loss of water that otherwise could be put to beneficial use by Arizona. It is known that flood irrigation is not conducive to efficient application of water in the sandy soils that are predominant in these areas, and that the effects of this application of excess water are diverse and far-reaching. The change to sprinkler irrigation would be advantageous in many ways and beneficial to all concerned. The change to sprinkler irrigation on the mesa of the Wellton-Mohawk Irrigation and Drainage District would benefit both the farmers and the district financially. At the same time, it would decrease the salinity of the Colorado River water, thereby improving the quality of the water that Mexico receives and, consequently, the relations between the United States and the Republic of Mexico. In the Yuma Mesa Irrigation and Drainage District, the change in the method of irrigation would increase the amount of water available for use by the State of Arizona. Furthermore, it would alleviate the drainage problem of the adjacent valleys and would thereby decrease the amount of drain water flowing back into the channel of the Colorado River. In this district, such a change may entail a small added cost to the farmer. Alternatives for augmenting the flow of the Colorado River, such as importation of water from other basins, desalting sea water, phreatophyte eradication, and evaporation suppression, were found to be economically unfeasible at present or still in the experimental stages.

Elderly recreational vehicle campers are attracted to the Lower Colorado River area during the winter season. Their numbers have grown in recent years and many are seeking alternatives to the usual practice of establishing residence in private trailer parks. As a result, various public land sites in the region are being subjected to concentrated winter use. Units in these camping areas represent users who are retired couples or individuals on fixed or limited incomes, living in "self-contained" campers, travel trailers or motor homes. Some of these visitors are utilizing designated campgrounds; others are squatting on the public domain where there are few, if any, sanitary or other facilities. The impact of elderly winter visitors on the public land resource of the Lower Colorado River basin area is varied. An understanding of environmental effects is important, but proposed solutions depend upon our ability to understand the people causing environmental deterioration. Answers have been sought to basic questions about winter visitor characteristics and behavior. The findings were applied toward the development of basic policy recommendations pertinent to appropriate public land management for the desert areas of the Southwest. Of theoretical interest was the evaluation of the relative importance of camping socialization experiences in explaining user behavior. Data were gathered from 580 visitor units during the winter of 1973-74 with a personal interview schedule. Important classes of variables included socio-economic characteristics, camping experience, and users' campground behavior and preferences. Interviews were conducted in seven sites representing various kinds of public and private camping facilities in the region. Discriminant function, correlational, multiple regression and bivariate analyses were utilized to render the collected data meaningful. The basic sub-groups in the sample were distinguished by significant differences in various socio-economic and experiential characteristics. The most important of these were income, education, age, value of mobile quarters, and pre-retirement adult camping experience. Length of stay in public land camping areas was not explained by differences in site characteristics. Differences in visitor characteristics accounted for 40-50% of variation in length of stay. Important predictor variables included income, age, average annual pre-retirement camping experience and the amount of previous recreational vehicle camping without utility and sewerage hookups. Support was evidenced for a basic theoretical orientation: that post-retirement behavior is, in part, a reflection of pre-retirement recreational socialization and leisure life style patterns and persistence. The results suggested certain implications for public land management. Recommendations include the desirability of moving elderly winter camper use to sites away from the Colorado River. High fees imposed along the river would discourage extended-stay winter use and restore a unique resource to the short-term water-oriented visitor. The establishment of a spectrum of "inland" camping sites with varying levels of facilities and fees would serve as a positive inducement to the older winter camper, and restore some order to what has been, in some areas, an uncontrolled camping environment. A public campground on Bureau of Land Management land in Why, Arizona, offers a possible solution to the problems posed by the limited resources available to most public land management agencies. There a parcel of public land has been leased by a non-profit community association and developed into a public campground with basic facilities for elderly winter visitors. Management expenses are met through the imposition of a modest graduated fee schedule which favors the extended-stay camper. In this case a squatting problem has been resolved through local initiative; the public land management agency, with its limited budget, has been spared the expense of development and that of direct management responsibility.

The characteristics of dissolved aquatic organic matter present in four natural water sources, as well as corresponding treated waters derived from eight water treatment plants, is described. An assessment is made of the performance of direct filtration, conventional treatment, and lime softening in removing trihalomethane (THM) precursors from a diverse array of water sources. A comparison is made between conventional treatment and direct filtration in removing THM precursors from a common natural water source, the Colorado River. In addition, the effect of selected initial conditions and operating parameters on the direct filtration process are evaluated by using a synthetic water/bench-scale apparatus. Important characteristics of the organic matter, including molecular weight (MW) distribution, carboxylic acidity and humic substances content, appear to affect the removal of this organic material. As a general rule, THM reactivity or yield (ug THM/mg C) increases with MW. The <10,000 MW range was found to be the most consistent reactive fraction of aquatic organic matter. All of the various treatments preferentially removed the most reactive fraction of precursor present in each MW range. None of the various treatments proved to be very effective in removing precursor material below a MW of <500. Humic molecules, with the highest carboxylic acidity and hence highest charge density, are generally more difficult to remove by alum coagulation. All of the various treatment processes studied preferentially removed hydrophobic over hydrophilic aquatic organic matter. None of the source related conditions (fulvic acid, kaolinite, pH) nor process-related conditions (flocculation velocity gradient, mixing time, prechlorination, preozonation) evaluated under the same experimental conditions exerted a major impact upon the performance of the bench-scale direct filtration process. Larger sized particles may be easier to remove by bench-scale treatment, but removal of the smaller particles may result in better removals of organic matter as quantified by NVTOC and UV Absorbance.

This is an American Indian ethnographic study for the Hoover Dam Bypass Project. The study sites included three bypass bridge alternatives, each located within one mile from where United States Highway 93 (U.S. 93), at the time of the study, crossed over the top of Hoover Dam at the Arizona-Nevada state line. Due to growth in population and commerce in the Southwest, the roadway at Hoover Dam has experienced a tremendous increase in traffic over the past 30 years, resulting in increased safety hazards to motorists, pedestrians, and the dam itself. Federal, state, and local governments have worked to find a solution to the impacts of increased traffic across Hoover Dam. This project was a continuation of EIS efforts that began in 1989. The goal of this project was to evaluate alternative crossings of the Colorado River near Hoover Dam. The goal of this study was to evaluate the potential impacts to American Indian cultural resources related to the three proposed crossing alternatives. This report is an expanded version of the draft produced in 1998. In 2000, funding became available to carry out further ethnographic research and involve Mohave, Hualapai, and Southern Paiute people.

Two surface water sources in the southwestern United States, Colorado River Water (CRW) and California State Project Water (SPW), were studied in bench-scale experiments examining two Trihalomethane (THM) precursor removal processes, activated carbon adsorption and ozone oxidation. Both source water contained bromide (Br-) ion leading to brominated THMs upon chlorination. Activated carbon removed THM precursors, as measured by dissolved organic carbon (DOC), while having little effect on bromide. The net result was an increase in the ratio of Br-/DOC and an increase in the relative abundance of brominated THMs. Ozone oxidized higher molecular weight precursor molecules into lower molecular weight by-products which were less reactive with chlorine. Moreover, ozonation transformed Br- to hypobromous acid (an "in-situ" oxidant), leading to an increase in the percentage of brominated THMs.

Fluvial terraces contain information about incision, deformation, and climate change. In this study, a chronostratigraphic record of Colorado River terraces is constructed from optically stimulated luminescence (OSL) dating of Pleistocene alluvium and real-time kinematic (RTK) GPS surveys of terrace form. This record is analyzed to relate terrace formation to late Pleistocene climate fluctuations, and terrain analyses and longitudinal profile patterns reveal recent salt-related activity in the northern Paradox Basin as well as patterns in Colorado Plateau incision. A well-preserved, correlative suite of mainstem (M) fluvial deposits exists along the Colorado River upstream of Moab, Utah. Absolute dates indicate sedimentation >70 ka (M7, M6/M5), 70-50 ka (M4), 50-40 ka (M3), and 35-25 ka (M2). The M4 and M2 formed during the crescendo to glacial maxima, but the M7, M6/M5, and M3 were deposited during variable climate of marine isotope stages (MIS) 5 and 3. Deposits include thin (<7 m) strath terraces and thick (10-20 m) fill terraces. Our results suggest that terrace sedimentation is linked to enhanced sediment flux during glaciations in Rocky Mountain headwaters (M4 and M2), but major deposits also formed during dryland tributary sediment loading with markedly different timing (M6/M5 and M3). Conversely, incision may be driven by higher deglacial flows. Clast provenance data demonstrate greater percentages of locally-sourced sediment in M6/M5 and M3 deposits. Valley-bottom geometry and neotectonics control terrace form, with strath terraces found in bedrock-restricted reaches and fill terraces in wider valleys. Previously speculated salt deformation in this area is confirmed by localized collapse preserved in M4 stratigraphy in the Cache Valley graben and ~15 m of broader subsidence upstream. Concavity and knickzone distributions in tributary profiles are discordant and represent subtle expressions of salt-tectonic activity. Finally, a surprisingly rapid incision rate of ~900 m/Ma over the past ~70 ka suggests that the Colorado River may be responding to flexural rebound in the central plateau, but is faster than that predicted by the debated bull's-eye pattern of regional incision. This locally high rate may also reflect a transient wave of incision, as suggested by increased Pleistocene rates interpreted by studies in Glen and Grand canyons.

Spatially-distributed water consumption was modeled over a segment of the Lower Colorado River, which contains irrigated agricultural and Tamarisk-dominated riparian ecosystems. For the irrigation scheme, distributed evapotranspiration data were analyzed in conjunction with point measurements of precipitation and surface flow in order to close daily and annual water balance. The annual closure error was less than 1% of the total water diversion to the area. In addition, it was found that the soil water storage component of the water balance cannot be neglected if the analysis is performed over time frames shorter than annual (e.g. growing season). Water consumption was highly uniform within agricultural fields, and all the full-cover fields were transpiring close to their potential rates. Mapping several new and existing drainage performance indicators showed that neither soil salinization nor water-logging would be of concern in this irrigation scheme. However, the quality of high-volume return flow must be studied, especially since the degraded water quality of the western US rivers is believed to act in favor of the invasive riparian species in outcompeting native species. Over the Tamarisk forest, the remotely-sensed evapotranspiration estimates were higher than the results of an independent groundwater-based method during spring and winter months. This was chiefly due to the fixed satellite overpass time, which happened at low sun elevation angles in spring and winter and resulted in a significant presence of shadows in the satellite scene and consequently a lower surface temperature estimate, which resulted in a higher evapotranspiration estimate using the SEBAL model. A modification based on the same satellite imagery was proposed and found to be successful in correcting for this error. Both water use and crop coefficients of Tamarisk estimated by the two independent methods implemented in this study were significantly lower than the current approximations that are used by the US Bureau of Reclamation in managing the Lower Colorado River. Studying the poorlyunderstood stream-aquifer-phreatophyte relationship revealed that diurnal and seasonal groundwater fluctuations were strongly coupled with the changes in river stage at close distances to the river and with the Tamarisk water extraction at further distances from the river. The direction of the groundwater flow was always from the river toward the riparian forest. Thus the improved Tamarisk ET estimates along with a better understanding of the coupling between the river and the riparian aquifer will allow the Bureau of Reclamation to re-asses their reservoir release methodology and improve efficiency and water savings.

The Vaquita marino (Phocoena sinus) is the smallest, most recently discovered, most limited in its distribution, and most highly endangered of all the Cetaceans. Two risk factors have been identified in the Vaquita’s conservation; mortalities due to bycatch in the artisanal fishing fleet in the Upper Gulf of California, and environmental disturbance. The habitat disturbance risk factor is a direct result of the desiccation of the Colorado River Delta because of extensive water diversions form the Colorado River by the dam system within the United States. Significant disagreements exist as to the relative impacts of the two risk factors and how a conservation plan should be developed. This paper utilizes existing data in the literature to display that in fact there is no correlation between the impact of bycatch, and that the Vaquita’s population is depressed because a critical portion of its ecosystem, the Colorado River Delta has been destroyed. This paper argues that a restored Colorado River Delta is critical habitat for the recovery of the Vaquita under the Endangered Species Act and that the ongoing diversion of water from the Colorado River Delta by the US dam system is a violation of the Endangered Species Act. The violation of the Endangered Species Act through the destruction of the Colorado River Delta can have significant economic and social impact in the Western United States.

Understanding the nature of Colorado River deposits in Grand Canyon helps reveal how the river responds to changes in its Colorado Plateau tributaries and Rocky Mountain headwaters. This study focused on Holocene alluvial deposits associated with archaeological sites excavated near Ninemile Draw in Glen Canyon and at Tanner Bar in eastern Grand Canyon. Two previously-developed conceptual models of deposition were tested based on previous work. Previous researchers have suggested that Holocene alluvial deposits in Grand Canyon are a series of inset aggradational packages that correlate to valley fills and arroyo-cutting cycles in Colorado Plateau tributaries and are laterally consistent throughout the river corridor. An alternate hypothesis is that alluvial packages record paleoflood sequences along the Colorado River with no Holocene change in river grade. In this model, deposits are preserved more variably as a function of local hydrologic geometry, and they should be less correlatable. Detailed stratigraphic columns of terrace deposits and several stratigraphic panels of archaeological trenches, combined with facies interpretations, were used to reconstruct a high-resolution alluvial history at two locations. Optically stimulated luminescence (OSL) and radiocarbon dating methods were used at both locations with consistent results. At both sites, the sediment includes multiple depositional facies of mainstem and local-source material, and it consists of stratal packages bound by unconformities. These stratigraphic relations, combined with geochronology, lead to the interpretation that the alluvium is composed of six correlatable alluvial packages at overlapping heights above river level throughout the canyon. The four older packages include facies that imply aggradation throughout the river corridor, suggesting oscillations in river grade. The youngest two packages consist only of mainstem flood deposits. These packages suggest that preservation of deposits over the past ~1 ky has not been driven by aggradation, although incision since ~1 ky is possible. Comparison of the interpreted chronostratigraphy to climate records suggests that this large river's grade has not responded visibly to smaller century to millennial-scale climate oscillations. This work is the first to document that the alluvial record in Grand Canyon spans the entire Holocene, and conclusions support to both previous conceptual models of deposition.