Delineation of Landslide, Flash Flood, and Debris Flow Hazards in Utah

During 1982, 1983, and 1984, abnormally wet conditions in Utah triggered flash floods, landslides, and debris flows. Pore pressures built in hillside soils below melting snows and during prolonged periods of rainfall until the mass suddenly gave way, sometimes as a landslide and other times as a non-Newtonian debris flow that moved rapidly long distances down mountain slopes until finally stiffened by moisture loss or velocity loss because of flatter gradients. Also, runoff from heavy rainfall bursts picked up weathered and other loose material that accumulated on land surfaces over long dry periods . The sediment laden waters flowed out of mountain canyons onto lowlands where they deposited their loads, filled channels and c logged culverts, and then spread over the land surface to infiltrate, except as intercepted and diverted by streets, storm sewers, and irrigation canals. These were in turn often over topped to cause flooding in areas with no natural hazard. Snow melt runoff continued over extended periods, keeping stream flows too high to be contained within the clogged streams, and causing water to flow down streets for weeks disrupting traffic and inundating low-lying property. In closed basins, the waters eventually drain into a terminal lake where rising waters gradually inundated large areas. This complex of interrelated phenomena created a hazard situation that is greatest at the toe of the mountain slopes and concentrates where mountain canyons drain onto alluvial fans and the water spreads in a pattern that varies substantially from storm to storm. These hillside areas are prime res identical site s and command a high pr ice in the market. Development that should not be located in high hazard areas is reasonable a little further down slope where the risk is less. Quantitative methods are needed for mapping flood, debris, and landslide risks in these basin margin areas so that objective decisions can be made on where to locate and how to landscape and design buildings. Monitoring programs and warning systems are needed to track emerging hazards, emergency plans, and get people to respond. During two spring months of 1983, Utah sustained direct damages from landslides and debris floods in excess of 250 million dollars. Public official.s and residents were prepared for water flooding. However, neither the scientific community nor the agencies responsible for dealing with emergency situations were prepared for the widespread 1andslides and devastating debris flows. At least 92 significant landslides along a 30-mile length of the Wasatch Front Mountains sent torrents of water and debris down on the residential areas below. Along the Wasatch Plateau, more than 1000 landslides occurred. Additional massive landslides in Spanish Fork Canyon, Utah County, created Thistle Lake, and in 12-Hile Canyon, Sanpete County, dammed a river and sent a 30-foot high flash flood surge down the canyon. These devastating floods, landslides and debris flows were so extensive that 22 of Utah\u27s 28 counties were declared national disaster areas

Combined mechanical loading of composite tubes

An analytical/experimental investigation was performed to study the effect of material nonlinearities on the response of composite tubes subjected to combined axial and torsional loading. The effect of residual stresses on subsequent mechanical response was included in the investigation. Experiments were performed on P75/934 graphite-epoxy tubes with a stacking sequence of (15/0/ + or - 10/0/ -15), using pure torsion and combined axial/torsional loading. In the presence of residual stresses, the analytical model predicted a reduction in the initial shear modulus. Experimentally, coupling between axial loading and shear strain was observed in laminated tubes under combined loading. The phenomenon was predicted by the nonlinear analytical model. The experimentally observed linear limit of the global shear response was found to correspond to the analytically predicted first ply failure. Further, the failure of the tubes was found to be path dependent above a critical load level

Antecedent Moisture Conditions for Utah Local Storm Probable Maximum Floods

Introduction: The critical inflow design flood for most dams in Utah is the probable maximum flood (PMF) resulting from the local storm probable maximum precipitation (PMP) event. Commonly, the Soil Conservation Service (SCS) curve number method is used to determine the PMF from the local storm PMP. An important factor in this determination is the assumption of antecedent moisture conditions (AMC) existing immediately prior to the onset of the PMP event. At one northern Utah dam site the use of AMC III increased the PMF peak flowrate by 50 percent over the peak obtained when AMC II was used (Win 1993). In this study we explore the occurrence of AMC II (average) and III (saturated) conditions at locations throughout Utah. The occurrence of AMC II or III, which is defined by the magnitude of rainfall over the previous five days, is shown to be independent of the magnitude of precipitation on the sixth day. Also, the probability of occurrence of AMC II and III during the critical months for local storm PMP is shown to be low. While these conclusions do not rule out the possibility of the joint occurrence of a PMP event and AMC III, they do demonstrate that it is an unlikely event. If AMC II is accepted for use in local storm PMF determinations in Utah, a significant reduction in Utah PMF peak flowrates can be expected. In any event, this study should be an important contribution to the evaluation of dam safety in Utah through providing a better basis for the selection of AMC conditions in PMF determinations. Throughout the course of this research, we have chosen to take the conservative approach to the study. It is the intent of this research to evaluate the use of AMC II or III in semi-arid and arid Utah. Trends were evaluated using upper limits instead of averages and snowmelt was included as a contributor to soil saturation. It is our belief that if one can disprove a theory or practice by being conservative, it is a much stronger case than if a more liberal approach were taken

Assessment of Control Alternatives for the Great Salt Lake

Introduction: Over the last few years, the rising level of the Great Salt Lake has changed Utah. It has inundated vast waterfowl feeding areas, crippled the salt industry, required raising transcontinental freeways and railroads, threatened metropolitan waste treatment plants, caused a major electrical outage, and damaged many properties. If nothing is done, approximately $3.6 billion of damages in 1985 dollars can be expected by 2050 (James et al, 1985, p.4). This threat led the State Legislature to set aside$100 million (an amount approximating the damages that had then occurred) in January 1985 to identify, select, and implement remedial measures. The rise has slowed. However, the lake entered February 1986 at its highest level since 1877, and a large storm of tripical origins brought a record one-month rise, tying the high of the previous spring at 4209.95, with heavy snowpacks in the mountains and at least three months of precipitation left before the normal date of the annual peak. Nevertheless, the legislature is diverting some of the funds to other purposes. As shown in Figure 2, the rise has greatly enlarged the surface area of a shallow water body. Table 1 shows how the historic variation has increased the lake surface area from 587,000 to 1,556,0000 acres, a range that varies normal annual evaporation from 1,470,000 to 4,800,000 acre feet. The lake will rise as long as inflow exceed actual evaporation. Total inflows were 5,300,000 acre feet in 1983, 6,200,000 acre feet in 1984, and 3,800,000 acre feet in 1985. The rise continued in 1985 because of abnormally low evapoartion

Model choice: An Operational Comparison of Stochastic Streamflow Models for Droughts

The rapid development of stochastic or operational hydrology over the past 10 years has led to the need for some comparative analyses of the currently available long-term persistence models. Five annual stochastic streamflow generation models (autoregressive, autoregressive-moving-average (ARMA), ARMA-Markov, fast fractional Gaussian noise, and broken line) are compared on their ability to preserve drought-related time series properties and annual statistics. Using Monte Carlo generation procedures and comparing the average generated statistics and drought or water supply properties, a basis is established to evalute model performance on four different Utah study streams. A seasonal disaggregation model is applied to each of the generated annual models for each of the four study streams at a monthly disaggregation level. A model choice strategy is presented for the water resources engineer to select an annual stochastic streamflow model based on values of the historic time series\u27 lag-one serial correlation and Hurst coefficient. Procedures are presented for annual and seasonal model parameter estimatino, calibration, and generation. Techniques are included such as normality, trend-analysis, and choice of model. User oriented model parameter estimation techniques that are easy and efficient to use are presented in a systematic manner. The ARMA-Markov and ARMA models are judged to be the best overall models in terms of preserving the short and long term persistence statistics for the four historic time series studied. The broken line model is judged to be the best model in terms of minimizing the evonomic regret as determined by an agricultural crop production function. Documentation and listings of the computer programs that were used for the stochastic models\u27 parameter estimation, generation, and camparison techniques are presented in a supplementary appendix

A User\u27s Manual for Computer Programs Used in: Model Choice: An Operational Comparison of Stochastic Streamflow Models for Droughts

The rapid development of stochastic or operational hydrology over the past 10 years has led to the need for some comparative analyses of the currently available long-term persistence models. Five annual stochastic streamflow generation models (autoregressive, autoregressive-moviing-average (ARMA), ARMA-Markov, fast fractional Gaussian noise, and broken line) are compared on their ability to preserved drought-related time series properties and annual statistics. Using Monto Carlo generation procedures and comparing the average generated statistics and drought or water supply properties, a basis is established to evaluated model performance on four different Utah study streams. A seasonal disaggregation model is applied to each of the generated annual models for each of the four study streams at a monthly disaggregation level. A model choice strategy is presented for the water resources engineer to select an annual stochastic streamflow model based on values of the historic time series; lag-one serial correlation and Hurst coefficient. Procedures are presented for annual and seasonal model parameter estimation, calibration, and generation. Techniques to ensure a consistent matrix for successful matric decomposition are included such as normality, trend-analysis, and choice of model. User oriented model parameter estimation techniques that are easy and efficient to use are presented in a systematic manner. The ARMA-Markov and ARMA models are judged to be the best overall models in terms of preserving the short and long term persistence statistics for the four historic time series studied. The broken line model is judged to be the best model in terms of minimizing the economic regret as determined by an agricultural crop production function. Documentation and listings of the computer programs that were used for the stochastic models\u27 parameter estimation, generation, and comparison techniques are presente in a supplementary appendix

Random Differential Equations in Water Quality Modeling

A probabilistic river water quality model is developed with the capability of determinging the joint and marginal probability density function of biochemical oxygen demand (BOD) and dissolved oxygen (DO) at any point in a river. The one dimensional steady-state model can be applied to a river system with any reasonable number of point loads and diversions and lateral surface and subsurface inflow. The model can simultaneously consider randomness in the intital conditions, inputs, and coefficients of the water quality equations. Any empirical or known distribution can be used for the initial condition. The randomness in the water quality equation inputs and coefficients is modeled as a Gaussian white noise process. The joint probability density function (pdf) of BOD and DO is determined by numerically solving the Fokker-Plank equation. Moment equations are developed which allow the mean and variance of the marginal distrubution of BOD and DO to be calculated independently of the joint pdf. An upper limit on the coefficient noise variance parameter is presented for which the BOD-DO covariance matrix will be asymptotically stable. The probabilistic river water quality model is applied to two problems, a sensitivity problem and a hypothetical problem. The sensitivity problem and a hypothetical problem. The sensitivity problem is used to gain familiarity with the simulation model and determine the sensitivity of the model responses to changes in the standard deviation parameter of the input and coefficient noise. The standard deviation parameter of the input noise if varied between zero and 30 percent of the respective input, while the standard deviation parameter of the coefficient noise is varied between zero and 50 percent of the respective coefficeitn. The model responses are foind to be fairly sensitive to changes in the standard deviation parameter of the coefficient noise but relatively insensitive to changes in the standard deviation parameter of the input noise. The possibility of using the moment equations and a normal approximation in lieu of calculating the joint pdf of BOD and DO is discussed. The accuracy of the numerical solution technique for the Fokker-Plank equation is also discussed. The hypothetical problem is used to evaluate the performance of the model in simulating a more complex river system (which included two point loads) and to evaluate the numerical quandrature algorithm used to determine the joint pdf of BOD and DO immediately downstream of a point load. The numerical solution technique used to determine the joing pdf of BOD and DO remained stable throughout the simulation and the computational costs are judged to be reasonable for a problem of this complexity. The quadrature algorithm was judged to have performed adequately for both the pont loads