• An Alternative Approach to the Operation of Multinational Reservoir Systems: Application to the Amistad & Falcon Reservoir System (Lower Rio Grande/Rio Bravo)

      Serrat-Capdevila, Aleix; Valdes, Juan B. (The University of Arizona., 2004)
      An optimization approach for the operation of international multi-reservoir systems is presented. The approach uses Stochastic Dynamic Programming (SDP) algorithms — both steady-state and real-time. — to develop two models. In the first model, the reservoirs and flows of the system were aggregated to yield an equivalent reservoir, and the obtained operating policies were disaggregated using a non-linear optimization procedure for each reservoir and for each nation's water balance. In the second model a multi-reservoir approach was followed, disaggregating the releases for each country's water share in each reservoir. The non-linear disaggregation algorithm uses the SDP derived operating policies as boundary conditions for a local time-step optimization. These models were applied to the Amistad-Falcon International Reservoir System as part of a dynamic modeling project between the US and Mexico for a better management of the water resources in the Lower Rio Grande Basin, currently enduring a severe drought.
    • The Automated Geospatial Watershed Assessment Tool (AGWA): Using Rainfall and Streamflow Records from Burned Watersheds to Evaluate and Improve Parameter Estimations

      Meixner, Thomas; Sheppard, Brian Scott; Valdes, Juan B.; Goodrich, David C.; Guertin, D. Philip (The University of Arizona., 2016)
      Precipitation and runoff records from several burned watersheds have been used to evaluate the performance of the Automated Geospatial Watershed Assessment (AGWA) tool as it is used to assign parameters to the KINmatic runoff and EROSion Model 2 (KINEROS2). This modeling scheme is used by the Department of Interior Burned Area Emergency Response (DOI BAER) teams to assess flooding and erosion risk immediately following a wildfire. Although DOI BAER teams use this parameterization/modeling framework to assess the relative change in watershed behavior following a wildfire by driving the model with National Oceanic and Atmospheric Administration (NOAA) design storms, calibrations performed on actual events using rainfall estimations provided by rain gages and radar to drive the model provides insight into the model's performance, and potentially informs changes and developments to the AGWA parameter estimation scheme. Results indicate that current parameter modifications made by AGWA to represent fire impacts provide reasonable results for DOI BAER relative change risk assessments, though additional modifications to saturated hydraulic conductivity may be necessary to represent a broader range of storm intensity.
    • Decision Support for Wisconsin's Manure Spreaders: Development of a Real-Time Runoff Risk Advisory Forecast

      Guertin, D. Phillip; Goering, Dustin C.; Valdes, Juan B.; Osterkamp, Waite R.; Hawkins, Richard H.; Guertin, D. Phillip; Restrepo, Pedro J. (The University of Arizona., 2013)
      The Runoff Risk Advisory Forecast (RRAF) provides Wisconsin's farmers with an innovative decision support tool which communicates the threat of undesirable conditions for manure and nutrient spreading for up to 10 days in advance. The RRAF is a pioneering example of applying the National Weather Service's hydrologic forecasting abilities towards the Nation's water quality challenges. Relying on the North Central River Forecast Center's (NCRFC) operational Snow17 and Sacramento Soil Moisture Accounting Models, runoff risk is predicted for 216 modeled watersheds in Wisconsin. The RRAF is the first-of-its-kind real-time forecast tool to incorporate 5-days of future precipitation as well as 10-days of forecast temperatures to generate runoff risk guidance. The forecast product is updated three times daily and hosted on the Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP) website. Developed with inter-agency collaboration, the RRAF model was validated against both edge-of-field observed runoff as well as small USGS gauged basin response. This analysis indicated promising results with a Bias Score of 0.93 and a False Alarm Ratio (FAR) of only 0.34 after applying a threshold method. Although the threshold process did dampen the Probability of Detection (POD) from 0.71 to 0.53, it was found that the magnitude of the events categorized as hits was 10-times larger than those classified as misses. The encouraging results from this first generation tool are aiding State of Wisconsin officials in increasing awareness of risky runoff conditions to help minimize contaminated agriculture runoff from entering the State's water bodies.
    • Evaluation of the Performance of Satellite Precipitation Products over Africa

      Valdes, Juan B.; Merino, Manuel; Gupta, Hoshin V.; Serrat-Capdevila, Aleix (The University of Arizona., 2013)
      In the context of the SERVIR-Africa project, the SERVIR Arizona Team is developing streamflow forecast systems on African basins using Satellite Precipitation Products (SPP) to drive the models. These products have errors that need to be addressed before using them to drive hydrologic models. An analysis of the errors of the Satellite Precipitation Products TMPA-3B42RT, CMORPH, and PERSIANN over Africa is presented, followed by bias correction and error reduction methods to improve the remote sensed estimates. The GPCP 1-degree-day reanalysis product was used as the rainfall truth dataset. The Bias Correction Spatial Downscaling (BCSD) method developed by Wood et al., was used successfully to reduce the errors of SPP. The original and bias corrected estimates from the three SPP are used to calibrate and simulate three catchments of the Senegal River basin using HYMOD, finding that the use of bias corrected estimates produces a significant improvement in streamflow simulation.
    • Relevance of Flood Heterogeneity to Flood Frequency in Arizona

      Hirschboeck, Katherine; Zamora-Reyes, Diana; Hirschboeck, Katherine; Baker, Victor R.; Valdes, Juan B.; Paretti, Nicholas (The University of Arizona., 2014)
      In the United States, the flood frequency analysis guidelines described in Bulletin 17B are followed to provide reliable flood discharge magnitude estimates for urban floodplain planning and flood insurance studies. The statistical analysis in Bulletin 17B has various assumptions, including that floods are generated by the same type of atmospheric mechanism (flood homogeneity). However, these assumptions should be carefully assessed before proceeding since they might not always be valid and could increase the potential for flood risk. This study focuses on flood frequency analysis from the perspective of flood heterogeneity, the hydrometeorological genesis of each flood event, in Arizona. This was done by analyzing the occurrence and magnitude of individual flood events, which were classified by their flood-producing atmospheric mechanism. Flood frequency curves were derived for each mechanism and combined using a new approach involving the Partial Duration Series peaks. The combined frequency curves were then compared to curves derived from the standard Bulletin 17B method. Results showed that in southern Arizona, the dominant flooding mechanism is characterized by brief, intense, and localized convective precipitation in the summer. However, the dominant flood-producing mechanism in the central Arizona topographic transition zone and at higher elevations is characterized by prolonged and widespread precipitation from synoptic activity in the winter. Tropical cyclone-enhanced precipitation is also an important, but infrequent, flood-producing mechanism throughout the state. Overall, the dominant mechanism does not necessarily produce the largest floods. In such cases flood heterogeneity can have a strong influence on the discharge estimates for the most extreme upper tail probabilities calculated from the flood frequency analysis. Thus, the most frequent floods may impose very little risk of flooding while uncommon floods can impose a much larger one. These results suggest that the flood homogeneity assumption is not valid in many Arizona watersheds. To produce the most accurate discharge estimates possible, it is critical that both analysts and flood managers become aware of the potential repercussions if these details are overlooked.
    • Sampling Frequency for Semi-Arid Streams and Rivers: Implications for National Parks in the Sonoran Desert Network

      Meixner, Thomas; Lindsey, Melanie; Meixner, Thomas; McIntosh, Jennifer C.; Valdes, Juan B. (The University of Arizona., 2010)
      In developing a water quality monitoring program, the sampling frequency chosen should be able to reliably detect changes in water quality trends. Three datasets are evaluated for Minimal Detectable Change in surface water quality to examine the loss of trend detectability as sampling frequency decreases for sites within the National Park Service's Sonoran Desert Network by re-sampling the records as quarterly and annual datasets and by superimposing step and linear trends over the natural data to estimate the time it takes the Seasonal Kendall Test to detect trends of a specific threshold. Wilcoxon Rank Sum analyses found that monthly and quarterly sampling consistently draw from the same distribution of trend detection times; however, annual sampling can take significantly longer. Therefore, even with a loss in power from reduced sampling, quarterly sampling of Park waters adequately detects trends (70%) compared to monthly whereas annual sampling is insufficient in trend detection (30%).
    • Water Age in Residential Premise Plumbing

      Lansey, Kevin E.; Schück, Sasha; Duan, Jennifer G.; Valdes, Juan B. (The University of Arizona., 2018)
      In most countries around the world, water is treated physically and chemically to a quality that is safe for human consumption. In spite of these efforts, every year people die as a consequence of drinking water-associated disease outbreaks. Legionella is arguably the deadliest pathogen in drinking water in the US and efforts are underway to reduce the likelihood of infecting potable water consumers. One of the primary factors to measure water quality degradation is water age. Water quality degrades with the time that the water sits in pipes. Over time, the residual disinfectant decays, disinfectant by products are created and the water becomes more susceptible to pathogen regrowth. This concern is not limited in the distribution systems but carries over to residential premise plumbing system. A key factor affecting water age in the premises is fixtures’ idle times. As a result, poorly designed plumbing layouts and intermittent usage patterns may lead to high residence times. In the present study, a methodology was developed to numerically quantify water age in residential premise plumbing systems. The scheme is composed of a hydraulic solver, EPANET with modifications, a demand stochastic simulator, SIMDEUM-UA, and a plumbing layout generator based on CAD models. This method was used to determine layout design practices that contribute to lower water ages. The layout is shown to have a significant impact on water age. Modified layouts reduced the water age metrics of absolute maximum age, mean maximum and mean water by up to 76%, 66% and 58%, respectively. A best practice is to connect the water closets at the end of the premise distribution branches. The effect of water heater types on residence times was also assessed. It was found that instant or on demand heater helps reduce water age across all layouts for all the metrics, at both the outlet and the point of connection of the fixture to the distribution system. To further decrease water age, auto-flushers were installed on certain nodes, as the USEPA (2016) recommends flushing the system at regular intervals, and further if combined with a flush of hot water at a temperature of at least 60 °C (140 °F), it would help sterilize the hot system between the heater and the flusher as recommended by the WHO (2007). Proposed methods to implement these so-called hot super-flushing were discussed for future research. However, none of the hydraulic approaches proposed here impact the “last foot” of pipe connecting plumbing fixtures with the premise distribution pipes. Lastly, when comparing the resulting pressures using the simulated demands against the peak demand estimates with flows from the plumbing code, code pressures are always lower than the simulated ones. This may indicate that the design method conservatively overestimates demands. Nonetheless, oversized pipes are detrimental for water age and should be avoided, as greater demands are required to flush the system.