Akhbari M.,University of California at Davis |
Grigg N.S.,Colorado State Univ.
Journal of Irrigation and Drainage Engineering | Year: 2014
Practical plans for agricultural water use within multiobjective frameworks require feasible solutions that meet the objectives of competing interests and this is the root of common decision problems that plague water resources systems. To find the best solutions among the set of feasible solutions, decision-makers can analyze their worth functions, which is the goal of the surrogate worth trade-off (SWT) method, which enables assessment of the worth functions after solutions that are optimal to separate groups are analyzed. The SWT method uses Lagrange multipliers to determine the set of Pareto optimal solutions and requires the exact equation of each objective function and its derivative or gradient. This is normally impractical in watershed scale problems because each objective function comprises a set of interactive physical and hydrological equations, but the problem can be partially overcome by incorporating a genetic algorithm. This approach was applied to a case study of California's San Joaquin River watershed to approximate optimum rates of reduction in agricultural water allocations for environmental purposes. In the case study, decision-makers were aided in assessing their worth functions on the basis of the optimal solutions presented to them. The genetic algorithm optimization tool was linked to a watershed simulation model using the soil and water assessment tool (SWAT) to simulate streamflow and salinity. Model results showed that SWAT provides satisfactory predictions for salinity, which can be used in the trade-off analysis. The compromised rates of agricultural water allocations resulted in a significant increase in the system's reliability and decreased its vulnerability to salinity. © 2014 American Society of Civil Engineers.
Mcshane R.R.,Colorado State Univ. |
Auerbach D.A.,Colorado State Univ. |
Friedman J.M.,U.S. Geological Survey |
Auble G.T.,U.S. Geological Survey |
And 4 more authors.
Ecography | Year: 2015
Management of riparian plant invasions across the landscape requires understanding the combined influence of climate, hydrology, geologic constraints and patterns of introduction. We measured abundance of nine riparian woody taxa at 456 stream gages across the western USA. We constructed conditional inference recursive binary partitioning models to discriminate the influence of eleven environmental variables on plant occurrence and abundance, focusing on the two most abundant non-native taxa, Tamarix spp. and Elaeagnus angustifolia, and their native competitor Populus deltoides. River reaches in this study were distributed along a composite gradient from cooler, wetter higher-elevation reaches with higher stream power and earlier snowmelt flood peaks to warmer, drier lower-elevation reaches with lower power and later peaks. Plant distributions were strongly related to climate, hydrologic and geomorphic factors, and introduction history. The strongest associations were with temperature and then precipitation. Among hydrologic and geomorphic variables, stream power, peak flow timing and 10-yr flood magnitude had stronger associations than did peak flow predictability, low-flow magnitude, mean annual flow and channel confinement. Nearby intentional planting of Elaeagnus was the best predictor of its occurrence, but planting of Tamarix was rare. Higher temperatures were associated with greater abundance of Tamarix relative to P. deltoides, and greater abundance of P. deltoides relative to Elaeagnus. Populus deltoides abundance was more strongly related to peak flow timing than was that of Elaeagnus or Tamarix. Higher stream power and larger 10-yr floods were associated with greater abundance of P. deltoides and Tamarix relative to Elaeagnus. Therefore, increases in temperature could increase abundance of Tamarix and decrease that of Elaeagnus relative to P. deltoides, changes in peak flow timing caused by climate change or dam operations could increase abundance of both invasive taxa, and dam-induced reductions in flood peaks could increase abundance of Elaeagnus relative to Tamarix and P. deltoides. Ecography © 2015 Nordic Society Oikos.