Multi-Time-Scale Input Approaches for Hourly-Scale Rainfall-Runoff Modeling based on Recurrent Neural Networks

This study proposes two straightforward yet effective approaches to reduce the required computational time of the training process for time-series modeling through a recurrent neural network (RNN) using multi-time-scale time-series data as input. One approach provides coarse and fine temporal resolutions of the input time-series to RNN in parallel. The other concatenates the coarse and fine temporal resolutions of the input time-series data over time before considering them as the input to RNN. In both approaches, first, finer temporal resolution data are utilized to learn the fine temporal scale behavior of the target data. Next, coarser temporal resolution data are expected to capture long-duration dependencies between the input and target variables. The proposed approaches were implemented for hourly rainfall-runoff modeling at a snow-dominated watershed by employing a long and short-term memory (LSTM) network, which is a newer type of RNN. Subsequently, the daily and hourly meteorological data were utilized as the input, and hourly flow discharge was considered as the target data. The results confirm that both of the proposed approaches can reduce the computational time for the training of RNN significantly (up to 32.4 times). Furthermore, one of the proposed approaches improves the estimation accuracy.Comment: 11pages, 5 figure

The color of environmental noise in river networks

The color of environmental noise, or degree of predictability in environmental variation, has important implications for ecosystem conservation and management. This study investigates the patterns and drivers of noise color across the US rivers

Space and Time Fractional Governing Equations of Unsteady Overland Flow

Combining fractional continuity and motion equations, the space and time fractional governing equations of unsteady overland flow were derived. The kinematic and diffusion wave approximations were obtained from the space and time fractional continuity and motion equations of the overland flow process. When the fractional powers of space and time derivatives go to 1, the fractional governing equations become the conventional governing equations of unsteady overland flow, and the conventional equations can be obtained as the special cases of the proposed fractional governing equations. Similar to findings of the fractional open channel flow process reported previously, the numerical example herein demonstrated that as the fractional powers of the space and time derivatives decrease from 1, overland flows have longer durations, and both the occurrence time and magnitude of the peak flows decrease. The proposed space and time fractional unsteady overland flow equations may allow modeling anomalous hydrographs by taking into account nonlocality in time and space, and may provide further insights into nonlocal transport in hillslopes reported in the literature

Fractal scaling analysis of groundwater dynamics in confined aquifers

Abstract. Groundwater closely interacts with surface water and even climate systems in most hydro-climatic settings. Fractal scaling analysis of groundwater dynamics is of significance in modeling hydrological processes by considering potential temporal long-range dependence and scaling crossovers in the groundwater level fluctuations. In this study, it is demonstrated that the groundwater level fluctuations of confined aquifer wells with long observations exhibit site-specific fractal scaling behavior. Detrended fluctuation analysis (DFA) was utilized to quantify the monofractality; and Multifractal detrended fluctuation analysis (MF-DFA) and Multiscale Multifractal Analysis (MMA) were employed to examine the multifractal behavior. The DFA results indicated that fractals exist in groundwater level time series, and it was shown that the estimated Hurst exponent is closely dependent on the length and specific time interval of the time series. The MF-DFA and MMA analyses showed that different levels of multifractality exist, which may be partially due to a broad probability density distribution with infinite moments. Furthermore, it is demonstrated that the underlying distribution of groundwater level fluctuations exhibits either non-Gaussian characteristics which may be fitted by the Lévy stable distribution or Gaussian characteristics depending on the site characteristics. However, fractional Brownian motion (fBm), which has been identified as an appropriate model to characterize groundwater level fluctuation is Gaussian with finite moments. Therefore, fBm may be inadequate for the description of physical processes with infinite moments, such as the groundwater level fluctuations in this study. It is concluded that there is a need for generalized governing equations of groundwater flow processes, which can model both the long-memory behavior as well as the Brownian finite-memory behavior. </jats:p

Fractional governing equations of transient groundwater flow in unconfined aquifers with multi-fractional dimensions in fractional time

In this study, a dimensionally consistent governing equation of transient unconfined groundwater flow in fractional time and multi-fractional space is developed. First, a fractional continuity equation for transient unconfined groundwater flow is developed in fractional time and space. For the equation of groundwater motion within a multi-fractional multidimensional unconfined aquifer, a previously developed dimensionally consistent equation for water flux in unsaturated/saturated porous media is combined with the Dupuit approximation to obtain an equation for groundwater motion in multi-fractional space in unconfined aquifers. Combining the fractional continuity and groundwater motion equations, the fractional governing equation of transient unconfined aquifer flow is then obtained. Finally, two numerical applications to unconfined aquifer groundwater flow are presented to show the skills of the proposed fractional governing equation. As shown in one of the numerical applications, the newly developed governing equation can produce heavy-tailed recession behavior in unconfined aquifer discharges

Evaluating the Applicability of a Two-dimensional Flow Model of a Highly Heterogeneous Domain to Flow and Environmental Management

Two-dimensional simulation of highly heterogeneous domains, especially those with disparate length scales, roughness conditions, and geometries, often leads to challenges such as long computation times and numerical instability. Simulation of challenging domains is often needed to guide flood management and environmental regulation agencies in operation and potential domain modifications. This work evaluates the ability of a two-dimensional unsteady hydrodynamic model to represent long-duration transient flows over a domain with highly heterogeneous roughness, geometric characteristics, and length scales through bed roughness representation. The domain includes 13km of Cache Creek and the 14.5km(2) Cache Creek Settling Basin, which traps both sediment and mercury. Calibration under different bed roughness methods, validation, and modeling results of bathymetric modification scenarios are presented. The modeling approach's performance supports its application as a tool for management of similar domains, such as settling basins, leveed floodplains, and reservoirs. Accurate representation of flow dynamics can also inform environmental management that involves transport of sediments, nutrients, and heavy metals. This study found that a two-dimensional unsteady flow model can accurately represent long-duration transient flow in a large settling basin with highly heterogeneous characteristics without parsing of the domain or flow events simulated

Two-dimensional sediment transport modeling in Cache Creek Settling Basin, California

© 2015 ASCE.The Cache Creek Settling Basin (CCSB) is subject to inflows with high sediment concentration. Originally designed to protect the floodway capacity in the Yolo Bypass, current performance of the CCSB is in question following over 70 years of high sediment loads. Operation plans dictate that alterations be made to the levees and/or overflow weir in the basin when trap efficiencies are less than 30 percent. CCHE2D model, a 2D depth-averaged hydrodynamics and sediment transport model, is applied to simulate the sediment transport process in the CCSB. Simulations are performed to evaluate the trap efficiency in the basin under current bathymetric conditions. Possible alternatives, such as raising the overflow weir, and removing portions of the levee, are also evaluated. Recent and historical flows and sediment loads are simulated. Preliminary modeling results are presented here