Rill erosion is a small-scale but universally occurring phenomenon. Given its potential to concentrate into larger-scale erosion and its non-negligible contributions to soil loss, substantial research has been dedicated to understanding its processes. In this article, we conducted a holistic review of the major achievements in rill erosion research over the past few decades, mainly from the following perspectives: 1) Hydraulic parameters to describe rill development; 2) morphological indicators to represent rill morphology; 3) commonly used measuring methods for rill morphology and rill flow; and 4) advantages and limitations of rill erosion modelling. In each of the perspectives, we also identified the challenges faced by current rill erosion research. Concrete suggestions on the pressing needs to help advance rill erosion research in the future are further presented.

Advancements and challenges in rill formation, morphology, measurement and modeling

Estimating sediment transport capacity for overland flow

Correction factor for rill flow velocity measured by the dye tracer method under varying rill morphologies and hydraulic characteristics

As a common type of microtopography in rill channels, the formation and dynamics of step-pools are prerequisites for the occurrence of rills. However, the evolution of step-pools in a rill (SPRs) is still unclear. Scouring experiments in field plots were conducted to explore the dynamic evolution of SPRs and the effect of steps on pools under conditions of strong runoff and soil-like materials aggregated with gravels in Yuanmou Dry-Hot Valley (SW China). Using three-dimensional laser scanning, spatial analysis of a GIS (geographic information system), and statistical analysis, 11 parameters were used to characterize step-pool morphology. The results showed that SPRs formed after several scourings at particular locations, and some of them disappeared in the late stage. A diverse range of SPRs formed, with geometrical parameters initially increasing, then stabilizing, and finally decreasing. During scouring, pool shape transformed from a deep V-shape to a shallow V-shape and then to a U-shape. The evolution of a typical pool included initial, active, stable and fading stages. There were 59 oval-shaped pools (88.06% of the total number of pools) in plane form and 37 deep pools (55.22%) in cross-section, and significant differences in the plane form and profile morphology of a pool presented themselves during its evolution. SPRs developed more easily in dry red soil-like materials compared with vertisol-like materials. The geometrical parameters of pools correlated with step size; and pools became deeper with increasing step height, and longer with increasing step height and decreasing step slope. The spatial heterogeneity of soil-like materials, as well as hydraulic conditions, led to complex and nonlinear SPR evolution. It is helpful to further understand the mechanism of rill incision and evolution.

Experimental investigations of the evolution of step-pools in rills with heterogeneous soils in Yuanmou Dry-Hot Valley, SW China

Real-time streamflow forecasting in a reservoir-regulated river basin using explainable machine learning and conceptual reservoir module.

Modeling sediment concentration of rill flow

• Establish numerical weather prediction-based ensemble streamflow prediction (ESP) models of cascade reservoirs. • Develop a forecast-informed operating rule based on Gaussian Radial Bias Function. • Investigate the application value of ensemble forecast in multi-objective operation of Hanjiang cascade reservoirs. Ensemble streamflow predictions (ESPs) play an essential role in reservoir operation in terms of flood control, water supply and hydropower generation, etc. However, the working mechanism of dam-regulated ESP is rarely explored even though a large fraction of major waterways is affected by artificial hydraulic infrastructure, let alone its application value in multi-objective multi-reservoir operating system. Here this study develops three-layered hydrologically-relevant long and short-term memory (LSTM) models to implement 1–3 days ahead ESP of cascade reservoirs with the help of numerical weather prediction (NWP), and designs operating policies based on Gaussian radial basis function which can explicitly incorporate ESP information into reservoir operating decision. The framework of our proposed ESP-based operating way is demonstrated on a cascade reservoir system in the upper Hanjiang River basin, China and assessed against two benchmark control ways (i.e., no-forecast and deterministic-forecast operations). Results show that (1) LSTM models have reasonable accuracy in short-term NWP-based ESP of cascade reservoirs, especially for high-flow regimes; (2) compared with the no-forecast operation, our ESP-based operation could harvest additional approximately 36 million kW·h of hydropower generation per year with a slight improvement in water supply over 11 years of operation during the flood season. These findings highlight the application potential of our numerically efficient and skillful NWP-based ESP scheme for multi-objective cascade reservoir operation to address water-energy shortage issues. 

Yuhang Zhang

Papers

Modeling sediment concentration of rill flow

Multi-objective operation of cascade reservoirs based on short-term ensemble streamflow prediction

How to resolve the conflicts of urban functional space in planning: A perspective of urban moderate boundary

A method for determining steady velocity of shallow water flow on hill-slope and the distance when water flow reaches stability