A Review of Payment for Ecosystem Services (PES) in Agricultural Water: Are PES from the Operation of Agricultural Water Control Structures Ubiquitous?

This paper reviews the consideration of the operation of agricultural water control structures (AWCSs) as sources of bundles of ecosystem services (ESs) and the subsequent design of payment for ecosystem service (PES) programs around these ESs. It is thought that PES schemes for AWCSs can complement irrigation service fees (ISFs) in funding the operation and maintenance of irrigation schemes. Case studies from Japan, the United States of America and Tanzania, representing a variety of socio-economic, geographic and climatic conditions, are discussed. In countries where the PES programs had legal backing, they showed evidence of sustainability and success. The measurement of marginal ESs flows from AWCSs proved to be one of the challenges to PES programs. There is a need to improve the measurement and modelling of hydro-meteorological and water quality parameters to ensure the transparency and success of the programs. In general, there was a realisation that ESs flow from irrigated agriculture, but there was no systematic design of PES programs around these ESs flows. An opportunity is seen to complement ISF through the design of PES programs around ES flows from the operation of AWCSs.

Multivariate statistical modelling of the drivers of compound flood events in south Florida

Miami-Dade County (south-east Florida) is among the most vulnerable regions to sea level rise in the United States, due to a variety of natural and human factors. The co-occurrence of multiple, often statistically dependent flooding drivers – termed compound events – typically exacerbates impacts compared with their isolated occurrence. Ignoring dependencies between the drivers will potentially lead to underestimation of flood risk and under-design of flood defence structures. In Miami-Dade County water control structures were designed assuming full dependence between rainfall and Ocean-side Water Level (O-sWL), a conservative assumption inducing large safety factors. Here, an analysis of the dependence between the principal flooding drivers over a range of lags at three locations across the county is carried out. A two-dimensional analysis of rainfall and O-sWL showed that the magnitude of the conservative assumption in the original design is highly sensitive to the regional sea level rise projection considered. Finally, the vine copula and Heffernan and Tawn (2004) models are shown to outperform five standard higher-dimensional copulas in capturing the dependence between the principal drivers of compound flooding: rainfall, O-sWL, and groundwater level. The work represents a first step towards the development of a new framework capable of capturing dependencies between different flood drivers that could potentially be incorporated into future Flood Protection Level of Service (FPLOS) assessments for coastal water control structures.

A Numerical Simulation for the Determination of the Shunt Ratio at a T-Junction With Different Branch Angles, Viscosities, and Flow Rates

T-junctions have been applied in water-control structures. A comprehensive understanding of shunt characteristics can contribute to the optimal design of T-junctions. In this work, we seek to understand the shunt ratio of fluids with different viscosities in a T-junction and to achieve a greater shunt ratio. The computational fluid dynamics (CFD) approach is applied to study the influence of the properties, such as the fluid viscosity, the branch angle, the channel shape, and the flow rate, on the shunt ratio in a T-junction. The viscosity of oil can be divided into three intervals, and the optimal angles of the T-junction are different in each interval. For the fluid viscosity in the 1–20 cP range, the optimal branch angle is in the 45–60 deg range. For the fluid viscosity in the 20–65 cP range, the branch angle should be designed to be 45 deg. For the viscosity greater than 65 cP, the branch angle should be designed to be 75 deg. The appearance of the eddy and secondary flow will reduce the flow. The secondary flow and eddy intensity on the branch increase with increasing angle. The secondary flow intensity of the main channel decreases gradually with the increase in the angle. This study provides an important guidance for the design of automatic water control valve tools.