Development of a Smart Monolayer Application System for Reducing Evaporation from Farm Dams: Introductory Paper

Abstract

Chemical monolayer films are potentially an economical low-impact means of reducing evaporative loss from farm water storages. However, their performance can be highly variable as they are affected by climatic and environmental factors: principally wind, wave action and biodegradation. These limitations must be accommodated for in the management of the applied monolayer by means of appropriate and timely autonomous application and re-application.Although a number of autonomous application systems for monolayer already exist, none has proved overly successful. It is argued that whilst this is in part due to sub-optimal performance of monolayer materials, it is also due in large measure to inaccuracies and/or inappropriate design in both application systems and particularly application strategies which are not adaptive to the prevailing environmental conditions. Therefore, a control system is being developed to adaptively and spatially vary monolayer application rates according to changing conditions monitored on-site. This will form part of an autonomous electromechanical system for the optimal application and spreading of chemical monolayer.This paper reports progress towards this objective; firstly by evaluation of the design requirements for automated systems at a range of spatial scales; and secondly via the construction of a first "preprototype" to act as an evaluation platform and concept demonstrator.

Evaporative loss and environmental impact of covers on water storages: A review

“…Monolayer formulations may be applied manually, or from prototype applicators programmed to release the product when automatic weather stations register favorable wind conditions (Brink et al., 2011). Monolayer products will be most effective if applied when wind turbulence induces a cold surface film, and when a wind speed of less than 3 m s −1 favors the formation of a condensed surface film (Pittaway, Martínez‐Alvarez, et al., 2015).…”

“…Multiple product applicators or application sites at intervals around the storage are required to ensure the maintenance of complete surface coverage on large water storages (>10 ha; Craig, 2008). Manually operated monolayer dispensers are available, and prototype programmed units have been successfully used (Brink et al., 2011). The number of application sites required to maintain full surface coverage suggests that the application of monolayers may be limited to storages of less than 100 ha.…”

“…In our review, only papers specifying light reduction and evaporation reduction values from paired water storages of at least the size of Class A evaporation pans (0.25 m depth, 1.207 m diameter) were selected, as the use of smaller containers increases the error margin of the calculation (Hancock et al, 2011). Simple linear regression (SigmaPlot 14, Systat Software Inc.) was used to compare the reduction in evaporation achieved by installing a cover (Equation 1), with the capacity of the fabric to reduce light transmission (Equation 2; R 2 = 0.683, standard error of estimate 7.062).…”

“…In one trial, chemical leachate from a recently replaced highdensity polyethylene tank liner had a greater impact on aquatic microbes than twice-weekly applications of a stearyl alcohol monolayer formulation (each dose of 0.28 ml m −2 equivalent to six times a monomolecular thickness; Pittaway, Martínez-Alvarez, et al, 2015). The inclusion of hydrated lime in powdered monolayer formulations of cetyl and stearyl alcohol (Barnes, 2008;Mozafari et al, 2019;Nejatian et al, 2022) has the potential to adversely affect microlayer processes, as in two trials the lime rapidly increased the pH of microlayer water samples (7.9-10.2, and 8.2-10.8; Hancock et al, 2011). Many aquatic organisms surfacing at the air-water interface to breathe, including fish and aquatic larvae, may be adversely affected by this sudden rise in pH.…”

“…The application of the silicone-based product varied from 7 to 50 L ha −1 . The silicone-based film does not self-spread as readily as monolayers but is more resistant to wind turbulence (Hancock et al, 2011), requiring re-application every 10-20 days (information provided by supplier; see Table 5).…”