1. Introduction

South Africa continues to confront challenges regarding electricity supply, and the future strategy relies on an energy mix; undoubtedly, coal will remain a significant component. A successful pilot can enhance productivity by assuring the efficient operation of the power plant and preventing partial or entire shutdowns through compliance with environmental regulations and the maintenance of the structural integrity of the ash dam facilities (ADFs) [2]. Minimizing the environmental impact of ash from power generation on surrounding ecosystems and flora will bolster the argument for coal as a clean energy source, hence enhancing the Nation's adherence to global sustainability standards.

2. Literature Review

Soil Moisture Active Passive (SMAP) is a metric utilized to measure soil moisture. The SMAP project is a global orbiting observatory that quantifies the water content in surface soil. Soil moisture is an essential indicator in agriculture, drought and flood forecasting, weather forecasting, and other domains [6]. SMAP quantifies the water content in the upper 5 cm of soil over all terrestrial regions that are neither frozen nor submerged in water. Furthermore, it differentiates between frozen and thawed soil. SMAP analyzes the moisture content within the minerals, geological materials, and organic particles found in soil globally, specifically in regions where the ground remains unfrozen [8]. SMAP cannot detect ice, but it can assess liquid water in the uppermost layer of the Earth [9]. The soil's moisture content influences the emission of microwave radiation, although this energy exists in all soil types [10]. Microwave energy escalates with arid soil and diminishes with moist soil. This radiation is quantified using radiometers, enabling scientists to ascertain the water content [11]. SMAP measures radiation in the L-band microwave spectrum (30–15 cm & 1-2 GHz frequency), as this wavelength may penetrate clouds, enabling SMAP to assess soil moisture under cloudy situations [12].

3. Methodology

The researchers performed a three-year examination of moisture content along the ADF to pinpoint areas with rising moisture content values [13]. An increase in moisture content may indicate inadequate drainage [14]. Historical analysis facilitates the identification of places with elevated moisture levels, which may be corroborated with historical data pertaining to the status of the ADF [15].

Soil moisture is quantified using Soil Moisture Active Passive (SMAP) [4]. The SMAP mission is an orbital observatory that quantifies the water content in surface soil globally. Soil moisture is a crucial metric for meteorological forecasting, drought and flood predictions, agriculture, and other applications. SMAP quantifies the moisture content in the first 5 cm of soil over all terrestrial regions that are neither submerged nor frozen [7]. It also differentiates between frozen and thawed ground. In areas where the ground is unfrozen, SMAP quantifies the water content present among the minerals, rocky substances, and organic matter in soil globally [8] (Feng et al., 2024). SMAP quantifies liquid water in the uppermost layer of soil but is incapable of measuring ice [9]. All soil types emit microwave radiation; however, the quantity of released energy varies with the water content. As soil moisture decreases, microwave energy increases; conversely, as soil moisture increases, microwave energy decreases [11] (Abdulraheem et al., 2024). Radiometers quantify this radiation, enabling scientists to compute water content [12]. SMAP quantifies radiation in the L-band microwave spectrum, namely within the 30–15 cm wavelength range and 1–2 GHz frequency (refer to fig.1) [4]. This radiation wavelength penetrates clouds, enabling SMAP to assess soil moisture irrespective of cloud cover.

SMAP was inaugurated in January 2015 and commenced operations in April 2015, equipped with two instruments for soil moisture measurement: an active radar and a passive radiometer (refer to table 1) [16]. The radar sensor became inoperative in early 2015 due to a malfunction in the radar power source, however it gathered about three months of scientific data, which may be accessed at the Alaska Satellite Facility [17]. The passive L-band radiometer acquires daily data at 6 a.m. 6 p.m. (descending) Local solar time ascends for comprehensive world coverage every 2 to 3 days [18]. This allows for the observation of global changes over time spans that encompass significant storms and recurring seasonal measurements [19].

Table 1: The Radiometer of SMAP.

Frequency	Polarization	Resolution	Relative accuracy
1.41 Ghz	H, V	36-km original, 9-km enhanced	1.3 K

SMAP's radiometer captures naturally emitted radiation from the surface using a 20-foot-wide mesh antenna that rotates 14 times per minute, the largest spinning antenna in space.

4. Results/Findings

The soil moisture analysis was performed from 2020 to 2024. An assessment of the water content in the surface soil was conducted. SMAP quantified the water content in the uppermost layer (5 cm) of soil. It was determined to average 0.09 cm³/cm³ due to the ashing and the associated damming required by the ashing process. The researchers choose the dam facility as their focal point on the SMAP visualization application, as illustrated in Figure 2.

The researchers delineated a polygon representing the study region of the fly ash dam plant and selected a four-year timeframe, as illustrated in Fig. 3.

The researchers selected the soil moisture tab for viewing and analyzed the generated results by adjusting the zoom level of our study region. Upon selecting the stop drawing tab and clicking on the map to display the soil moisture value, the researchers obtained a measurement of (0.09 cm3/cm3) in this instance (see fig.4). Figure 3 (highlighted in red) indicates that any value beyond 0.6 cm³/cm³ is deemed worrisome.

Figures 5 to 9 clearly indicate that soil moisture peaks throughout the summer months at the ash dam site. Soil moisture is diminished throughout the cold months. Precipitation occurs consistently throughout the summer months. The winter months are likely drier. Fly ash facilities operate continuously throughout the year. The water dams remain operational year-round. This renders ashing throughout the summer months essential. Monitoring soil moisture throughout the hot months is therefore essential.

5. Conclusions and recommendations

Soil moisture is diminished throughout the cold months. Precipitation occurs consistently throughout the summer months. The winter months are likely drier. Ashing at the ADF occurs year-round. The water dams at the ADF are functioning year-round. This renders ashing throughout the summer months essential. Monitoring soil moisture during the hot months is consequently essential. Phreatic levels must be meticulously monitored during the warmer months. In summary, it is necessary to examine whether the triggering criteria have evolved over time to associate the trend in soil moisture with rainfall.

6. Acknowledgement/Funding

This study is part of a collaborative effort at ESKOM, the Centre of Applied Research and Innovation in the Built Environment (CARINBE). It was financed under task order 2, pertaining to the research and development of a proof of concept for ash dam monitoring (Geomatics), under the project titled: Civil & Structural Engineering and Ash Dams, contract number: 4600074129. The authors assert that there is no conflict of interest.

7. References