Non-perennial rivers (NPRs) account for more than 50% of the world’s river network and their occurrence is expanding. Some rivers that were previously classified as perennial have evolved to be NPRs in response to climate change and socio-economic uses. There is inadequate understanding of the spatio-temporal dynamics of flows and pools along these rivers due to lack of data, as a priority of river monitoring has been placed on perennial rivers. The current understanding and methods used for monitoring NPRs are mostly derived from perennial rivers perspective. This review paper examines challenges for collecting data on these hydrological attributes of NPRs using current methods. Furthermore, this paper provides an overview of the potential and limitations of using remote sensing data for monitoring NPRs. Remote sensing data are successfully used for monitoring wetlands and lakes, but little is known about their capabilities for monitoring pools along NPRs. Remote sensing has also been successfully used to estimate discharge of large perennial rivers; however, this has not been fully explored for NPRs. Remote sensing has the potential to extract more hydrological information that currently cannot be extracted using conventional in-situ measurement methods. With advancements, remote sensing technology could become useful for managing NPRs.

Rural areas in Limpopo Province (South Africa) are in urgent need of interventions for safe and secure water supply to adapt to climatic changes and the increased frequency of droughts. A feasibility study was conducted for the adoption of solar-powered groundwater pumping systems and Multiple Water Use Services (MUS) in Greater Giyani Municipality (Limpopo). Stakeholder engagement, geotechnical data and socio-economic information were used in the feasibility study. The Solar Powered Irrigation Systems (SPIS) tool (GIZ and FAO, 2021) was used to design solar-powered shallow groundwater pumping systems at nine case study sites: four villages (water supply for domestic use) and five small-scale farms. Given the technical design configurations, peak water requirements ranged from 28.8 to 58.9 m³/d, peak power requirements from 1.2 to 3.4 kWp and required solar panel surface areas from 8.0 to 22.3 m². Viable financial mechanisms for the operation and maintenance of MUS are leasing, cooperatives, informal saving groups and pay-per-use. The adoption of the technology appears to be financially and technically viable to augment the water supply. However, groundwater levels will have to be monitored and water purification plants for drinking water will have to be established to ensure long-term sustainability.

This study explored the use of multi-source remotely sensed data in monitoring the spatial distribution of pools and pool dynamics in two distinct semi-arid sites in South Africa. The factors that control the pool dynamics were also examined. Three water extraction indices were used, these included Normalised Difference Water Index (NDWI), Modified NDWI and Normalised Difference Vegetation Index. In addition, random forest classifier and Sentinel-1 SAR data were used in mapping pools and pools dynamics for both sites. Overall, the remotely-sensed methods detected and mapped pools with acceptable accuracy, except for small pools (<400 m²). The results suggest that flow occurrences and rainfall are key in controlling temporal changes in pools sizes, and there was no interaction between pools and groundwater. The study showed that remote sensing methods are essential for filling ground monitoring gaps in non-perennial rivers and determining hydrological processes and water availability from pools in semi-arid environments.

Non-perennial rivers (NPRs) have three hydrological states; each state has its importance, function and implication for water resource management. The dynamics of these states have been inadequately assessed and understood. Hence, this study sought to determine the spatiotemporal variations in the hydrological conditions of NPRs, focusing on the Touws River–Karoo drylands and Molototsi River within the semi-arid region of the Limpopo Province of South Africa. Additionally, the study aimed to delineate and characterize the primary areas contributing to runoff in these two river systems. Sentinel-1 and Sentinel-2 satellite data sources were employed in this study. Specifically, the modified normalized difference water index (MNDWI) derived from Sentinel-2 was utilized to delineate water surface areas along the two rivers. Subsequently, these derived datasets were utilized to assess the hydrological states over a 32-month period (2019–2022). Based on the presence of water, the river's state was classified as flowing, pooled, or dry. The results showed that remote sensing can be used to determine the hydrological state of the two river systems with ~90% overall accuracy. However, there is about a 30% chance that a flow event can be missed using Sentinel-2 due to clouds and temporal resolution. Some of these gaps can be filled using synthetic aperture radar (SAR) data (Sentinel-1), as demonstrated with the Molototsi River. In the Molototsi catchment, the upper catchment contributes the majority of flows. For the Touws River, the southwestern part of the catchment was determined as the major contributing area for the observed flows. This suggests that the chosen observation site might not be representative of upper catchment dynamics; therefore, a monitoring site in the upper catchment is required. This study provided hydrological information and an approach that can be used to monitor the hydrological states for better understanding and management of NPRs and catchments.