Volcanic River Research Articles

Mapping the vulnerability of irrigation sand traps in a tropical volcanic basin, Indonesia

Sand traps in irrigation networks are typically used in mitigating canal sedimentation. In irrigation networks located in basins of high sediment yield due to the presence of volcanoes, it is essential to assess the vulnerability of sand traps. Using sediment yield at irrigation scheme inlets, sand trap vulnerability can be evaluated. This study aims to understand the vulnerability of irrigation sand traps throughout the Progo–Opak–Serang (POS) Volcanic River Basin, Indonesia, via mapping the sediment yield distributions in the basin. We employed the Revised Universal Soil Loss Equation to estimate soil loss, where the results show that the average soil loss in the POS River Basin is 179.69 tons/ha/year that falls under the category of moderate erosion potential, while the average sediment yield for the whole basin is 51.04 tons/ha/year. Parts of the basin with high yields of more than 180 tons/ha/year were mostly found along the volcanic mountains such as Sindoro, Sumbing, Merapi, Merbabu, and Telomoyo, and the Menoreh Hills. The model demonstrated relatively high performance with R2, NSE, RMSE, and MAE of 0.89, 0.82, 0.14, and 0.11, respectively. Within the POS Basin, Badran, Kalibawang, and Blawong are the three most vulnerable irrigation sand traps, with sediment yield values of 252.83, 178.92, and 63.49 tons/ha/year, respectively; they are all located in sub-watershed outlets. The vulnerability assessment conducted in this study can be used for the decision support system to prioritize irrigation sand traps towards a more effective irrigation system development.

Magnetic susceptibilites of suspended sediment and microplastic abundance in a tropical volcanic estuary

Coastal and estuarine ecosystems are seriously threatened by pollutants, according to the literature. In the estuary, the zone that traps suspended particulate matter, namely, estuarine turbidity maxima (ETM), needs to be identified to prevent ecological threats, namely migration and species death. Magnetic measurements of sediments in volcanic rivers have also attracted attention because the sediment contains a high abundance of magnetic minerals. The method in this paper provides a low-cost, rapid, and nondestructive approach to environmental monitorings and assessments. However, the validity of magnetic measurements has not been investigated for their use in identifying the ETM zone in estuaries in volcanic regions. Therefore, this research aims to identify ETM zones in the estuaries of volcanic regions using magnetic properties to correlate the characteristics to microplastic abundance within suspended and surface sediments. The measurements consist of magnetic susceptibility at low frequency, magnetic susceptibility at high frequency, frequency-dependent magnetic susceptibility analyses, and acquisition of a hysteresis curve. Magnetic minerals were also identified using X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy. The results showed that the values of magnetic susceptibility at low frequency significantly correlate with total dissolved solids and microplastics abundance in sediments. The frequency-dependent magnetic susceptibility values were significantly correlated with total dissolved solids, microplastics abundance, turbidity, and microorganism cells. This phenomenon indicates that the magnetic properties of suspended sediments can be used to identify an ETM zone in estuaries in tropical volcanic regions.

Bedload transport analysis using various methods

Mount Merapi, located between the provinces of Central Java and Yogyakarta, is one of the most active volcanoes, regularly spewing lahar material and supplying sediment to the surrounding rivers. These rivers are classified as volcanic rivers and some are utilized as irrigation water sources, flowing through densely populated areas that require the construction of river structures such as retaining walls, bridge pillars, weirs, and groundsills. Bedload transport calculation is an essential part of planning such as river constructions. As bedload transport calculations are continually evolving, scientists have developed several formulaic approaches. To determine the appropriate formula, evaluating existing formulae is necessary. In this study, we compared bedload transport calculations to laboratory measurements using sediment materials sourced from rivers originating from Mount Merapi. The formula used in the study was based on the sediment material's d50 diameter parameter. Our analysis indicates that the equation proposed by Lajeunesse, Malverti, and Charru (2010) yields the closest results to those obtained in the laboratory.

Spatial variability of the sources and distribution of fluoride in groundwater of the Sanya alluvial plain aquifers in northern Tanzania

Groundwater contamination from geogenic sources poses challenges to many countries, especially in the developing world. In Tanzania, the elevated fluoride (F−) concentration and related chronic fluorosis associated with drinking F− rich water are common in the East African Rift Valley regions. In these regions, F− concentration is space dependence which poses much uncertainty when targeting safe source for drinking water. To account for the spatial effects, integrated exploratory spatial data analysis, regression analysis, and geographical information systems tools were used to associate the distribution of F− in groundwater with spatial variability in terrain slopes, volcanic deposits, recharge water/vadose materials contact time, groundwater resource development for irrigated agriculture in the Sanya alluvial plain (SAP) of northern Tanzania. The F− concentration increased with distance from steep slopes where the high scale of variation was recorded in the gentle sloping and flat grounds within the SAP. The areas covered with debris avalanche deposits in the gentle sloping and flat grounds correlated with the high spatial variability in F− concentration. Furthermore, the high spatial variability in F− correlated positively with depth to groundwater in the Sanya flood plain. In contrast, a negative correlation between F− and borehole depth was observed. The current irrigation practices in the Sanya alluvial plain contribute to the high spatial variability in F− concentration, particularly within the perched shallow aquifers in the volcanic river valleys. The findings of this study are important to the overall chain of safe water supply process in historically fluorotic regions. They provide new insights into the well-known F− contamination through the use of modern geospatial methods and technologies. In Tanzania's context, the findings can improve the current process of drilling permits issuance by the authority and guide the local borehole drillers to be precise in siting safe source for drinking water.

Towards liveable volcanic cities: A look at the governance of lahars in Yogyakarta, Indonesia, and Latacunga, Ecuador

The physical and governance challenges posed by urban planning and integrated water resources management (IWRM) are gaining momentum worldwide. Yet, the governance of Volcanic River Basins (VRB) remains vastly unexplored. There are at least 500 active volcanoes worldwide, with 600 million people living near them. Through a multiple-case study methodology, we aim to contribute to the understanding of how lahar risks management is being conducted in two distinct urbanized volcanic river basins: Yogyakarta in Indonesia, and Latacunga in Ecuador. Both are located in the “ring of fire” with recent eruption threats in the last decade. The two cases were conducted independently, both triangulated by international and national literature reviews, policy analysis, and in-depth interviews. The Indonesian case study focuses on the governance intricacies for water and disaster management after 2010 eruption during pre, onset, and post-eruption. The Ecuadorian case study looks at risk governance from the perspective of households after a volcanic eruption in 2015, highlighting how bottom-up risk management strategies interact with top-down governance policies. Based on both case studies, a synthesis framework for Volcanic River Basin Management (VRBM) is formulated. This framework can be used as the way forward to analyze disaster and resources management in urbanized volcanic areas.

Implementing the integrated water resources management approach in a volcanic river basin: a case study of Opak Sub-Basin, Indonesia

ABSTRACT The ways in which integrated water resources management (IWRM) is implemented in a volcanic river basin (the Opak Sub-Basin) on the flanks of Mt Merapi volcano in Indonesia is examined. Data deriving from semi-ethnographic fieldwork and in-depth interviews are analysed through a multilevel governance lens that considers three pillars of management – conservation, utilization and hazard control – and three levels of governance – national, regional and municipal. The research shows that the regional level is the priority playing field; that the degree of integration differs between levels of government; and that actors called ‘whisperers’ support higher integration levels, have the greatest ability to form bridges between communities and government.

Sediment transport pre-measurement as revealed by the hydrophone monitoring technique at a volcanic river

Recognizing the real-time sediment transport phenomena of rivers in the Mt. Merapi area has become an important issue, particularly in the efforts to mitigate risks of lahar flow disasters. The development of a lahar-related monitoring system in the Mt. Merapi area has currently become more challenging since contact and direct lahar flow measurement is very risky. Former techniques for lahar flow occurrences such as cable sensor and video shooting are considered good enough in terms of identifying the occurrence, but not the intensity. Furthermore, after the cable is cut, re-installation often meets its practical limit. The hydrophone measurement technique seems to be an acceptable technique subject to sufficient field calibration. This paper reports the performance of a hydrophone equipment, which can be used for monitoring bedload transport with diameters greater than 4 mm.

Dynamics of lahar-affected river tributaries of the Progo river after the 2010 Mt. Merapi eruption

Riverbeds in the Mt. Merapi area are dominated by gravel originating from Mt. Merapi. The 2010 Mt. Merapi eruption has formed a riverbed consisting of sediments of various size. Since then, the morphology of the rivers has changed dynamically, depending upon the natural and the anthropogenic factors. Most of the rivers drain into the Progo River, whereas the main river system of Progo River drains into the Indian Ocean. The dynamics of the tributaries of volcanic rivers along the Progo River are the major concern to identify the capacity of the tributaries against potential lahar flow disasters that may occur. This paper presents the results of a series of observations of several tributaries of the volcanic rivers, taking into account the natural flow phenomena as well as the sediment mining activity along the river under investigation. The investigation included the hydraulic simulation, which employed a numerical model. The results of the simulation showed that the downstream part of the Progo River is influenced by sediment from Mt. Merapi through its tributaries. These also suggest cost-effective river tributary maintenance to mitigate the risks of lahar flow disasters.

Iron buffer system in the water column and partitioning in the sediments of the naturally acidic Lake Caviahue, Neuquén, Argentina

Sedimentary iron partitioning was studied for five sediment strata (16cm depth) at three sampling sites of the naturally-occurring acidic Lake Caviahue (Patagonia, Argentina). Additionally, water column iron was modeled based on five-year period input loadings to study a possible iron buffer system. The partition coefficient between the water column and the total iron content of the sediments was also addressed. Sedimentary iron was found to be distributed, on average, in the following forms: exchangeable (6%), iron oxides (4%), pyrite and reactive organic matter (38%) and residual (non-andesitic) materials with a high content of humic acids (52%). Furthermore, we found that the dissolved iron in the lake was nearly constant throughout the five year period we studied. This is consistent with the existence of an iron buffer system in the lake at pH between 2.0 and 3.0, which may cause differential iron precipitation at the delta of the volcanic river with respect to the deeper northern and southern arms. Sedimentary iron measurements taken at the delta further support the existence of a buffer system, where it was found that the iron content in the sub-superficial stratum (2cm) was double that of the remainder of the vertical profile at the same site.

The principles of ecological classification of rivers in areas of contemporary volcanism (Exemplified by Kamchatka)

We examine the diversity of formation conditions for river ecosystems within the boundaries of the volcanic territories of Kamchatka in the context of the specific changes in water discharge, turbidity and sediment yield, the temperature and channel regimes as well as in chemical composition of river waters. On the basis of ranking the factors under consideration according to the degree of impact on the state of communities of aquatic organisms, we explore the possibilities for a classification of rivers. An analysis is made of the ecological consequences of the manifestation of volcanic processes for the diversity, structure and spatiotemporal distribution of the fish fauna. An assessment is made of the conditions under which there is taking place a degradation and extinction of the ichthyofauna. We suggest a subdivision of the streams of the volcanic territories into three groups: without specific manifestations (ordinary rivers), with volcanic manifestations, and volcanic rivers.

River Morphology Modeling at the Downstream of Progo River Post Eruption 2010 of Mount Merapi

Mt.Merapi is one of the most active volcanoes in Indonesia. Some of the rivers that the origin is located at Mt.Merapi have a large amount of sediment resources after eruption in October-November 2010. The total volume of sediment is estimated at 130 million m3.The deposited sediment flows to the downstream area as a debris or bed load transport in high density. Few studies considered downstream change along volcanic rivers due to a high density of bed load transport. Using numerical simulation, the impact of high concentration of bed-load transport is applied in Progo River, Yogyakarta, Indonesia. The results show that the high bed-load transport rate increases the mid-channel bar grow rate and the bed degradation near the bank toe. The increase of bed degradation is an important parameter of bank erosion process. Furthermore, the bed morphology on the downstream after 2010 eruption of Mt. Merapi should be considered intensively.

Benthic diatom assemblages and their response to human stress in small-sized volcanic-siliceous streams of central Italy (Mediterranean eco-region)

The river typology ‘volcanic rivers’ represents a unique typology in the Mediterranean eco-region in Europe but its type-specific diatom assemblages are still poorly investigated. The main aims of this study were (i) to analyse the diatom diversity of this river type, (ii) to investigate the relationships between diatom diversity and environmental variables and (iii) to identify the characterizing diatom community structure of different environmental groups. To this end, we selected 13 streams located in central Italy, belonging to a single river type and covering the whole quality range from human impacted sites to those in ‘reference conditions’. Most frequent and abundant diatom species found were Cocconeis placentula var. lineata, Planothidium lanceolatum, Rhoicosphenia abbreviata and Amphora pediculus. Species richness in reference and less impacted sites was not higher than in intermediate and heavily degraded ones, but non-metric multidimensional scaling (N-MDS) analysis revealed a substantial difference among their diatom community structure. The indicator species analysis defined the characteristic species of three environmental groups identified by N-MDS. The findings of this study represent a contribution to the knowledge on diatom communities of Mediterranean volcanic-siliceous rivers and provide information for a data-driven implementation of the Water Framework Directive in Italy for this specific river typology.