Fazlul Karim

Flood water quality and marine sediment and nutrient loads from the Tully and Murray catchments in north Queensland, Australia

Current estimates of sediment and nutrient loads from the Tully–Murray floodplain to the Great Barrier Reef lagoon are updated by taking explicit account of flood events. New estimates of flood discharge that include over-bank flows are combined with direct measurements of sediment and nutrient concentrations in flood waters to calculate the loads of sediment and nutrient delivered to the ocean during 13 floods that occurred between 2006 and 2008. Although absolute concentrations of sediment and nutrient were quite low, the large volume of water discharged during floods means that they make a large contribution (30–50%) to the marine load. By not accounting for flood flows correctly, previous estimates of the annual average discharge are 15% too low and annual loads of nitrogen and phosphorus are 47% and 32% too low respectively. However, because sediments may be source-limited, accounting for flood flows simply dilutes their concentration and the resulting annual average load is similar to that previously estimated. Flood waters also carry more dissolved organic nitrogen than dissolved inorganic nitrogen and this is the opposite of their concentrations in river water. Consequently, dissolved organic nitrogen loads to the ocean may be around twice those previously estimated from riverine data.

Flood-hazard assessment and risk-based zoning of a tropical flood plain: case study of the Yom River, Thailand

Abstract This study contributes to the comprehensive assessment of flood hazard and risk for the Phrae flood plain of the Yom River basin in northern Thailand. The study was carried out using a hydrologic–hydrodynamic model in conjunction with a geographic information system (GIS). The model was calibrated and verified using the observed rainfall and river flood data during flood seasons in 1994 and 2001, respectively. Flooding scenarios were evaluated in terms of flooding depth for events of 25-, 50-, 100- and 200-year return periods. An impact-based hazard estimation technique was applied to assess the degree of hazard across the flood plain. The results showed that 78% of the Phrae flood-plain area of 476 km2 in the upper Yom River basin lies in the hazard zone of the 100-year return-period flood. Risk analyses were performed by incorporating flood hazard and the vulnerability of elements at risk. Based on relative magnitude of risk, flood-prone areas were divided into low-, moderate-, high- and severe-risk zones. For the 100-year return-period flood, the risk-free area was found to be 22% of the total flood plain, while areas under low, medium, high and severe risk were 33, 11, 28 and 6%, respectively. The outcomes are consistent with overall property damage recorded in the past. The study identifies risk areas for priority-based flood management, which is crucial when there is a limited budget to protect the entire risk zone simultaneously. Citation Tingsanchali, T. & Karim, F. (2010) Flood-hazard assessment and risk-based zoning of a tropical flood plain: case study of the Yom River, Thailand. Hydrol. Sci. J. 55(2), 145–161.

Fish larvae and recruitment patterns in floodplain lagoons of the Australian Wet Tropics

Floodplain lagoons in the Queensland Wet Tropics bioregion, Australia, are important and threatened habitats for fish. As part of studies to assess their ecological condition and functions, we examined patterns of occurrence of fish larvae, juveniles and adults in 10 permanent lagoons on the Tully–Murray floodplain. Lagoons contained early life-history stages of 15 of the 21 native species present, including 11 species that complete their life cycle in fresh waters and 4 that require access to saline habitats for larval development. Lagoon connectivity to the rivers, distance from the coast and flood dynamics influenced temporal variation in fish abundance, population size structures and recruitment patterns. This study and the literature show that wet, post-wet and dry-season habitats are utilised by small opportunists (e.g. Melanotaenia splendida), an equilibrium species (Glossamia aprion) and larger periodic strategists (neosilurid catfishes). Maintenance of natural seasonal patterns of flow and connectivity, and active protection of permanent floodplain lagoons from riparian and land-use disturbance, will be essential if their roles in fish recruitment are to be sustained.