Hydrology & flood engineering
Hydrologist — Denmark, Western Australia
Overview
Fiord Group is a hydrology and flood engineering practice based in Denmark, Western Australia. Principal Blake Marxsen — MIEAust, BEng (Environmental) with Honours — is a hydrologist and environmental engineer working in flood studies, catchment and floodplain modelling, drainage and surface water design, and the hydrological work that sits underneath DWER and EPA approvals. The practice works throughout the Shire of Denmark and the wider Great Southern, and delivers flood and water projects across Western Australia and the Northern Territory.
Services in Denmark
- Flood studies and flood impact assessment for development applications — Flood Impact Assessment
- Catchment and floodplain modelling to Australian Rainfall & Runoff (ARR) 2019 — Flood Hydrology & Modelling
- Surface water management plans, drainage design and erosion control — Surface Water Management
- Culvert, levee and basin design through to construction drawings — Hydraulic Structure Design
- Watercourse realignment and creek diversion design — River & Creek Diversions
- Flood immunity assessment for access roads and critical infrastructure — Flood Resilience of Infrastructure
- Hydrological input to DWER and EPA Western Australia approvals — Hydrology for Approvals
Working in the Wilson Inlet catchment
Denmark sits near the bottom of the Wilson Inlet catchment — roughly 2,250 square kilometres draining to a single bar-built estuary. Five waterways feed it: the Hay and Sleeman rivers and Cuppup Creek from the east, and the Denmark and Little rivers from the west. The Hay and the Denmark between them drain about 88 per cent of the catchment, which means a storm concentrated over either one moves most of the water that reaches the inlet. Catchment-average rainfall is a poor predictor here; where the rain falls matters more than how much.
The Denmark River rises near Pardelup and runs south through the Denmark Pipehead Dam and the townsite before discharging to Wilson Inlet, joined upstream by Scotsdale Brook and Cleerillup Creek. Across the catchment as a whole about 47 per cent has been cleared — for grazing, plantations, horticulture and residential land.
Clearing at that scale changes the hydrology twice over. It raises runoff volumes and shortens time to peak, which is a flood problem. It also mobilises salt: at the Mount Lindesay gauging station the Denmark River rose from around 40 mg/L in the 1940s to a peak near 1,520 mg/L in 1987, before catchment recovery work brought it back under 500 mg/L by 2012 — the first time in nearly forty years it met drinking water guidelines. A hydrological assessment on this catchment that treats the landscape as static is answering a question nobody asked.
The estuary itself is the other complication. Wilson Inlet is a seasonally open estuary — a sandbar closes it from around late January through to August, and in some years it is breached artificially at Ocean Beach rather than opening on its own. That means the outlet condition is not fixed: any hydraulic model of the lower Denmark River has to represent a tailwater that moves with the state of the bar, not a constant level. On this catchment that single assumption, more than the rainfall input, is usually what decides whether the modelled flood levels survive review.
Being based in the catchment is worth something specific: local rainfall behaviour, the state of the bar, which crossings overtop and which do not are things you learn by being here rather than by reading a data file. The modelling is the same modelling delivered on much larger projects elsewhere — the local knowledge is what tells you whether the answer it produces is believable.
Common questions
- Is there a hydrologist in Denmark, Western Australia?
- Yes. Fiord Group is a hydrology and flood engineering practice based in Denmark, WA. Principal Blake Marxsen (MIEAust, BEng Environmental Honours, Murdoch University) works in flood hydrology, catchment and floodplain modelling, surface water management and hydraulic design.
- Who does flood studies in Denmark and the Great Southern?
- Fiord Group prepares flood studies and flood impact assessments across the Shire of Denmark and the Great Southern — including 1% AEP assessments for development applications, calibrated catchment and floodplain modelling to ARR 2019, and the supporting hydrology for DWER and EPA approvals.
- What is the difference between a hydrologist and a hydrogeologist?
- A hydrologist works with surface water — rainfall, runoff, catchments, rivers, flooding and drainage. A hydrogeologist works with groundwater — aquifers, bores, water table behaviour and groundwater licensing. Fiord Group is a surface water practice. If your question is about a bore, a groundwater licence or soil testing for effluent disposal, you want a hydrogeologist.
- Do I need a flood study for a development application?
- Generally when a proposal sits on or near a mapped floodplain, alters drainage or overland flow paths, or when the local authority or the Department of Water and Environmental Regulation (DWER) requests one as a condition of assessment. Requirements vary by shire and by site, so the fastest way to know is to ask before lodging rather than after.
- What does a hydrologist actually do?
- Quantifies how water moves across and off the land — how much rainfall becomes runoff, where it goes, how deep and how fast it flows in an extreme event, and what infrastructure is needed to manage it safely. On a development that usually means establishing flood levels, showing whether a proposal changes flood behaviour, and designing the drainage that follows.
Sources
Every catchment figure on this page comes from a published agency record. Where two agencies publish different numbers for the same catchment, the more recent is used and the earlier is stated alongside it rather than quietly dropped.