Drought resilience
The Coastal Great Southern Regional Drought Resilience Plan covers the City of Albany, the Shires of Denmark and Plantagenet, and the Frankland River sub-region. It is jointly funded by the Australian Government’s Future Drought Fund and the Department of Primary Industries and Regional Development, and delivered by the Great Southern Development Commission with DPIRD. Its case studies are worth reading closely, because three of the four describe the same hydrological problem in four different vocabularies: the catchment stopped yielding what the storage was sized against. A horticulture operation answered it by building thirty-five hectares of roaded catchment. A vineyard is losing to it, with dam evaporation rising from 22–30 per cent in a normal year to 40–45 per cent in a dry one. A small landholder describes a "green drought" — enough green to look fine, not enough water or feed to run stock. The pattern matters, because it points at where the leverage sits, and it is usually not the dam.
What the plan is
Regional Drought Resilience Planning is a Future Drought Fund program, jointly funded with the State and delivered here by the Great Southern Development Commission and DPIRD, with input from technical experts, universities, CSIRO, industry groups and agencies. The Great Southern is covered by two subregional plans. The Inland plan — Broomehill-Tambellup, Cranbrook, Gnowangerup, Jerramungup, Katanning, Kent, Kojonup and Woodanilling — was completed in 2023 in the program’s first year. The Coastal plan, covering Albany, Denmark, Plantagenet and the Frankland River sub-region, published its documents in 2025.
It is published as a set rather than a single report: the plan itself, a regional context volume, and a separate case studies volume. The case studies are the part most worth a landholder’s time. They are first-hand accounts with real numbers in them, and unlike most strategy documents they record what did not work as well as what did.
Three of the four case studies are the same problem
The horticulture case study describes a thousand-hectare mixed operation that has never had to destock completely, because it invested in storage and catchment before it needed them — larger dams, a thirty-five hectare roaded catchment, a gutter system capturing runoff from hard-surface covered cropping, and a negotiated arrangement to draw on a neighbour’s disused dams. Its own assessment is that a drought running beyond two years would still force destocking for lack of water in the paddocks.
The viticulture case study is the same problem with the outcome running the other way. A seventy-hectare catchment feeding seven satellite dams, built for a district where a below-average year meant 450 millimetres — against a normal closer to 600. Consecutive dry seasons have left the main irrigation dam, overflowing in 2020, at levels the grower describes as threatening the vineyard’s viability. Shiraz yields that average eight to ten tonnes per hectare dropped to 3.5. The 2019–20 vintage lost forty per cent of its yield. Twenty per cent of the lowest-yielding vines have been pulled to preserve water for the rest.
The small landholder case study, on sixty-five to eighty hectares, describes 2024 as the first year hay had to be bought in, and makes the point that destocking is not a one-season decision — rebuilding a herd takes more than two years, so a single dry year propagates through the fresh meat supply chain for three.
Different sectors, different scales, one mechanism. None of the three says "it stopped raining". All three describe a catchment that no longer converts the rain it does get into water in a dam.
Why runoff falls faster than rainfall
This is the part the case studies feel and do not name, and it is the single most useful idea in the whole document. Rainfall and runoff do not decline together. Runoff declines faster, because runoff is a threshold behaviour rather than a proportional one.
DPIRD publishes the numbers for exactly this landscape. Winter rainfall in Western Australia is often low intensity, with daily falls under ten millimetres common, and a natural catchment generally needs continuous rain of up to fifty millimetres before it runs water into a farm dam. Everything below that threshold wets the soil and stops there. So a season that delivers its rain in many small falls and few large ones can arrive at a respectable annual total and put almost nothing in the storage.
That is why a drop from 600 millimetres to 450 — a twenty-five per cent reduction in rainfall — does not produce a twenty-five per cent reduction in dam inflow. It produces a much larger one, because what was lost was disproportionately the events that cleared the threshold. The EPA makes the regional version of the same observation in its Inland Waters guideline: reducing rainfall over the past forty years has driven a significant overall downward trend in runoff and recharge across the South West, and it assesses proposals against that trend rather than against a historical baseline.
The most important number in the plan is thirty-five hectares of roaded catchment
A roaded catchment is graded, clay-surfaced and compacted so that water runs off it instead of soaking in. DPIRD’s published figures are the reason the horticulture case study reads the way it does: where a natural catchment needs up to fifty millimetres of continuous rain to yield, a clay roaded catchment brings the runoff threshold down to about eight to ten millimetres, and with chemical treatment of the clay surface as low as four to six.
Set that against a winter of sub-ten-millimetre daily falls and the consequence is stark. The unimproved catchment yields close to nothing across the whole season. The roaded catchment yields from most of it. That is not a marginal efficiency gain — it is the difference between a storage that fills and one that does not, in the same paddock, under the same sky.
And it is the reason the instinctive response to a dam that will not fill is usually the wrong one. Enlarging the storage does not change the threshold. If the catchment above it only runs three times a year, a bigger dam captures the same three events into a larger empty hole. The catchment is the variable with leverage; the storage is the one with the invoice.
Evaporation scales with surface area, which is what enlarging a dam adds
The viticulture case study supplies a figure most water balance work leaves implicit: evaporation losses on dams in this district running at 22–30 per cent in a normal year and 40–45 per cent in a dry one. Nearly half the stored volume, gone to the air, in the year it is most needed.
That number interacts badly with the enlargement instinct. Evaporative loss is a function of surface area; usable storage is a function of volume. Widening a dam adds both, but it adds surface area immediately and across the whole footprint, while the volume gained depends on how much depth comes with it. A storage enlarged by spreading sideways can end up losing a greater share of what it holds than it did before. Deepening rather than widening is the version of the same investment that does not carry that penalty.
Storage depth over surface footprint is the same conclusion the WaterSmart Dams work reached, and it is why the current state-level programs — DPIRD’s WaterSmart Farms, and WaterSmart Dams delivered with the Grower Group Alliance and UWA — put their emphasis on evaluating dam strategy before earthworks rather than after.
The arithmetic worth running on any harvesting number
The horticulture case study reports a gutter system on hard-surface cover contributing roughly half the farm’s production water. Whether a harvesting proposal is worth its earthworks comes down to one line of arithmetic, and it is short enough to run on a phone: contributing area, multiplied by annual rainfall, multiplied by a runoff coefficient.
A sealed surface — a roof, or hard cover — runs at a coefficient near 0.9, because almost nothing infiltrates. One hectare of it under 800 millimetres of annual rainfall yields in the order of 7,000 cubic metres a year. A well-built clay roaded catchment sits lower than a roof but far above bare paddock. Unimproved pasture on a drying profile can be near zero in a year of small falls, which is the whole point of the section above.
Run that line on every harvesting figure you are given, including the ones in published documents and vendor proposals. Where the answer and the claim diverge, the difference is usually a contributing area larger than the one being described, or a wet year doing work an average year will not repeat. Neither is dishonest. Both change what the number means for planning.
The fourth case study, and the limits of this reading
The fourth case study is not a water-supply account and should not be flattened into one. It covers the Wagyl Kaip Southern Noongar region — the Menang, Goreng, Keneang, Wilman and Wudjari language groups across roughly 52,246 square kilometres — and its subject is cultural heritage under longer dry seasons and more intense fire cycles: bush fire damage to and disrupted access to cultural sites, loss of bush foods, and the difficulty of passing on Traditional Ecological Knowledge between generations. Its central recommendation is the integration of TEK into fire mitigation, with the resourcing and ranger training that requires. That is a different discipline from hydrology and a different kind of resilience, and it belongs to the people who wrote it.
It does record water-linked impacts within scope of a reading like this one: water scarcity and inconsistent rainfall disrupting seed cultivation and revegetation work in community nurseries, and with it the economic sustainability of the enterprises built on them. Revegetation programs are catchment interventions whether or not they are described that way, and a nursery that cannot rely on water is a catchment program that cannot rely on its plants.
What in this is a hydrology job
Two of the case studies ask directly for things that are hydrological work. The small landholder asks for early identification of triggers — data and early warning that would let a decision on destocking or buying feed be made before the situation forces it. The horticulture operation suggests aerial imaging to identify emergency water supplies across a district, for firefighting as much as for drought.
Underneath both sits the same short list of questions: what a given catchment actually yields in a dry sequence rather than an average year, how much of that a storage can capture and hold once evaporation is taken out, what a roaded catchment or a sealed surface would change, and whether the take is licensable where it sits. That last one is not a formality in this region — parts of the Albany area are proclaimed, and a farm dam’s exemption turns on whether it causes a sensible reduction in the volume of a watercourse or wetland, which is a hydrological calculation before it is a legal answer.
Plenty in the plan is not hydrology. Feed budgeting, hay quality grading, cash flow support, pricing mechanisms and mental health services are all named needs and none of them are answered by a catchment model. The water questions are the ones worth bringing to a hydrologist, and they are usually cheapest to answer before the earthworks are quoted rather than after.