Why Monitor Wagga Wagga River Flows?

1. Where is Wagga Wagga?

Geographical Background

Wagga Wagga, commonly known as "Wagga," is a major regional city in New South Wales, Australia, 452 kilometers southwest of Sydney and 15 kilometers north of the Victoria state border. It is on the Murrumbidgee River in the fertile Riverina plain—a flat to gently rolling country bounded by the Great Dividing Range in the east and the South West Slopes in the north. It has an area of 145 square kilometers at an elevation of 147 meters above sea level and has a temperate climate with defined seasons.

Human/Cultural

Aboriginal inhabitants of the Wiradjuri people inhabited the region of Wagga Wagga for over 40,000 years, and the Murrumbidgee River formed the center of their culture as a source of food and spirituality. The European settlement began in the 1830s, and the city was established as a river port as well as an agricultural hub. Today, Wagga Wagga (population 72,000) is the New South Wales largest inland city outside the Sydney basin, with a reputation for educational facilities (such as Charles Sturt University), military history (being home to the Royal Australian Air Force Base), and vibrant community events such as the Wagga Wagga Show. It was named by the Wiradjuri people for "place of many crows," after the natural heritage of the area.

Hydrology and River Overview

The Murrumbidgee River is the lifeblood of Wagga Wagga. It starts its 1,600-kilometer run in the Snowy Mountains, running west through the Riverina, Wagga Wagga, before emptying into the Murray River at Balranald, ultimately emptying into the Southern Ocean.

For Wagga Wagga, the Murrumbidgee is hydrologically important: it supplies 90% of the city's water for domestic consumption via the Wiradjuri Reserve Water Treatment Plant and irrigates farms in the area that produce wheat, cotton, and livestock. Ecologically, its riparian zones (lined by river red gums) provide habitat for platypuses, eastern grey kangaroos, and waterbirds including the white ibis.

At Wagga Wagga, the Murrumbidgee has a width of 80–120 meters and depth of 3–8 meters under normal flows. The major tributaries are the Wollundry Lagoon (a built-up wetland that is connected to the river) and the Gumly Gumly Creek, which enters the river upstream. The river floodplain, extending 2–3 kilometers from the riverbanks, is prone to recurring flooding—a natural process that brings nutrient-rich matter to the soil but causes damage to urban settlements built along its edge. The stormwater drainage network of the city drains into the river, thereby creating an immediate link between urban runoff and river health.

2. What is the River Flow Situation near Wagga Wagga?

Influencing Factors

Precipitation and Runoff

Wagga Wagga receives 566 mm of rain annually, 70% falling in winter-spring. Summer droughts are typical, with scattered thunderstorms bringing 30–50 mm over 24 hours. The Murrumbidgee flow is controlled by Snowy Mountains snowmelt (October–December), supplementing volumes by 30–50%. Catchment runoff from the 84,000-square-kilometer area reaches Wagga Wagga in 48–72 hours, and therefore flow prediction is challenging.

Topography and River Morphology

The Murrumbidgee at Wagga Wagga has a wide, low-lying valley (gradient 0.1 m/km) with slow currents (0.2–0.5 m/s) under normal conditions. Its sandy/muddy bed contains submerged logs and gravel bars to provide habitat for fish. Meanders along the course of the river slow flow in certain sections, while natural constrictions (e.g., "The Narrows" downstream) can exacerbate flooding by reducing discharge capacity.

Reservoir Operation

Upstream reservoirs like Burrinjuck Dam (1,028 gigaliters capacity) regulate flow. During dry periods, releases maintain minimum flows (100 ML/day) for irrigation; flood storage diverts 20–30% off downstream peaks. But heavy rains can overflow storage, as occurred in 2012.

Historical Hydrological Events

1956 Floods

Australia's worst inland flood saw the Murrumbidgee at record 10.7 meters at Wagga Wagga, covering 2,000 homes and 100 stores. The flood caused AUD 5 million in damage (1956 dollars) through bridge and crop destruction. (Source: NSW State Archives, 1956 Flood Commission Report)

2012 Floods

January 2012 floods saw Burrinjuck Dam spill for the first time in a decade. Wagga Wagga's Murrumbidgee reached a peak of 9.2 meters, flooding 500 properties and shutting the Hume Highway. Over AUD 100 million damage led to the upgrade of levees and warning systems. (Source: Riverina Water County Council, 2012 Post-Flood Review)

Monitoring these events informs floodplain zoning and water allocation, critical as climate change amplifies extremes.

3. Recording River Flows in Wagga Wagga: How?

Traditional Methods

Surface Drift Buoy Method

Wooden planks with flags previously marked surface speed. Aboard bridges, their 100-meter journey took 5–10 minutes to time. It only measured surface flow (is usually 20% higher than the subsurface current) and was not applicable under wind or high flow.

Current Meter on Cableway

It was mounted on Wagga Wagga's Gobbagombalin Bridge, with a cableway spanning the river and dropping a mechanical current meter to measure velocities at 1-meter intervals. Vertical profiles were thus supplied but at 4 hours per survey, which made only monthly snapshots of data. Replaced in 2005 by ADCPs due to maintenance costs.

ADCP Introduction

Acoustic Doppler Current Profilers (ADCPs) transformed monitoring. ADCPs on bridges or boats use sound waves to measure velocity at 50+ depths at once. A whole river cross-section survey takes only 45 minutes, capturing flow fluctuations lost to traditional techniques. Riverina Water runs ADCPs every two weeks, with additional surveys during floods to refresh levee operation.

4. How Does ADCP Work Based on the Doppler Principle?

ADCPs emit 300–1200 kHz sound pulses that rebound off sediment particles. Doppler effect frequency changes (shifts) indicate speed: higher frequency indicates particles are approaching, lower frequency indicates particles are receding. Four transducers calculate 3D flow with river width/depth readings to determine discharge. In Wagga Wagga, it quantifies flood volumes and irrigation releases, allocating water equitably.

5. Requirements for High-Quality Measurements

Equipment Needs

• Durable: Titanium components resist the Murrumbidgee's variable water chemistry.
• Portable: 2–10 kg sensors are deployed from small boats into shallow sections close to the riverbank.

6. How to Choose the Appropriate Equipment?

Deployment Method

• Boat-Mounted ADCP: Used by Riverina Water on a monthly discharge survey, mapping flow along the river to identify erosion hotspots.
• Fixed ADCP: Installed over the Hume Highway bridge, providing 15-minute interval data for flood warnings and irrigation control.
• Cableway ADCP: Retrofitted over the cableway of the Gobbagombalin Bridge, measuring flows safely under high water without the use of a boat.

Working Frequency

• 600 kHz ADCP: Appropriate for normal flows, high resolution to identify gravel bar impacts on flow.
• 300 kHz ADCP: Deployed during flood events, sufficient range to determine whole water column velocities.

Brand Recommendations

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Here is a table with some well known ADCP instrument brands and models.