Floods can be devastatingand 2007 was a year that saw floodwaters wreak havoc around the world. From the destruction rose at least one positive outcome – unprecedented volumes of data on velocity and level that will help planners in flood-prone areas deal with future deluges.

Massive Malaysian Flood
The residents of Kuala Lumpur (Malaysia) are no strangers to floods, which rush out of the nearby mountains via the Klang, Ampang, Gombak, Keroh, Bunus and Batu Rivers and meet in the concrete metropolis that spreads around their confluences. On 10 June 2007, the city was inundated for hours as the rivers – which together normally flow at approximately 15 cubic metres per second – surged to 360 cubic metres per second at their confluence just west of downtown. The Klang River peaked at over a metre above its banks and flooded the city.

It was a vivid illustration of why the Malaysian government was so eager to complete construction of the revolutionary Stormwater Management and Road Tunnel (SMART) Project, a basin-and-tunnel system designed to capture, store and move up to 4 million cubic metres of water away from downtown Kuala Lumpur.

Huge Project Demands Data
What captivates many people about the SMART Project is the tunnel itself. Just under 12 metres in diameter and approximately 12km long, the tunnel is designed to serve as a massive underground storage vessel and floodwater pipeline when capture basins at ground level threaten to fill. In full flood-protection mode, the tunnel stores water, then transports it to the Kerayong River downstream of the city to safely drain it. For the majority of the time, however, a 3km section of the tunnel offers an alternative motorway for drivers seeking to avoid Kuala Lumpur’s traffic-choked downtown. When floods are imminent, the tunnel is evacuated and traffic is re-routed.

Forecasting those conditions and tracking floodwaters makes the SMART Project’s flood detection system, designed by Greenspan Technology Pty Ltd, vital. Accurate and timely water level, velocity and flow data are vital to the operation of the tunnel, the protection of the city and the safety of thousands of drivers.

Close Watch
To maintain a close watch on conditions throughout the system, Greenspan deployed 22 rain gauges, 50 pressure sensors coupled to gas-bubble systems to gather water level data, and 16 SonTek Argonaut acoustic Doppler current meters to offer real-time water level and velocity data. The Argonauts are positioned at specific heights to be ready for high-flow situations, the result of exacting research beforehand to predict conditions in the system and channel surveying that includes 80,000-point cross-sections for every measurement site.

Avoiding Hysteresis Effects
Floods in Kuala Lumpur are strongly impacted by tidal action just a few kilometres downstream, where the Klang meets the sea. As river levels rise and the backwater effect gains in importance, the Greenspan model shifts over from the level data from the pressure gauges to the water level and velocity information flowing from the Doppler units. The Argonauts use acoustic beams to measure the actual water level and velocity of real parcels of water, rather than relying on the calculated depth:discharge relationships that pressure sensors are calibrated to assume. The result is reliable data in spite of hysteresis or backwater effects.

Keeping Connected
To keep the data flowing as floodwaters surge, each Argonaut outputs the data to Greenspan’s models and Supervisory Control And Data Acquisition (SCADA) system. Some stations are connected by ethernet and report every minute; others, connected by high-speed VHF link, broadcast their data at 5- to 10-minute intervals. At the control centre, a team views the data as they are integrated with rainfall information and run through proprietary discharge and velocity models.

Better Understanding
Data from the SMART project are also helping scientists and officials better understand the local river system. For instance, analysing readings from the system’s safeguard sensors illustrated that, after a flood event, the Klang stores a surprising amount of water in its groundwater table and releases it over a longer period of time than originally assumed. That sort of insight will help fine-tune management of the tunnel and the floodwaters itcaptures.

Replacing Under-recorded Data
Just 16 days after Kuala Lumpur was flooded – and halfway around the world – the British Midlands experienced some of the worst summer flooding in 150 years. The River Derwent peaked at more than 257 cubic metres per second, well above the previously recorded high of 167 cubic metres per second.

That extraordinary flow was dramatically underestimated using a traditional moving boat measurement method. In fact, the moving boat method estimated flow at approximately 90 cubic metres per second – an under-recording of 65%. Such a dramatic underestimate could have devastating effects on cities and farms downstream.

Moving Bottom Creates Challenges
The low estimate was caused by the dramatic re-suspension of the riverbed during the flood. The movement of bed sediments can confuse the readings taken with the moving boat method, significantly lowering the calculated flow. To get a more accurate reading, hydrologists used a SonTek RiverCat, a catamaran-mounted Doppler profiling system, deployed from a bridge on a fixed length of rope. Its stationary measurement system software was able to account for both the highly turbid conditions near the bottom, as well as the movement of the water column. The experiment provided important data to British hydrologists for a once-in-a-lifetime flood event and demonstrated an accurate method of collecting reliable flow and velocity data over fast-moving bottoms – or where bottoms are weedy or water is highly turbid.

Big River, Big Challenges
Measuring water level and velocity in a river system is really put to the test in the US’s Lower Mississippi River, the main artery of the nation’s inland shipping network. Though storm surges from Hurricanes Katrina and Rita in 2005 made world news, a flood in the same region in May 2007 garnered relatively little media coverage. However, the 2007 flood illustrated the day-to-day challenges of maintaining the safe flow of shipping on one of the world’s busiest waterways.
Towboats on the Lower Mississippi commonly push 30 barges at a time, a half-mile-long string of cargo vessels with no brakes. Water level and velocity are matters of life or death on the river, which is one reason that the data collected by the US Geological Survey (USGS) is carefully scrutinised by river traffic managers. Though USGS hydrologists use the data to track discharge, towboat captains use it to gauge horsepower needs and plan their approach to tricky stretches of the river.

Long Reach
USGS’s Baton Rouge discharge team has three side-looking Argonauts on the Mississippi/Atchafalaya system near Baton Rouge and plans to set two more in the Old River and Red River to monitor discharge from those key tributaries. The acoustic sampling beams reach 100 metres or more to the centre of the channel, providing users with data that were impossible to obtain with electromagnetic point velocimeters.

The acoustic Doppler current meters can find the bottom themselves, allowing researchers and traffic dispatchers to see true flow data in widely varying conditions – and recognise the significant differences in channel depth – across the river. They also can be programmed to block out interference from bridges or other structures to which they are mounted.

Tidal Action
The other large influence in the Lower Mississippi is tidal action from the Gulf of Mexico downstream. Similarly to hydrology teams in Kuala Lumpur, hydrologists in the Lower Mississippi cannot rely on a water level/discharge method to estimate flow.

Prepare for Next Season
Whether it is along the Mississippi, under a medieval bridge in England, or beneath the ultra-modern streets of downtown Kuala Lumpur, acoustic Doppler technology has proved itself under the worst that Mother Nature could deliver in 2007 – and helped people, from towboat captains to civic leaders, prepare for the next season of flooding.