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The Australia Letter<\/em><\/a> is a weekly newsletter from our Australia bureau. <\/em>Sign up<\/em><\/a> to get it by email.<\/em><\/p>\n Whenever there\u2019s rain in the forecast for the desert town of Mparntwe, otherwise known as Alice Springs, the same question usually surfaces: \u201cDo you think the Todd will flow?\u201d<\/p>\n This week, the answer was yes. The normally dry Todd River swelled with water on the back of a week\u2019s worth of rain that dropped 184 mm (about 7.2 inches) from the skies after months of unrelenting heat, according to the Bureau of Meteorology<\/a>. The rain picked up piles of debris, washed out roads and turned the usually pastel red-yellow landscape of the area in central Australia into a rich tapestry of brown-green.<\/p>\n Local officials issued severe flood warnings, but in a region usually defined by arid heat, people were excited \u2014 even more so when the water started to rise. People swarmed the Todd\u2019s banks, reveling in the majestic sight of a river in motion.<\/p>\n It\u2019s something people in this part of the world get to see only a few times a year. Although the land is never completely dry \u2014 a rich groundwater table makes itself known through the rows of mature river red gum trees<\/a> that line the banks \u2014 aboveground flows of any significance are contingent on big rain.<\/p>\n<\/div>\n<\/div>\n John Wischusen, a hydrogeologist based in Alice Springs, said that the usual formula for determining whether the Todd would flow was 40 millimeters of rain at a rate of 50 millimeters per hour. That\u2019s a heavy downpour typical of a summer thunderstorm, but he added that consecutive days of wet weather at a lower intensity also would (and this week, did) tip the scales.<\/p>\n \u201cIt\u2019s like a roof and a water tank,\u201d said Mr. Wischusen, explaining how the high concentration of Precambrian rocks (including gneiss and granite) in and around Alice Springs encouraged water runoff. \u201cBut the ground underneath has to be wet up to a certain level before it can flow past. That\u2019s why you need a certain amount of rain and or intensity to get water to flow over the ground and into the river channels and through town.\u201d<\/p>\n As it travels, the water recharges the landscape. Animals that previously kept a low profile suddenly show up. \u201cYou\u2019ll hear all the frogs that have been dormant in the soil for a year come out and start chirping,\u201d Mr. Wischusen said. Valleys transform into water holes, and groundwater storage systems replenish their stocks.<\/p>\n The water corridors are not what they once where \u2014 urbanization, invasive weeds and pollution have transformed the landscape \u2014 yet the river ecosystem is healed, nurtured and powered by these annual flows.<\/p>\n \u201cThose big buildings built along the banks of the Todd are pretty hard on the eyes. But after a few flows, you notice they suddenly disappear, swallowed up by the growth of river red gums,\u201d said Peter Renehan, a Central Arrernte man who leads the Centre for Appropriate Technology, a science and technology hub based in Alice Springs. \u201cFor us, that\u2019s country doing its work.\u201d<\/p>\n<\/div>\n<\/div>\n For many years, Mr. Renehan has spearheaded programs and working groups trying to rejuvenate the damaged riverbed. He pointed out trash (from small plastic wrappers to full-fledged mattresses) floating downstream because of illegal campers, gutters that drain too quickly for the river to properly absorb, and the masses of invasive Buffel grass choking the corridors. Unlike native plants, these weeds encircle the bases of old native river gums, thwarting their capacity to serve as a frontline defense against deadly fires, and making it harder for the water to move as it should.<\/p>\n \u201cWe really want to be able to shine a light on the water systems within the town to actually show how beautiful it could be and how it used to be,\u201d Mr. Renehan said, adding that the way the town breathes when the river runs is exactly why it warrants time, resources and sustained investment.<\/p>\n \u201cAll the negativity around the town just drops away as everyone comes together to view the river.\u201d<\/p>\n There has been a lot of negativity for the town recently, a place noted by national media and politicians as a hotbed for youth crime.<\/a> This week, the Northern Territory Chief Minister declared a state of emergency for Alice Springs, ordering a youth curfew<\/a> and \u2014 along with other officials \u2014 calling on the federal government to send the Australian Federal Police to help ensure safety.<\/p>\n