context: The city is roughly bisected by the North Canadian River (recently renamed the Oklahoma River inside city limits). The North Canadian once had sufficient flow to flood every year, wreaking destruction on surrounding areas, including the central business district and the original Oklahoma City Zoo. In the 1940s, a dam was built on the river to manage the flood control and reduced its level. In the 1990s, as part of the citywide revitalization project known as MAPS, the city built a series of low-water dams, returning water to the portion of the river flowing near downtown. The city has three large lakes: Lake Hefner and Lake Overholser, in the northwestern quarter of the city; and the largest, Lake Stanley Draper, in the sparsely populated far southeast portion of the city.
question: డౌన్టౌన్ సమీపంలో ఉన్న నదికి నీటిని తిరిగి ఇవ్వడానికి సహాయపడటానికి 1990లలో ఏమి నిర్మించబడింది?
answers: low-water dams