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sources, such as transbasin diversions, add water to the system. Development of other sources, such as native flows, decrease river flows. The Colorado program looks at six basic sources of water supply that will be developed to serve new population: • Native South Platte Flows (Surface and Underground). Generally, new development of South Platte flows will be in wet years during portions of the spring runoff, and will involve surface or underground storage. Development of this source will deplete the river when water is stored, and add water to the river from return flows after use. • Transmountain Diversions. Return flows from Colorado River Basin imports enhance South Platte River flows. • Non - tributary Groundwater. Large amounts of water are withdrawn from the Arapahoe and Larimie -Fox Hills" formations of the Denver Basin aquifer. Return flows enhance South Platte River flows. • Conservation. Conservation will become increasingly important to Front Range municipal water providers. However, conservation will have no net effect on downstream river flows. • Wastewater Exchange and Reuse. Water providers who develop non - tributary groundwater and transbasin water supplies have the right to reuse that water under Colorado law. Although as a practical matter these water providers will never put this water to 100% consumptive use, reuse and exchange programs will deplete river flows. • Changes in Use. As urban demands increase, agricultural land will be taken out of production and irrigation rights transferred to domestic use. Under Colorado law, such changes can be made only if no injury to downstream water rights will result. Generally, the change in use from irrigation to municipal leaves some additional water in the river. The Colorado program makes assumptions where new population will locate in the Front Range. The program then looks at the sources of water that will likely be developed by major water providers to serve that new population, imposes transit loss factors, and predicts how the development of those sources of supply will, in the aggregate, affect South Platte River flows at the state line. As new people move to the Front Range, South Platte flows will increase in the fall, winter and spring, and decrease in the summer. To mitigate this effect, Colorado will implement new water regulation projects, like the Tamarack project, to shift river flows back to the summer period. The size of these projects will be calculated. based on new population increases in the Front Range. On an order of magnitude, about 1,800 acre-feet 11