From Colorado State University (Aditi S. Bhaskar):
The following discusses work presented in a journal article by Fillo, Bhaskar, and Jefferson (2021), published in Water Resources Research.
Excess lawn irrigation may contribute to flow in urban streams when more water is applied than plants can use or when sidewalks or driveways receive water from mis-aimed sprinklers. We have applied a new approach to estimating how much flow in streams originally came from excess lawn irrigation by using a tracer that is different between tap water in the Denver, Colorado USA area and local rain. We applied this approach to 13 urban streams and 2 grassland streams in 2019 in the Denver area. We found that, on the dry weather days analyzed, over 65% of flow in urban streams was from tap water, and lawn irrigation was a larger source of water in the streams than leaking water pipes. We also found that grassland streams in the region have less streamflow than urban streams, and are generally dry for part or most of the year whereas urban streams generally flow all year. Lawn irrigation and leaking water pipes contributing to changes in streamflow from part of the year to all year round would be expected to lead to dramatic changes in water quality, bank stability, stream ecosystems, and water yield to downstream rivers. This work gives a new way to analyze how much flow is coming from different sources in urban areas that could be applied to other semi-arid regions. Further work in Denver is looking at applying the same tracer for a longer period looking at how contributions to baseflow change seasonally and from wet years to dry years.