Nonpoint source urban stormwater runoff degrades aquatic ecosystems, and causes flooding. To mitigate its effects on natural and human environments best management practices (BMPs) became popular strategies to protect the integrity of water quality. Similarly, to mitigate the effects of stormwater quantity, detention basins (DBs) were put into place as flood control structures. Water quality control remains an unexplored and important aspect of DB utility, particularly, in arid regions. Since DBs are depressions in the earth and retain water over the course of several hours to days after a rain event, they can potentially act as BMPs. A key pollutant that DBs serve to settle out is Phosphorus (P). This study examines P concentration, and its relationship to particle size of flooded and dry sediment microcosms obtained from pre and post-rain samples of six DBs located in Clark County, Nevada (NV). DBs were allotted a land use classification (high, mid, or low development) to determine if there was a correlation between P soil concentration and surrounding land use. The results from this study indicate that: (1) overall post rain sediment samples have higher P than pre rain samples and that outside vs. inside sediment P concentrations are variable based on the individual DB, (2) majority of the particulate sediment P comes from DBs in low developed areas while majority of the dissolved P comes from DBs in mid to high developed regions, (3) there was a correlation between particle size and sediment P concentration, with finer particles having higher P concentration than larger particles, and (4) a correlation between particle settling rate was found which, therefore, affects P accumulation within a DB. As management recommendations, installation of berms, conversation to a two stage formation and changes in riser/outlet structure are suggested for certain DBs. This research establishes a guideline for DB and BMP related research in arid regions, especially since these areas are characterized with infrequent rain events; making it difficult to monitor infrastructural water quality outcomes. Further research implications include a need to study BMP and DB inflow and outflow water pollution concentrations and a comparison between sediment nutrient concentrations of DBs with constructed wetland sediment concentrations as a control.