Civil engineers design them, landscape architects loath them, developers wonder why we need them and municipal engineers often require them - I hate them. Retention and Detention ponds have become the standard for stormwater management on commercial and residential projects throughout most of the US. They were originally intended for flood control and were later incorporated into water quality requirements as well. They serve in their capacity to attenuate peak flows from new development reasonably well, but their usefulness stops there. Here are a few of the reasons that I'm not a fan of detention/retention ponds:

Reservoirs are used for storing a supply of usable fresh water. They are most commonly created by damming a natural surface water tributary in an existing basin, but they can be artificially constructed as well.  Water stored in reservoirs can have various functions, including serving as a source of potable water, irrigation, recreation and hydroelectric power.  Reservoirs are designed and evaluated based on their storage capacity, which is commonly measured in acre-feet.  Changes in reservoir storage capacity over a given time period are defined by an assessment of inputs and outputs.  Inputs include tributary inflow, precipitation, and water from groundwater flow nets.  Outputs are made up of draw-downs for irrigation and potable water, regulated flow to release excess storage or provide turbine power, and losses due to evaporation and seepage.  Reservoir (and pond) covers and liners are sometimes used on a smaller scale project to prevent losses from surface evaporation and seepage into the containment basin.  Subsurface water stored in soils as groundwater or in aquifers is a variation of the reservoir concept.