This can effect the shape of a river's hydrograph. Rivers that have a high drainage density will often have a more 'flashy' hydrograph with a steep falling limb. High densities can also cause a greater flood risk.
New Environmental Water Research Study Findings Recently Were Reported by Researchers at University of Connecticut
Jan 13, 2012; "The literature contains contradictory conclusions regarding the relative effects of urbanization on peak flood flows due to...