What typically causes an increase in runoff velocity after development?

The increase in runoff velocity after development is primarily attributed to the creation of impervious surfaces such as parking lots and roads. These surfaces do not allow water to infiltrate into the ground, which increases the volume of water that runs off. When natural landscapes are converted into developed areas, the ground becomes less permeable, leading to a reduction in interception, evaporation, and infiltration of rainfall. This enhanced runoff can lead to more significant and faster flows into drainage systems, potentially causing flooding and erosion.

In contrast to this, the removal of trees and shrubs can contribute to increased runoff, but it's primarily the transformation of land into paved surfaces that directly alters the hydrology on a larger scale. Similarly, installing stormwater basins is a management practice designed to mitigate runoff, rather than exacerbate it. Natural landscape preservation, while beneficial for maintaining water balance, does not lead to increased runoff velocity. Thus, the direct correlation between the addition of impervious surfaces and the increased runoff velocity makes the second choice the most accurate.