Explain three factors that may produce a short time lag on a storm hydrograph.

Compare the effectiveness of alternative stream management strategies, other than dams.

A short time lag is usually associated with overland flow linked with any of the following factors:

• the characteristics of the precipitation input (type and duration of precipitation, speed of snow melt, antecedent rainfall)
• the shape and size of the drainage basin (including tributaries / drainage network)
• characteristics of the drainage basin (land use, gradient, geology, vegetation, urbanization).

For example: Short lag time is caused by an unvegetated drainage basin [1] in which surface runoff is accelerated/interception does not occur [1]. Also linked with impermeable clay soil [1] and the lack of infiltration [1]. Also linked with drainage basins that are round [1] because all water reaches the measuring point at roughly the same time [1].

There are many alternative strategies that could be examined. For example, building of dykes/flood barriers or artificial levees, channel management (straightening, deepening, widening), flood relief channels/basins, river/wetland restoration.

Land uses strategies are acceptable if they are purposely designed to manage streams. Do not credit indirect/unplanned impacts of urbanization, deforestation, etc.

Good answers may focus on, and compare, the effectiveness of strategies (may look at different perspectives, user groups). Another approach might be to compare the effectiveness at different spatial/temporal scales.

At band D, expect a description of one or more stream management strategies.

At band E, expect either a more detailed explanation of two or more different strategies or a structured comparison of their effectiveness (costs, benefits and perspectives on these).

At band F, expect both of these elements.

Marks should be allocated according to the markbands.