Chapter 7: Human Alterations to Riparian Areas
Urbanization
- As the population of Arizona increases, so will urban areas.
Figure 7.14. Homes, buildings, roads, sidewalks and parking lots in Tucson have increased the area of impervious surfaces of its watersheds (left). Newly developing housing in Arizona right along a stream (right).
- Urbanization increases the impervious surfaces of a watershed.
- These impervious surfaces consist of:
- homes,
- buildings,
- roads,
- sidewalks, and
- parking lots.
- Impervious surfaces eliminate infiltration.
- Most precipitation becomes overland flow.
- Overland flow is also enhanced by:
- gutters,
- culverts,
- stormwater sewers, and
- lined channels.
- Higher overland flow leads to more frequent and higher discharge volumes and flooding events that accelerate stream incision and bank erosion and riparian habitat degradation.
Figure 7.15. As impervious surface increases in urban areas so does runoff (graph left). The increase in runoff leads to increase stream discharge (graph right). The graphic presentation of stream discharge through time is called a hydrograph.
- Less infiltration decreases groundwater recharge, groundwater contributions to the stream, and eventually decreases stream base flow.
- Streams can also have increased loading of nutrients, bacteria, oils, grease, salts, heavy metals, and other toxics from overland flow on the impervious surfaces that will lead to degraded water quality and riparian habitat.
- The actual impacts of urbanization will depend on the types of the development
- Urban areas that are more lightly developed, that have parks, trails, ball fields, grassed or cobble waterways, etc. and also maintain large functional riparian areas will have significantly less negative impacts.
- These basins have been effective in reducing, but not eliminating increased peak flows associated with urbanization.
- This type of urban development will not only mitigate negative impacts on riparian areas but also enhance the appeal and marketability of the urban developments.
- Protection of riparian areas is more difficult in already developed urban areas that have had traditional planning.
