Special Site Conditions

Instability All sloped ground has an unsteady feeling to it for several reasons. First, it is difficult to get stable footing on sloped ground. A person must exert continual en­ergy to stay put in any given location because there is a constant feeling of being pulled downhill. While standing on sloped ground, one foot is invariably higher than the other (Figure 13—16). This is also true for buildings and other structures placed on a sloped site. They, too, must be designed to get “stable footing” by creating level ter­races for their location or by special structural systems that connect them to the sloped ground. In either situation, extra time and money must often be spent to over­come the inherent instability of a sloped site.

The instability of a sloped site is also a visual one. When compared with a level or horizontal plane, a sloped plane visually implies potential movement, action, or change. The eye is invited to move along a sloped plane rather than resting as it is able to do in a level surface. This can be exciting in some cases, but disconcerting in others.

Downhill Orientation Both objects and views on a sloped site have a tendency to move downhill. It is obvious that any mobile object that is placed on sloped ground will likely move downhill. Water, soil, stones, debris, and so forth all gravitate down

the slope over time. Even people usually find it easier to walk down a slope than up one. In addition, the visual orientation for people on a slope is also toward the lower slope. People readily see objects or areas of the landscape located at the bottom of a slope very much like they do in an outdoor amphitheater (Figure 13—17). On steep sites, the orientation is very likely to be away from the site toward some distant area of the landscape. Steeply sloped sites located in areas of distinct topography are fre­quently valued for the views they afford.

Drainage Surface drainage is a constant issue on a sloped site. Unless the house is located on the crest of a hill, it is quite likely that some portion of a sloped site will drain toward the house (Figure 13—18). As discussed in Chapter 11, it is necessary to

Figure 13-19

A slope analysisidentifies different categories of slope steepness on a site.

regrade the uphill area of the site to divert the surface drainage around the house. If not handled correctly, some walls and floor areas of the house may get wet, causing vi­sual and structural damage. Drainage becomes more problematic as the degree of steepness increases. Steeper slopes have a greater amount of surface water moving across them at faster velocities than do more gentle slopes or level ground. Therefore, there is more water to drain away on steeper slopes. The likelihood of erosion in­creases as well on steeper slopes because exposed soil is easily washed downhill by a greater volume of surface water draining at a faster velocity.