Ingreso a México

Hillside retention and erosion control are two key issues in slope landscaping. There are two factors, which are partly driven by aesthetics, partly by cost considerations and influenced by steepness. If slope is left natural, plant selection is doubly important. Shallow-rooted plants on a hillside are of less importance on slopes than deeply rooted plants. They help to retain the hill and avoid erosion. Perennials that have deep root systems and well-rooted grasses and small and medium shrubs  perform this function well.

Erosion has always been a problem for hillside. Each slope demands a slightly different approach to erosion control techniques. Cut slopes are more prone to surface erosion problems. Fill slopes experience surface erosion too, but are also prone to subsurface problems that result from incomplete compaction prior to construction. Worst case is so much underground moisture contributes to liquefaction that destabilizes the earth.

How the slopes are treated matters because there's always potential for erosion. Every raindrop that falls on bare soil dislodges soil particles. As it gathers and runs down the slope, more soil particles are picked up. Every particle lost in the water has to go somewhere. They will settle out when the runoff slows, and in these spots silt builds up. It is a huge problem when silt deposits interfere with driveway stability of other structures. It becomes a community issue when it clogs neighborhood drainage structures and storm drains. (Gilmer, Landscaping Network)

4.4.1. Factors responsible for Erosion Control

There are many factors which are responsible for erosion control out of which angle of repose and soil types are most important:

4.4.1.1. An gle of r epose

The angle of repose of a soil is the gradient of the slope at which the soil settles naturally. A firm soil will have a steeper angle of repose than a loose soil. The angle of repose can range from 0° to 90°. Smooth, rounded sand grains cannot be piled as steeply as can rough, interlocking sands. The steeper the slope, the faster water runs off, which creates challenges getting enough moisture to every plant.

2:1 - This is the steepest incline capable of supporting plants. Sometimes these slopes will require retaining walls due to the great amount of siltation they produce.

3:1 - This is the steepest incline allowed for a lawn due to the limitations of lawn mowers.

4:1 - This is a more ideal slope which can be easily planted, and irrigation water is more likely to soak in.

4.4.1.2. Soil T ype

Most fill slopes have no difficulty with soil types, but on cut slopes it can be a real challenge. This not only influences how much time it takes to dig a planting hole or trench for irrigation, it greatly affects the speed at which water penetrates the ground. Low fertility makes it tough for young plants to become established. Very dense soil resists moisture absorption unless it is applied at a very slow rate. Irregular soils with

fail to hold together once disturbed, leading to future erosion problems, particularly in sandstone and shale. (Gilmer, Landscaping Network)

4.4.2. How Plants Control Erosion

Plants are natural protectors of soil. They cloak the ground in foliage which prevents rain drops from falling directly onto soil particles. Instead, the plants diffuse the energy of raindrops so they filter down to the soil surface more gently. Plant roots help to bind soils underground. Those species with a large proportion of fine roots that spread over a large area prove the best choices for slope stabilization.

The nature of how a plant roots as well as its growth habit dictate its value as erosion control plants.

The planting should be a mix of groundcover, shrubs, trees, and perennials with the areas between plants covered with mulch or boulders. A mix of plants and vegetation layers ensure that when it rains, the force of the water hitting the ground is deflected. In most cases, if the slope soil is deeper, a mix of deep-rooted plants like  bougainvillea and shallow-rooted plants like monkey flowers or sagebrush are needed to secure the top soil to the bottom rock. Groundcover best prevents the surface erosion. English ivy is a good example of how many plants installed into the slope will bind the surface tightly and cover it all with dense foliage. This planting strategy must be irrigated with broadcast sprinklers. Creeping shrub, like prostrate rosemary has just one stem that spreads out in every direction with a carpet of foliage. That coverage slows the raindrop energy too. Shrubs are watered only at the t runk, which is  better suited to drip or bubbler irrigation for water conservation.

Hydroseeding is a method of sowing seed on a large scale for immediate coverage. It is often required at the completion of a project to provide soil holding capacity until other plants mature. This quick-cover reduces the problem of sediment and runoff the first rainy season after completion. It is common to plant the slope with container grown shrubs and groundcovers, then spray the hydroseed right over the top of them for both short and long term solutions.

A local contractor is the best resource for solving erosion control issues for residential  building sites. Knowledge of local soils, rainfall and plants that thrive in the microclimate as well as irrigation techniques aids in creating a palette of plants for the

slope. The best planting design solutions include a diversity of plants. (Gilmer, Landscaping Network)

4.4.3. Geotextiles for Erosion Control

 Newly graded slopes are vulnerable before and after planting. Erosion control plants take time to become established and fill in both above and below ground. Until this happens the slopes will be temporarily exposed to erosion. For that time, geotextiles should be used, which are man-made materials, laid on the earth and pinned into  place. Because they are biodegradable, landscaping can be done right through it knowing that by the time plants fill in the fabric will decompose and eventually disappear. Following are the different types of geotextiles:

Burlap: Used for immediate erosion control on very steep slopes prone to disintegration.

Jute mesh: Large square jute mesh is the standard for landscaping because it is easily  planted through the grids.

Coir mat: A byproduct of coconut processing. Coir has great water holding capacity and resists decomposition for more long term use. (Gilmer, Landscaping Network)

4.5. Conclusion

Slopes offer a great challenge than flat ground when it comes to landscaping. Planning a garden with slopes will surely be a challenge, but changes of level certainly give any garden added interest, and add an extra aspect to sloping landform design. Factors to be considered while planning a landscape on slope include drainage, soil, access and maintenance, rainwater and runoff management, irrigation and other issues. Whether it is a natural undisturbed slope or one composed of cut- and-fill, there are five essential principles that should be taken care of while designing on slopes.

Different ways of landscaping is also discussed in this chapter which includes terracing, tiering, change in levels and rock landscaping. Hillside retention and erosion control are two key issues in slope landscaping which is also taken into consideration.

CHAPTER-5.

CASE STUDIES OF DIFFERENT BUILDINGS

ON SLOPING SITES

Buildings on sloping sites have different architectural and structural considerations. Case study of different residential buildings makes better understanding about the incorporation of contours into the building design, architectural features, and effective structural systems.

5.1. Car park house, Los Angeles

This modern house on stilts has one level floor plan with flat roof at street level as a carport and deck terrace space (see  Figure 5.1). Skylights element also installed on the roof for better lighting inside this rectangular modern house on stilts. Floating structure used for efficiency because of difficult terrain topography and create single access for the house. (ArchInspire)

From street to this house a bridge is built. This modern house on stilts plan accommodate single space for living-kitchen-dining (kitchen area placed in the center of interior), three bedrooms, two bathrooms, laundry area and balcony spaces. The exterior of this modern house on stilts is gray compare to its whiteness interior design. Although there are glass walls installed along side of balconies area, skylights installation still needed to make sure natural light intensity inside this modern house on stilts.