The slope aspect analysis studies the direction of the slope facings.
Slope angle and orientation determines the climatic
conditions of an area. The word climate is in fact derived from the Greek
for slope. For example north-facing slopes have very different implications
for urban planning than south-facing slopes. In the plains water is a crucial
factor in selecting the site for a city. In the mountains the orientation
of the habitable valley is crucial. In choosing a north-south orientation
valley for Thimphu the founders understood the benefits of slope and orientation.
Within the valley there is a large variety of slope aspects, each having its
optimum function. Thus, slope aspect analysis helps in planning out which
function should go where.
The slope aspect analysis along with climatic data identifies the micro-climatic
zones of the valley. The most significant application of slope aspect is identifying
the best possible sites for residential and horticultural land uses. The south
and the south-west facing slopes are the most suitable for residential land
uses, since these slopes receive the maximum direct sunrays, especially during
the winter. The North-facing slopes receive the least sunrays and have relatively
low temperatures and are best suitable for the Blue Pine forests. Steep slopes
(20%–30%) with east to west aspect, in clockwise direction, and north-east
facing slopes, are most suitable for apple orchards.
Note: Please click the following links to view the
maps.
MAP
NO. 3.5 SLOPE ANALYSIS
MAP
NO. 3.5A SLOPE ANALYSIS
MAP
NO. 3.5B SLOPE ANALYSIS
MAP
NO. 3.5C SLOPE ANALYSIS
TABLE 3.2: Slope Analysis
| Sr. No. | Slope (%) | Slope Ratio (in Meters) |
Slope Range (in Percentage) |
Slope Range (in Degrees) |
Slope Classification | Areas with Predominant Slope Ranges | Area of Slope Ranges within TMC Boundary (in Sq.kms) | Characteristics and Significance | Land Use Suitability |
| 1 | 5 | 1:20( 1 meter vertical rise in 20meters horizontal distance) | 0 - 5% | 0 - 2.86 | Flat Terrains | Lower Babesa, Lower Simtokha, Land below(west of) the Lungtenphu - Simtokha road, Chang Jiji housing, Proposed FIFA grounds and the land on the opposite bank of the river, Changlimithang Grounds, Vegetable Market area, Chang Lam, Area around the Ministry of Trade and Industry, IMTRAT area, Dzong and its surrounding area, SARRC building area and the area near the foot bridge to Dzong, Cremation ground, Hejo, India House, Samteling, Jongshina, Some parts of Dechencholing and area near Pangri Zampa. | 4.93 (18.9%) | 1. These are the flattest terrain in this valley 2. Suitable for high-density residential areas, commercial land uses and sports grounds. 3. Best suitable for providing infrastructure facilities, especially roads. 4. Some of these lands are Lower River Terraces which are best ground water resources and also prone to floods. Development on these areas is not advisable. |
1. The lands under this classification of slope
are suitable for all land uses, but in Thimphu valley most of these slopes
occur near the banks of the river and they are the Lower River Terrace
which has to be protected. 2. Areas with 0 - 5% slope which are not Lower River Terraces can be used for high-density residential and commercial use. 3. The Lower River Terrace can be used for recreational open spaces and as sports grounds. |
| 2 | 10 | 1:10 (1meter vertical rise in10 meter horizontal distance) | 5 - 10% | 2.86 - 5.7 | Low / Gradual Slope | Lower Wangchutaba, Lungtenphu, Changzamtog local area, Changzamtog Lhakhang area, Changzamtog School area, Hospital area, RBP area, Changangkha area(below the Lhakhang),Lower Motithang, Upper Motithang, Golf course, Kawang Jangsa, Below Zilukha school, Langjophaka, Taba, North of Jongshina and Major parts of Dechencholing | 6.42 (24.65%) | 1. These slopes are best suitable for urban development,
and most of the existing developments are on these slopes. 2. Providing infrastructure facilities like roads and other networks is better compared to other, higher slope categories. 3. Since most of the existing urban settlements are on this slope category, development on these slopes can use the existing infrastructure. |
1. High-density residential land uses, commercial, recreational land uses, public Institutions and light Industries. |
| 3 | 20 | 1:5(1meter vertical rise in 5 meters horizontal distance) | 10 - 20% | 5.7 - 11.3 | Moderate Slope | Chang Gedaphu area, area above Memorial Chorten, foot hills of Changangkha area, Yangchenphug School area, foot hills of Zilukha area and foot hills of Jongshina area. | 5.32 (20.4%) | 1. Moderate slopes are also suitable for development,
but construction of roads and other infrastructure facilities will be
costlier than the lower slope ranges. 2. Development on these slopes will increase the surface runoff, which can be controlled by proper storm water networks and minimizing the ground coverage. |
1. Suitable for residential and public institutional land uses. |
| 4 | 30 | 1:3(1meter vertical rise in 3 meters horizontal distance) | 20 - 30% | 11.3 - 16.69 | Steep Slope | Upper Babesa(the land above(East of) the existing road), Upper Simtokha, The area above Simtokha -Lungtenphu road, Mountain slopes(existing forest) of Changzamtog, Forest Areas of Yangchenphug, Forest lands and settlement of Zilukha, Some slopes of Jongshina mountains and Forest areas above(West of) the RBG golf course. | 4.78 (18.3%) | 1. Construction of Buildings/ Roads involves more
damage to slopes, clearing of vegetation, thus inducing soil erosion,
increased surface runoff and disturbing the surface drainage. 2. The cost of construction and providing infrastructure is much higher. |
1. Suitable for medium- and low -density developments
like educational institutions, Diplomatic Enclave, farm houses etc. 2. These slopes are also suitable for orchards. |
| 5 | Above 30 (eg.45) | 1:2.2 (1 meter vertical rise in 2.2 meters horizontal distance) | above 30% | above 16.69 | Very Steep Slope | Some parts of the slopes above (west of) Changzamtog, Slopes above Chang Gedaphu area, Tandin Ney Lhakhang area, Slopes above (west of) Changangkha -Changzamtog road, Some parts of Zilukha Settlement, Slopes above (west of) the approach road to Dechenphodrang Lhakhang, Slopes of Dechenphodrang Lhakhang, Slopes south of Samteling water tank, Slopes south of Dechenphu Goempa and Some parts of Dechencholing forests. | 4.65 (17.8%) | 1. These slopes are not suitable for development
and are prone to soil erosion and landslides. 2. Development on these slopes involves cutting of slopes, clearing of vegetation thus damaging the slope characteristics, affecting the stability of the soil and slopes. This will cause soil erosion and increased surface runoff. |
1. The existing 30% and above slopes are within
forest areas. So it will be suitable to conserve the slopes and forests. 2. Areas which fall in this category of slope, with no forest cover and have established infrastructure facilities (roads, sewage network, water supply, storm water drain) can be permitted to have land uses like large scale institutions, eco resorts and farm houses. 3. These developments must get clearance from National Environment Commission. |
Issues:
1. Most potential slope ranges (0 - 5% and 5 - 10%) for urban development
in terms of densification and ease of providing infrastructure are occupied
by low density institutional land uses like India House, IMTRAT, RBP, RBA,
RBG, proposed diplomatic area and other institutions, which can be accommodated
in moderate and steep slopes (10 - 20% and 20 - 30%) or even out of the city
limits.
2. Development on very steep slopes (30% and above) should be restricted,
since development on these slopes will cause soil erosion, increase the surface
runoff and these slopes may be prone to landslides.
Slope Aspect
The slope aspect analysis determines the slope facing direction thus determining
the suitability of land use in relation to slope direction and sun angle.
1. The SOUTH and the SOUTH WEST facing slopes are the best suitable for residential
land uses, since these slopes receive the maximum direct sun rays during the
winter.
2. The EAST to WEST aspect in clockwise direction and NORTH EAST facing slopes
are best suitable for apple orchards.
3. NORTHERN aspects are suitable for Blue Pine forests since they do not require
direct sun rays.
MAP
NO. 3.6 ASPECT MAP (DIRECTION OF SLOPE FACING)(Click to view the map)