Such studies may be carried out through Survey of India or local survey teams, and by reference to the Central Water Commission and the concerned department of Gujarat State.
3.1. Land Use Zoning for Flood Safety
Some important considerations for regulating the land use in the planning areas are given below :
i. Every settlement needs some open areas such as parks, play-grounds gardens etc. In one way it will be possible to develop such areas by restricting any building activity in vulnerable areas. Such a development will be in the interest of providing proper environment for the growth of such settlement.
ii. On the same analogy, certain areas on either side of the existing and proposed drains (including rural drains) should be declared as green belts where no building or other activity should be allowed. This will not only facilitate improvements of these drains in future for taking discharge on account of growing urbanisation, but will also help in minimising the damage due to drainage congestion wherever rainfall of higher frequency than designed is experienced . These green belts at suitable locations can also be developed as parks and gardens.
iii. In the existing developed areas, possibilities of protecting/relocation/ exchanging the sites of vital installation like electricity sub-station/power houses, telephone exchange etc. should be seriously examined, so that these are always safe from possible flood damage. Similarly, the pump station the tube wells meant for drinking water supply should be raised above the high flood levels.
iv. Similarly, possibility of removing or bypassing buildings/structures obstructing existing natural drainage lines should be seriously considered. In any case, with immediate effect unplanned growth can be restricted so that no construction obstructing natural drainage or resulting in increased flood hazard is allowed.
APPROACH FOR LAND USE ZONING
Following two alternatives can be adopted for dealing with the disaster risk problems.
a. Leaving the area unprotected. In this case it will be necessary to specify Land Use Zoning for various development purposes as recommended under Para 6.
b. Using protection methods for the areas as a whole or in the construction of buildings, structures and infrastructure facilities to cater for the hazard intensities likely in the planning area as recommended under Appendix-B.
it will be appropriate to prioritise buildings, structures and infrastructures in terms of their importance from the point of view of impact of damage on the socio-economic structure of the society. Prioritisation scheme is suggested under Para 5.
5. PRIORITISATION
In regard to Land Use Zoning, different types of buildings and utility services may be grouped under three priorities as indicated below.
Priority 1. Defence installation, industries, public utilities like hospitals, electricity installations, water supply, telephone exhange, aerodrums, railway stations, commercial centres, libraries, other buildings or installations with contents of high economic value.
Priority 2. Public institutions, Government offices, universities and residential areas.
Priority 3. Parks, play grounds, wood lands, gardens.
6. REGULATION FOR LAND USE ZONING
i. Installations and Buildings of Priorityl should be located in such a fashion that the area is above the level corresponding to a 100 year flood or the maximum observed flood levels whichever higher. Similarly they should also be above the levels corresponding to a 50 year rainfall flooding and the likely submersion due to drainage congestion.
ii. Buildings of Priority 2 should be located outside the 25 year flood or a 10 year rainfall contour, provided that the buildings if constructed between the 10 and 25 year contours should have either high plinth level above 25 year flood mark or constructed on columns or stilts, with ground area left for the unimportant uses.
iii. Activities of Priority 3 viz. play grounds, gardens and parks etc. can be located in areas vulnerable to frequent floods.
Appendix – B
PROTECTION OF BUILDINGS STRUCTURES AND INFRASTRUCTURES IN HAZARD PRONE AREAS
A. PROTECTION OF AREAS FROM EARTHQUAKES
i. In those areas where there are no dangers of soil liquefaction or settlements of landslides, all building structures and infrastructures should be designed using the relevant Indian Standards as provided in the Building Regulations and the National Building Code
ii. Soils subjected to liquefaction potential under earthquake shaking, can be improved by compaction to desired relative densities, so as to prevent the possibility of liquefaction.
iii. Buildings and structures could be founded on deep bearing piles going to non- liquefiable dense layers.
iv. Steep slopes can be made more stable by terracing and construction of retaining walls and breast walls, and by ensuring good drainage of water so that the saturation of the hill-slope is avoided.
v. Any other appropriate engineering intervention to save the building structures or infrastructure from the fury of the earthquake.
Note: The protective action given under (ii) to (v) will usually involve large amount of costs and should only be considered in the case of large and costly structures. For ordinary buildings the cost of improvement of the site will usually be uneconomical, hence bad sites should be excluded by Land Use Zoning.
B. PROTECTION FROM CYCLONIC WIND DAMAGE
i. Buildings, structures and infrastructures in the cyclone prone areas should be designed according to the Indian Standards and Guidelines as provided in the Regulations and the National Building Code.
ii. Light utility structures used for electrical transmission and distribution, and towers for communications, chimney stacks of industrial structures require special design considerations against teh cyclonic wind pressures, suctions and uplifts.
iii. In case the buildings, structures and infrastructures are founded on marine clay deposits it will be advisable to adopt either under-reamed piled foundations, or individual column footing with a reinforced concrete beam located at the level of the ground, or a continuous reinforced concrete strip footing.
iv. Wherever, the top soil could become slushy due to flooding, the top layer of 30 cm depth of soil should not be considered for providing lateral stability
v. In storm surge prone areas, it will be preferable to construct the community structures, like schools, cyclone shelters, etc. by raising the level of the ground protected by provision of retaining walls at sufficient distance away from the building, taken to such depth that no erosion takes place due to receding storm surge. Alternatively, construct the community structures on stilts with no masonry or bracing up to the probable maximum surge level.
PROTECTION OF AREAS FROM FLOODS
This may require one or more of the following actions.
i. Construction of embankments against the water spills from the source of flooding like rivers, large drain etc.
ii. Construction of high enough embankments/bund around the planning area.
iii. Raising the planning area above the high flood level.
iv. Construction/improvement of drainage paths to effectively drain the water from the planning area.
v. Construction of buildings and structures on deep foundations going below the depth of scour or on stilts with deep enough foundations under water.
vi. Flood proofing works such a» the following :
Providing Quick Drainage facility, consisting of
• Revitalisation of secondary and primary drainage channels after establishing the drainage blockage points;
• Provision of additional waterways;
• Clearing of clogged cross drainage works;
Providing Human and Animal Shelters for population living within embankments in the form of raised platform or use of available high ground.
vii. Anti-erosion actions in affected areas.
viii. Any other suitable measure.
Note:
1. Similar protection methods could be used against flooding caused in cyclone prone areas by high intesity rains or by the storm surge.
2. The concept of land zoning should be kept in mind for areas where protection works are taken up to decide inter-se priority for location of structures considering possibility of failure of protection works during extreme disaster events.