1. STORM WATER DRAINAGE

2. Precipitation on any ground finds its own way to run off to the point from where it can flow in line and continue to meet generally a larger water body which too often continues to drop into the oceans. This is in short the passage of the storm water flows which come as a result of precipitation on ground. RAIN FALL AND ITS FLOW ON GROUND

3. Obviously this is such a process which has its origin in the history of precipitation and run off pattern itself going back to the formation of grounds, and the buildups of which we would like to take care for smooth run off and drainage. NATURAL DRAINAGE SYSTEMS

4. In any urban area which has a sizeable age the drainage lines and drains of various descriptions must be present and running. These drainage lines and drains have often been disturbed, disrupted or even obstructed for one or the other man made, creations and causes or in some case even erosions, which could cause the change of passage or un required accumulation of water on a particular pocket of the area. AGE OLD DRAINS, NALAS, RIVULETS & PONDS

5. In fact it is this un-required accumulation of the precipitation and run off that could cause inundation of inhabited areas or those around such areas after causing flooding and disturbance to normal smooth healthy life. INUNDATION OF INHABITATED AREAS & FLOOD WATERS

6. It is this part of the accumulation of precipitation and run off which needs to be taken care of by the local body and the city management units, through renovation of the drainage structures & water bodies. UPDATION OF DRAINAGE SYSTEMS, & PREVENTION OF FLOODS

7. STORM WATER RUN OFF AND DRAINS Storm water flows as a result of the precipitation on ground and finds its own way to arrive at the point of natural mitigation with a larger body of water i.e. the river or lake etc which is often termed as the nearest point of disposal. In this way the drainage lines are always formed by natural flows and if unobstructed, erode natural grounds to form drainage lines and the drains. KATCHA DRAINS, PONDS, RIVULETS & LAKES

8. STORM WATER DRAINAGE AND THE MULTI DISCIPLINARY INTEGRAL APPROACH The problem of drainage can not have a single point approach by just making every drop reach the point of made up drains and so to flow to the ultimate point of disposal. It has to have the natural components which have hitherto fore been working to give relief from the floods ever since the creation of earth and the cycle of precipitation on it. MULTIPRONG MULTI DISCIPLINARY APPROACH

9. STORM WATER DRAINAGE AND THE MULTI DISCIPLINARY INTEGRAL APPROACH MULTIPRONG MULTI DISCIPLINARY COMPONENTS These components obviously are: Presence of plant life and grass area in the catchments. Natural ponds giving adequate relief from all climatic effects. Ground water flows and infiltration. Rain Water Harvesting.

10. IMPORTANT DRAINAGE STRUCTURES Infrastructural network of the drainage, especially, the storm water drainage consisting of the main drains which are very conspicuous and actually carry the ultimate flows to the rivers or generally the nearest water body which may further flow to the ultimate points of disposal, are often discernible and would generally require to be improved for sustainable development besides addition of some structures for giving relief to some low lying areas which are often the cause of nuisance. IMPROVED DRAINS & WATER CONSERVATION

11. PONDS, THEIR RETENTION, BEAUTIFICATION & MAINTENANCE Some ponds may also be seen within the municipal limits of the town. While it may appear to be unnecessary to hold these ponds in larger areas but with restricted sizes and modified shapes, the benefit of retaining some of these ponds may be studied in detail for further planning of this aspect for concerned areas. WATER CONSERVATION SYSTEMS

12. INTENSITY OF PRECIPITATION INTENSITY OF PRECIPITATION The intensity of rainfall decreases with duration. Analysis of the observed data on intensity duration of rainfall of past records over a period of years in the area is necessary to arrive at a fair estimate of intensity- duration-relationship for given frequencies. The longer the record available, the more dependable is the forecast. In Indian conditions, intensity of rainfall adopted in design is usually in the range of 12mm/hr to 20mm/hr, as given under article 3.3.1.3 of the Manual on Sewerage and Sewage Treatment.

13. TIME OF CONCENTRATION 4.7.5.1 Time of concentration (t c ): The time taken by the run-off from the farthest point on the periphery of the catchment (called the critical point) to reach the site of the culverts is called the “concentration time”. In considering the intensity of precipitation it was said that the shorter the duration considered the higher the intensity will be. Thus safety would seem to lie in designing for a high intensity corresponding to a very small interval of time. But this interval should not be shorter than the concentration time of the catchment under consideration, as otherwise the flow from distant parts of the catchment will not be able to reach the bridge in time to make its contribution in raising the peak discharge. Therefore, when examining a particular catchment, only the intensity corresponding to the duration equal to the concentration period (t c )of the catchment, needs to be considered. (As given under Guidelines for the Design of Small Bridges and Culverts)-Indian Roads Congress 2004 Continued--------

14. 4.7.5.2. Estimating the concentration time of a catchment (tc): The concentration time depends on (1) the distance from the critical point to the structure; and (2) the average velocity of flow. The slope, the roughness of the drainage channel and the depth of flow govern the later. Complicated formula exist for deriving the time of concentration from the characteristics of the catchment. For our purpose, however, the following relationship [11] will do. tc= 0.87 x L 3 H 0.385 Where t c = the concentration time in hours L= the distance from the critical point to the structure in km. H= the fall in level from the critical point to the structure in m. L and H can be found from the survey plans of the catchment area and tc calculated from Equation (4.9). The formulae and the methods of calculation shown here are ILLUSTRATIVE ONLY- applications should be based on site conditions & appropriate computation methods available. ---------- (4.9)

15. RAIN WATER HARVESTING It is most appropriate to include the rain water harvesting structures in drainage schemes to supplement the management, conservation & disposal of storm water. This will also reduce the cost of drainage while providing relief from the problem of flooding in congested areas where drainage from buildings can be fruitfully diverted for ground water recharging. Appropriate provision for rain water harvesting and recharging from some selected important institutional and government buildings having large roof top areas would give relief in drainage works.