Delineation of spring watersheds must for Shimla

By: Meesha Tandon

I am an Architect Environmental PLanner and had undertaken a study on the Himalayan city of Shimla as a part of my dissertation at University of Leeds. The findings of that study showed a unique hydrological process which is in place in Himachal and is very less documented.

But putting it in very simple words, the findings of that study have empahsized that much of the summer water in the streams of Shimla is dependent on the survival of the springs in Shimla which flow through the cracks in the rocks and join the small streams to maintain flow in the rivers. This I am sure every Himachali would agree with. What you would also agree with is that these springs are being destroyed by uncontrolled urbanisation and construction.

This is my humble request to kindly raise a voice for the protection of these streams and the forests, which help in sustaining these streams. The Master PLan for Shimla is about to be released shortly and the delineation of spring watersheds must be included in this, otherwise it would become difficult to protect these springs from urbanisation because if you dont know where they are on the map you can’t ensure that nobody builds around them.

The authorities should be requested to delineate the watershed of the springs. I know that the delineation of watershed in rocks is difficult but atleast 500 metre around main springs has to be safeguarded as forests to ensure survival of the springs.

I am sure that residents of other Himachali cities would also agree with this as this phenomenon is not only confined to Shimla but to the entire Himalayan region. So please join hands to protect the springs before we start regretting our inaction.

Excerpts from my Dissertation for CDM (Catchment Dynamics and Management)

Study Findings:
Hydrological modeling studies in Shimla showed that springs are extremely crucial for sustaining base flows¹ in streams (crucial for water supply). Thus, main springs in Shimla Planning Area need to be identified and land use change in their catchments should be avoided.

Pressure for development is high on Shimla requiring more land to be put under urban uses. The proposed land use plan for Shimla envisages an approximate doubling of the area under urban use. Even after abstraction of 20MLD water from downstream River Giri, the city is likely to face a shortage of around 20MLD by 2021 which would require more expenditure on abstracting water from sources several kilometers away from Shimla. Urbanization has been known to impact the summer base flows in the streams, and thus increased urbanization is likely to further reduce the yield of present and future water resources in the region.

Hydrological modeling studies (using TOPMODEL) were conducted on Shimla watersheds using daily climatological data for more than 10 years (precipitation, evapotranspiration and temperature). The climatological data showed a trend which is contrary to the observed discharge²: Infrequent rainfall events occur during summers but no rain is registered during November/December whereas evapotranspiration³ during November December is nearly as high as that in summers (probably due to high radiation). This should imply that the rivers should have lowest flows during the dry period of November/December rather than during summers. But all the tributaries which are not largely dependent on snow fed watersheds show lowest water levels during summers.

Shimla is underlain with hard rocks comprising of Schist, Phyllite or Quartzite with thin soils which provides low scope for groundwater recharge. Running the hydrological model showed that deficits (water scarcity) in the watershed are high (especially during summers) and penetrate deeper than the soil profile, extending into the weathered bedrock/detritus profile. Thus, any rainwater inputs during summers are utilized in filling these deep lying deficits.

The high deficits along with the high evaporation rates during summers lead to rainwater being absorbed within the soil matrix such that it does not contribute immediately to the river flow but this water from early summer rains and winter snowmelt gradually keeps flowing through the upper surfaces of weathered bedrock and through cracks/fissures. It finally re emerges from the hill slopes as springs in such a way that this water contributes to the base flows in rivers several days or even months after rainfall events. These springs are thus extremely important to sustain base flow in the streams of Shimla during summers. But several studies like Choubey et al., 2000 have shown that the flow in springs can reduce and even vanish due to land use change. Thus, studies need to be conducted in the area to identify the main springs so that any land use change in their watersheds can be avoided. Model runs also showed that forests are most important in conserving base flows in streams as they help in retaining water and allow it to percolate slowly into the bedrock.

CONCEPT NOTE (Based on Choubey et al., 2000)

CONCEPT NOTE: Urbanisation Scenario (Based on Choubey et al., 2000)

Concept Note
It is known that due to the steep slopes in Himalayas, rain water flows off quickly and hence, water levels in the rivers rise quickly after the rains leading even to floods and recede within one or two days but these springs contribute water slowly to the rivers making sure that a sustained supply to the streams is maintained, especially in those which are not fed by snow. Increased hard surfaces will not only reduce the water percolating in to form springs but will also increase flooding.

Due to the uneven cracks in the bedrock, it is difficult to delineate the exact watershed of the springs but methods like tracer studies⁴ can be used to identify watersheds. In case the authorities in Shimla find it difficult or expensive to undertake these studies, then the simplest solution can be to leave a minimum of 500 metres forested buffer strip along the main springs to ensure that the springs don’t run completely dry. Apart from this, rainwater harvesting should be made compulsory in all buildings near the springs so that the water can be re routed to the bedrock. Also, permeable pavers (which are partially hollow and allow grass to grow as well as allow water to percolate) should be used in all parking areas to reduce the hard cover.

¹ Here: Base flow implies low summer flows in rivers
² Volume of water in the river
³ Evaporation + transpiration from trees; Evapotranspiration in Shimla is not likely to be too different from evaporation as most of the area is covered with Conifers which have very low transpiration rates.
⁴ Where the watershed of the main springs is delineated based on gravity and harmless tracers like coloured dyes or chemicals are injected in the soil during or just before rainfall and traced in the spring water.

Acknowledgement
The author would like to thank Prof Mike Kirkby for his guidance and the authorities and Officials of Shimla for their support in providing the data.