The    Asan    Barrage, popularly known as Dhalipur lake,  was  created   in  the year 1967 as a result of the construction of Asan barrage at the confluence of the river Yamuna & Asan through Dhalipur power house. Asan Barrage is famous for bird watching.

It    is   said  "birds  could exists  without  man  but   that  man   would perish without birds". Every one enjoys birds, the beauty of their forms and  coloring,  the  vivacity  of   their movements,   the  buoyancy  of  their flights and sweet- ness of their songs.

Waterfowl Profile
 
         The asan reservoir attracts 53 species of water birds of which 19 are winter migrants from Eurasia. During winter months 90% of the waterbird population comprises the following 11 migratory species, namely 

Brahminy Duck, Pintail, Red Crested Pochard, Gadwall, Common Pochard, Mallard, Coot, Wigeon, Common Teal, Tufted Duck, Shoveller 

Research 

         A number of research Institutes  like Zoological survey of India make regular census of waterfowl population of the wetland. Satellite monitoring of the wetland is also jointly carried out by ZSI with Indian Institute of Remote Sensing. 
 
LOCATION
 
        The Asan Reservoir is a small man-made wetland of ca. 4 sq km area, located 40 km west of Dehradun, in the west of Dehradun valley on Dehradun-Paonta road.

        Geographically it is situated between latitude 30^o 24’-30^o 28’ N and longitude 77^o 40’-77^o 44’ E, near the confluence of the rivers Asan and Yamuna. The barrage is 287.5 m long, the river bed being 389.4 m above sea level, with minimum and maximum water levels respectively at 402.4 m and 403.3 m asl. 

       The Asan reservoir exists throughout the year and is fed from the river Asan and the discharge channel of Yamuna through Dhalipur power house. 

       Although the water level is controlled, it often goes down, and swampy islands in the middle become visible, attracting a variety of marsh-loving birds like egrets, herons and lapwings, etc. 
 

CLIMATE

         North Indian monsoon climate, with distinct summer and winter months. Temp: summer, max.38^o C, min. 14^o C; winter max. 21^o C, min. 2^o C; average rainfall 250 cm; sw monsoon during June to September. 
 

1. Pond Heron (in breeding plumage) 
2. Pheasant-tailed Jacana (in breeding plumage) 
3. Black Ibis (Winter Migrant)
 
PRINCIPAL VEGETATION

        The aquatic vegetation of the reservoir consists of Eichhornia crassips, Potamogeton pectinatus, Typha elephantina, and Ceratophyllum demersum. The surrounding bushes include Xanthium strumarium, Eclipta prostrata, Ipomoea sp., Mimosa pudica, Achyranthus aspera, Polygonum glabrum, P. lanigerum, Aeschynomene sp., Ageratum conyzoides, phyllanthus sp.,  Monochoria hastata, Mosla dianthera, and Lantana camara. On the southern side, the barrage is surrounded by agricultural fields. Further south there is mixed forest in Siwaliks comprising principally Shorea robusta, Anogeissus Latifolia, Lannea coromandelica, Dalbergia sissoo, and Bombax ceiba. 

Habitat Utilisation by Waterbirds

Open water
Redcrested, Common, & Tufted Pochards, Gadwall 

Shallows/Swamps/Shores
Pintail, Mallard, Wigeon, Greylag Goose 

Mudflats
Brahminy Duck, Common Teal, Bharheaded Goose 

Birding Season
 

        The Garhwal mandal Vikas Nigam (GMVN) has created a water sports complex on the reservoir since 1994. This includes water skating, motor boats, paddler’s  rides, as well as catering and staying facilities. The wetland attracts a large number of tourists regularly from Dehradun and adjoining areas. 

       The peripheral road has become a preferred route from Himachal, Punjab, Haryana and Chandigarh resulting in great traffic. Moreover, being a major wetland attracting a large number of migratory waterfowl during winters many local schools, training institutes and NGOs undertake nature excursions to the wetland. 

DISTURBANCES AND THREATS

• Several factors at present are contributing to the deterioration of ecological conditions in the Asan reservoir:

 
• The rapid spread of the Typha, Ipomea  and Ecihhornia is a serious problem, since proper and periodical eradiction of the weeds is not undertaken regularly.

 
• The problem of soil erosion in the Catchment areas of both Asan and Yamuna rivers is acute and the reservoir silts rapidly.