River Yamuna a tributary of River Ganga flow in a stretch of 1376 km from Yamunotri to Allahabad. The river is affected during its course by three major urban centers i.e. Delhi, Mathura-Vrindavan and Agra. Among these three urban centers, Delhi stands first based on the pollution contribution into river Yamuna (Table 7.3). The treated, partially treated or untreated wastewater generated from the capital city finds its way into the river or canals by twenty-two major drains. Out of these, twenty drains join Yamuna directly while two drains join Agra and Gurgaon canal respectively. The total pollution load in terms of Biochemical oxygen demand, disposed off into the river by these drains is about 368.54 tonnes/day (Table 7.4). Out of this, about 327.18 tonnes/day BOD load joins Yamuna River and rest i.e. 47.36 Tonnes/day join the canals. On the basis of waste water discharge, Najafgarh drain is the largest drain having average discharge of about 25.65 m3/sec (51.75 % of total contribution by 22 drains) followed by Shahdara drain (8.96 m3/sec) and drain near Sarita Vihar Bridge (4.43 m3/sec). Moat drain is the smallest drain having average discharge of only about 0.06 m3/sec. Similarly, on the basis of BOD load Najafgarh drain stand first with average BOD load of 121.57 Tonnes/day (about 33% of total BOD load of 22 drains) followed by Shahdara drain (64.71 Tonnes/day) and Sarita Vihar drain (39.93 Tonnes/day). Moat drain is having average BOD load of only 0.1 Tonnes/day. Out of the twenty-two drains, 10 biggest drains contribute 95.9% of the total discharge and 96.3% of the Total BOD load to the river.

The Yamuna river water quality data for Delhi stretch is depicted in Table 7.5. The river water samples were also collected from the origin of river Yamuna i.e. Yamunotri in the month of June. The Total Coliform values were recorded much higher (20700 Nos./100 ml) against the standard Total Coliform values for `B' class of water (500 Nos./100 ml). It indicates that the river water is suitable for bathing purpose. The reasons for high coliform count at Yamunotri are the significant number of visiting tourists and Pilgrims. The high coliform count at Yamunotri is observed only during the period of about six months, when the Yamunotri temple is opened for the visitors.

Table : 7.3 Discharge contributed by drains into River Yamuna in Delhi Stretch

Table : 7.4 BOD Load contributed to River Yamuna in Delhi Stretch

Table : 7.5 Water quality of River Yamuna in Delhi stretch in respect of
selective physico-chemical parameters between January to December, 2000