CONCLUSION

The water, soil and sediments of Sharavathi downstream and upstream catchments were analysed for their physico-chemical and biological parameters. The upstream and downstream catchments were divided into various sub-basins and their quality in terms of water, soil and sediment was evaluated.

• Field and laboratory investigations of the water quality of the Sharavathi upstream catchment reveal that the tributaries flowing through the sub–basins of Nandiholé (US1), Haridravathi (US2), Sharavathi (US4), Mavinaholé (US3) and Hilkunji (US8) (Group A) are relatively more polluted as evident from transparency, turbidity, suspended solids, phosphates and coliform than the tributaries in the sub-basins of Yenneholé (US5), Linganamakki (US9), and Hurliholé (US6) (Group B and C). The reasons for pollutions in these sub-basins are due to the agricultural and other anthropogenic activities in the catchment area.

• The Sharavathi downstream catchment shows that the streams flowing through the sub-basins of Magod (DS3), Dabbefall (DS4), Mavinagundi (DS5), Kathalekan (DS6) and Gudankateholé (DS7) are fresh and unpolluted. But streams like Dabbod in sub-basin 3 (Magod) showed variations in the physico-chemical characteristics like turbidity because of the increased run-off from the nearby agricultural fields. In certain months, the water is dammed for agricultural purposes and during the months of February, March and April, the water is highly turbid. The tributaries flowing through Chandavar (DS1) and Haddinabal (DS2) of the downstream catchment are prone to salinity (high values of sodium, chlorides, sulphates, hardness, conductivity, TDS, alkalinity, etc.,) as there is seawater intrusion. 

• The analysis of the soil samples collected from representative sites in the Sharavathi upstream catchment revealed that the soils of the sub-basins of   Linganamakki (US9), Yenneholé (US5), Nagodiholé (7), Nandiholé (1), Haridravathi (US2), Mavinaholé (3) were fertile compared to the sub-basins Sharavathi (4) and Hurliholé (6) (indicated by high organic content and low bulk density values).

• The analysis of downstream catchment soil samples showed that the soils of Haddinabal (DS2) and Kathalekan (DS6) sub-basins are relatively fertile compared to the sub-basins Dabbe falls (DS4) and Magod (DS3). Most of the areas in the sub-basins DS4 and DS3 come under different plantations and have maximum anthropogenic activities in the catchment area compared to the other two sub-basins.

• The sediment samples collected from the Sharavathi upstream area revealed that the sediments were rich in organic carbon but were poor in other nutrients.

1.  ACTION PLANS

• Introduction of any local grass species like Dichanthium annulatum, Panicum antidotale, Sehima nervosum, Cenchrus ciliaris, Csetigerous and Chrysopogon fulvus along the edges in agricultural fields or along the streams near Gudankateholé, Dabbod, Hennur, and Hebbankere. This conservation measure will prevent runoff and preserve soil and vegetation, improve soil moisture, prevent direct contamination of the streams and provide fodder for livestock. Preferably this conservation strategy should be strongly adopted at all agricultural fields near riparian habitats. This can be implemented by bringing awareness among the farmers and adopting the above method to conserve the natural resources like soil and water in the Sharavathi downstream catchment.

• Afforestation or plantation of hardy evergreen tree species like Olea dioica, Aporosa lindleyana along with grass species that slow down and retain water, which prevent excess nutrient wash and direct fall of water from the evergreen forests near Vatahalla. This conservation measure preserves the fertility of evergreen forest existing there, prevents soil erosion, reduces excess nutrient flow to the stream and reservoir preventing sedimentation of the reservoir.

• Construction of bunds to prevent seawater intrusion into the stream at Haddinabal as practiced between Badagani and Gudankateholé or permanent embankment as suggested in the subsequent recommendation.

• Back intrusion of seawater into the stream at Gudankateholé can be overcome by constructing a permanent embankment or dam wall near Badagani with provision for regulating the flow of water from the upstream to downstream from period to period. 
• Afforestation programme to be undertaken extensively in the catchments of major tributaries like Nandiholé, Haridravathi, Mavinaholé, Sharavathi and central part of the Sharavathi upper catchment.

• Stream bank afforestation to be undertaken near major tributaries like Nandiholé, Haridravathi, Mavinaholé, Sharavathi, Hilkunji and other lower order streams in eastern part of the Sharavathi upper catchment.

• Utilisation of excessive inorganic fertilisers for cultivation of crops has affected the water quality and soil in the eastern parts like Haridravathi, Nandiholé, areas surrounding Hosanagara in the Sharavathi upper catchment and streams near Gudankateholé, Haddinabal, Dabbod, Magod in the downstream. Therefore, it is recommended to practice organic farming and utilise bio-pesticides. Utilisation of excessive inorganic fertilisers for cultivation of crops has affected the water quality and soil in the eastern parts like Haridravathi, Nandiholé, areas surrounding Hosanagara in the Sharavathi upper catchment and streams near Gudankateholé, Haddinabal, Dabbod, and Magod in the downstream. Therefore, It is recommended to promote organic agriculture, vermiculture etc. in these regions. Local farmers should be educated about the significance of aquatic habitats and possible impacts of unplanned agricultural activity, use of excessive fertilisers/pesticides and discharge of excessive agricultural contaminants directly into the aquatic bodies and its consequences, etc.