Yettina holé River is catering water needs in the catchment and downstream users with the existing natural flow regime. Higher discharge of water during monsoon transport nutrients, silt, etc., which gets deposited in the flood plains, river bed and estuaries. This helps the riparian’s, aquatic life, human activities such as fishing, horticulture, agriculture etc. As many  streams are perennial, helps to sustain aquatic life with rich diversity; and horticultural, agricultural activities (up to 3 crops are grown due to the availability of water), and fishery.

Our computation shows the water yield in the catchment is only 9.5 TMC, which is required to sustain the current level of activities in the catchment (agricultural, horticultural) apart from ecological and environmental needs. The diversion of water would lead to reduced crop yield in the catchments and downstream, and silt and nutrients that otherwise flow downstream, gets trapped in the weirs constructed across the streams. This would result in the variation in the natural flow regime affecting the biodiversity of riparian’s and aquatic habitats and more importantly people’s livelihood who are dependent on fisheries, etc. in the downstream.

Now, Karnataka Neeravari Nigam Limited, Govt of Karnataka has planned construction of weirs along the 8 streams (Yettina holé, Yettina holé T1, Yettina holé T2, Yettina holé lower reach, Keri holé, Hongadahalla, Kadumane holé1, Kadumane holé2) and divert the water uphill by pumping to a common storage point, then allowing the water to flow by gravity to supply water for i) agricultural and industrial usage, ii) filling the major tanks to cater the domestic needs.

The diversion scheme planned to supply 24 TMC water to (i) Kolar district comprising of all taluks, (ii) Chickaballapura district comprising of all taluks, (iii) Tumkur district comprising of areas in Palar and Pennar basins including Chiknayakanahalli and Sira Taluks along with selected villages in Tiptur and Gubbi Taluks, (iv) Hassan district comprising of villages in Arasikere taluk, (v) Chikamagalore district comprising of selected villages in Kadur taluk (vi) Ramanagara district, (vii) Bangalore Rural district comprising of Nelamangala, Doddaballapura, Devanahalli and Hoskote Taluks, (viii) Augmenting the water to T.G.Halli reservoir, (ix) Augmenting water to Hesaraghatta reservoir, (x) Drinking water supply to Devanahalli Industrial area and surrounding areas.
Combined yield of 24 TMC (DPR) is arrived at considering discharge measurements at the gauged station near Bantwala of Netravathi river (maintained by the Central Water Commission) and the proportional area of individual catchments relative the Netravathi catchment.  Due to variations in rainfall across space and time, and also variations in land use, measurements at one location cannot be extrapolated to other regions in the catchment.

In contrast to this approach, water yield estimated using parameters at catchment level such as rainfall, land use, evaporation, etc.  show the water yield of 9.55 TMC which is about 40% of the yield obtained by DPR. Based on measurements by KPC (Karnataka Power Corporation) at Kadumane holé 1, the yield in the catchment is 0.813 TMC, whereas the yield computed by us at this location is 0.702 TMC (based on the hydrological model). Thus the accuracy of the hydrological model is 86% in relation with the measurements of KPC. Based on these validations, model was used to estimate the water yield in other catchments. Higher water yield in DPR is mainly due to (i) considering uniform rainfall of 6000 mm in all catchments (though it varies from 3500 to 4700 mm), (ii) spatial variations in land cover / land use. Also, during the process of transporting water through gravity canals would account to loss of 1 TMC of water due to evaporation. Implementation of Yettinaholé project would lead to water scarcity in Hassan and Mangalore, while not benefitting Chikkballapur, Kolar, etc. Livelihood of Yettinaholé and Gundia catchment would be affected severely due to lowered agricultural and fisheries yield  similar to the residents of Nellore district with the implementation of  Telugu-Ganga project.

The sustainable option to meet the water requirements of arid regions in Karnataka is through (i) decentralized water harvesting (through tanks, ponds, lakes, etc.), (ii) rejuvenation or restoration of existing lakes/ponds, (iii) reuse of waste water, (iv) recharging groundwater resources, (v) planting native species of herbs and plants  in the catchment, (vi) implementation of soil and water conservation through micro-watershed approaches.