Hydropower development in the Himalaya: Identifying critical river stretches

doi:10.21203/rs.3.rs-1632553/v1

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Hydropower development in the Himalaya: Identifying critical river stretches

https://doi.org/10.21203/rs.3.rs-1632553/v1

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published 01 Feb, 2023

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Two hydroelectric projects are operational in the upper and lower stretches of the river Alaknanda near Lambagarh and Srinagar that are respectively ~ 140 km apart. The health of the river ecosystem in the flowing stretches between and below these projects was bio-assessed, based on widely used diatom indices and van Dam ecologic values computed by OMNIDIA software. Samples were collected from Birahi, the semi-natural stretch - 53 km downstream of power-house, Narkota, the impacted stretch 27 km upstream Srinagar dam and Bagwan, the highly regulated stretch 22 km downstream Srinagar. IPS and IBD revealed mild pollution in upper and lower stretch compared to relatively elevate at Narkota. However TDI indicates moderate organic pollution at Birahi and Narkota, whereas the IDSE indicates low degradation at all stations. The prevalence of tolerant N-autotroph, β-mesosprobe, mesotrophic and aquatic to aerophilic categories of van Dam environmental variables indicate that a certain level of impact already persists due to organic-cum-nutrient load and perturbed flow-regime. The prevalence of eutrophic and moderate O2 categories shows that the ecosystem is in critical state at Narkota, causing a disrupted continuum.

Himalaya

Hydropower development

diatom indices

ecological criteria

critical stretches

The mountains are a favourable terrain for hydropower development. The Indus, Ganga and Brahamaputra river systems are visualized as a vast potential in the Indian Himalayan region (IHR). Government of India aims to construct 292 dams throughout IHR, which is projected to meet ~ 6% national energy needs by 2030 (Grumbine and Pandit 2013). The Ganga river system constituted by the tributaries Alaknanda and Bhagirathi, each ~ 200 km long, accounts for 24% of the hydropower in IHR.

The 400 MW and 330 MW hydroelectric project (HEP) at Vishnuprayag (VHEP) and Alaknanda hydropower corporation Ltd. (SHEP) near Lambagarh and Srinagar respectively, have modified the Alaknanda almost along its whole length except for ~ 30 km stretch between the holy pilgrimage shrine of Badrinath at ~ 3100 m asl and VHEP. Based on steep fall of ~ 2100 m in upper 100 km length of the river compared with a gentle fall of ~ 500 m in lower 100 km, they were considered as upper and lower stretch, alias ecosystems. The upper stretch is characterized by shooting currents that cause considerable scouring and hence support lower densities of benthic producer and consumer communities (Mishra et al. 2013; Nautiyal unpublished). Declining gradient in the lower stretch allows development of relatively higher densities and diversity of benthic algae (Nautiyal 2005). Consequently, snow trout fishery becomes an economic activity in the lower stretch, characterised by wider valleys that allow operation of the indigenous fishing traps and nets. Besides small quantity of detritus, adequate primary production by diatom dominated benthic communities (Nautiyal et al. 1997) is essential to sustain this fishery (Nautiyal et al. 2005), as snow trouts are herbivores (primary consumers), a grazing-chain element.

Thus, the lower stretch is a subject of concern and deeper scrutiny. Past studies on biotic communities in relation to HEP focused only on river sections just upstream (u/s) and downstream (d\s) of the dam and barrages (Nautiyal et al. 1988; Badoni et al. 1997; Rajvanshi et al. 2012). Studies in the flowing sections of the river between two or more HEP’s are scarce (Smolar and Mikos 2014; Kumar and Nautiyal 2019).

The flowing sections of the Alaknanda were classified as flow-deficient (F-D) from dam to power house (PH) and flow-regulated (F-R) downstream of the PH. There is a need to identify and designate critical stretches in the flowing sections of a river modified for HEP. The assessment was restricted to the use of ecologic criteria (van Dam 1994) and some frequently used diatom indices as a measure of river health impacted by HEP. They have been successfully used in Himalayan rivers and streams (Nautiyal and Mishra 2013; Nautiyal et al. 2015; Singh 2018; Bartwal et al. 2020) as the species reported from Himalayan rivers (Nautiyal et al. 2004) are similar to those present in the database of the software. Their efficacy was also tested. Study also identified the most probable physical or chemical factor(s) that influence the abundance of species responsible for the ecological category. This will allow the possibility of restoring the concerned factor(s) for better management.

The area of influence (AoI) for SHEP extends for ~ 27 km consisting of ~ 20 km long impounded section u/s of the Srinagar dam site and a short ~ 7 km F-D d/s section from dam to PH. Beyond PH, the remaining ~ 30 km stretch till Devprayag is the F-R section. Since the interest lies in the flowing sections that are distantly located from the modifying structures (as long distances allow the river to regain the ecosystem integrity), the Alaknanda sampled at S3, S5 above SHEP impoundment and S8 in the F-R section below SHEP (a study funded by National Mission for Himalayan Studies, GBPNIHED, Kosi-Katarmal, Almora), were considered for this study.

i). S3 (Birahi): This station outside VHEP-AoI lies in the beginning of the lower Alaknanda river ecosystem. It carry F-R discharges from VHEP but is considered here as reference location and a surrogate for unhindered but impacted flow representing a semi-natural zone as it is ~ 53 km d/s of the VHEP-PH and is far u/s of the SHEP impoundment.

ii). S5 (Narkota): This location is ~ 1.5 km u/s of the tail of SHEP impoundment and 73 km d/s of Birahi.

iii). S8 (Bagwan): This represents F-R stretch and lies in the middle of the total F-R section from Srinagar to Devprayag.

The OMNIDIA ver 6.0.8 software requires valve-count of each diatom species to compute the indices and van Dam ecologic criteria to assess the river health based on benthic diatom communities in the selected sections. The acid-peroxide treated diatom Naphrax mounts from each sampling station were examined using three replicates collected from 3 x 3 cm² surface area of cobble substrate in varying flows from riffle-pool-riffle sequence at monthly intervals. Species count were generated from each replicate and pooled for year 2016-17. Inventories were prepared and imported in the software. The following indices serving as a measure pollution and eutrophication were computed using OMNIDIA ver 6.0.8;

Index Score Quality

Diatom Biological Index (IBD) 1–7 Worse to Best (W-B)

Pollution Sensitivity Index (IPS) 1–5 Worse to Best

Diatom Saprobic Index (IDS/E) 1–5 Worse to Best

Trophic Diatom Index (TDI0 to > 61 Low to High (L-H)

The ecologic values for the categories with higher shares of each characteristic were recorded to determine the river health. Since each environmental variable, excluding unknown, has 4 to7 categories, only those with highest share of the variable were considered for the present analysis. The order of categories extends from excellent to good and bad to worse for O₂ requirements, saprobity, trophic state, moisture-aerophily and N₂ uptake. pH is one instance where acidic or highly alkaline conditions do not represent a healthy river.

Diatom indices based assessment

IBD indicates very low pollution at S3 and S8 stations and low at S5. IPS shows almost no pollution at S3 and low pollution at S5 and S8. IDS/E ranging from 4.2–3.6 shows low degradation at all stations. TDI range from 41 to 60 at S3 and S5 implied that organic pollution is likely to contribute significantly to eutrophication. At S8 the TDI range varied from 20 to 40 implying some evidence of organic pollution at this site. The low value of each index at S5 indicates the stressed state of this river section (Fig. 1).

The dominant categories (those with relatively higher shares) of van Dam environmental variables are used as indicators of river health (Table 1). Tolerant N-autotroph and β-mesosprobe are dominant in the total river stretch. The alkaliphilic and occasionally aerophilic categories are dominant only in the lower-half stretch (S5-S8), while neutrophilic and aquatic-aerophilic are restricted to S3. The polyoxybiontic and mesotrophic are dominant in discontinuity (S3, S8), while moderate O₂ and eutrophic categories prevail at S5. Based on the dominant categories, the river stretch was classified as “polyoxybiontic-cum-mesotrophic” at S3 and S8 while “moderate O₂-cum-eutrophic” at S5, implying higher organic and nutrient load in the river section at S5.

Table 1

The categories of various van Dam environmental variable that are dominant (as %; shown in bold) in different stretches of the river.
	Categories (as %) at
van Dam environmental variables		S3	S5	S8
pH	Neutrophilic	51	27	27
pH	Alkaliphilic	40	64	47
N₂ uptake	Tolerant N-autotroph	47	57	24
O₂ requirements	Polyoxybiontic	42	28	33
O₂ requirements	Moderate O₂	13	38	10
Saprobity	β- mesosprobe	50	65	36
Trophic state	Mesotrophic	34	23	27
Trophic state	Eutrophic	18	49	23
Moisture-aerophily	Aquatic -aerophilic	36	20	16
Moisture-aerophily	Occasionally-aerophilic	17	46	26

Grumbine and Pandit (2013) projected a very grim situation of one dam for every 32 km of river channel, if all the proposed dams are constructed in IHR and suggested evaluation of environmental degradation with the progression of dam building. Nineteen HEP have been commissioned in the Ganga river system of IHR. Besides, sizable investments have been made on seven projects in the Alaknanda basin. Others have been withdrawn in the spirit of 1916 document originating from conference held at Haridwar between the then Government, Princely States and eminent social leaders including Bharat Ratna, Pt. Madan Mohan Malviya, wherein it was concluded that a constant unfettered flow of river Ganga should be maintained and 1000 cusecs water in natural streams and natural course in all seasons of the year (vide Affidavit respondent no. 3 - Union of India Ministry of Environment Forest Climate Change, dated 17 Aug 2021).

River regulation is a practice to maintain a constant discharge for generating required hydropower. Since discharge is inherent to a river, its modification to suit generation of hydropower to full potential, impairs the ecosystem. Each hydroelectric project differs from the other by its design and hence the impacts cannot be generalised. Below the PH, the HEP either terminates into another project immediately or after flowing for some distance. In some instances the river may appear to be free-flowing but actually carries regulated discharges. The F-D and F-R river sections with modified flows are crucial for a serially impounded river ecosystem like Alaknanda. This bio-assessment uses diatom indices and ecological criteria (van Dam et al, 1994) to measure the impact vis-a-vis response of diatom (producer) communities to HEP operations. All the indices show that the river is more stressed at S5, which is also indicated by the ecological values. TDI and IDSE are more sensitive in HEP impacted river in comparison to IBD and IPS.

Notably, in contrast to the continuum of gradual change, the tolerant N-autotroph and β-mesosprobe (BOD-2-4 mgl^− 1) category respectively, persisted in the whole stretch of the Alaknanda under observation while alkaliphilic and occasionally aerophilic categories only in the lower half of the river. Contrarily, mesotrophic and polyoxybiontic categories persist at both ends of the stretch (S3 and S8) but turn eutrophic and moderate O₂ (50% saturation) at S5. Nautiyal (2009) also reported alkaliphilous, tolerant N-autotroph, high oxygen requirements and β-mesosprobe in the river and streams of Himalaya.

The flow modifications seem to have homogenized the river. Considerable share (not mere presence) of these categories in merely ~ 200 km length of the river from its source shows that the river is in a state of low-level impact as a pristine river should contain greater share of sensitive N-autotroph, neutrophilic, oligotrophic, polyoxybiontic and aquatic categories of respective variables. The river gets perturbed at S5 as the tail of the impoundment swells and shrinks according to the discharge requirements for power generation, thus impeding the flow and creating eutrophic conditions. Evidently the hydraulic and hydrological regime around tail of the impoundment aggravates the impact of organic and nutrient load due to lack of flushing and facilitates the bloom of CPLE. Moderate O₂ category was attributed to decrease mechanical mixing. The river stretch was hence classified as “polyoxybiontic-cum-mesotrophic” at ends of the selected stretch (S3 and S8) while “moderate O₂-cum-eutrophic” at S5, implying higher organic and nutrient load in the river section at S5. Thus the river stretch around S5 was considered critical.

The van Dam ecological criteria and diatom indices shows that the continuum is disrupted near the tail of SHEP impoundment as the O₂ requirements (polyoxybiontic) and trophic state (mesotrophic category) occur in discontinuity at S3 and S8, while moderate O₂ and (50% O₂ saturation) and eutrophic categories prevail at the tail of impoundment (S5) which was thus identified to be “critical”.

Acknowledgments

Authors are thankful to G. B. Pant National Institute of Himalayan Environment and sustainable development Kosi Katarmal for financial assistance under National Mission on Himalayan Studies Ministry of Environment, Forest & Climate Change and the Head, Department of Zoology, HNB Garhwal University, Srinagar Garhwal for lab facilities.

Author information

Affiliation

Aquatic Biodiversity Unit, Department of Zoology

Hemvati Nandan Bahuguna Garhwal University (A Central University)

Srinagar Garhwal, 246174, Uttarakhand, India

Tanuja Bartwal & Prakash Nautiyal

Ethical approval

Not applicable

Consent to participate

Not applicable

Consent to publish

The authors consent to publish in the journal Environmental Science and Pollution Research.

Author contributions

Prof. Prakash Nautiyal managed generation of diatom count data for preparing inventories for the software and edited the manuscript. Ms Tanuja Bartwal analyzed the inventories in software, prepared and communicated the manuscript to the journal.

Funding

The data required for this MS was generated for a research project supported by a grant from the G. B. Pant National Institute of Himalayan Environment and sustainable development Kosi Katarmal-National Mission on Himalayan Studies, Ministry of Environment, Forest & Climate Change vide NMHS Reference No. NMHS/2016 17/SG12/01.

Competing interests:

The authors declare they have no competing interests to disclose.

Availability of data and materials

The datasets generated during this study are available from the Co-author on reasonable request.

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Hydropower development in the Himalaya: Identifying critical river stretches

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