Environmental flows A methodology of calculation for India (Part 1)

In order to maintain the ecological goods and services of rivers and other hydrological regimes like wetlands, lakes, etc., environmental flow allocations (eflows) are a necessity. At the same time, water demands in India are increasing and will keep increasing and solutions like waste water treatment, pollution control, correction of leakages and wastage of water, efficient irrigation systems, efficient agricultural systems, etc., will take considerable time to evolve, even with our best efforts. So what should we do in the meantime? There are vulnerable ecological systems on the verge of collapse..How do we respond to these challenges?

One of the options is to adopt an approach which allocates eflows on priority. This involves working out a specific ‘Environmental Management Class’ (EMC) of a river based on ecological and physical criteria. River basins and hydrological systems which have high biodiversity and unique habitats, or which provide considerable ecological goods and services to its dependant population, or which are seriously threatened due to challenges like abstraction, pollution, impoundment, etc. will have a higher EMC and need to be prioritized for conservation and eflow allocation.

Currently, this approach only involves ecological criteria. But in India, social and cultural criteria can also play an important role in river conservation. As the field of environmental economics progresses, no doubt an economic criterion can be added to these!

In 2007, a team from IWMI, including Dr. Arunachalam worked on “Developing procedures for assessing Ecological Status of Indian River basin in context of Environmental Flow Requirements”. This is a summary of the report in two parts. The current post describes the methodology, and a succeeding post will describe the results of applying this methodology to some Indian rivers.

Dr. Arunachalam, head of the Sri Paramakalyani Centre for Environmental Sciences, from Manomaniam Sundarnar University, Alwarkurichi, Tamil Nadu is an aquatic ecologist who has been trying to link flows, regulation, pollution, with aquatic diversity. He has worked extensively on ecological assessments of rivers in India, especially in the Western and Eastern Ghats and has discovered several fish species. He can be contacted at: drarunacm@gmail.com.

Introduction:

Methodology:

• What is the ecological sensitivity and importance of a river basin? The rationale for this is that the higher the ecological sensitivity and importance of aquatic ecosystems in a river basin is, the higher the EMC should be, ideally.
• What is the current condition of aquatic ecosystems in a river basin? The more natural the current condition of the basin is, the greater the incentive for its maintenance as such.
• What is the trajectory of change? This question aims to identify whether a river is still changing, and in what direction, how fast and due to what impacts. The rationale is that if the deterioration of aquatic environment continues, it will be more difficult to achieve a higher EMC, even if it is necessary, due to its high importance and sensitivity

As this is the first time that such an approach is introduced in India, the focus should be on highlighting the main aquatic features and problems of each basin. This means that aggregate environmental indicators, which reflect different features or conditions of a river basin, could be used for scoring. Among the recent relevant works on this,  

The first question above may be seen as an attempt to design a condensed measure of the ecological value of the basin, albeit in non-monetary terms. An arbitrarily selected set of semi-quantitative and quantitative indicators includes:

• Presence of rare and endangered aquatic biota
• Presence of unique (e.g., ‘endemic’) aquatic biota
• Diversity of aquatic habitats
• Presence of protected areas, areas of natural heritage and pristine areas, which are crossed by the main water course in the basin
• Sensitivity of aquatic ecosystems to flow reduction

Indicators from this group are calculated using national ecological surveys and databases. Considering that most of the ‘ecological’ attention in countries like India has so far been given to fish, such indicators as rare and endangered biota and unique biota are calculated here using available fish data. Rare and endangered fish species are first identified using IUCN (1994) categories such as CR (critically endangered) and EN (endangered). Their cumulative number is then expressed as the proportion of the total number of fish species found in a river basin. The assessment of diversity of aquatic habitats and sensitivity of aquatic ecosystems to flow reduction requires expert judgment and knowledge of a particular river. Presence of protected or pristine areas can be assessed against existing guidelines for protected area management, i.e., IUCN (1980), which sets the aim of 10 percent of the basin to be protected.

The second question above relates to what the river system looks like at present, compared to a reference condition in the past (e.g., prior to construction of major dams), or compared to some similar and relatively undisturbed subbasins in the same physiographic settings. The indicators used in this study include:

• percentage of the watershed remaining under natural vegetation cover types
• percentage of the floodplain areas remaining under natural cover types
• percentage of aquatic biota that are exotics
• overall richness of aquatic species
• the degree of flow regulation
• the degree of river fragmentation
• human population density in a river basin
• (percentage of population density in the main floodplains)
• overall water quality in the basin

The first two indicators are normally estimated from the GIS maps, remote sensing data, or already published literature sources. In some cases, a percentage of the floodplain areas actually remaining in a basin compared to some past reference condition may be used as an alternative to the second indicator. A proportion of exotic species (e.g., fish), can be calculated as a percentage of the number of total fish species recorded in the basin. Overall species richness may be assessed as a proportion of the total number of species in a country, or in a larger geographical region, whichever is more appropriate, or by an expert score on a scale from low to high. The most straightforward way of calculating the degree of flow regulation is as a ratio of total storage of all dams to the long-term mean annual natural flow volume of the basin. It is acknowledged though that this approach does not recognize timing or types of flow events that are altered—which may be more critical than change in volume per se. A degree of river fragmentation can be represented by a simple indicator of spatial changes to habitat—longitudinal and latitudinal (river-floodplain) connectivity of rivers. Human population density in a river basin as a percentage of population density in the main floodplains (which could be seen as an aggregate indicator of human pressure on aquatic ecosystems) may be calculated using Census data and GIS, where the floodplains are arbitrarily defined as areas within 2.5 kilometers (km) of either side of the main channel and the channels of the main tributaries. (It is acknowledged that such a definition does not fully recognize the difference between the typical riparian zone and floodplains). An approximation of the overall water quality in a river is indexed using Indian national water quality categorization, which has several classes, from A to E —depending on the level of pollution—expressed by ranges of several constituents.

With regard to the third question above, no specific indicators are used and ‘trend assessment’ is left primarily to professional judgment. It may be seen as an attempt to foresee how the river will look like in the short-term (e.g., 5 years) and in the long-term (e.g., 20 years) in case of a ‘do-nothing-toprotect- aquatic-environment’ scenario.  Regardless of the original units and ways of estimation of every individual indicator, all indicator values in this study are then converted to a standard scoring system, which includes ratings: 1 (none), 2 (minor), 3 (moderate), 4 (high) and 5 (very high). Table 1 summarizes the indicators which have been used in this study, and explains why an indicator has been considered and how it is relevant in the context of the estimation of environmental water demand. The scores for individual indicators are then summed up and their sum is expressed as a percentage of the maximum achievable score. The actual percentage shows the degree of the deviation of a basin from its natural condition and, therefore, the most probable EMC. The latter, in turn, may be related to the amount of water that needs to be allocated for environmental purposes in this basin.

Table 1