Site characteristics
Ideally, this phase of the approach should be used to collect all the available information on the environment(s) concerned by the intervention, e.g.:
n dimensions, surface areas, water depth(s), difference between high and low water levels;
n hydrological characteristics (flood and low-flow levels), development work and regulation of water levels;
n connections with other aquatic environments;
n plant and animal communities;
n types of banks and riparian vegetation;
n site accessibility;
n available or necessary equipment;
n regulations governing the site(s) and the planned work.
It is generally easy to collect this information, however it does not always exist in forms that are of immediate use for the analysis prior to setting up the intervention. In some cases, the information has already been collated in existing documents, however it is necessary to check the validity of the information.
Uses and the people using the environment
Effort should also be made to obtain the best possible information on how the site or the area are used. Uses may be defined in quantitative terms (energy production, irrigation, mitigation of low flows and of flooding in rivers, etc.) or qualitative terms (drinking water, swimming, hunting and fishing, etc.). They may take place in the specified environment or throughout the river basin. In the latter case, they may create functional limitations in the specific environment (Dutartre, 2002).
137 For safety reasons, certain uses have for many years been regulated by the creation of zones (e.g. lines of
buoys in a lake) or other limitations in order to reduce or eliminate the risks of accident. Examples are swimming areas cordoned off from boating sites, other areas where boating is forbidden, etc. (see Figure 53). These rules, intended strictly to ensure the safety of users, take into account only the physical characteristics of the environment (depth, etc.) and, in some cases, bank characteristics, but do not necessarily acknowledge the implications for environmental management.
In other cases, contradictions may exist. For example, the presence of dense beds of submergent plants close to the surface may be highly troublesome for certain water sports, but very favourable for fish. Should efforts be made to eliminate or regulate the plants simply to benefit the water sports? At the end of the 1980s, the rapid colonisation of Blanc Pond (Landes department) by curly waterweed, in the form of dense beds covering approximately 100 out of the 180 hectares of the pond) elicited negative reactions on the part of all users, including anglers (see Figure 54 on the next page). A few years later, the reactions of the anglers had become more nuanced because it had been discovered that the plants enabled the development of a large perch population (Perca fluviatilis) thanks to the shelter provided to the alevins by the dense beds. Since that time, regular management work has been carried out on a part of the beds each year to enable boating activities (see the management report, vol. 2, page 23) and the pond continues to attract numerous anglers. Similar reactions of anglers confronted with such colonisations have been noted elsewhere.
Dense beds of amphibious species, such as water primrose, can hinder the travel of boats in lakes.
Figure 52
© A.Dutartre, Irstea
These beds of parrot-feather watermilfoil block all access to parts of the pond where boating has already been prohibited. (Léon Pond, Landes department).
Figure 53
© A.Dutartre, Irstea
User groups, often organised in associations frequently try to highlight the importance of their particular use and in some cases neglect to mention the impact of that use on the environment. This lobby work increasingly focusses on the positive impacts that can result from growing tourism. These requests and defensive activities often lack any prior analysis of the issues and risks involved in the specific use, but they should be assessed taking into account the impacts they may cause for the environment. Their compatibility with the environment should also be examined. For example, if a large number of activities can co-exist in a large lake without endangering users, the same may not be true in a pond covering just a few hectares.
Similarly, certain uses in areas not conducive to that particular activity can rapidly oblige managers to undertake unforeseen interventions made necessary by the type of activity. For example, the creation of a swimming area in a lake or basin fed by a river, where algae or macrophytes may develop due to the high level of nutrients in the water, may turn out to be very costly in terms of maintenance. In some cases, an economic analysis of the maintenance work required could lead to the conclusion that a swimming pool may be a better choice that is less “natural”, but for which maintenance is easier in terms of planning, cost estimates and implementation These uses consume, in the widest sense of the term, environmental resources (see Figure 55 for an example of how a lake may be used and the corresponding resources). However, the availability, evolution and renewal capacity of the resources are frequently not assessed, which can lead to significant differences between the expectations of users and the mid to long-term capacity of the environment, and consequently to dissatisfaction on the part of the users.
An analysis may therefore need to set priorities among uses (determining the main use and the remaining secondary uses), thus facilitating later decisions on intervention.
Colonisation of Blanc Pond (Landes department) by curly waterweed (the dark section in the photo).
Figure 54
© A.Dutartre, Irstea
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