Table 3.7: Summary list of methods for lakes and wetlands from the decision-making framework, with pros and cons for use

1. Historical time series analysis

Absolute recorded/estimated inflows/outflows, capturing seasonal variability. In the case of wetlands, delineation is required.

Quick and easy, uses existing data, available data, allows variability without going to detailed level of analysis.

Assumes a linear relationship between inflows and lake/ wetland habitat; inconsistencies in estimating flow data; difficult to apply in un-gauged systems without accurate models; natural mistrust of method due to being too simple, doesn’t target the needs of specific values. Being poorly applied in high value/high change contexts.

2. Expert panel

Independently appointed panel of experts to advise.

Quick, cheap, has credibility (dependent on experts), can help overcome mistrust if well managed.

Not predictive; can’t accurately determine how character of lake/wetland changes with inflows/outflows and levels; can be used as a political tool; implied consensus can lead to poor ecological outcomes.

3. Site and catchment mapping

Applicable to wetlands rather than lakes. Ground mapping on existing topographic or landcover/soil maps, and or the use of aerial photographs (real or infra-red).

Spatial data, and photographic images are often easy to obtain. Spatial relationships can be inferred and mapped. Department of Conservation is currently developing national database.

Limited ability to predict the extent of level change anticipated or the effects of changing levels.

4. Wetland record sheet (MfE methodology)

Applicable to wetlands rather than lakes. Uses a set of tables to classify wetlands in a wider context (MfE methodology).

Robust initial analysis using only a set of structured tables to complete.

Requires a good knowledge of wetland systems.

5. Habitat analysis in drawdown zone

Define lake/wetland habitats on basis of substrate and depth, prevailing wind (in case of lakes) and position of inflows; requires both GIS and field observations (divers/boats for lakes and field surveys for wetlands).

Explicit relationships are obtained between water levels and habitats. Enables location of sensitive habitats, and extent of different habitat types and estimate of non-linear changes in habitat extent with depth.

Only moderately predictive if variability of inflows/outflows/ levels changes but not the average values.

6. Species-environment models

More complete/detailed definition relating to biodiversity and structure of these communities. Emphasis on rare species/ unusual communities, or communities that influence the rest of the lake/wetland. For fish, account for feeding/ spawning migrations.

Explicit relationships are obtained between water levels and communities. Enables location of sensitive communities, and extent of different community types. For fish it involves the identification of critical areas for fish movements between lakes/wetlands and streams.

Predictive ability is dependent on knowledge of community responses to variable water levels. (Constraints on predictive ability only applies if change in variability of flows and levels is proposed.)

7. Wetland hydrological condition assessment and model change

Applicable to wetlands rather than lakes. An extension of the Wetland Record Sheet above but more detail and has a data requirement for the scoring of wetland condition (MfE methodology).

Robust analysis using both a set of structured tables and existing data to complete a defined scoring system. Some predictive ability but based on expert opinion.

Requires a data set including some biodiversity and physico-chemical parameters and an expert knowledge of wetland systems.

8. Water balance models

Model that relates lake change in storage (and therefore levels) to inflows / outflows knowing the lake bathymetry.

Can be used dynamically (daily or fewer time steps), spreadsheet approach.

Dependent on quality of inflow/outflow information and unknown groundwater inputs, and estimates of evaporation (note on method).

9. Residence time vs water quality modelling

Applies to lakes and any wetlands with significant areas of standing water. Empirical model relating nutrient loads and residence time to algal blooms and water clarity.

Simple method for professional practitioners.

Some information on nutrient loading and lake/wetland water quality. Applicable to residence times > 10 days and < 10 years. Need limnological experience.

10. Detailed local delineation

Applicable to wetlands rather than lakes. Delineation is the precise mapping of the wetland boundary at different water levels.

Allows detailed identification of communities in wetlands in relation to hydrology to assist with predictions of effects of change.

Requires expertise in wetland ecosystems including knowledge of hydrology, soils and vegetation.

11. Bank stability and geomorphology analysis

Assessment of erosion potential of lake shorelines and sensitivity to sediment slumping in response to reduced water levels.

Incorporates an effect of changes in lake water level that is known to be important and is already well understood.

Requires thorough engineering expertise to carry out.

12. Full ecohydrological assessment

Applicable to wetlands rather than lakes.

Standard international method for detailed understanding of wetland species distribution in relation to hydrology.

Requires a high level of expertise to complete accurately.

13. Microtopographic survey

Applicable to wetlands rather than lakes.

Refines prediction of effects of water level changes to specific species and communities.

Can be expensive, especially for large sites, and requires expert practitioners to complete accurately.

14. Wave action assessment

An important aspect of hydrology affecting shoreline species distributions in lakes.

Considerable evidence and good models already available.

Requires some expertise in modelling.

15. Water clarity assessments

Optical assessments of lake water in varying field conditions.

Strong relationships between lake levels, wave action, inflows and clarity can be obtained. Predictive.

Requires expert field work and a good knowledge of factors affecting lake water clarity.

16. Temperature modelling

1D models of lake vertical structure in the open water or, if requires adjacent to inflows to determine effects of inflows.

Well documented in the literature and predictive.

Requires expert in lake systems and in computational modelling.

17. Groundwater/ surface water interaction

Often critical in controlling species distribution through effects on nutrient inputs.

Often critical in controlling species distribution in wetlands.

Requires interdisciplinary teams for accurate and sound implementation.

18. Hydrodynamic water quality models

1D, 2D, or 3D representation of temperature (salinity), currents and mixing used alone when physical structure of water column and the outflows are of concern. May also include dissolved oxygen, nutrients and chlorophyll (algal production/ species).

Better able to predict ecosystem response.

Data, computationally intensive, requires hydrodynamic modelling expertise and expert in-lake process understanding.