New!Delta - Theme 5

Accommodation Space

Changes in sediment storage capacity over Holocene timescale (10,000 years).

Advection-Diffusion Models

Calculates the movement and dispersion of a constituent (particle matter or solute), given an initial concentration field (e.g. dispersion of heat from a power station outfall).

Behaviour models

Describes the net behaviour of the system (or some aspect of it) using simplified descriptions, or relationships derived from the use of more detailed process models.

Carrying capacity analysis

Uses thresholds of impact, to assess projects relation to carrying capacity or threshold limit. It addresses the accumulation of impacts against thresholds and considers trends, but is limited by data availability and it is not always possible to establish the threshold or carrying capacity for a receptor.

Checklists

Provide a systematic way of ensuring all likely impacts are considered, providing a standard checklist for similar projects. However, they can allow oversight of important effects, with the cause-effect relationships not specified.

Compatibility appraisal

Compatibility appraisal is aimed at ensuring strategic action is coherent and consistent with other strategic plans/actions by comparing in a x:y format each element of the proposal and environment to assess if they are/are not compatible or if there is no link between them.

Coupled hydraulic and entropy relationships

As per coupled hydraulic and entropy relationships but defines a target steady state based on the concept of minimum work on the system as a whole.

Coupled hydraulic and regime relationships

Given a perturbation to the estuary system this method uses a target equilibrium, defined by some form of regime relationship, to iterate to a new equilibrium.

Coupled hydraulic and energy relationships

Examines the distribution of bed shear stresses and compares these with erosion thresholds for the types of sediment present.

Ecological modelling

Models to describe the interactions between physical, chemical and biological components. Generally these are limited to specific interests (e.g. bird/fish populations, benthic communities, vegetation cover etc).

Ecosystems analysis

Ecosystems analysis considers the full range of ecological resources and the interactions with the environment, which may involve establishing the region of influence, modelling the economic effects and determining the significance of others.

Estuary Translation (rollover)

Defines the vertical and horizontal movements of the whole system as a consequence of changes in sea level.

Experimental methods, such as illustrative models, physical models, laboratory experiments and field experiments

There is no one model that can be used, with some being specific to certain processes, others used on their own and some needing to be interactively linked. Need an input from a modeller.

Expert Geomorphological Analysis

Using a combination of assessment methods, together with an understanding of how different types of landform evolve, to assess the expected development of the estuary system.

Expert judgment/opinion Qualitative method

Essentially involves one or more experts evaluating and discussing the issue and forming a decision based on available data and past experience. Can both identify and assess indirect and cumulative impacts and impact interactions. Not always auditable.

Form Analysis

Uses shape descriptions to characterise the estuary form (e.g. exponential width decay, or power law width and depth).

Habitat suitability evaluation procedure (Alterra)

The procedure attempts to quantify effects of changing habitats - i.e. species occurrence related to environmental characteristics is analysed quantitatively. The relationships may describe species occurrence as a function of an attribute of the habitat. The plan or project is assumed to affect the attribute of the habitat, and thus directly or indirectly change the suitability of the area for the given species. A large pro is that in many cases, existing information can be used; a large con is that one implicitly assumes that there is a causal relationship between the occurrence of a species and its abiotic environmental characteristics.

Historical Analysis

Documents changes to estuary over time from charts, maps and historical archives (e.g. parliamentary records). Identifies any trends. Should include a chronology of human developments (reclamation, dredging etc).

Holocene Analysis

Description of geological development of basin. Usually includes estimates of sea level change and identification of periods of marine regression and transgression.

Hydrodynamic Models

Process based modelling of water levels, discharge, current speed and direction, waves, density currents and secondary circulation patterns.

Hydrological model of silt and nutrients (Alterra)

Based on hydrological modelling, the distribution of silt and nutrients can be simulated, and thus the effects on primary and secondary production estimated.

Impact matrices

Impact matrices enable interactions between activities and receptors to be identified. They provide a visual summary of impacts, impacts can be weighted/ranked and it can be adapted to identify and evaluate indirect, cumulative and impact interactions. A more complex checklist can be used qualitatively and evaluate impacts to a degree. However, they can be complex and cumbersome to use and not quantitative.

Integrated Habitat System (IHS)

IHS is aimed to provide an integrated approach to collection, management and analysis of habitat data, optimising the use of existing habitat data through effective translation and providing a basis for overviews of the habitat resource. It includes a software translation tool, which can translate various data types into priority habitats, manuals for field survey, protocols for GIS use etc. Set up and run by the SOmerset Environment Records Centre (www.somerc.com).

Intertidal Form Analysis

Considers the equilibrium shape of the cross-shore profile.

Land use partitioning analysis (LUPA)

Linear infrastructure cuts across habitats, leading to habitat fragmentation. Land use partitioning analysis identifies, assesses and records the effect of partitioning on the size and quality of areas of non-fragmentation. It can identify non-fragmented areas, areas of high biodiversity value, grade areas of no-fragmentation by size and quality and represent grades on a map. It deals with a topic not usually addressed, with good visual representation, however it is expensive, time consuming and limited to a few topics.

Mathematical models, such as empirical models (both general and specific) and process descriptive models (steady state and dynamic)

Provide a quantifiable estimate of the likely effects of a number of variables. An analytical method that enables a quantification of cause-effect relationships by simulating natural conditions.Quantifies the cumulative effect, the spatial and temporal boundaries are usually explicit and it addresses specific cause-effects.Such a system often requires large investment of time and money, it can be difficult to adapt existing models and the value depends on baseline data.As regards response models, these are represented by a collection of computational models, rules and subjective judgments to enable a link between the cause and consequence to be made. There is no one model that can be used, with some being specific to certain processes, others used on their own and some needing to be interactively linked.Need an input from a modeller.

Model to assess how many dives a diver needs to make to maintain its energy balance (energy expenditure:energy consumption) (Alterra)

To gain a better understanding of the prey choice and energy budget of common eiders, Alterra developed a model using published data. It constructs for a diving cycle the heat and energy budgets involved and calculates how many dives are needed to maintain energy balance. Model has several assumptions that may be incorrect, but the inaccuracies were considered minor.

Modelling Nutrient Cycles (Alterra)

EcoWasp divided the western parts of the Dutch Wadden Sea into a number of compartments, each having a littoral, sublittoral and deep water part, together with sediment. External input from a lake, internal exchange between compartments and exchange with the open North Sea was described in terms of flows and concentrations of matter. For each compartment, primary and secondary production and degradation of organic matter was described, together with the exchange of matter between air and water and between water and sediment. Filter feeders were introduced to the model. The model could be run to see the effect of changing light, nutrient, filter feeders etc on the system.

Morphological (Bed updating) Models

Prediction of changes to bed levels based on sediment transport modelling. The bed is updated at regular intervals to provide a feedback to the hydrodynamic and sediment transport models.

Multi Criteria Analysis

MCA analyses and compares how different alternatives achieve different objectives, assisting in identifying preferred methods. It involves choosing relevant assessment criteria for each impact/indicator, identifying alternatives, scoring how each alternative affects each indicator, assigning a value of importance to the indicator, aggregating the score and weight of each alternative. In essence, it weighs up the relative degree of impact from individual criteria, enabling significance of impact and mitigation to be more accurately targeted.

Network and Pathway/Systems Analysis/Causal Chain Analysis

Used to classify, organise and display problems, processes and interactions. The method visually shows relationships and interactions among proposal and resource. It differentiates individual, additive and synergistic interactions and can give a causal analysis of cumulative impacts. The approach is based on the premise that the environment operates in a complex web of interactions and when one element is affected it has an effect on those elements that interact with it, both directly and indirectly. The mechanism of cause and effect is explicit. Such assessments are quick, cheap and can involve public participation. However, if not done fully can miss important impacts. They do not deal well with spatial impacts or temporal impacts, with diagrams potentially being too complex.

Other hybrid combinations

Other forms of hybrid model that combine some form of goal seeking target steady state with process based calculations at discrete time intervals, to iterate towards a solution.

Particle Tracking (Lagrangian) Models

Pr edition of particle movement by seeding particles into the flow regime with given properties (size, density, settling velocity etc) and tracked in a langrangian manner.

Public participation, consultation and questionnaires (Qualitative method)

The public often have good understanding of local issues and problems, although the focus is often on the obvious and attractive (such as mammals). Provides an opportunity to gather information about a wide range of actions that may affect the impact of a project, including past, present and future. It is flexible, considers potential impacts early on and can be focused to specific information. However, it is prone to errors of subjectivity, can be time consuming and have a poor response.

Regime Relationships

Relates estuary form properties such as cross-sectional area, plan area of intertidal or subtidal to tidal prism, volumes to given elevations, sediment type, and erosion threshold.

Risk assessment

Risk assessment involves estimating the probability and severity of hazards, requiring identification of possible hazards, identification and analysis of consequences, and estimation of frequency. The result is statements of probability for a specified event to occur in a given time period. Risk assessment can be used to compare alternatives on the basis of the risk inherent in each option, although extrapolation in the process leads to uncertainties, the degree of which depending on assumptions made. Many risk assessments do not assess certain effect, instead assessing whether some consequence would be expected. There are several problems attached to risk assessments, such as whether thresholds of effect differ.

Saltmarsh Analysis

Relates properties of exposure and tidal range to the presence and distribution of species

Scenario/sensitivity analysis

The impacts of a plan/project or benefits of different options will depend on outside variables, e.g. the achievement of conservation targets may depend on whether a development crosses the boundary of the habitat or if a site is managed. Comparison of impacts from different scenarios identifies uncertainties, ways of reducing uncertainties, and enables the formation of the most robust plan to be identified.

Sediment Budget Analysis

Reconciliation of sediment inputs, outputs and sources/sinks within the estuary.

Sediment Quality

Techniques to establish the transport pathways of sediment and the way in which contaminants are adsorbed and released from the sediment.

Sediment Transport Models

Process based modelling of bed load and suspended sand and/or mud movement, with relationships to determine the rates of erosion and deposition.

Socio-Economic

Techniques to address the pressure-state-impacts-response cycle, usually in terms of some form of economic valuation, as a basis for predicting societal responses and so identifying how the pressures may change in the future.

Spatial analysis techniques/GIS

Mapping data in GIS links attributes to mapped areas, enabling the data to be analysed e.g. for areas of habitat, interpolation between data points etc. The results are visually accessible, with images containing data on more than 1 layer. Maps can be overlaid to identify where cumulative impacts may occur and to establish areas where impact significance is greatest, and assist in determining temporal and spatial boundaries. However, it can be expensive, time consuming, difficult to quantify and there are problems with updating overlays. It is generally only used for spatial data and not temporal. Essentially, it provides a tool for data description rather than data analysis.

Statistical, Spatial and time series analysis

Uses standard data analysis techniques to identify dominant components, trends, cycles and relationships between variables, to give insights into the dynamics and complexity of the system.

Tidal Asymmetry Analysis

Examines changes in tidal wave propagation as a function of estuary form.

Uniform sediment flux or sediment balance

In this type of model, sediment is moved within the estuary until a steady state is achieved when equal amounts are moved on the flood and ebb tide.

Valued Ecosystem Components (VECs)

VECs provide a focus for assessment, by identifying the valued and protected features. The vulnerability of a VEC to a given development is assessed by the following: V1=ExS and V2=V1xR (Where V2= Vulnerability, V1= vulnerability (not weighted against recoverability) E= Exposure, S= Sensitivity, R= Recoverability).

Vulnerability analysis

Vulnerability analysis combines GIS and MCA to assess impacts of an activity on vulnerability of an area. Vulnerability is defined as the combination of sensitivity and value. A typical vulnerability analysis involves the following steps:· Define the impacts and receptors;· Prepare vulnerability maps of receptor sensitivity and evaluation criteria (e.g. 0 = not vulnerable, 4 = very vulnerable);· Overlay vulnerability maps in GIS, to identify areas of high vulnerability;· Using GIS, overlay expected impacts onto vulnerability maps and add weighted impacts to identify alternatives with least impacts. Vulnerability analysis enables a quantitative description of spatial impacts at all scales. However it can be costly and time-intensive, only works with impacts that can be mapped, and ‘hides’ value judgments about the sensitivity and value of receptors.

Wader Energy Balance and Tidal Cycle Simulator (WEBTICs model) (Alterra)

The model simulates the food uptake of oyster catchers and a distribution of the birds over exposed parts of tidal areas. The mudflats are described on input as a number of spots with position, height and area. Spots may contain prey items characterised by type, weight and density. The programme simulates tidal cycles and calculates the fraction of time the average and ideal bird has to spend feeding to meet its energy requirement. The foraging intensities are combined into a stress index for winter.

Water Quality

Models that represent the advection and dispersion of suspended matter, dissolved oxygen and contaminants