Visual Impact Assessment Guidebook


Table of Contents


Visual impact assessment procedures

Visual impact assessments estimate, in perspective view, the potential visual effect of proposed operations on the scenic landscape. These assessments are used to confirm whether visual quality objectives for these sites will be achieved. This section describes a five-step process for completing a visual impact assessment and identifies the various products that are required as part of the VIA report.

Figure 5 The five-step visual impact assessment process.

In practice, the VIA process may not be carried out in such a straightforward sequence of steps as shown in Figure 5. Many aspects of steps 1 and 2 may have already been completed in developing the forest development plan. In addition, a certain amount of interactive work may be required to develop visual design options and test, through visual simulations, their ability to meet visual quality objectives. Refer to the Visual Landscape Design Training Manual to assist in designing various options for proposed operations.

The following pages describe in more detail the typical procedures and sequence of events for each step of the visual impact assessment process.

Step 1: Planning and pre-field trip preparation

The purpose of this step is to gather and transfer onto maps all of the information that is known prior to carrying out the fieldwork. It is also a good time to contact district staff to discuss any assessment uncertainties and confirm viewpoint selection.

Step 2: Conducting fieldwork

The purpose of the fieldwork is to gain an on-the-ground familiarity with the planning area from a visual perspective, to locate the pre-selected viewpoints, and to gather data. This step is also necessary to confirm whether these pre-selected viewpoints require updating on the basis of the actual viewing conditions.

Step 3: Developing design options and preparing visual simulations

Step 4: Assessing visual simulations

The purpose of this step is to evaluate whether a proposed operation will achieve the established visual quality objective.

The evaluation is conducted at all important viewpoints. In addition, the existing non-visually effective green-up alterations within, and immediately adjacent to, the unit must be considered in this evaluation. Three variables are used to assess the visual simulation(s).

  1. Basic VQO definition: Does a proposed operation meet the basic visual quality objective definition?
  2. Visual design: Does a proposed operation exhibit elements of good visual design?
  3. Numerical assessment: In perspective view, what proportions of the landform or unit are represented by existing non-visually effective green-up alterations and a proposed operation? What percent volume or stems will be left in the block? What level of site disturbance will be present?

In order to receive approval, it is imperative that all existing and proposed operations meet the basic VQO definition and exhibit elements of good visual design. The numerical assessment should be used only as a yardstick to help determine into which class the cumulative alterations on a landscape fall.

More detailed information about each of these variables is presented in the following subsections.

1. Visual quality objective definition

This is a measure of the ability of proposed operations, in combination with non-visually effective green-up alterations, to achieve the basic VQO definition. Table 1 presents an outline of these definitions.

Table 1 Visual quality objectives: five levels of landscape alteration

Preservation (P)

No visible activities

Retention (R)

Activities are not visually evident

Partial Retention (PR)

Activities are visible, but remain subordinate

Modification (M)

Activities are visually dominant, but have characteristics that appear natural

Maximum Modification

(MM)

Activities are dominant and out of scale, but appear natural in the background

The assessment summary form in Appendix 2 outlines a process to evaluate and report on whether proposed operations will meet the visual quality objectives. This summarization will become an integral part of the assessment report.

2. Visual design of proposed operations

This is the measure of the ability of proposed operations to achieve the visual design concepts and principles as set out in the Visual Landscape Design Training Manual. Answering the following questions will help to guide the assessment.

Key visual design concepts and principles

Incorporating the following important design concepts and principles into the planning of landscape- and stand-level forest development proposals will lead to better visual design. Refer to the Visual Landscape Design Training Manual for visual representations and more in-depth explanations of the principles presented below. The manual also provides additional concepts and principles.

Landscape-level cutblock design The following guidelines provide some clues for designing cutblocks at the landscape level based on internationally recognized design concepts and principles.

Table 2 A guide to determine appropriate opening size in perspective view at the landscape level

Factor

Appropriate opening size


Smaller <-----------------------------------------------------------> Larger

VQO

Viewing distance

Landform scale

Slope

Viewing angle

Natural openings

Vegetation patterns

Non-timber values

Preservation --------------------------------------Maximum modification

Foreground --------------- Middle ground ----------------- Background

Small, continuous ----------------------------------------- Large, broken

Steep ------------------------------------------------------------ Gentle

Direct, focal ---------------------------------------------------- Oblique

Small, discontinuous, or none ------------------------- Large, connected

Subtle, distinct -------------------------------------------- Large, mixed

High -------------------------------------------------------------- Low

Stand-level cutblock design The following guidelines provide some clues for designing cutblocks at the stand level based on internationally recognized design concepts and principles. More information on these and additional concepts and principles can be found in the Visual Landscape Design Training Manual.

Road design The following guidelines provide some clues for designing roads on the landscape based on internationally recognized design concepts and principles. More information on these and additional concepts and principles can be found in the Visual Landscape Design Training Manual.

3. Numerical assessment

The numerical assessment provides a measure of the ability of a proposed operation to achieve the numerical standards that predict a VQO. Percent alteration is used to assess the impact of clearcutting, volume or number of stems removed is used to assess partial cutting, and the level of site disturbance within a cutblock is used to assess the impact of roads.

Clearcutting: Percent alteration

Percent landform (unit) alteration is a reasonable predictor of achieved visual condition. To achieve a specific visual quality objective, this measure should fall within the ranges presented in Table 3 for those units harvested using a clear-cutting or seed-tree system. Factors that can influence the appropriate position within each alteration range include: visual absorption capability, slope, viewer position, viewing distance, quality of design, and number of residual trees.

If the other two variables are dealt with satisfactorily, an acceptable rationale can be submitted to support alterations beyond this range. Larger cutblocks may be accepted and approved if appropriate design principles and techniques are employed and these cutblocks meet the basic definition for the visual quality objective.

The following describes the general steps for making a numerical assessment of a clearcut. Refer to Appendix 8 for a more detailed account of the calculation procedures for percent alteration.

Use a planimeter or computer digitizer to measure (in perspective view) the visible landform unit that contains the proposed clearcut or seed-tree operation and to determine the size and scale of the operation itself. Include all previous operations that have not yet achieved visually effective green-up.

Table 3 Predicting visual quality objectives based on percent alteration only (for clearcut and seed-tree silvicultural systems). Shaded areas indicate the most probable range for predictions based on percent alteration in perspective view only.

Visual quality objective

(VQO)

Percent alteration per VQO


Percent of visual landscape or landform permitted
to be in non-vegetated statea



0------------10---------------------20 -----------------------30
Preservation 0
Retention 0–1.5

Partial Retention 1.6–7.0


Modification 7.1–18.0


Maximum Modification 18.1–30.0

a These percentages apply to the visible green portion of the landscape in perspective view. Rock and ice patches are excluded from the calculation.

Partial cutting: Volume or stems removed

Partial-cutting silvicultural systems must also be designed and carried out to meet established visual quality objectives. Partial-cutting systems always result in the retention of some volume or basal area on a cutblock. The net result is a change in the forest canopy texture. On cutblocks where a very low volume or basal area is removed, the change in texture is minimal. On cutblocks with a high level of removal, the texture becomes coarser. In situations where the removal rate is such that the ground becomes readily visible (e.g., seed-tree operations), the public no longer see a partial cut; they perceive a clearcut with only a few trees left.

Table 4 shows the likelihood of achieving a VQO for various combinations of volume or stems removed by tree height. Within the 10–40 m tree height range,
a 90% confidence of achieving the VQO is shown. For example, if 50% of the volume is removed for a tree height of 30 m, Table 4 shows that 90% of the time you will achieve partial retention. In some circumstances, the number of stems or volumes proposed for removal will fall outside of the data presented in this table, but will still achieve the visual quality objective.

Table 4 Predicting visual quality objectives using even-distribution, leave-tree, partial-cutting silvicultural systemsa.
Column values across top = mean height (m) of residual trees.
Row values down left = volume (stems) removed (%).

  5

10

15 20

25

30 35

40

45 50
10 Rb

R

R R

R

R R

R

PR PR
20 R

R

R R

R

R PR

PR

PR PR
30 R R

R

R PR

PR

PR PR

PR

PR
40 R

R

PR PR

PR

PR PR

PR

PR M
50 PR PR PR

PR

PR PR

PR

M M

M

60 PR

PR

PR PR

PR

M M

M

M M
70 PR

PR

PR M

M

M M

M

M M
80 PR

PR

M M

M

M M

M

M M
90 M

M

M M M

M

M M

M

M

a To use this table: First determine what percent of the stand you wish to remove, either in volume or by stems, along
Y-axis. Then determine the mean tree height of your stand along X-axis. Follow volume (Y) axis across and the tree height (X) down; their intersection point will yield the VQO you will most likely achieve.

b R = retention; PR = partial retention; M = modification. See Table 1 for definitions of visual quality objectives.

Table 4 is based on the assumption that each stem proportionately contributes an equal volume to the stand. The data presented here were derived from forest stands with the following characteristics:

Note: Use caution when extrapolating beyond these parameters.

Table 6 in the report Visual Impacts of Partial Cutting provides a much more detailed breakdown on both volume and stems removed. In addition, the report provides some guidance (see its Table 5) on use of basal area for achieving visual quality objectives. As long as a sufficient number and distribution of overstorey trees are retained to meet the visual quality objective, no maximum opening size is specified for partial-cut areas.

Observing the following guidelines will help to achieve the visual quality objective.

Note: Observer position (i.e., above, level, or below the unit being viewed) can influence the number of stems or volume that must be left.

Appendix 9 contains a set of photo sheets that provide visual resource management practitioners with examples of the range of impacts acceptable for and within each visual quality class/objective category.

Roads and other site disturbances

Roads and other site disturbances can create some of the most severe and longest-lasting visual impacts on the landscape, unless carefully designed, constructed, and maintained.

Guidelines for designing roads on the landscape are presented earlier in this guidebook (see Step 4: "Visual Design of Proposed Operations" in the "Visual Impact Assessment Procedures" section). Table 5 identifies the amount of site disturbance found to be socially acceptable within a cutblock.

Table 5 Acceptable amount of visible roads and other site disturbances within a cutblock by visual quality objective

VQO

Amount of visible roads and other site disturbancesa

Preservation
  • No visible roads or other site disturbances.
Retention
  • Roads or other site disturbances, if visible, will be difficult to perceive.
Partial Retention
  • Roads and other site disturbances may be visible, but will not dominate.
  • The visible impact should have disappeared by the time visually effective green-up is achieved.
  • In instances where logging activities have created site disturbance within a cutblock, the total area of visible site disturbance should be less than 5% of the logged opening.
Modification
  • Roads and other site disturbance will be visible and may initially dominate.
  • The visible impact should have disappeared by the time visually effective green-up is achieved.
  • Where logging activities have created site disturbance within a cutblock, the total area of visible site disturbance should be less than 10% of the logged opening.
Maximum Modification
  • Roads and other site disturbance may dominate.
  • The visible impact may not have disappeared by the time visually effective green-up is achieved.
  • Where logging activities have created site disturbance within a cutblock, the total area of visible site disturbance should be less than 20% of the logged opening.

a The allowable percent disturbance figures presented here are based on very preliminary research done in this subject area. These data will be refined with public perception research in the near future.

Important considerations related to Table 5:

Step 5: Preparing a visual impact assessment report

A recommended visual impact assessment report format and content is described below. Following this format will ensure consistency and may accelerate the review and approval process where the district manager has requested to see an assessment or the assessment is to be presented publicly. The assessment report or package should be self-contained and must be completed before the silviculture prescription is approved or before a road layout and design is submitted for approval. Where districts have standard operating procedures for visual resource management, district managers may wish to provide specific direction as to their requirements.

While there are many factors influencing the type and amount of information needed in a visual impact assessment report, the following basic information is considered essential to any report.

Basic content

  1. Topographic map (1:50 000 or larger scale) showing:
  2. Pre-operations colour photograph(s) from important viewpoints (minimum size: 4 x 6").
  3. Visual simulation product (sketch, photo, digital terrain model, or hybrid) showing proposed operations.
  4. Completed visual impact assessment summary form (Appendix 2).

Note: The form has enough space for four viewpoints only. If an assessment involves more than four viewpoints, use additional copies of this summary form to capture all data.

Additional content

Depending on the visual sensitivity class, visual quality objective, number of viewpoints, complexity of the proposed operations, and/or silvicultural system proposed, additional supporting information may be required to accompany the assessment report (see Table 6).

Table 6 Additional supporting materials for visual impact assessment reports

Content

When required

Sight-line plots from key viewpoints and map showing viewpoint locations and lines of sight (1:20 000 scale or larger) to confirm visibility and visual impact. In support of manual simulations, such as sketches, annotated (touched-up) photographs, or acetate overlay on photographs.
Digital terrain model presentation criteria as per Appendix 5. When computer simulation used.
Visual force analysis on topographic map and photograph overlay. For all areas with a medium or high VSR or areas with a VSC of 1,2 or 3.

Usually not required for partial-cut systems with at least 50% of the basal area remaining.

Digitally retouched photographs. Areas with high public concern and expectations and where public presentations are required.

 

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