Five Existing Natural Conditions To Identify in a Site Inventory

Site Inventory Series Logo for the California Supplemental Exam (CSE) for landscape architects.Landscape architects regularly inventory existing natural site conditions as part of a site inventory. There are several different natural existing conditions that landscape architects should be familiar with for the California Supplemental Exam (CSE) for landscape architects.

According to the CSE landscape architect candidate guide, the exam may test your knowledge of “knowledge of types of natural conditions that should be identified.”

Let’s review some natural site conditions that we should be confident identifying in California. Some of this will be a good review for those who have already passed the LARE. Other natural conditions will highlight some of the unique natural and environmental conditions in the Golden State.

Existing Natural Conditions

Many natural existing site conditions provide opportunities or constraints further along in the design process. These are some existing conditions to consider when conducting a site inventory in California:

  • Geological Substrate
  • Topography and Landform
  • Soil
  • Hydrology
  • Vegetation

We will look at each condition and discuss what salient observations should be made in order to pass the California Supplement Exam for landscape architects.

Geological Substrate

The geologic substrate of a site an potentially have an immense direct and indirect affect on site development and construction costs.

The geologic substrate is the make-up of the strata of rock and soil underneath your site. The composition of a site’s geology can play both direct and indirect roles in determining to opportunities and limitations of a site.

Direct effects of the geological substrate include limitations on building and landscape feature foundations due to bearing capacity and through constraints placed on activities that can introduce instability (i.e. landslides, etc.).

Indirectly, geologic substrate affects the types of soils that develop on a site which influences the plant and animal communities which naturally will occupy the area.

Here are some things to look for when inventorying geologic substrate elements of a site:

  • Solubility
  • Prone to movement (i.e. landslides)
  • Expansive soils
  • Excessive permeability
  • Impermeability
  • Low bearing capacity for structures
  • Excessively shallow soils

Topography is composed of soil and geologic substrate. Now, we will review the site inventory process for topography.


Topography can be defined as the physical shape or form of the land. No other single factor has such an influential impact on the location and type of development as the site’s topography. During the site inventory phase, landscape architects observe and record a site’s landform and note areas suitable for development and locations that may pose some degree of difficulty for the designer.

Topography and landform greatly influence other existing natural conditions by directing energy flows through a site. The grades found on the site determine how water moves over the surface of the site. Landform dictates where areas of flow, erosion, and deposits occur. Wind, microclimate, and ventilation are also affected by topography.

Here are some items to inspect for when conducting a site inventory:

  • Areas with exceedingly low slopes that may not drain well
  • Excessively steep slopes that are difficult to develop
  • Locations with grades most suitable to development
  • Exposed bedrock or rock outcroppings

Identifying existing topography features and conditions will help fuel a good site analysis.


Hydrology is the study of water’s behavioral properties and characteristics as it interacts with the environment. Water flows across the surface of a site and below a site.

While rain is normally a blessing for a dry place like California, occasional destructive flooding can occur. Understanding a site’s hydrology is critical for protecting the safety of a site’s inhabitants.

For the sake of this discussion, we will limit the scope to the site level.

Hydrology is divided into two categories: subsurface hydrology and surface hydrology. We will discuss each type of hydrology and review which things landscape architects should investigate during a site inventory.

Surface Hydrology
Surface hydrology is the study of surface water flows on a site. The surface flow of water is strongly influenced by topography.

While visiting a site, a landscape architect will likely identify major drainages and existing surface water.

What may not be immediately evident from field observation are minor drainage paths and sheet flow patterns.

Fortunately, landscape architects can refine their observations by studying a detailed topographic survey of the site.

Some surface hydrology items to look for on a site include the following:

  • Active rivers, steams, creeks, springs or other forms of surface water
  • Dry washes or intermittent streams or other seasonal water courses.
  • Areas of erosion caused by water flow.
  • Areas where water-borne deposits settle and accumulate in the landscape.
  • Drainage patterns on and off-site.
  • Is the site within the 100 year flood zone?

Surface hydrology has immediate impacts on site development that can benefit a client or endanger the site’s users. A thorough site inventory greatly improves the outcome of a project because it leads to better site analysis and design solutions.

Subsurface Hydrology
Subsurface hydrology is the study of water and it’s behavior underground. Water flows below grade as well as above grade.

Groundwater can provide opportunities for recharging the aquifer or providing a site’s potable and irrigation needs through wells.

High water tables can also pose problems for development and increase the risk of catastrophic earthquake damage through liquefaction.

Some items to investigate during a site inventory include:

  • Does the site show any evidence of a high water table?
  • What is the water table height
  • Are there any existing wells on the site?
  • Liquefaction potential
  • Subsidence caused by overdrawn water tables
  • Does the water table affect soil and slope stability?

A site’s subsurface hydrology can impact development and design opportunities.


Soil is the thin crust of minerals and organic matter that blanket the earth.

Understanding a site’s soil is an important step in the site inventory process for many reasons.

Soil supports buildings and structures. Before designing new structures and spaces, landscape architects must be confident that a site’s soil is up to the task.

Second, soil supports plant life. No all soils are equal when it comes to supporting healthy plant life on a site. Understanding the soil early in the design process can identify problems and opportunities which can be addressed and incorporated into the final design solution.

Some things to keep in mind about soils when conducting a site inventory:

  • Are there areas of rich, fertile soils that support abundant plant life?
  • Do areas of barren or infertile soils exist in some parts of the property?
  • Has the site been exposed to toxic chemicals from past land uses? For example, manufacturing and agriculture uses sometimes leave behind toxic residue in the soul long after these activities have stopped.
  • Do the soils permit septic leach fields?
  • Is the permeability adequate for site drainage?
  • Is there a significant risk for shrinking or swelling due to changes in soil moisture?
  • Is erosion an issue?
  • What is the soil type and morphology?
  • Are corrosive soils present on the site?


As landscape architects, we naturally gravitate towards all things green.

Unless a site has been totally striped, there will be some existing vegetation to observe. There are two reasons why landscape architects are concerned with vegetation on a site.

First, existing vegetation can reveal a lot of hidden information about a site.

Second, vegetation can be a valuable site feature that may be integrated into any new site development. We will dig deeper into each of these concepts.

Landscape architects are environmental detectives. Plants in the landscape are like clues to a detective for us. Here are some things plants can tell us about a landscape:

  • Poorly-drained areas
  • Fertile soils
  • Sterile soils
  • Areas of soil compaction
  • Wind conditions and predominant wind direction
  • Water table height
  • Wildlife potential
  • History of human development

In addition to providing clues about a landscape’s hidden potential and history, vegetation may also be a striking site feature worthy of further consideration in the site process.

Some items to inventory include:

  • Specimen or significant native trees and vegetation
  • Locations of masses of existing vegetation.
  • What plant community or plant communities are present on the site?
  • What plant associations are on the site?
  • Presence or invasive weeds or plant species.
  • Identify endangered species on the site.

Vegetation is another existing conditions that landscape architects need to inventory during the site inventory phase of the design process.

Site Inventory = Good Site Analysis = Good Design

Natural existing conditions are just one set of observation that landscape architects make during the inventory phase of a design project. The better quality these initial inventory observations are, the better the site inventory and subsequent design will be.

Ask questions and dig into the existing natural conditions.


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John is a landscape architect who is currently preparing to take the California Supplemental Exam to become licensed in California. He is currently a licensed professional landscape architect in Georgia and Florida. John graduated from California State University, Pomona with a BSLA degree in landscape architecture in 1997 and has extensive practice experience in residential and commercial landscape design.

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