The Proposed Visiting Centre At Elkhorn Slough Environmental Sciences Essay

Elkhorn Slough has a visitors’ centre that focuses on the conservation of natural resources and biological history of the area. The Strategic Plan for 2006-10 (Elkhorn Slough Foundation [ESF], 2006) has an objective to increase membership and numbers of visitors but laments the limited capacity of the existing centre. It is therefore necessary to build a new centre to cater for the increased membership and visitors.

Global Information Systems [GIS] analysis methods were employed to analyse the environmental sensitivity issues of the Slough area and subsequently locate a proposed visitor’s centre. The new Visitor’s Centre will complement the existing one, but focus on stimulating visitors’ interests in the terrain (physical geography) of the Slough area. The new visiting centre will be located north of Empire Road.

Keywords: Boolean maps, Environmental sensitivity, GIS, Suitability, Visitors’ centre

Introduction:

Located 1.29x 103 m south of Watsonville [approximately 36° 20′ 18.72″N, 121° 31′ 17.17″W], Elkhorn Slough is the drainage delta for Salinas River and its tributaries in the surrounding farmlands (Cartier, 2009). Its watershed is an impressive 1.23×108 m2 and is part of a larger network of estuaries. Waters from Gabilan and Moro Cojo watersheds drain into the Elkhorn Slough through the Old Salinas River Channel at Moss Landing South Harbour (EFS, 2010).Totalling an area of 4x 10 m2, the estuary is a tidal, coastal salt marsh.

The estuary is home to 780 species of birds, a variety of plants, including several that are slowly becoming extinct (EFS, 2010). Elkhorn Slough consists of 1.09x107m2 of unique habitat types. (ESNERR, unpublished data) and has 2.83 x 107 m2 designated protected lands.

The Elkhorn Slough has a visitors’ centre that concentrates on the natural history of the slough area. Activities at the centre include show-casing the unique plant and animal life, birds as well as marine life of the watershed. It has an educational theme which focuses on the conservation of the resources and natural history of the slough area.

The Strategic Plan for 2006-10 (Elkhorn Slough Foundation [ESF], 2006) set out to increase membership and numbers of visitors to Elkhorn Slough area. However, the document noted the limited capacity of the existing centre to cater for increased numbers of visitors to the area.

As a compliment to the existing centre, it is proposed that the establishment of a second visiting site would be appropriate in trying to achieve the objective of increasing membership at the foundation thus boosting the number of visitors to the area. The concept for the new centre will focus on physical surroundings of the estuary and stimulate the local community and visitors’ interests in the historical and contemporary geography (terrain) of the Slough area. The centre will include an environment or conservation theme that will hopefully stimulate sustainable use of natural resources in the area, especially for the local community.

GIS techniques will be employed to site the location of the proposed second visitor’s centre at Elkhorn Slough.

Literature Review:

2.1 Location and History of Elkhorn Slough

Located at the midpoint of Monterey Bay, on the west cost of America, Elkhorn Slough is a large tidal salt marsh estuary in central California. Figure 1 below shows the location of Elkhorn Slough.

Figure 1: Location of Elkhorn Slough (ESF, 2010)

The estuary is referred to as a coastal embayment and consists of deepwater habitats with intertidal wetlands. It is the remnant of an ancient river flooded at the last sea level rise (EPA, 2010) that has been filled with sediment from the surrounding area.

An artificial opening to the Monterey Bay was constructed in 1947 exposing the Elkhorn Slough estuary to increased tidal exchange (ESF, 2010). The marshlands were also artificially drained to make way for the farmlands (ESF, 2010). This has vastly altered the natural flow of the estuary and changed the physical properties of the slough.

2.2 Environmental Sensitivity

The changes to the physical properties of the area have raised several environmental issues. The most important issues in the estuary are pollution [water quality degradation]; invasive plant species and hydrology alterations (Cartier, 2009). Brackish water habitats have been lost due to the redirection of water from the Salinas into the farmlands. Channel bank erosion rates ranging from 3×10-1 to 6.1×10-1 m per year and interior marsh dieback rates of at least 1.22x 104 m2 per year have led to marsh and habitat loss (ESF, 2010). These changes have affected the estuary’s animals and plants habitat, as well as public access sites and railroad and road infrastructure.

There are 2.83×107 m2 of protected lands in the Elkhorn Slough watershed. The estuary is also an important fish (recreational and commercial) nursery and prime stopover for migratory birds (ESF, 2010). The Moss Landing Power Plant at the mouth of the slough at bay end also lends to the sensitivity of the area (ESF, 2010).

As a measure to conserve the area, the ESF was established in 1982 by the Elkhorn Slough National Estuarine Research Reserve [ESNERR]. In 2006, the Foundation noted that the capacity of the visitors centre to meet the needs of increased number of members was limited. As such, one of the strategic objectives for 2006-10 was to increase membership and numbers of visitors to the area.

It is against this background that a new visitors’ centre is proposed to cater for increased membership and to stimulate interests in physical geography, encouraging sustainable use of estuarine resources.

Methodology and Data Processing

According to Sahoo et al (2000), GIS provides ample opportunity for reasoned land evaluation. GIS are quick methods and tools used by decision-makers to address and cope with uncertainty in decision-making where there are environmental sensitivity concerns.

GIS data processing and spatial analysis are used to define the location of a proposed development. This method along with modern decision analysis techniques can be used to improve habitat suitability evaluation over large areas (Store and Kangas, 2000). Analysis methods included investigations into accessibility, location, environmental sensitivity of the area as well as location-specific hazards.

In environmental studies, several factors are taken into account when deciding where to locate a new development. One of the most common approaches for locating new developments is Multi-Criteria Analysis [MCA] (Sahoo et al, 2000).

Employing the MCA technique, a mask is created and used as the extent of analysis. Raster calculations can be used to create Boolean maps (graphic representation of binary equation whereby 0 = no data, 1 = data present) that simplify the data to the specified criteria. Threshold values are then employed to simplify the decision making process into whether certain feature data can be included or excluded from the final choice of location.

Areas are included or excluded based on environmental sensitivity. For example, the United Kingdom’s [UK] Environment Agency recommends that protected areas remain free of development (Environment Agency, 2010).

According to the UK’s Highways Agency no development shall take place within, on average; 300 m of a busy road (rank-1). This is to create a buffer for noise pollution given that heavy goods vehicles can be very noisy at close proximity (Environment Agency, 2010). Similarly, distance of settlements from roads is important for easy accessibility reasons.

A further factor to exclude from the model is areas that contain vegetation because some areas sink due to diking and draining (ESF, 2010). Woodlands and marshlands lend diversity to the habitat and therefore have conservational importance. They are thus unsuitable for building/development. Similarly, surface water areas are unsuitable for development due to likelihood to cause pollution in areas such as the estuary (ESF, 2010).

Based on exclusion of environmentally sensitive areas, raster calculations are performed using the Boolean logic. Therefore, the remaining area is the potential location of the proposed development.

4 Data Analysis

Data used was originally obtained from the Elkhorn Slough website and the projection is UTM Zone 10N, WGS84 datum. In addition to the GIS data supplied, a digital elevation model [DEM] data of the area was obtained from the SRTM data on Google Earth [GE]. The data was re-projected with Global Mapper to overlay the two data sets in ArcGIS. The DEM was used to visualise the terrain of the area and guide decision-making on the suitability of the terrain for the proposed development. Other sources of data included available maps and literature on the area in question. The data used is illustrated in Figure 2 below.

Figure 2: Original data used (ESF, 2010)

ArcGIS 9.3 was used for data processing. All data was adjusted to cell size 50, with each pixel on the resultant Boolean maps being 50 m long.

5 Findings

As outlined in section 4 above, environmental organisations, such as the UK’s Environment Agency, Figure 3 below shows the raster of the protected area that is excluded in the final calculation.

Figure 3: Protected Area

Using data on the road network of the Elkhorn Slough area, Figure 4 below shows the buffer created around the busy roads [rank-1] which are unsuitable for locating the new visitor’s centre. The light-shaded areas are, theoretically, suitable for locating the centre.

Figure 4: Buffer Zone around Rank-1 Roads

Taking into consideration data on the vegetation in the Elkhorn Slough area which requires exclusion from the analysis due to diking and draining for cultivation, Figure 5 below shows that the new visitors’ centre can be located in the light-shaded areas. The dark-shaded areas have conservational importance for the wood and marshland species.

Figure 5: Vegetation areas

Surface water areas are also excluded from possible location of the new development due to likelihood of water pollution, as shown in Figure 6 below.

Figure 6: Water Areas

The wetlands area was also excluded from the possible location of the centre because these areas are known for their ecological diversity. Vast numbers of birds and plants as well as micro-organisms (mud species) would be in this area. Figure 7 below shows the wetlands areas of the Elkhorn Slough which was also excluded as potential areas for locating the new visitors centre.

Figure 7: Wetland areas

An elevation of 40 to 195m was chosen as the optimal height above sea level for the development. The elevation is considered suitable to facilitate transport logistics of building materials. The elevation also takes into consideration the tidal nature of the area to ensure that the new visitors centre is protected from any possible tidal effects.

Applying the necessary measurements and raster calculations leaves the areas that are potentially suitable for siting the new centre as illustrated in Figure 8 below.

Figure 8: Optimal Elevation for New Development

Another important consideration was the distance to roads for ease of accessibility to the new centre by visitors. This is illustrated in Figure 9 below.

Figure 9: Distances to roads

Figure10 below shows the final results excluding environmental sensitive features and measurements.

Figure 10: Location of Visitors’ Centre

Corroborating the Boolean logic with Google Earth, the second visitors’ centre can theoretically be sited at a location north of Empire Road.

Limitations

Three areas with data on the resultant Boolean map match the criteria defined. Potentially, these are the locations for the new visitors’ centre. However on closer inspection by overlaying with data on the road network, an area between Elkhorn and Dolan rank 1 roads [close to Empire Road] remains after further scrutiny using GE. Using this database imagery, the proposed site is just outside a forested area.

Crucial information is missing from the analysis above. For example, information was missing on the location of current buildings on which the proposed site cannot be located. Information was also missing on the heaviness of traffic at different times to better estimate the buffering distance of the rank-1 roads (assuming they are asphalt). Other information missing was on tidal range and volume of the coastal zone with the attendant high flood risk.

Therefore, given that the data available for this analysis was not entirely straight forward rendering the proposed location of the new visitors centre tentative. Digital Terrain Models (DTM) by using Light Detection and Ranging (LIDAR) technology to obtain more complete and accurate surface data. Had data been more complete and accurate, the positioning of the centre would be more conclusive; without the need to use a further data source.

This analysis shows that although data processing and software can sometimes be expensive, GIS methods can conclusively be used in defining areas for development, and are quicker than traditional methods of exploration of new areas. (Store and Kangas, 2000).

Conclusion and Recommendations

Available data shows that the proposed location of the new visitors’ centre is close to Empire Road. Due to incomplete data, the proposed location of the second visitors’ centre is tentative. The evaluation has highlighted the need to have a more conclusive data set to avoid the need for re-projection from other sources, which may cause inaccuracies in positioning.