Geography 85
Applications on GIS and Related Technology


image1Putting Together a GIS for the Dry Creek Conservancy - Part I

Where to begin?  So much data already existed, such as creek location surveys for various reaches (stream sections), bug surveys (to indicate stream health), fish surveys (to measure the amount and extent of salmon spawning), historic changes to the stream channel, flood maps, and numerous other specialized studies in the form reports, tables, CAD drawings, and paper maps.  Virtually all of this data was not "GIS ready" or "georeferenced" to be easily placed in a GIS.

Then came along CALFED (1994) - "a framework agreement by state and federal agencies with management and regulatory responsibility in the Bay-Delta Estuary" regarding water supply and water quality to meet all stakeholders' needs (agriculture, urban users, wildlife, etc.) and deal with flooding.  As the Bay-Delta region is fed by a vast watershed system feeding into the Sacramento River, this cooperative program could not ignore upstream sources of water too.

CALFED provided funding to form local watershed groups, such as the Dry Creek Conservancy (DCC), and since then hundreds of watershed groups have been formed around the State to protect, restore, and maintain the health of local watersheds.  Other measures and propositions have been favorable to watershed groups, such as Prop. 204 and 13 (the new one).

Enormous urban growth in the Western Placer County has also driven the need to protect the Dry Creek watershed.  A major tributary known as Secret Ravine runs through Sierra College.  Other parts run right through downtown Roseville.  Salmon still spawn up these small tributaries like Secret Ravine and bravely swim to the upper reaches of the watershed in Loomis.  The fish must also pass over several dams and obstacles.

The main water corridor then travels north of McClellan A.F.B. and into the flat Rio Linda area, eventually spilling into (canal-like channel) called Steelhead Creek or the Natomas East Main Drain;  then it eventually flows into the confluence area of the American and Sacramento Rivers.  In addition to maintaining and improving this amazing salmon journey from the sea to Sierra College, much work remains to identify what else impedes this fish migration.  Flooding is also of paramount concern for downstream residents, as mentioned in the Secret Ravine Adaptive Management Plan.

Another reason the Dry Creek watershed is so important to local planning efforts (spearheaded by the DCC and Placer County, is the planning of a potential open space corridor (called the Dry Creek Greenway) to connect the watershed corridors with Sacramento County's greenbelt system (

Thus a GIS base map was essential.  But funding was limited.  Creating a base map involved gathering existing data, such as Placer Legacy data from the County, the City of Roseville, Sacramento County, and private environmental consulting firms such as ECORP consulting and Foothill & Assoc.  All of the data had to be brought together into the same geographic coordinate system and projection (State Plane, North American Datum 1927 [NAD27].  Accuracy had to be attained so that all the layers' boundaries matched.  This was a challenging task, especially when the base map involved using parcel data with many polygons to correct.  (Still the Placer Co. and Roseville parcel maps are inaccurate as of 2004). 

Subsequently, the DCC discovered that other agencies had created partial base maps for their own projects, such as CalEPA, which could have been used.  Communication, coordination, and sometimes who you know comes into play.  In order to ease communication barriers and expedite the transfer of data, Sierra College offered to provide a FTP site (a server to remotely exchange data).  In fact, much of the data gathered locally was placed on the FTP server for the base map contractor -- the Geographic Information Center at California State University, Chico -- to access and assemble.
The DCC base map, however, will be the most encompassing, robust and accurate.  The watershed area covers numerous political boundaries, has more street names and details, and will be more accurate than previous base maps.  For example, the DCC base map brought together many sources that were previously missed.  In regard to robustness, Thomas Guide maps were used to insert more names into the roads attribute table.  In regard to accuracy, much of the upper watershed stream lines were created by walking the streams with a GPS units.  This method captures the meanders and nuances that would be otherwise missed by digitizing the streams.  Eventually other control points will be field checked with GPS units.

To keep the base map accurate is always a challenge.  Recently I received a loose note that said the "Taylor Ranch" was actually the "Traylor Ranch."  Parcels are always changing because of new, larger subdivision or individual subdivision.  Lot line adjustments and easements happen yearly as well.  Newer orthorectified imagery will also influence how parcel lines are adjusted.  For example the City of Roseville has parcels off (not in line with real-world coordinates) by as much as 50 feet.  The newer aerial photos should be flown soon and will be used to correct these errors.  Existing and subsequent parcels will then have to be corrected (sometimes called "rubber-sheeting") to match the aerial landmarks, control points, right-of-ways (streets), and parcels.


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