Showing posts with label hydrography/hydrology. Show all posts
Showing posts with label hydrography/hydrology. Show all posts

Friday, July 24, 2015

Add a Web Mapping Data Service to ArcMap

I have a hole in my current coverage of waterbodies - I need to know the name of a few streams, and the dataset of Rivers doesn't include the stream I need. I don't necessarily want to download and manage another whole dataset of flowing waters. Temporarily referencing a Web mapping service in my ArcMap project would be great.

The best database I am aware of that includes comprehensive waterbody geometry and names is the USGS's National Hydrography Dataset. Thankfully, they do indeed provide a Web mapping service!

Search for a Mapping Service

A quick Google search with the phrase nhd web map returns a direct link to the USGS National Map's map service endpoint:

http://services.nationalmap.gov/arcgis/rest/services/nhd/MapServer

  • Copy this URL from the browser for use in the next section
These Map or Feature Service URLs (referred to as "service endpoints" or simply "endpoints") aren't always so easy to find, so other projects/data services may require more digging. Look for clues in the URL itself such as the /rest/services/ directories, and for minimal styling (basic-looking fonts, colors, lists, etc.).

To link to a specific portion of the map service (for instance a specific layer or layer group within the main service layer), follow some of the links under the Layers list (see below). Copy that specific URL for use in the next step if you would like. Compare the following URL that represents the Waterbody layer which is layer position 11 in the service package:




Add a Service to ArcMap

  1. Click the Add Data button 
  2. Change the Look in category to GIS Servers

  1. Double click on Add ArcGIS Server to launch the Add ArcGIS Server wizard
  2. Accept the default value to simply Use GIS services and click Next
  3. Paste the Server URL that was copied from where you found the chosen service endpont
  4. Leave the User Name and Password blank if the server is open for public use, and click Finish

Adding the Service Layer to an ArcMap Project

  • Hit the Add Data button again if you aren't already there
  • Ensure your Look In category is pointing to GIS Servers, just as we did in the last section
  • Double click on NHD on services.nationalmap
! Note: Slow double click on this element to rename this to "National Hydrography Dataset" or anything else if you don't prefer this title

  • Double click the nhd service layer to add the dataset to your project
! Note: This is a large dataset with that's referencing a ton of layers and information. Depending on the speed of your computer, your network connection, and the size of your existing ArcMap project, it may take some time for the layer to be added to your project.


Structure of the NHD map service. Notice that scale-
dependent drawing is set for a number of layer groups.

Tuesday, January 26, 2010

Research Needs for Water Resource Applications of GIS

Water resources are challenging to model in a geographic information system because these features are often so temporally variable. John P. Wilson, et al. discuss in the article, “Water Resource Applications of Geographic Information Systems” many methods of water resource management and assessment. Often, these topics reiterate the relation of data sharing with the increasing level of technology. These advancements allow a greater number of less professionally trained individuals to contribute what can possibly be high quality data with a varying degree of uncertainty. For this reason, future technology will need to incorporate these individuals’ level of training and geographic and scientific understanding into the framework of tool building. Thus interfaces for using such tools must be created to suit a wide audience efficiently. Otherwise, difficulty in using technology directly translates to uncertainty. Scale is addressed often as well when reviewing other issues ranging from the integration of spatial data acquisition technology to data sharing practices.
Primarily, it is stressed that raster grid resolution selection should attempt to match the size of the smallest features that are being modeled.  Accuracy of these resources is quickly degraded due to excess aggregation of topographic features.  Generalization in this regard minimizes the number possibilities of variation for a given area where a smaller stream feature, for instance, could exist in reality.  Using a raster resolution of 30 meters rather than the 2-10 meter resolutions suggested by several studies mentioned easily smoothes over smaller changes in topography.  Further, a 30 meter cell size yields only 21% - 30% of correct slope gradients.  However, if only larger (major) features are required to be analyzed or communicated, 30 meter resolution can sometimes be quite sufficient.

Many water resource applications are GIS-based.  The National Hydrography Dataset is a prime example of how to digitally store and communicate a hydrologic network by logically displaying geographic information with its organizational and descriptive parameters embedded within in a GIS environment.  An example of temporal water quality monitoring is the Florida DEP's Watershed Monitoring program and EPA & FDEP’s STORET (“STOrage and RETrieval” database) program, where water quality data from across the state of Florida is collected, managed in databases, and can be served internally or publicly via internet mapping service, while being provided to in-house personnel for GIS analysis via ArcSDE & ArcGIS Server. Advancements in technology such as these increase the dissemination of information to a growing number of skilled as well as improperly trained stewards and contributors of information.  Increased availability must be mirrored by an increased accounting of data collection information in the form of metadata to ensure reliability.  A method of controlling uncertainty for every step of data collection is currently available by reporting appropriate metadata parameters prior to distribution of any data.  Although this information is mainly included on official final-drafts of published datasets, more can be done deeper within an organization to include metadata to aide in the quality assurance of final versions of disseminated data.

Overall, it will be important to develop efficient models of water resources that can be used by an audience with contrasting degrees of familiarity with geographic information.  By conducting further research on the most effective way to properly incorporate data with varying degrees of uncertainty, as well as investigating the most efficient scales at which modeling hydrologic networks should take place, the GIS community can continue to accurately model water resources in the future.

Sunday, January 24, 2010

Hydrograpic Vocab: Streams

Parts of a stream:
Some of these were obtained, or altered from the (Wikipedia entry on Streams)

Spring - The point at which a stream emerges from an underground course through unconsolidated sediments or through caves. A stream can, especially with caves, flow aboveground for part of its course, and underground for part of its course.
Swalette -  The portion of a disappearing stream where the water drains into a sinkhole into an aquifer or subterranean cave or culvert; characteristic of Karst hydrology and topography.  This system may return to the surface at a spring.
Source - The spring from which the stream originates, or other point of origin of a stream.
Headwaters - The part of a stream or river proximate to its source. The word is most commonly used in the plural where there is no single point source.
Confluence - The point at which the two streams merge. If the two tributaries are of approximately equal size, the confluence may be called a fork.
Run - A somewhat smoothly flowing segment of the stream.
Pool - A segment where the water is deeper and slower moving.
Riffle - A segment where the flow is shallower and more turbulent.
Channel - A depression created by constant erosion that carries the stream's flow.
Floodplain - Lands adjacent to the stream that are subject to flooding when a stream overflows its banks.
Stream bed - The bottom of a stream.
Gauging station - A point of demarkation along the route of a stream or river, used for reference marking or water monitoring.
Thalweg - The river's longitudinal section, or the line joining the deepest point in the channel at each stage from source to mouth.
Wetted perimeter - The line on which the stream's surface meets the channel walls.
Nickpoint - The point on a stream's profile where a sudden change in stream gradient occurs.
Waterfall or cascade - The fall of water where the stream goes over a sudden drop called a nickpoint; some nickpoints are formed by erosion when water flows over an especially resistant stratum, followed by one less so. The stream expends kinetic energy in "trying" to eliminate the nickpoint.
Mouth - The point at which the stream discharges, possibly via an estuary or delta, into a static body of water such as a lake or ocean
Meander - The natural bending and winding of a section of river; usually indicative of a mature or old, established  feature.  Meandering is the result of water's mechanics of erosion, sediment transportation.  Faster, turbid water has a higher capacity to carry load, whereas the same water column will drop its load when it slows.  As a stream approaches a turn in a watercourse, water will flow more slowly along the inside shoreline where sediment load is dropped and deposition occurs.  Conversely, water moves faster along the outer edge, where undercutting and erosion of the shoreline occur, which can be deposited downstream.  Over time, this process deviates the section of river laterally (from the stream run), creating a turn which can occur in succession along a watercourse.
Oxbow Lake - A relic of a stream meander which has exceeded its maximum potential to change course.  A meander eventually erodes through neighboring shorelines to connect again as a straight, shorter stream run.  This process leaves a closed segment of the meander's previous course as a non-flowing U-shaped lake to the side of the current stream.  Over a long period of geologic time, a floodplain may exhibit signs of meander scarring, where many iterations of sinuous variation have occured.

Temporal Establishment:
Perennial - Established waterbodies, present throughout a year under a normal hydroperiod
Intermittent - A stream that is present for most of the year, which stops flowing for weeks or months at a time
Ephemeral - Short lived features, usually flowing after significant precipitation events
Winterbourne - A stream which flows only during winter months and is dry during the summer (dry season)

Drainage Patterns:
Images courtesy Michael E. Ritter. Read more about these drainage patterns in his free e-book: The Physical Environment: an Introduction to Physical Geography


Dendritic - A very common branching fractal pattern found nature that can also be found in leaves, branches, tree roots, and veins to name a few.
Large scale example in Apalachee Bay south of St. Marks, Florida (be sure to zoom in and out, and pan to the east for a few miles to observe the varying scales in which these patterns exist in nature)
Smaller scale example showing the confluence in Pensacola Bay in western Florida

Dendritic drainage pattern

Read more about these additional types of drainage in the free e-book, The Physical Environment: an Introduction to Physical Geography.


Parallel - Similar to dendritic features, but the branches are skewed to run more or less in a similar direction influenced by changes in elevation

Parallel drainage pattern


Trellis -Read more about this pattern here.

Trellis drainage pattern


Rectangular - Read more about this pattern here.

Rectangular drainage pattern



Radial - Caused by centrally located elevated land forms; from uplift, volcanoes, or other geological phenomena.

Radial drainage pattern



Centripetal - Caused by centrally located depression in geography which can drain into a number of features including a depressional wetland, a swalette in a disappearing stream, an intermittent or ephemeral lake which can leave a salt flats in the dry lake bed, etc.

Centripetal drainage pattern


Deranged - A sign of significant disturbance of historically established features.

Deranged drainage pattern