|
giswr
> events
> 1st nhda symposium
> tuesday >
nhd stream order possibilities
NHD Stream Order Possibilities
The National Hydrography Dataset (NHD) combines the USGS
Digital Line Graph mapping standards and the EPA Reach File
capabilities into a single, more powerful system. Like the
previous versions of the EPA Reach Files, the NHD contains
three characteristics that are of great importance to analysts
and modelers: (1) Each feature has a unique numerical identifier
that permits cross-linking many different types of geo-referenced
data; (2) the features contain a digital map representation
which is very helpful for displaying and georeferencing
of data; and, (3) reach-to-reach connectivity information
is included that permits routing through the system both
upstream and downstream. The NHD routing table design is
more flexible than the previous Reach File routing tables,
for instance, it permits much more flexible update capabilities
(e.g., 1:100k to 1:24k) and junctions with more than two
reaches at a confluence.
The routing/networking capabilities of the Reach Files,
including the NHD, permit the development and application
of a variety of analytical tools, including calculation
of stream orders and water quantity and quality models.
In addition, opportunities exist to define subsets of the
reach network that can provide varying degrees of stream
density. This ability to define different stream densities
can play a critical role in future applications by being
able to develop uniform coverages based on hydrologic factors;
this general topic is referred to as "hydrologic equity".
This presentation will demonstrate the ability to use the
NHD flow table and routing "engines" to calculate stream
orders. Other examples will highlight methods for defining
stream densities based on factors such as total river length,
drainage area, and streamflow.
|
