ice cover should only be made by USGS, Corps of
NRC
Branch Site
Branch Site
Engineers or CRREL personnel. The competence
Home Base
of an upstream ice cover might be assessed by
noting the existence of cracks or leads, the pres-
HARD DISK
Branch Site
Branch Site
ence of water on top of the ice, and whether can-
dling is visible.
Ice Database
Information on stage data at different locations
along an ice jam is extremely important because it
Figure 18. System connectivity.
is stage that determines the level of flooding. Stage
data are collected at USGS gages, but it would be
more useful to develop a system of staff gages
The home base will act as the repository for the
within the jam reaches so that stage could be mea-
Ice Report data. The database format and design
sured at several locations for each jam. A staff
is standardized by the home base. It provides the
gage could be as simple as painted markings on a
means (using Microsoft Access) for all the branch
bridge pier that are monitored or photographed,
sites to enter their local ice data. These local files
or it could be as complicated as a pressure trans-
uploaded by the branch sites to the home base are
ducer connected to a data acquisition system ca-
merged into one main database. The home base
pable of relaying the information via telephone.
also is responsible for system administration, log
Monitoring of stages could be incorporated into a
tracking, data backups and security of the main
detection and warning system as well as the data-
database. The minimum requirements for the
collection program.
home base are a 486/66-MHz PC with 16 mb of
Stage data can also be obtained indirectly,
RAM, a 500-mb hard disk, a 14.4-kbps modem,
assuming that ice levels can be related to water
Internet connectivity using a bridge/router with
levels. Ice jams can damage trees, leaving scars
TCP/IP software, Microsoft Access software (ver-
that can indicate the level of the ice. When ice
sion 2.0) and PC Anywhere software (version 4.5).
jams move downstream, they can leave behind
Observers at the branch sites will enter their
walls of ice along the bank, termed shear walls.
Ice Report data on their local PC using the Mi-
The height of these shear walls can also indicate
crosoft Access program provided by the home
the ice levels, although if the river geometry is
base. That program also allows them to automati-
favorable for pushing ice upwards, the shear walls
cally transfer the updated and newly added data
may be higher than the actual ice level. If the ice-
to the home base. The branch sites have the capa-
jam flooding occurs during freezing weather, a
bility to retrieve both raw and processed data from
collar of ice may form around trees or other ob-
the home base. The branch site is responsible for
jects. When the water recedes, the ice collar may
the system administration, security and backup
remain. Photographs of buildings or other objects
of their local data. Minimum requirements for a
showing water or ice levels may also be used to
branch site are a 386/33-MHz PC, with 8 mb of
determine stage.
RAM, a 200-mb hard disk, a 14.4-kbps modem or
Internet connectivity using a bridge/router with
TCP/IP software, Microsoft Access software (ver-
DATABASE STRUCTURE
sion 2.0) and PC Anywhere software (version 4.5).
Figure 19 shows how data transfer can be
The Nebraska Natural Resources Commission
achieved from the branch site to the home base
(NRC) was tasked with providing a database struc-
using either a modem or Internet connection. Each
ture to allow easy entry and retrieval of informa-
branch site is assigned a directory at the home
tion collected by the ice observers. The NRC will
base. The branch site will transfer updated or new-
set up each branch site and provide training for
ly added data to the home base over the modem
entering the ice data, transferring the data to the
or through the Internet to an assigned directory.
home base, and retrieving data on-line or through
The home base monitors these branch directories
file transfer. The Commission will also serve as
and merges the uploaded data into the main
the long-term ice-data repository. A conceptual
database automatically.
overview of the connectivity between the NRC
The two ways for a branch site to retrieve data
(the home base) and other agencies responsible
from the home base are by on-line access or by
for data collection and retrieval (branch sites) is
downloading the complete database. Each meth-
shown in Figure 18.
od has its advantages and disadvantages. Access-
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