A Day Of Watching Water Levels

Wednesday, May 09, 2007 11:09 AM

The rising level of the Nechako has prompted the closure of Cottonwood Island Park

The Regional District of Fraser-Fort George continues to monitor river and tributary levels throughout the district, but says, so far, the situation has changed little from yesterday.

The District's Manager of Projects and Communications, Finlay Sinclair, says, "Nothing's changed for now anyway - we're all good."

Sinclair says district staff huddled this morning, getting updates from the provincial hydrologist. He says field monitoring will continue throughout the day and some sandbags will be dropped off in Willow River as a precautionary measure.

"I do know one dwelling's been impacted (in that small community to the east), but, from what I understand, it's more a sump pump issue and not being able to remove some water that's showing up versus the river overflowing."

As for the weather's impact, Sinclair says, "There's a bunch of water left to come and whether it's through rain or warm weather, I think we're going to start seeing it, so we're just trying to be cautious and prepared."

But, he says, "So far, so good - we haven't seen anything to suggest that we have a problem at this point."

Cottonwood Island Park was closed to pedestrians this morning, after the Nechako River rose overnight and flooded some of the walking trails along the river's edge.

According to Environment Canada's monitoring station, the current primary water level of the Nechako in Vanderhoof is now 4.264 metres (there is no local monitor).

The Fraser River's level has climbed from 7.5-metres last night and was reading 8.16-metres in South Fort George as of 8am this morning.

The City's Emergency Program spokesperson, Fire Chief Jeff Rowland, says the river is expected to peak at somewhere around 8.6-metres tomorrow.

Rowland says monitoring continues and the City issued a precautionary warning yesterday. The flood level is 9.2-metres.

Picture below shows the Fraser River this morning looking south from the Yellowhead Bridge

Previous Story - Next Story

Email |

Print |

Facebook |

Twitter |

Digg |

Del.icio.us

Posted on Wednesday, May 09, 2007 11:09 AM in News by Michelle Cyr-Whiting

Return to Home

Comments

Posted by: owl on May 9 2007 4:26 PM

Preparation for flood in New Westminster.

http://flickr.com/photos/23881196@N00/tags/floodpreparationsnewwestminsterbc

Does anyone know how the 9.2 metre flood level relates to the 200 year flood plane. Iis it lower? If so, by how much?

9.2 metres has no meaning to me. Where is the 0 metre mark in relation to sea level? The rest I can figure out myself.

Posted by: Chadermando on May 9 2007 5:23 PM

It makes no sense to measure Alcans flows from Vanderhoof and then have the Stewert and Chilacko rivers which are major uncontrolled river basins dumping into the river before PG with no monitoring station in between?

Owl your answers on the water level calculation can be found at this link.
[url}http://srmwww.gov.bc.ca/aib/fpm/[/url]

Also I found the monitoring stations but can't figure out how to get the web site to work. It seems all that happens is you go through a disclaimer circle every time you request the information?
http://scitech.pyr.ec.gc.ca/waterweb/selectProvince.asp

Posted by: owl on May 9 2007 9:13 PM

Chadermando. You have to put in the station in the pull down menu or go to the map and click on it, then on BC part of map and a new window will open up with all the stations in circles. Hovering the mouse cursor over the circle will bring up the name of the station. Click on it and the graph will show up in the original window.

If that does not happen on your computer, I cannot help. Sorry.

Posted by: owl on May 9 2007 9:24 PM

As far as floodplain goes, thanks for that.

I still have the question of how the flood level of 9.2 metres relates to that. Given the elevations shown, I am wondering whether it is 569.2 metres at the South Fort George station?

Posted by: Chadermando on May 9 2007 11:23 PM

Thats a dumb question.

Posted by: owl on May 10 2007 1:59 AM

And exactly why would that be a dumb question?

Do you have the answer?

What is the datum for 9.2 metres is hardly a dumb question.

When the ceiling is at 2,000 metres, then it is 2,000 metres above sea level, which would make it about 1,400 metres above the airport in PG. The datum is sea level.

So what is the datum for 9.2 metres of water?

Posted by: owl on May 10 2007 2:11 AM

The water in Vanderhoof is at 4 metres or so. The datum in the two locations is obviously different since the water flows from Vanderhoof to here and not the reverse.

At McBride the water level is at 5 metres ...at Red Pass, further up river on the Fraser it is at 2 metres.

Anyway .. I found it ... the datum at PG South Fort George is 557.784 metres. So flood level is at 566.984 or so above sea level.

The 200 year flood plain at SF George is 568.5 metres. So what they consider to eb flood level is actually about 1.5 metres lower than the 200 year flood plain.

Thanks ... :-)

Posted by: Chadermando on May 10 2007 11:03 PM

Thanks ... ;-)

But you didn't answer your own question? LOL

"At McBride the water level is at 5 metres ...at Red Pass, further up river on the Fraser it is at 2 metres."

---------------
Flood Levels and Depths

The location of a floodplain is determined by plotting calculated flood levels on a topographic map. Within the floodplain, flood level information is calculated at cross-sections along the watercourse and plotted as flood level isograms.

Each isogram represents regular vertical increments. Isograms indicate the 200-year flood level, which is the designated flood in British Columbia.

Flood levels between isograms can be interpolated. To determine the depth of the flood, ground elevation must be determined by ground survey. The depth of the flood at any given location is the difference between the flood level and the ground elevation at that location.

Professional assistance and site surveys may be warranted to ensure accuracy.

Flood levels as indicated on a floodplain map usually make an allowance to accomodate uncertainties (hydrologic and hydraulic variables). Referred to as freeboard, this allowance varies based on site-specific conditions. It must be remembered that flood levels indicated on the maps are the minimum recommended elevations for floodproofing requirements.

--------------------

Hence your datum is location specific as per the cross-sections along the watercourse and plotted as flood level isograms.

---------------------

Having determined the geodetic ground elevation, flood levels and depths can be calculated as follows.

Scale the distance from the desired location to the upstream flood level isogram (x).

Scale the distance between the flood level isograms located upstream and downstream of the desired location (y).

Subtract the downstream flood level from the upstream level (z).

Calculate the flood level.
Flood Level = Upstream Flood Level - {(x/y)z}

Calculate flood depth
Flood Depth = Flood Level - Ground Elevation*
*Determined by ground survey