Weekend rain helps, but not much
This graph of the streamflow in the Little Patuxent River shows that the weekend's rain did help to boost the amount of water in the river. But the benefit did not last long, and water levels quickly began to fall back toward previous levels. In short, the rain was welcome, but it has not ended the dry conditions thast state faces as spring arrives.
Rainfall at BWI totaled 1.27 inches from Thursday through Sunday. That brought the month's total to 2.07 inches. That's a big boost from where we stood at this time last week. But it remains 1.63 inches below the long-term average for March. So we continue to sink deeper into a moisture deficit.
Here's how USGS hydrologist Dan Soeder put it to me this morning:
"The weekend rain helped some, but the National Weather Service is still showing us in a precipitation deficit. http://www.erh.noaa.gov/marfc/Maps/SOP_counties_ytd_color.htm)
"The USGS has not changed the designation of the Mid-Atlantic region as being under a moderate drought (http://water.usgs.gov/waterwatch/?m=dryw&w=map&r=us)"Streamflows responded to the weekend rain as expected by rising, but most are now falling rapidly. Smaller streams like the Little Patuxent (graph above) are showing a drop off in flow that appears to be trending back toward below normal levels. Bigger watersheds like the Potomac (http://waterdata.usgs.gov/nwis/uv?01646500) show a steadier increase in flow from the weekend rain, but are still below normal. The low streamflows are related to groundwater deficits."High water tables in the spring generally produce more robust base flows.
"Our water tables are not as high as they should be, thus making base flows (the streamflow between runoff events) lower than normal.
"Groundwater levels in the Coastal Plain have not yet responded to the rain. It's a little too soon for the water to have made its way to the water table, but maybe we will see a rise in groundwater in a week or so.
"Piedmont aquifers have responded in some cases, showing once again that flow through fractured rocks is much faster than flow through porous sediments. Gentle rains with cool temperatures will help to recharge groundwater levels."
