Green Gabbro

One of my New Year’s blogolutions was to clear out my to-blog folder, and bring closure to my unfinished drafts by simply posting them as-is. This is one of those drafts. Disorganized paragraphs, unfinished sentences, and general incoherence enhance the natural character and beauty of a half-written blog post and should not be considered flaws or defects.

Draft date: November 10, 2008

i-5935b09cd0ec544c65d530b23b22566d-city-park-floods.jpg

i-f9a2219f195824c517f0b0ab6517952b-city-park-sand.jpg

While on the craton, I just missed the chance to take my own peek at the deposits left along the Iowa River by the flooding this summer. Cleanup crews have been busy removing sediment and other crap left by the river (sometimes literally crap, as the beleaguered city of Cedar Rapids was for some time dumping untreated sewage upstream) and scraped the sand you can see in the pictures off of City Park a couple weeks ago. By the time I got there, the flood plain had been reseeded with grass.

Last Tuesday, Johnson County voters approved a $20 million bond measure to fund the gradual purchase of available land for an unspecified mix of conservation and recreation projects. While the bond was not billed specifically as a flood control measure, arguments like this one, about the benefits of restoring native prairie grasses and sloughs, have been on many people’s minds.

In Iowa’s “natural” state, . I put “natural” in scare quotes here because the streams and hills in the upper Midwest are not in long-term equilibrium. The landscape we see today, with small marshes and sloughs filling the depressions between gently rolling hills, owes more to glaciers than to rivers and streams.

During periods of sustained heavy rain, the soil will become waterlogged. As soon as there is no more room in the top of the soil for the water to be absorbed, it will run off, potentially causing floods (and taking valuable topsoil with it).

Waterlogging can happen quickly or slowly, though, depending on the soil.

Farmers aim for a water table ~1 m bgs: http://ohioline.osu.edu/b871/b871_32.html

ET 5-6 mm/day for forest and 2-4 mm/day for corn and grass: http://www3.interscience.wiley.com/journal/114102631/abstract?CRETRY=1&SRETRY=0

Infiltration rates 0.3-0.4 cm/min for subsoil tilled fields in WA/ID: http://cat.inist.fr/?aModele=afficheN&cpsidt=1061145