For more information, please contact Sigrun N. Gadwa, MS, PWS, Carya Ecological Services, LLC at 203 537 1989 or 203 271 1949.
A gentle, rounded, elongated hill in the Connecticut landscape is probably a “drumlin”. The best known is Horsebarn Hill on the eastern side of the UConn campus at Storrs. Landing Hill in East Haddam is currently in the local limelight. The word “drumlin” comes from Ireland, where this land form also occurs.
Rather than bedrock, the core of a drumlin hill is fine-textured, compact glacial debris, that may be over 100 feet thick, and dates from the prior Illinoisan glaciation (over 128,000 thousand years ago). Only the top layer, usually just a few feet deep, is sandier, looser soil, formed from the melting ice masses of the more recent Wisconsin glaciation, underlain by compact till (scientists’ parlance) or “hardpan” soils in common parlance. These soils are seasonally wet, and are quite challenging to develop because of their absorption and drainage characteristics – they are prone to flooding during wet seasons, drought characteristics during dry seasons, and a lack of the more typical cleansing function of more absorbent, permeable soils leading to problems with water and chemical (i.e., fertilizer) runoff and septic leachate migration.
All soils characterized by a hardpan with a relatively thin overlay share these challenges, whether on drumlins or elsewhere, such as plastered onto the sides of traprock ridges. Only ten to fifteen percent(?) of Connecticut’s soils are compact tills but a disproportionate share of construction site fiascos and problem-plagued new subdivisions occur on hardpan soils. Drumlin soils can become a mire for heavy construction equipment because the snowmelt and spring rains “perch” on top of the hardpan.
Saturated silty soils are often an erosion control nightmare. Flooding problems are more severe than on absorbent soils, and water pollution from lawns and septic systems becomes a problem at lower home densities.
This article is a plea from an experienced wetlands consultant: that CTDEP and our Conservation Districts provide us with more guidance on how to deal with their multiple constraints, and the wisdom of using them as open space. Land use boards, developers, engineers, pesticide applicators, and homeowners are all in need of such guidance. Note that excellent on-line mapping (Web Soil Survey or WSS) available from the Natural Resource Conservation Service (NRCS) does show the locations of seasonally wet, hardpan soils, like the Paxton, Woodbridge, and Wethersfield series.
With careful home and septic system placement, curtain drains, and appropriate landscaping, one can avoid typical complaints of drumlin residents: wet and moldy basements, icy sidewalks, fungus-infested or burned-out grass, extended sump pump operation, mosquitoes, dying shade trees, smelly septic systems, and polluted downstream ponds – but this is possible only if home densities are relatively low. Ironically, because the loose upper soil layer of a drumlin is usually so shallow that it holds little reserve water during summer dry spells, drumlin lawns need much irrigation. Solutions: small lawns, partially wooded yards, and/or a meadow landscape with drought-tolerant grasses like Little Blue Stem, a.k.a. Poverty Grass.
Another reason to maximize the amount of remaining tree cover when subdivisions are built is that flooding – and dangerous icy sidewalks - become more of an issue for seasonally wet, drumlin soils, because less water soaks into already wet soils. (Runoff coefficients are higher, in engineering jargon.) The reason is two-fold: 1) to slow the velocity of the falling rain, and 2) because trees spew thousands of gallons of water into the air as water vapor (transpiration), helping dry out those surface soils.
Clear-cutting may be more economical for the developer, but it is not wise in this geologic setting. After clear-cutting, a drumlin slope that used to be wet only in March and April may stay wet to the surface though June – and before long one will see the tell-tale mottles of a jurisdictional Connecticut wetland soil.
Developers and land use commissions need guidance as to what approximate percent tree cover should be left in place for lots of different sizes, slopes, soil types, and configurations, in order to prevent flooding and water problems for future residents and existing neighbors. Technical guidance would also help with road design on drumlin soils. Some, but not all engineers know to correctly design roads on drumlins, with features like underdrains and clay stops, so as to prevent frost heave damage that wastes tax dollars, and allow shallow groundwater to continue to seep downslope to wetlands that depend on this water source. Fertilizers and pesticides tend to run off drumlin soils, more than off more absorbent soil types, especially when the soils are already soggy, such that additional rain and “turf products” cannot soak in.
Glyphosate herbicide (Round-up) is instantly adsorbed and quickly degraded when it enters the soil, but it will wash down a wet drumlin slope – and can kill “non target” vegetation. In 2006 I reported a half-acre emergent marsh and shrub swamp that had turned crispy brown in July. An investigation by the CTDEP Pesticide Division showed that glyphosate had washed into the marsh down a moist, non-absorbent slope from an upslope utility corridor. Although pesticide labels and pesticide applicator curricula do advise against applying products before rains, somehow this important matter is not adequately emphasized, based on the experience of my neighbors and colleagues. Schedules and dollars take precedence, such that landscapers are usually not told to stay home by their companies when heavy rain is forecast. Homeowners should also be aware of this runoff/rain issue, to avoid fertilization if they know that rain has just occurred, and more is forecast.
More guidance “from above” is also needed with regard to the appropriate watercourse setbacks and s septic system densities on compact till soils, to protect downgradient wells, streams, ponds, and lakes from lawn runoff and excessive nitrogen in septic leachate. Finally, CTDEP and conservation districts could educate town landuse boards about the multiple development constraints for hardpan soils on drumlins, as well as their valuable natural resources. Typically these landforms support ecologically valuable pools and streams; scenic hayfields; or productive forests.
Communities would benefit if substantial portions of these compact till areas were set aside to be rural streetscapes, nature preserves, habitat linkage corridors, or even dog parks, woodlots, or rifle ranges.
