Title: Managing landscape disturbances to increase watershed infiltration Author
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 2013
Publication Date: N/A
Interpretive Summary: A study of land-use management for improving watershed infiltration by managing the soil surface and soil profile was conducted using readily available runoff data from experimental watersheds in Ohio. The objective was to document the runoff-volume and peak-flow impacts of low percentage rooftop imperviousness (~1%; downspouts connected to and disconnected from the stream channel on two roof structures), pasture where cows trample the soil surface, meadow, and results from a mine-reclamation study where there was complete disturbance to the soil profile. No statistical effects on runoff and peak flow rates were found due to low-level impervious surfaces. After 29 years of pasture, watershed infiltration and peak flows significantly recovered during the following 3.7-yr period of meadow. Runoff can remain high without recovery if the soil profile is disturbed as found in a mine reclamation study where the entire soil profile is disturbed. Results from the pasture runoff recovery and landscape management practices provide guidance to graziers, urban-development practitioners, engineering firms, and regulators for inexpensive management that can improve watershed infiltration.
Technical Abstract: Agricultural land undergoing conversion to conventional urban development can drastically increase runoff and degrade water quality. A study of landscape management for improving watershed infiltration was conducted using readily available runoff data from experimental watersheds. This article focuses on watershed infiltration changes that can be expected from soil surface and soil profile changes and provides support for low-impact development (LID) options. The investigation uses data from a controlled study of the effects of low percentage imperviousness (~0.6%) and connected and disconnected rooftop-channel configurations (189 m2 roof structures), as well as agricultural land management types including pastures where cows trample the soil surface and watersheds in hay production (meadow, no land disturbance). Additionally, a published study on the effects of soil profile destruction and equipment compaction in a mine-reclamation study is presented as a comparison and represents disturbances similar to those in urbanization. Impacts are determined through curve number (CN; ordered asymptotic procedure) and peak flow rate changes using two ~3 ha experimental agricultural watersheds located at the North Appalachian Experimental Watershed at Coshocton, Ohio. No statistical effects on CN and peak flow rates were found due to either percentage imperviousness or spatial location at a low level of percentage imperviousness. CN and peak flows for pasture were significantly larger compared with meadow. One watershed was pastured for 29 years followed by a 3.7-year period of meadow, resulting in a statistically significant recovery of watershed infiltration (CN decreased 17.4 CN units from 77.0 to 59.6). Peak flow response to rainfall for the pastured watershed also significantly decreased during hay. These results suggest that watershed infiltration recovers and peak runoff decreases in a short period of time when transitioning from soil surfaces disturbed by pasture-like disturbances to undisturbed grass. This benefit is partly attributed to minimal disturbance of the soil profile and structure that maintains macropore connectivity, and to freeze-thaw cycles affecting the soil. However, CN can increase and remain high if the soil profile is disturbed and is subjected to compaction, as found in a study of the hydrological effects of drastically disturbing the landscape during mine reclamation. In that study, the entire soil profile was disturbed, causing a CN increase to approximately 89 even after reclaiming the landscape by planting grass, regardless of the composition of soil derived from the original geological profile. No recovery of CN was apparent during a three-year post-reclamation (revegetated) monitoring period. The results quantify the conservation principles advocated in LID and green infrastructure. The sum-of-squares-reduction statistical test works well to identify differences in CN and k due to watershed treatments, but the results can be sensitive to the distribution and clustering of rainfall and CN values. Existing experimental watershed data can provide guidance on managing soil surfaces and profiles to minimize CN under conversion of agricultural land to urban development.