Using Pilot Test Data to Refine an Alternative Cover Design in Northern California

Abstract

Two instrumented test sections were constructed in summer 1999 at the Kiefer Landfill near Sacramento, California to test the hydraulic performance of two proposed alternative final covers. Both test sections simulated monolithic evapotranspiration (ET) designs that differed primarily in thickness. Both were seeded with a mix of two perennial and one annual grass species. Oleander seedlings were also planted in the thicker test section. Detailed hydrologic performance monitoring of the covers was conducted from 1999 through 2005, The thicker test section met the performance criterion (average percolation of <3 mm/y). The thinner test section transmitted considerably more percolation (average of 55 mm/y). Both test sections were decommissioned in summer 2005 to investigate changes in soil hydraulic properties, geomorphology, and vegetation and to collect data to support a revised design. Field data from hydrologic monitoring and the decommissioning study were subsequently included in a hydrologic modeling study to estimate the performance of an optimized cover system for full-scale application. The decommissioning study showed that properties of the soils changed over the monitoring period (saturated hydraulic conductivity and water holding capacity increased, density decreased) and that the perennial grasses and shrubs intended for the cover were out-competed by annual species with shallower roots and lesser capacity for water uptake. Of these changes, reduced ET from the shallow-rooted annual vegetation is believed to be the primary cause for the high percolation rate from the thinner test section. Hydrologic modeling suggests that the target hydraulic performance can be achieved using an ET cover with similar thickness to the thin test section if perennial vegetation species observed in surrounding grasslands can be established. This finding underscores the importance of establishing and maintaining the appropriate vegetation on ET covers in this climate.

The effect of cover system depth on native plant water relations in semi-arid Western Australia

“…Choosing species with higher growth rates like A. acuminata (Figure 3) may lead to better immediate vegetation coverage and water extraction thus increasing initial ET performance. However, it is important to consider that species with high initial biomass production and water use may outcompete species with slower biomass production and water use (Zea-Cabrera et al 2006), eventually resulting in decreased ET cover performance (Smesrud et al 2011). Additionally, the co-existence of species with varying growth and water use strategies may be necessary to attain balanced transpiration on ET covers (Gwenzi et al 2014).…”

Field Hydrology of Water Balance Covers for Waste Containment

“…The inadequate depletion in the spring and summer reduced the available water storage capacity the following winter, and insufficient capacity existed to store the winter infiltration. Consequently, the storage capacity was exceeded and significant percolation occurred in the winter of and the winter of 2003-2004. Smesrud et al (2012 decommissioned the test sections in Sacramento and determined that the original plant community comprised of perennial grasses transitioned to shallow-rooted annual grasses common in the surrounding landscape.…”

“…Consequently, the storage capacity was reduced, and the cover transmitted more percolation than intended. Water balance modeling conducted by Smesrud et al (2012) demonstrated that sufficient soil water storage capacity would have been available each year and percolation would have been minimal if the original perennial grasses had been maintained. The lesson from this site was to select vegetation that exists in the surrounding landscape if possible and to understand the transpiration capacity of the local vegetation (e.g., wilting point, root depth and distribution, growing season).…”

The limited impact of vegetation on the water balance of mine waste cover systems in semi‐arid Australia

“…Therefore, given the historic climate of western New South Wales, it is not surprising that both intensive and extensive water users can prosper, and it is reasonable to expect that stable ecosystems can be established on engineered covers (Gwenzi et al, 2013). However, the initial re-establishment of these ecosystems might be challenging because intensive water users with elevated initial biomass production may outcompete extensive water users if both species show similar drought adaptations (Zea-Cabrera et al, 2006;Smesrud et al, 2012). Nevertheless, the coexistence of species with contrasting water use patterns is favoured by the irregular spatial distribution of soil moisture (Zea-Cabrera et al, 2006), which is likely to occur on reconstructed ecosystems because of the high likelihood of spatial heterogeneity of soil physical properties (Krümmelbein et al, 2010;Schneider et al, 2010;Gwenzi et al, 2011;Mazur et al, 2011).…”

“…The plant contribution to ET from cover systems may vary from 44% to 93% in temperate Eastern Australia (Yunusa et al, 2010) to about 22% in Mediterranean Western Australia (Gwenzi, 2010). Furthermore, plant community maturity and composition are likely to substantially affect the water usage of vegetation (Barnswell and Dwyer, 2011;Smesrud et al, 2012). By contrast, empirical information about the effect of vegetation composition on ET losses from waste cover systems in semi-arid climates is limited.…”