Meadow Restoration Increases Baseflow and Groundwater Storage in the Sierra Nevada Mountains of California

Abstract

We discuss a recent paper which evaluated the hydrologic changes resulting from a pond-and-plug meadow restoration project in the Sierra Nevada Mountains of California. In the study, measurements of streamflow into and out of the meadow suggested late-summer baseflow increased as much as five-fold when compared with prerestoration conditions. However, the volume of streamflow attributed to the restored meadow (49,000-96,000 m 3 over four months) would require that 2.5-4.8 m of saturated meadow soils drain during summer months. The groundwater data from this meadow record only 0.45 m of change over this timeframe, which is less than might be expected from plant use alone (0.75 m), suggesting this restored meadow may be acting as a water sink throughout summer rather than a source.

Discussion: “Meadow Restoration Increases Baseflow and Groundwater Storage in the Sierra Nevada Mountains of California” by Luke J.H. Hunt, Julie Fair, and Maxwell Odland

“…The restoration project described in this paper encompassed a 0.1 km 2 (100,000 m 2 ) wet meadow in which soils were mapped as silt‐loams (Soil Survey Staff ). Prior to restoration in 2012 the streamflow attributed to meadow drainage was 7,000 m 3 (table 1, Hunt et al ), or approximately 0.07 m of free liquid water over the 100,000 m 2 area which, with a 20% drainable porosity, would be accounted for by a 0.35 m change in the water table. The prerestoration well data (figure 5, Hunt et al ) indicate that the typical change in water table depth from June to October was approximately 0.2 m, with a maximum change in approximately 0.5 m (i.e., well 5, prerestoration, figure 5, Hunt et al ) and thus the reported changes in streamflow are generally consistent with the reported change in the water table elevation over the summer assuming no plant use, which gives confidence in our estimate of drainable porosity.…”

“…Following restoration, the authors report that 49,000–96,000 m 3 of water drained from the meadow in 2013 and 2014, respectively (table 1, Hunt et al ). This amounts to approximately 0.49–0.96 m of free liquid water over the 100,000 m 2 area which, when stored in soils with a 20% drainable porosity, would be accounted for by a 2.5–4.8 m change in the water table.…”

“…This amounts to approximately 0.49–0.96 m of free liquid water over the 100,000 m 2 area which, when stored in soils with a 20% drainable porosity, would be accounted for by a 2.5–4.8 m change in the water table. The authors report a maximum water table rise of 0.64 m from pre to postrestoration (table 2, Hunt et al ) and that the change in water table elevation from early summer to late summer (the total volume “spilled”) for all wells is less than 0.5 m (figure 5, Hunt et al ). These changes are too small to provide 49,000 m 3 of water, let alone 96,000 m 3 .…”

“…Field data has, however, been relatively scarce given how difficult it can be to accurately constrain the dynamic and often small hydrologic fluxes in these environments. There is thus considerable interest in the data presented by Hunt et al (), who measured streamflow into and out of a restored meadow in the Sierra Nevada Mountains of California, concluding that summer streamflow increases nearly five‐fold when compared with prerestoration conditions. The increased streamflow is attributed to larger volumes of water being stored in and drained from meadow soils.…”

“…This reasoning is, however, contraindicated by their groundwater data, which show both that there was little change in the drainage dynamics of the meadow following restoration, and that the volume of water draining from the meadow soils was insufficient to account for the volumetric increase in outgoing streamflow. In this Discussion, we present a conceptual model of the physical processes necessary for meadows to act as sources of water that augment summer streamflows, and then examine data from Hunt et al () in light of that conceptual model, identifying the inconsistencies leading us to question the streamflow benefit attributed to meadow restoration.…”