Journal of Irrigation and Drainage Engineering

The Hooghoudt equation is widely used as a simple means of specifying drain spacing when designing networks of parallel drains in drainage systems, based on estimating the maximum water table height between two drains. It is shown via comparison with a numerical model that the Hooghoudt equation can overestimate water table height and therefore yield drain spacings that may be too wide. This is because the Hooghoudt drain-spacing equation in fact has a concealed dependency on Van Genuchten soil-water retention curve parameters, which can bias the water table estimates unless adjustments are made explicitly. A modification of the Hooghoudt equation is presented that incorporates two new dimensionless coefficients to make allowance for this dependency. The modified expression yields improved accuracy as measured against the numerical reference model.

It is well known that crop coefficients are not necessarily transferrable from one location to another, for a variety of reasons. For example, the United Nations Food and Agricultural Organization (UN FAO) 24 publication on evapotranspiration listed ranges of midseason crop coefficients for particular crops, depending on wind speed and humidity. In the more recent UN FAO 56 publication, an equation was presented that adjusted crop coefficients for wind speed, humidity, and crop height. Climate correction is important for sharing and adjusting crop coefficient data. However, it was found that the FAO 56 equation gave inaccurate corrections for a crop having the same characteristics as the reference crop surface, and it is likely that it also will be inaccurate for other crop surfaces. Consequently, the aim of this research was to develop and test a new method to correct midseason crop coefficients for climate differences. Climate data were used from the California Irrigation Management Information System and a similar approach was used to develop standardized reference evapotranspiration equations for short and tall canopies, to develop and test the new method. The method estimates the aerodynamic resistance of crops in a base climate as an inverse function of wind speed. This function of wind speed was used in a modified Penman-Monteith equation to account for climate effects on midseason crop coefficients in nonbase climates. The methodology to account for climate data and estimate midseason crop coefficient values in a nonbase climate from base climate crop coefficients is presented in this paper.

Soil water plays a key role in crop growth and yield formation. A sustainable irrigation management depends on a reliable soil water monitoring. The present study was conducted to derive site-specific and pedotransfer calibrations for Aquaflex time domain transmission (TDT) soil water sensors and to test their performance under field conditions. In spring 2009, two soil moisture networks were installed in the Kraichgau region and in the Swabian Alb, southwest Germany. Each network consists of 21 stations, each equipped among others with an Aquaflex TDT sensor installed 15-cm-deep in the soil. At each station, soil samples were taken and analyzed for the gravimetric soil water content, bulk density, soil texture, electrical conductivity, pH, and organic nitrogen and carbon content. The factory calibration delivered highly biased soil water contents [$\sim -8.0\mathrm{Volume}$ (Vol.) %]. The root mean square errors (RMSEs) were high, reaching on average 8.3 and 12.6 Vol.% in Kraichgau and Swabian Alb, respectively. The RMSEs of pedotransfer calibrations declined to 3.7 Vol.% in Kraichgau and to 3.4 Vol.% in Swabian Alb. In both regions, the slope of the calibration curve was affected by soil bulk density. High-leverage independent variables affecting the intercept were electrical conductivity in Kraichgau and silt fraction in Swabian Alb. Site-specific calibrations performed best. On average, the RMSE in Kraichgau was 3.0 Vol.%, in Swabian Alb 1.9 Vol.%. The pedotransfer-based approach proposed in the present study is a good compromise between labour effort and accuracy for soil landscapes with similar texture and properties.

Poor stormwater management is one of the primary factors behind the environmental degradation of water bodies. As a result, best management practices (BMP) and low-impact development (LID) have been implemented and promoted in many cities. This study presents some interesting results from a 1-year monitoring program for a rain garden located at a car park in Longueuil, Quebec, Canada (near Montréal). The design was specific in nature as it combines a perforated underdrain, an internal water storage zone of 0.97 m, an almost impervious surrounding soil, and a flow regulator at the outlet. A monitoring program was conducted to assess the performance of the rain garden in warm and cold conditions. Inflow volumes were estimated with an SCS method using precipitation data, but runoff resulting from snowmelt was not monitored. Outflow rates were directly measured. Results from this monitoring program showed that the bioretention system retained $35.0\%\pm 11.6\%$ of the total runoff during the cold season, whereas $59.7\%\pm 3.3\%$ of the total runoff was retained during the warm season. The event’s hydraulic retention efficiency depends highly on the rain garden water content at the beginning of the event and on the time since the previous precipitation event. The average event hydraulic retention efficiency reached 54.8% in warm conditions and $-188.8\%$ in cold conditions only for events producing outflows. The use of a vortex flow regulator at the outlet efficiently limited flow rates, but generated very long runoff events, which made the system sensitive to consecutive rainfall events. The water-quality monitoring activities showed that concentrations in Escherichia coli, fecal coliforms, polycyclic aromatic hydrocarbons, petroleum hydrocarbons, lead, and zinc were effectively reduced during the study period. The total suspended solids (TSS) concentrations were also well reduced by the bioretention, as average TSS concentrations in effluents were $4.1\mathrm{mg}/\mathrm{L}$ even in winter. However, removal of copper and nickel was not efficient and heavy metals concentrations were sometimes higher in the outlet than in the inlet. The same leaching phenomenon was seen for nutrients (total Kjeldahl nitrogen and phosphorous). The chlorides’ concentration significantly increased in effluent during the cold season ($p=0.0001$) because de-icing salt was spread on the parking lot during winter. No clear evidence was observed that the wintry conditions had any effect on any other contaminants during this study (with a 95% confidence level).

Increased runoff rates and volumes from urbanizing watersheds are generally attributed to increased imperviousness within the watershed. While pervious surfaces in urban areas are often credited with having little runoff contribution, soil compaction can reduce infiltration capacity, leading to increased runoff. The objective of the research reported in this paper was to evaluate the hydrologic response of potential treatments for mitigating urban soil compaction. In the lysimeter study of the research reported in this paper, two Florida soils [(1) Arredondo fine sand, and (2) Orangeburg fine sandy loam] were compacted and potential mitigating treatments were applied to evaluate runoff reduction. Treatments combined two incorporation depths [(1) 10 cm, and (2) 20 cm] with three amendment cases [(1) no amendment, (2) compost, and (3) fly ash] and were applied to both soils. A set of compacted lysimeters for each soil were designated as controls and remained compacted (no treatment) throughout the research reported in this paper for comparison with amendment type and depth treatments. Runoff volumes were collected from 19 natural and simulated events over a 5-month period. Natural rainfall events ranged in depth from 4–59 mm over 3–23 h (average intensity, $1–7\mathrm{mm}/\mathrm{h}$), while simulated events ranged from 50–114 mm depths over 32–61 min (average intensity, $91–124\mathrm{mm}/\mathrm{h}$). Bulk densities, cone index profiles, and infiltration rates were also measured on each of the 42 lysimeters. Due to greater infiltration rates and lower bulk densities, tillage with or without compost at either incorporation depth produced significantly less runoff than compacted soils (mean runoff coefficients, $p<0.005$ and 0.03–0.14 compared to 0.19 and 0.46, respectively; mean effective curve numbers, 62–71 and 40–49, compared to 87 and 75, respectively). Fly ash treatments did not significantly reduce runoff production compared to controls and increased runoff production on Arredondo soil. Based on a standard method, runoff production from control lysimeters was similar to dirt roads, while tillage treatments with or without compost produced runoff similar to vegetated open space in fair condition. These results suggest that 10-cm tillage alone may be an effective practice to substantially reduce runoff generated from shallow (20–25 cm) compacted urban soils. Future research should focus on investigating shallower tillage depths and long term runoff reductions of tillage on urban soils, as well as potential effect of tillage and amendments, on landscape plant health and performance.

Seepage is the dominant process by which water is lost from well-managed earthen distribution channels. Pondage tests are acknowledged as the best direct method for seepage measurement, and the recorded water level data from automated systems during periods of gate closure can be treated as pondage test data. A new computer model that applies pondage test methodology to automated channel control data during periods of shutdown to estimate seepage rates in different channel reaches was developed recently by the authors. In this paper, the model is applied to the total channel control (TCC) data for the entire Coleambally irrigation area during three consecutive irrigation seasons between 2009 and 2012 to estimate the seepage rate for each depth gauge, pondage, and pool. Various features affecting the estimated seepage rates were evaluated for selected pools. The evaluation considered two groups of factors. The first group consists of factors that affect the estimation of the seepage rate, including rainfall and evaporation during the pondage period, number of water level measurements in the pondage, and duration of gate shutdown. The second group consists of factors that affect the rate of seepage, including surface water elevation at the start of the pondage condition and its relation to supply level of the channel at each gauge, seasonal variations in seepage rate, and suspected leakage through macropores in banks of the channels.

An elliptical sharp-crested weir design was developed for detention pond outlets to address discharge, pollution, and maintenance concerns. The weir was designed in an effort to efficiently pass debris through an outlet as well as having the ability to easily remove any debris attached to the weir plate. Interactions between various types of debris materials were investigated using a 1:2 Froude-scale physical model. Stage discharge data were collected to quantify reduced hydraulic efficiencies with the presence of debris in the weir plate. Nine debris tests were conducted using plastic bags, newspapers, and turf reinforcement mat material. Reductions in hydraulic efficiencies were quantified from the resulting data. Plastic bags and newspapers produced the greatest reduction in hydraulic capacity, whereas turf reinforcement mat material generated the smallest reduction. Observations regarding the ability of debris material to pass through the weir at increased flows were also made using the physical model.