Discussion # 3 (26 June 2009)

Article Reference:
David J Sample, James P Heaney, Integrated Management of Irrigation and Urban Storm Water Infiltration, October 2006, Journal of Water Resource Planning and Management

Introduction:
The paper focuses on integrating the water conservation, irrigation management planning and storm management for a study area of a subdivision in Boulder, Colorado. Paper illustrates different studies carried out in integrating the storm water and usage of LID techniques which has received recent attention in the research community. According to the studies carried out LID is considered to be better mimic of the pre development conditions and LID relies in managing the runoff at the site thereby reducing the directly connected impervious area (DCIA) thereby reducing the storm runoff produced. DCIA runoff as is collected by the storm conveyance system which have the potential of being transported away from the irrigation users, therefore for in-site storm management we need concentrate on the non-DCIA and pervious areas.

Methodology:

Study area: Sub-division of Boulder, CO
Area: 11 acres
Drainage: generally running downward to the swale to the south

Approach used in hydrologic analysis: simple water budget principles (setting a control volume around the soil column)
Method to determine Infiltration: Green Ampt Method (Parameters dependent are hydraulic conductivity, soil suction head and difference between the moisture content and porosity)
Network: Building runoff (impervious) is directed to the pervious areas and eventually drained into the conveyance channel.

First approach:
• They used the weather data to predict the PET (hourly)
• Infiltration, Runoff is calculated using Green Ampt method (5 min)
• Soil Moisture conditions assumed to be same over the hour
• Irrigation/rainfall (hourly)
• Total Water balance is estimated using (Infiltration, runoff, rainfall, soil moisture, and irrigation)
• Runoff from each impervious block is determined by routing through the drainage channel
Comparative approach:
• SCS method to estimate the rainfall-runoff response
• Model depends on CN and time of concentration
• Varying the CN with hydrologic conditions will adapt the model to different soil moisture conditions

Cost Estimating Procedure:
In order to evaluate different water management options we need to see the cost effectiveness of different approaches on micro level. From customers point of view the cost can be split into three categories- Water use, on site water management and water pollution control. Investments made on on-site water management typically reduce the water use costs. Water pollution control cost is mostly not borne by the customer unless there is substantial outdoor water demand.

Results:
They have carried out different options of irrigation management plans and studied the water budget of the area. Few of the options studied are mentioned below:
• No irrigation
• Irrigation 1in/week
• Irrigation 2in/week
• Irrigation = 70% of 24 h ET
• Irrigation = 1 in/week with soil moisture sensor which cuts off the irrigation once the soil is saturated
• Irrigation = 1 in/week with Rain water storage (50000L) which is 50% full therefore 50% is catered to peak flow control
Cost comparison was carried out between these options with respect to the three categories of the outdoor costs. They have carried out study to find out the optimal rain water storage volume to result in highest net benefits, it was found to be for the capacity of 10000L that results in highest net benefit.

Discussion:
Author concludes about how the most benefited (Net benefit) option is associated with conserving the water (storing in cisterns) for the irrigation options. I was not very sure about how they have calculated the cost components for the irrigation options they have considered. On a whole this paper was very informative about how the design and analysis of the combining water supply and storm water management is done. This paper will be very useful for my literature review and would be helpful if I further extend my research taking into consideration the irrigation plans for the rain water harvesting.